Just came back from my first ride after "needle shim mod"

[David Bo]

Wow, I really felt the difference... I shimmed my needle earlier this weekend and turned my carb's bottom screw open about a half turn (after drilling out that little metal plug). I cut the airflow restricter off of my existing air filter and opened up the holes in my muffler a from 1/4" to about 3/8" to relieve some additional back pressure. It feels like these mods added "at least" a couple of ponies to the engine. I can't wait to install the new exhaust next weekend. I am also planing on installing a K&N filter to replace the cut-up factory one.

It is pretty cold in New England today so I only went about 8 miles before my face started to freeze. Thanks for all the "How to's" guys!!! :cool:

[Easy Rider]

Originally Posted by David Bo

I am also planing on installing a K&N filter to replace the cut-up factory one.

I didn't think there was a direct K&N replacement ???

Anyhow, be careful with that. If you REALLY open up the intake, you will probably need to re-jet too. Since you got through the needle shim, that wouldn't be much of a problem though.

You can see roughly what the K&N will be like by running briefly without an air filter at all.

[patrick_777]

If you shimmed, you should have also drilled out the mixture screw, right? You might can get away just richening up the fuel/air ratio without a filterbox on. That might get you where you need to be without jetting.

Might. I haven't done it, so others will definitely know better.

[music man]

[quote=Easy Rider]

Originally Posted by "David Bo":33jj7x5h

I am also planing on installing a K&N filter to replace the cut-up factory one.

I didn't think there was a direct K&N replacement ???
[/quote:33jj7x5h]


Yes there is, but it is listed for a Suzuki GS500, not the GZ. But it is a direct replacement, just like the Hi Flo brand that I have in my bike is.

[David Bo]

Thanks Easy... I was actually planning on replacing the jet too. I figure since I already did the other two carb mods, what the hell... I was surprised to see how easy it was to get to the jet. I actually have it in my hand as we speak. After reading the post entitled "rejetting part 1", I think I am going to purchase a #147.5 jet. Do you have an opinion on this?

[Easy Rider]

Originally Posted by patrick_777

If you shimmed, you should have also drilled out the mixture screw, right?

That is an IDLE (low speed) mixture screw.

It has so little affect at med. and high speeds that the placebo effect doesn't even come into play !!! :biggrin:

[Easy Rider]

Originally Posted by David Bo

I think I am going to purchase a #147.5 jet. Do you have an opinion on this?

Not really. A wild guess would be not to go bigger than the European models.......but that might not be enough with no intake restriction. Don't know.

I would expect your gas mileage to go down a tad.
Isn't that what others have reported ??

[David Bo]

The K & B Filter Number I ordered was SU-5589. I'll let you know if it does not fit but I believe it will as it is the one for a GS500. Yes, I did drill out the metal cap for the idle screw. I drilled it about an 1/8" inward until I could see that tiny hole in the middle of the plug start to widen from my drill bit. Then I hooked the remaining portion of the plug with a little hook tool I have. A little yank and it popped right out. I was "overly" careful because I did not want to hit the actual adjustment screw with my drill bit.

So, I have read in other posts that the factory jet is most likely a #120 and the best replacement is a #147.5? Does anyone want to offer any advise before I drop 3 bucks on the wrong size replacement jet?

Thanks! David Bo

[David Bo]

OK... The Suzuki place did not have any of the correct jets for the GZ so yesterday I ordered a #140 and a #145 and they came in today. Having done the other carb mods this weekend, I was excited to see what going from a #120 jet to a #140 jet would feel like. All I can say is WOW!!! I purposely went for a ride where I could approach a steep hill at around 40 mph in five gear and then gun it... After 1/4 mile of up hill I was approaching 55 MPH!!! That is pretty good considering two weeks ago, I practically would have to downshift to forth going up that same hill. On a good day (last summer) the bike could only hold it's own at a steady 40 MPH in fifth gear...

Anyway, if anyone is considering doing the "three step carb modification", I would highly recommend it. Keep in mind that I already had drilled out my muffler and cut the in-take restricter out of my stock air filter. Next weekend (I hope) I plan on swapping the exhaust pipe with a JC Whitney extra long reverse megephone muffler and installing a K&N air filter (if they come in before then). At that point, I will most likely stick the #145 jet in the carburator too.

Fun, Fun, Fun !!! :2tup:

[Easy Rider]

Originally Posted by David Bo

Anyway, if anyone is considering doing the "three step carb modification", I would highly recommend it.

Ah, but the whole story isn't in yet. Will be interesting to see what your gas mileage does after all the changes are done. IIRC, the others who did it ended up in the low 60's ....down from the low 70's.

And for those who are not mechanically inclined or are just plain lazy, I found a one-step modification: exchange the GZ for a Honda VT600C Shadow. It still gets about 60 MPG with conservative riding. Well, maybe.....test ride tomorrow. :biggrin: