I brought this here from another thread as to not anger there off topic police
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Originally Posted by trykemike
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.
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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. 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?