GZ250 power increase.

[Jaime]

This is a translation of my how-to published in the spanish GZ250 forum. My English is not perfect, so maybe there some wrong words... :blush:
I'm simplifying it too, so it's easier for me to translate.

We're going to increase the power output of the Suzuki GZ250 "Marauder", with small and cheap mods in intake, carburettor and exhaust. This is a mid-hard how-to.

I haven't checked my bike in a dyno, but the max speed in a certain track has been increased from 78 mph to 81-84 mph; for Stage 1, and over 87 mph; for Stage 2.

The first thing is to get a higher flow air filter. You can:

Cut the original air filter around the inner tube.

http://img.photobucket.com/albums/v248/hellcracker/filtro2.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb34.jpg

[/*:m:1u3qpmum]
Or, for best results, buy a K&N SU-5589 on Amazon (https://amzn.to/3NDYF0G) and not using the air flow restrictor.

http://www.kandn.com/images/m/SU-5589.jpg[/*:m:1u3qpmum]
I took option a, as my filter was so new to discard it.
Once modified or replaced, the bike will run so bad. That means that it has a good empowering potential. I've replaced the exhaust can too (Stage 2) but it's not needed.
Let's carburate it.


STAGE 1 Air filter modded

Carburetting a vehicle is not easy, it's more like an art, so your results may differ of mine. It's about checking and correcting.

There are 3 systems: low-speed, mid and main, having influence on low to high rpm, respectively. Our bike is equiped with a Mikuni BSR32SS.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb0.png

The low-speed fuel system is controlled by the pilot jet and the pilot screw, the mid-speed by the jet needle and needle jet (less important), and the main fuel system basically depends of the main jet. There are other parts involved, but I'm not modifying them.

http://img.photobucket.com/albums/v248/hellcracker/carb/circuitos.jpg

The following chart shows the config of my carburettor (spanish GZ250K6):

http://img.photobucket.com/albums/v248/hellcracker/chicls.jpg

The best config of my bike once recarburated is the following:
STAGE 1:
- Main jet #145
- Jet needle at 5th slot (richest)
- Pilot screw at 1.75-2 turns out

STAGE 2:
- Main jet #150
- Jet needle at 7th slot (virtual, see "STAGE 2" for details)
- Pilot screw at 2.25 turns out

The main jet is a Mikuni type N102/221 (N102.221). I've bought some through eBay (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=014&sspagename=STRK%3AMEWN%3AIT&viewitem=&item=330123027667&rd=1). We'll need some different measures around the ones told above. Also, you have to consider your climate, height over sea level, etc.

http://i16.ebayimg.com/04/i/000/a0/6f/b53f_1_b.JPG


Let's see the process.

Carburate your bike in the following order:
Main fuel system (main jet)[/*:m:1u3qpmum]
Mid-speed system (jet needle)[/*:m:1u3qpmum]
Low-speed fuel system (pilot screw)[/*:m:1u3qpmum]Never modify more than one part at a time, and test the bike after it. It's the only way to do a good work.


1. Main fuel system

To access the jets, proceed this way:
Find a proper tip or a small screwdriver.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb4.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb5.jpg

[/*:m:1u3qpmum]
Empty the float chamber unscrewing the lowest bolt.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb1.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb2.jpg

[/*:m:1u3qpmum]
Unscrew the 4 bolts of the float chamber.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb3.jpg

[/*:m:1u3qpmum]
Take out the float chamber.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb9.jpg

[/*:m:1u3qpmum]
Find the main jet.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb6.jpg

[/*:m:1u3qpmum]
Unscrew it, and only it (not the jet holder).

http://img.photobucket.com/albums/v248/hellcracker/carb/carb7.jpg

[/*:m:1u3qpmum]
Install a jet that you think it has a good measure and revert the steps before.

[/*:m:1u3qpmum]
Turn the gas valve to PRI for a few seconds, so the float chamber is filled again.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb8.jpg

[/*:m:1u3qpmum]
Run the bike and test it.

NOTE: I'm not explaining/using the spark plug color method, you can check this link (http://www.dansmc.com/sparkplugs1.htm).

Remember the max speed before any mod.
Run the bike at full throttle and don't upshift (in 2nd, 3rd and/or 4th gear). Check the acceleration at very high rpms and watch for any jerks.

[list:1u3qpmum] If the acceleration is slow or it lacks of power for reaching max rpm, the main jet is too small. Go back to step 2.
[/*:m:1u3qpmum]
If the acceleration is not slow but the bike jerks, the main jet is too big. Go back to step 2.
[/*:m:1u3qpmum]
If the acceleration is good and the bike reaches max rpm with no jerks, you've found the right jet. Don't confuse jerks with the normal ignition cut while overeving, in vehicles equiped with electronic ignition. Go to the following section.[/*:m:1u3qpmum][/*:m:1u3qpmum][/list:o:1u3qpmum]
2. Mid-speed fuel system

It's harder than main fuel system. You have to modify the height of the jet needle and check the acceleration after every change; a tedious work.

Empty the float chamber as explained in step 2 of the section before.

[/*:m:1u3qpmum]
Loosen the flanges filter-carburettor and carburettor-engine.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb10.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb11.jpg

[/*:m:1u3qpmum]
Separete the carb from the nozzle till you see the position bulge.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb12.jpg

[/*:m:1u3qpmum]
Disconnect the vacuum tube of the gas valve.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb31.jpg

[/*:m:1u3qpmum]
Rotate the carb clockwise looking the bike from behind. Help pushing the throttle cables.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb14.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb13.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb15.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb16.jpg

[/*:m:1u3qpmum]
Unscrew the 2 bolts of the top cap.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb18.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb19.jpg

[/*:m:1u3qpmum]
Take out the piston valve/diaphragm without breaking the fragile membrane.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb20.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb21.jpg

[/*:m:1u3qpmum]
Extract the jet needle holder. Don't lose the inside little spring.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb22.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb23.jpg

[/*:m:1u3qpmum]
Extract the circlip from 3rd notch and put it on the 5th notch.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb25.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb26.jpg

[/*:m:1u3qpmum]
Mount everything back the same way. Push the jet needle to check if it's mounted properly.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb24.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb28.jpg
http://img.photobucket.com/albums/v248/hellcracker/carb/carb29.jpg

[/*:m:1u3qpmum]
Revert step 7 and don't break the membrane while closing the top cap!

http://img.photobucket.com/albums/v248/hellcracker/carb/carb30.jpg

[/*:m:1u3qpmum]
Revert all steps and fill the float chamber.

[/*:m:1u3qpmum]
Test the whole rpm range, with special interest on 1/4 to 3/4 throttle. You can shift gears normally this time.
[list:1u3qpmum] If the acceleration is smooth, but slow or lacks of power, the jet needle is too lean (too low). Back to step 1.
[/*:m:1u3qpmum]
If the acceleration is normal, but the bike jerks at any time, the jet needle is too rich (too high). Back to step 1.
[/*:m:1u3qpmum]
If the acceleration is the best and the bike revs up without jerks, the jet needle is at the proper height. Next section.[/*:m:1u3qpmum][/*:m:1u3qpmum][/list:o:1u3qpmum]
3. Low-speed fuel system

Locate the pilot screw and adjust it. Maybe you have to drill a cap to access it. European GZs have direct access to this screw:

http://img.photobucket.com/albums/v248/hellcracker/carb/carb17.jpg

Count the turns clockwise to get it seated and leave it stock again.

You have to adjust this system with the bike turned on, at a normal function temperature and idling (idle shouldn't be too high or too low). Turn counterclockwise the pilot screw by 1/4 turns every time, waiting a few seconds to see the effect.
You must find the point where the rpm maxes. If it's reached between 2 and 3 turns out, it'll be better for performance setting it near 3 turns out (around 2.75 will be ok).

Once adjusted, turn the throttle suddenly up to 1/3 in neutral from idle, then release it.

If the engine revs up smoothly but takes a while to rev down and keep idle stable, you have to richen the screw more (counterclockwise).
[/*:m:1u3qpmum]
If it looks like stalling or it doubts, you have to make the mixture leaner (clockwise).
[/*:m:1u3qpmum]
If it revs up fine and constant, and it revs down inmediatly to idle (and stays constant) when releasing the throttle, it's finely adjusted. Check the idle speed again, if it's needed. The work is done.[/*:m:1u3qpmum]


STAGE 2 Air filter mod and exhaust can replaced

Same process, bigger main jet (about 2 sizes in my case; 145->150).
I had to cut the jet needle head at the first notch, as it was too long after the needle shim. It was shimed to emulate a 7th notch, needed for a good adjustment.

http://img.photobucket.com/albums/v248/hellcracker/carb/carb32.jpg

The exhaust mod makes is noticeable at low and mid rpm, not that much at higher rpm (that's what I feel).


Well, I hope this how-to helps. If you have any doubt, problem, suggestion or correction, don't hesitate to post a message. ;)

Sorry again about my English.

[Dupo]

Very nice and thorough write up and translation. Thanks Jaime.

[Water Warrior 2]

Jaime, well done. Excellent pictures and directions. You have managed to make the carb a lot less imtimidating.

[jonathan180iq]

That's Friggin's awesome! I knew Su-5589 would work. I'm glad someone finally verified it. :rawk:

[trykemike]

Thanks for the how-to .

I am familiar with rebuilding carbs but the older styles do not have a diaphram .

the carb on my honda 200cc has both an idle screw and a mixture screw. turning the mixture screw out richens the mix .

what is the equilvalent screw for the gz250 carb ?

I wonder if adjusting mixture is the 1 st modification that should be made.

I have in the past used a larger main jet with mixture adjustments to compensate for unrestrited air flow and less restricted exhaust on a honda with noticeable performance improvement.

Re: exhaust : less restrictive exhaust also has less back pressure which may result in shortened valve life or burned piston crowns. ( did that in the past )

[Jaime]

Sorry, Trykemike. I haven't read this topic for months... :oops:

The equivalent to the mixture screw is the "pilot screw", #13 in the diagram. It enrichens the mixture when turning it out too. When it's located in the air filter side, it usually enrichens when turning in.

The first thing to do is choosing the proper main jet, as it causes the biggest impact on the mixture. The needle jet isn't used to be changed much, but in the GZ250 it's a need. The mixture screw, on the other hand, only affects the first 1/3 of throttle range.

The increase in performance is noticeable, but not astonishing. Anyway, I've "raced" a stock GZ250 and mine blowed it away, I had to wait for him at tiny throttle.

[trykemike]

Thanks Jamie.

[Quimrider]

Thanks Jamie! btw your english is as good if not better than most english speaking people. Obviously if you're using the extra available power to accelerate quicker and drive at 80+mph it's going to drop your fuel economy. Other than that, have you noticed any change in fuel economy before / after the modification?

[Jaime]

Thanks, Quimrider.
The fuel economy of the stock bike was around 61 mpg. It's true that now I cruise at quite higher speeds, and the fuel economy has dropped to 54 mpg.

[trykemike]

Jamie I have noticed that when I apply a slight bit of choke @7000 rpm in 5 th gear then back off on throttle I get to 7500 + so I concluded that the mixture was a slight bit lean . I have a 125 main jet but before installing it I wanted to ask if it would make the mix too rich. I have a drilled exhaust and stock air cleaner.

I don't plan on riding consistently at speed above 6000 rpm ( 5000 - 5500 rpm ) but am experimenting.

I want reliability.

[Quimrider]

My experiences with the K&N filter if anyone else wants to try that:
130 or 132.5 pilot jet (can't decide which is better.) (120 factory jet)
needle shim eliminates flat spot.
pilot screw set at 1 1/4 turn out. (1 5/8 turn out from factory)

Caveat: Each bike is different, climate variables and modifications affect carburettion. My results are presented as a starting point for someone wishing to do the same.

My bike has always had a flat spot approx 5-6k rpm. Modifications include, 4 extra 3/8" holes in exhaust from a previous owner, and 16t front sprocket. Prior to doing anything else I would hit a brick wall at 70mph and if there was any wind 65mph was difficult to maintain. I purchased a K&N SU-5589 air filter and installed it. Took it for a spin knowing it would be bad. Wow! it was so lean it would misfire like crazy even with the supposed flow restricter. I first tried a 140 jet. It ran smooth, flat spot was gone, but the exhaust smelled awfully rich. It also sounded/felt slightly different. Very subtle and hard to distinguish over the now very audible intake noise. The best adjective I can think of is a slight "chug." I next tried a 130 jet. Flat spot was back, slightly worse than it was with the original jet and air filter. My needle valve has no adjustable slots so I did the "needle shim" and simply moved the washer to the other side of the e-clip. This seemed to be the ticket. constant pull thru entire rev range. The acceleration is ever so slightly weaker than with the 140 jet so I think it may be a tad on the lean side. I may try the 132.5 jet. While testing with the 140 jet I was able to hit 83mph with a slight tail/cross wind yesterday. While trying to maintain 70mph it only dropped to 68mph a couple of times. While my top speed hasn't increased much, It's noticeably stronger in the 65-70mph range which is what I was looking for. It's hard to draw any conclusions from my speeds since it's been quite windy here in northern Ohio the past couple of weeks. Also I wasn't able to get the idle screw to go lean. It was about 1 5/8 turns from factory. I backed it out to 1 3/4 turns and started the bike (already warmed up engine) and screwed it in at 1/4 turn increments. At 1 turn out it would idle rough and stall. I settled on 1 1/4 turn out as this seems to idle fine. I'm open to suggestions on this as the idle still seem rich.

[trykemike]

Hey quimrider how you doing ? I followed your instructions for the tach . Great enhancement.
my bike is running perfectly.
since I drilled 4 7/32 holes inside the ring 1 '' from the centre outlet the idle remains 1300-1500 steady before it rose when hot to 2000 rpm
the accelleration is smooth and quicker
I tested 50 -70 yesterday with a strong head wind 25-40 kph it was smooth and responsive did not run wide open because of the cross wind.
I can easily pass 8000 rpm in 3 rd and 4 th but have not tried 5 th yet ( too windy )
I just did not want to run too lean if I do manage 8000 rpm in 5 th ( I will only touch it then back - off ) I just thought it may need a little more juice.
No rush I just bought the jets along with other parts ( oil filters etc )
I'll be patient then wait before messing up a working combination that I have now
I have 13000 km on the bike.
thanks for the feed back. I like you only need good power mid-range

[Quimrider]

trykemike,
Glad to hear someone has got some use out of my posts. My bike runs much smoother now. I'm not sure if it's the tweaks to the carb or the free flowing air filter. The biggest difference I've noticed is that at lower speeds I'm using significantly less throttle which I'd expect with a less restrictive intake. I gotta keep an eye on my speed. I find myself wanting to use the same throttle position as before and end up speeding. I suppose I'll adjust after a few weeks. Also I switched to using the horn for the tach. power supply. I should probably update that how to. Since I changed that at the same time I was messing with the carb I'm not sure what made the difference, but the tach doesn't seem to bounce as much and the idle is more consistent. It feels like I have faster acceleration, but I think that's probably just in my head :) I have gotten mine to idle fairly consistently at 1000-1300. My idle creeps up toward 2000 when it's hot too. 9 of my 15 mile commute is expressway so I'm usually 7/8 to WOT. The 16t front sprocket took a little off the top end but made the freeway more comfortable. It also allows me to drop down to 4th on the freeway if I need the extra power. Either these engines are pretty tough or I got lucky. I did once accidentally down shift to 3rd instead of upshifting at 68mph. I guess I was quick enuff to get on the clutch. I was shocked at how little difference there is between a 130 and 140 jet. I figured it would run aweful if it was rich. I first bought 140-150 jets from the same guy Jame got his. When 140 seemed too rich I got the 130-137.5 jets I figure I could get a little more power with the 132.5 jet, but I'd rather run a little lean to get better fuel economy. I plan to add one of those brake light flashers and put in a relay to cut off the head light when you start the bike.

[jonathan180iq]

When you get around to electric work and the hedlight relay, a picture is worth a thousand words.

[trykemike]

hey quimerider looks like I sent multiple posts a glitch on my part.

I will install the 125 main jet this weekend.

[Water Warrior 2]

QuimRider, just a heads up for you. If you want a brake light modulator they can be supplied by ridesafer.com. Got a combo pack from them that included the headlight and brake light modulators. Actually a good deal in my opinion as both ends modulate. Installation is quick and easy with decent instructions for technically challenged old guys like me. If I remember correctly the brake controller in under the left sidecover stuck in place with 2 sided tape. The headlight controller will actually fit in the headlight bucket and be protected from prying eyes and the elements. A very sanitary install for both units. Lynda's bike also has a SilverStar bulb in the front which is quite an improvement with not too much expense.
If you only want the brake light mod it is a good safety device that is relatively cheap.

[Quimrider]

trykemike If you're using the stock air filter and haven't tried the needle shim. You may want to try that before you swap out the main jet. I was AMAZED at how much difference the needle shim made. If I were to go back to the stock air filter I think the needle shim with the stock 120 jet would do the trick.

Water Warrior. Thanks for the heads up, but I already got the Back Off XP modulator from custom dynamics last fall. It just got too cold too quickly for me to install it. http://www.customdynamics.com/signal_dy ... ulator.htm (http://www.customdynamics.com/signal_dynamics_back_off_brake_light_modulator.htm ) It looks really simple to install.

[Water Warrior 2]

Quimrider, just had the seat off and found where the brake light mod is attached. So much for my memory !! It is actually mounted with 2 sided tape to the top off the air filter box just aft of the tank hold down bolts. I wouldn't look normally but I wanted to pull the tank and see if there were signs of anyone doing a valve inspection today. Looks like Lynda got what she paid for. Good thing too. She really hates to pay good money for nothing.

[trykemike]

Hey quimrider. I did the needle shim. You are correct the power delivery is smooth. Re top speed I still stop at 120 kph 7500 in 5 th gear but there is wind. I did notice that I can get there solidly and faster. I now have good power in the 80-100 kph range regardless of wind or hills. Acceleration is good to 105 kph.

I took the bike for a 200 km ride on saturday cruising 80 - 100 kph avg 90 kph ( 5500-6000 rpm ) . I ran 20 km on ther freeway @ 90-100 k/hr . I got off then ran secondary hwy avg 80-90 k/hr. The big hwy was very busy , windy with lots of big trucks and busses etc. NO FUN !

I will stay with the 120 jet for now.

I can hit 8000 rpm + in 4 th gear ( 105 k/hr )

[Quimrider]

trykemike, I can usually keep a steady 120kph (75mph), but I use the 16t front sprocket so the engine is turning about 500 rpm less. That is with no head wind. With a head wind I can only maintain a consistent 112kph(70mph) sometimes having to shift down into 4th. there is a chart here that shows rpm vs speed: http://www.gz250bike.com/viewtopic.php? ... c&start=90 (http://www.gz250bike.com/viewtopic.php?t=317&postdays=0&postorder=asc&start=90)

[trykemike]

Hey Quime rider

I did a test yesterday evening. The temp was about 20 c ( 70 ) degrees and almost no wind. I got out on an open stretch of highway
no hills . The bike was running well. I could easily hit 120 k/ph so I got upto 100 k/h then pulled the choke lever about 1/8 forward. I
opened the throttle and pulled easily to 120 k/h then open the rest of the throttle I looked over at the tach it read 8000 rpm ( 5 th gear ) and the speedo was touching 130 k/hr (81 mph ) it was still pulling but I had run out of space so I let off .

Very rare to get ideal conditions but 80 mph is acheivable. ( still have stock 120 main jet ).

I read that the choke pulls a plunger that opens an ericher jet and air jet to feed the engine. I spoke to qa mechanic who did and engine rebuild for me in the past about this phenomenon. He said that the mix had been enrichened enough to allow the engine to reach
its power potential.

Now that it is done I will slow back and drive to enjoy the ride. I just had to see the bike reach it's potential.

BTW I get 85 mpg regularly .

[Quimrider]

Wow! What type of driving do you do to get that high of mileage? I do about 85% freeway @ 105+k/h(65mph+) and the rest in town. I got about 70-75mpg with the stock air filter and stock 120 jet. I take back my earlier statement. I think I'm running rich because my mileage has dropped to ~55mpg after doing the needle shim, 130 jet and K&N filter. Other than being much noisier I do have a little more pep at the high end, but still about the same top speed. I did manage to hit 84mph briefly before the proximity of the bumper in front of me convinced me to slow down :) I think I'm going to try the 122.5 jet that I have with the K&N and see how that works.

[trykemike]

Hey quimrider

I usually drive on the outskirts of toronto . back roads at speeds varying from 80 -90 km/hr when I get the 85 mpg ( 150 km / 5 litres of gas ).

The mechanic that I spoke to actually suggested a 122.5 main jet for the bike because they are jetted low to acheive great fuel economy at the expense of a slight decrease in performance.

He is a good mechanic he rebuilt the engine on my 25 year old honda 250 3 wheeler.

[themarauderer]

Your doing well with 75+ MPG...I have the 125 and get about 75-78 MPG approx.

This is mostly town riding, doing no more than 40mph most of the time....that said, I sometimes take a wee ride about and can reach, on a good day 60ish MPH...not much more tho . Going down hill, APPARENTLY the GZ125 can touch 70ish .... I, have my doubts.

Its a 4 stroke, 125cc bike. It does have limits. The 250, without doubt but the 125, if its hitting 70ish, God himself must be blowing it along ;-)

[trykemike]

hey Easy I did a test with the air filter. I took it out to have it cleaned at work with compressed air. I took off the diverter and inhaled to check the air flow near the bottom of the filter. I then put the diverter back on and performed the same test I noticed more restance. I drilled a 1/2 inch hole in the centre of the diverter. I reattached the diverter and installed the filter ( which was clean ) I took the bike for a 100 km ride on the main highway ( speed limit 100 k/hr ) the bike hit a flat spot on accelleration and top end stopped @ 110 k/hr so I pulled the choke lever a little bit top end went to 125 k/hr and the flat spot was eliminated.

[Easy Rider]

hey Easy I did a test with the air filter.

What? I have no messages in this thread. What you say is mildly interesting but why did you put it HERE.....if you are responding to something that I said (presumably in another thread) ???

[trykemike]

hey Easy I was just passing on this observation based on a test that I did. You rightly informed me that the "choke " on the carb is not a butterfly but an enricher circuit that opens a secondary jet so I have been experimenting with it because the bike does perform as I had expected when I bought it. I have in the past driven a triumph bonneville and a norton commando so I did not expect a lot of power. I did however drive a honda 305 dream when I was a kid ( 19 ) it could just touch 80 mph ( slight down grad ) and cruise all day @ 55-60 mph it also weighed about 300 lbs. I was looking for cruiser styling and the same functionality as that dream. I have 14000 km on the gz now most at hwy speeds 50-60 mph . So far with maintenance tips from this forum I have been able to keep it reliable.

[Quimrider]

I brought this here from another thread as to not anger there off topic police :)
hey quimrider did you back out of your power mods ?
I still have 4 7/32 holes in inner ring on exhaust and 1/2 hole in intake hood and use 1/16 enricher circuit with hot idle set to 1500 rpm. Tip of plug is black but rest is light brown.
no starting problems runs good 100-115 kph on hwy cruise mainly 80-100 kph get top of 130 kph and 90-95 mpg (32 k/l ). pipes are blue/gold until 1st bend then chrome the rest some blue at weld where 2 pipes join.

I don't know if you read my other post about my cylinder head warping but that put a damper on things for a while. Still not sure what caused that. If anything I'd have to say my riding style. It would seem overheating, but I'm not fully convinced. I guess maybe it just happens sometimes with the higher running temps of air cooled engines. A couple things I learned from trying to increase power is that at least for me it isn't worth it. I could run rich as hell and gain an extra 5mph sacrificing 10-20mpg. Since I bought the GZ for it's fuel thriftiness, this was unacceptable. When they had my engine tore apart they said there was a "mound of carbon" that they scraped off the top of the piston. I suspect that was from when I was running very rich while playing with the carb. In case you don't remember I was using a K&N air filter, needle shim, have 4 3/8" holes in the exhaust (from previous owner) and experimented with almost every jet up to a I think it was a 150. I came to the conclusion that it's a 250cc and Suzuki has it tweaked pretty closed to as much power as you're going to get out of it with decent fuel economy without some serious re-engineering.

I also read about a reason not to open up the exhaust. Contrary to popular belief back pressure isn't always a bad thing. without back pressure, the momentum of the exhaust gases in the exhaust pipe will pull some of the incoming gas/air from the carb thru the combustion chamber and into the exhaust pipe the brief moment when both the exhaust and intake valves are open. If you have the carb sufficiently enriched you will get some more power, but take a big hit in fuel economy and your chrome pipes will blue due to excess heat from the combustion occurring in the exhaust pipes. since my exhaust has 4 3/8" holes, I verified that there is indeed some overlap in the intake/exhaust valves, and my pipes are very blue, I would tend to believe that this is true and applies to the GZ250.

So to answer your question, Sort of yes. With the weather getting cold and a leaking head gasket last fall, I decided I was done changing things until spring. Plus with the winter formulated gas and more dense cold air it's difficult if not impossible to compare results.
I ended up returning to something closer to stock for now. I didn't want to burn up my pipes anymore than they already are (blue thru the entire first bend and then some). I plugged 3 of the 4 holes had to tap them at 1/2" and use 1/2" bolts as plugs with loctite. one bolt had to be shortened otherwise I couldn't screw it all the way in. I had the 4th hole plugged but can't get anything to keep it plugged permanently (bolt rattles loose and disappears). I do want a little extra breathing, but I don't know if I want an extra 1/2" hole in my exhaust. The increased intake noise got to be annoying after a while so I went back to the stock filter. I removed the diverter (I think the same thing you're calling "intake hood") to get a little more air. The carb has the needle shim mod and 1 size up from stock on the main jet 122.5 IIRC. I wish I knew how you got your mileage. I still only get ~66mpg although 11 of my 16 mile commute is freeway WOT so if I kept closer to your speeds I'd probably get closer to your mileage. When it warms up I'm going to tweak the main jet and needle shim to see if I can get an improvement. I haven't done the plug check at various rev ranges to see how rich or lean I'm running. If we ever get it fixed I could borrow the combustion analyzer we have at work. It shows just about everything you'd want to know, %O2 %CO2 %CO %HC (hydrocarbon aka unburned gas)

Another thing I've considered is fuel injection borrowing parts from the TU250 and improvising other parts. There is an open source fuel injection project called mega squirt. (http://www.megasquirt.org/megasquirt.html) It would be expensive I'd guess in the neighborhood of $1000 for a total conversion which then begs the question of why? The only reason I could think of would be nice to be able to customize and tweak the FI which you wouldn't otherwise be able to do. If I really wanted FI I'd probably just wait till I could get TU250 parts and swap them. I couldn't bring myself to buy a TU250 because it reminds me too much of the moped I had as a kid.

What's this about a "1/16 enricher circuit?" you talking about the choke? Does that really make any difference?

[Sarris]

QR; Great observations. My GeeZee has over 13k miles, all stock mechanicals, no carb or exhaust mods, and no blueing headpipes at all, and runs like a champ. I think that for the price, Suzuki did a great job right out of the box. Remember too, the entire third world gets around (the whole family, chickens, etc.) on GZ's in either the 250cc or the indescribably slow 125cc model.

I guess your motive for owning a GeeZee has a lot to do with your expectations. If it is/was your first bike, it's time to move up to a larger bike when it starts feeling too slow or too small. If it was a financial decision to save some money, you may be unhappy with the performance, perhaps feeling relegated to a fate worse than death by riding one. If you bought it for the sheer joy of riding a lightweight zippy motorcycle, it fills the bill perfectly.

:2tup:

[trykemike]

Hey sarris.

Your last statement sums it up for me . The joy of riding a light zippy motorcycle. It's a hobby
for me but as 1 of my buddies said "Mike you just had to change something !!!!." So I kept it very minimal.

My pipes went bluish/gold from new . Dealer serviced under warranty. Now I maintain it.

I really don't push the bike. I want to enjoy the ride there and BACK.

:)

[trykemike]

Hey Quimrider re: the "choke" use your tach for this test. When the engine is warm and at idle
with the choke off move the lever slightly until the rpm just starts to increase. Take a test ride
it may/may not improve the performance. I have the spot marked so I use it on most cooler days and when I run on the freeway because acceleration improves on my bike. Try it.

:??:

[Quimrider]

Thanks for the tip. I've tried messing with the choke and couldn't really tell a difference. When it gets warmer, I'll have to do a couple checks of the spark plug at freeway speed to see if I'm running rich or not. I suspect I may be a tad rich since there is more carbon build up on the exhaust that I would expect and the enricher aka "choke" seems not to make a difference.

[Quimrider]

I changed my needle shim a little. I have excessive carbon on the end of the exhaust which made me think it might be slightly rich. I moved the washer back to the stock position, went to lowes and bought some #4 stainless steel washers. They are almost exactly the same size as the carb's washer, but approx 1/2 as thick. I used one of these as a needle shim. It ran about the same. We'll see how it affects my mileage. Now on to my point... When I put things back together I forgot to tighten the boots between the airbox and engine. It ran fine at low speeds. I got on the freeway and it must have been sucking air around the boots. I could barely hit 60mph. I tried your choke trick and it sped up to 65-68ish. I guess with the boots tight my bike was already running rich enuff that the choke made no difference.

[trykemike]

Hey Quimrider. Thanks for the feed-back re: the "choke test" I was contemplating changing the main jet before I read your posts. I just took the bike out of storage. I set the fuel to prime for 5 secs then used normal starting procedures . The bike started right away and settled down to idle approx 1400-1500 rpm. I used the choke trick moving until rpm rose to 1750. The bike accelerated briskly ( easily left all cars way back off the line at the intersection. I went onto the main hwy ( our equivalent to the inter-state ) I took 3 rd to 65k 4 th to 90 k and 5 th went easily to 110 k . I kept rpm under 7000 about 6500. She is running perfectly. With fresh oil rapid shifting in either direction was smooth. Tried a speed shift @ 6500 all gears from a stop light after the hwy run. Not a "jet-bike" but quick enough. Now waiting for more warm days for the run to the lake and some lazy 80 k cruising in the country side.

[MadCityRider]

Anyone looking to switch to the 130 Main Jet (or wanting to swtich back) I've got some extras:

viewtopic.php?f=11&t=4616 (http://www.gz250bike.com/forum/viewtopic.php?f=11&t=4616)

:rawk:

[geezer]

well i decided to do what jaime did and move the needle over a ton. tomorow ill see what it does. ill be on a nice long ride with a chick on a suzuki 800cc. i still out ride her on the little gz! :rawk:

[Water Warrior 2]

well i decided to do what jaime did and move the needle over a ton. tomorow ill see what it does. ill be on a nice long ride with a chick on a suzuki 800cc. i still out ride her on the little gz! :rawk:
Does that include very long hills with a headwind ?? Yeah, I had to say it. :lol: :lol: :lol: :lol:

[geezer]

HA! shes a beginner so around turns and stuff i can! :cry:

[GinetteHuber]

I will install the http://emailblog.eu/wp-content/uploads/2012/10/email_marketing_spam_can.jpg main jet this weekend.

[burkbuilds]

Hey GinetteHuber,

Although this is a fairly old thread, I'm glad you resurrected it. The original poster's pictures and explanations of how to do this are the best I've seen, and I somehow missed this when it started and stayed active for a long time originally.

Good luck with your mod and let us know how it works.

[Fawlty]

Hey GinetteHuber,




I think he may have something to do with an old brand of canned meat.

[Water Warrior 2]

Time will tell. I know Alantf hasn't had the chance to yell at some one lately.

[alantf]

Oh shit!!!!! I missed that one!!!! :lol:

[golem]

I don't feel confident doing this myself, can I just go to a mechanic and ask him to " shim my needle"? Or is it a little bit more tricky than that?
I'm asking because I don't get the whole stage 1/stage 2 etc. Thank you

[jonathan180iq]

Leave the stage 1 and stage 2 stuff alone. There is not a factory made jet kit for our bike.

You don't have to do any of these carb adjustments if your bike is running fine. If it currently fits your needs, just ride and enjoy it :)

All of these threads on power increases and modifications and stuff are only there are guides for others if/when they decide they want to tackle something. It doesn't mean you HAVE to do this stuff

[golem]

Is there any advantage into adding a better air filter than the stock one if there is no other modification done to the bike? something like this http://www.amazon.com/dp/B001GMAJQG/ref=wl_it_dp_o_pC_S_ttl?_encoding=UTF8&colid=3U89P0E7HLZW4&coliid=INSHJTWKB0L9T

[raul10141964]

yes I modify the factori filter see pic but do not work with out changing the main jet, i runing a 140

[Water Warrior 2]

Is there any advantage into adding a better air filter than the stock one if there is no other modification done to the bike? something like this http://www.amazon.com/dp/B001GMAJQG/ref=wl_it_dp_o_pC_S_ttl?_encoding=UTF8&colid=3U89P0E7HLZW4&coliid=INSHJTWKB0L9T
If it is cheaper than a Suzuki air filter then go for it. Hi-Flo makes a good product.
You can also use their HF-136 oil filter on the GZ. I know it is cheaper than a Suzuki oil filter and is identical.

[golem]

Ok thanks