I just got my engine fixed after having it suck a screw into it, and now I have a new Mikuni carb. for it and K&N. I just need a little help tuning it. My first problem I've come upon is that if I go from low throttle to wide open really fast, nothing happens. It won't accelerate or slow down, just stays the same. I remember reading about how to fix this once, I just forgot.

 

Ok, I've got it down to my main jet is my problem. But I can't figure out what's up with it. I have three main jets, a 180, 270, and 290. With a 180 the sound it makes seems like it's too rich, it burbles and misses, and eventually dies. When I do the Roll Off technique with it, it sounds like it's too lean, I let off and it accelerates. With the 270, it will eventually get it's power, after studdering, without dying. Now it sounds like a little bigger one, right? So with the 290, it will get the same symptoms as with the 180! So I can't figure out what to do.

 

A little info on what bike this is, mods, and what type/size of carb will be helpful.
Basically, you should put the bike is 3rd/4th gear and hold it at almost WOT. If it starts "backfiring", it is too lean. If it is blubbering, it is too rich.

 

It is a Suzuki lt230s quadsport. The carb. bore is 28mm, it has a K&N and a Cobra exhaust. I just rode it in 3rd gear around my house, and it would actually start backfiring with the 290 main jet! I looked at the spark plug, and it was bone white. It makes no sense how a 28mm carb with such a big jet could be too lean. I'm thinking it's not just the main jet that isn't right. But it only misses when it goes to the main jet.

 

Have you made certain you don't have an air leak somewhere? Cracked or loose boot clamps on the carb or filter?
Barring that, why don't you do a really proper test ride & plug read using a brand new unused plug to avoid a contaminated reading.Riding around the house is not a test ride even at full throttle.

 

I didn't actually mean that I was doing circles around my house. Just around the area of my house, not a few miles away. And my spark plug used to have carbon all over it. Then it turned white. I probably could use a new one though, that one had a dip in an oil pan. I cleaned it, but it may not be enough. One of my carburetor boots is a little loose, but would it make that much of a difference? It's tightened all the way down, and it's the intake clamp.

 

To the surprise of FTZ and myself, I had problems jetting my carb that I bought for my 250x right after they built the 273cc big bore that was in it. It only had 10.5:1 compression, but I couldn't find a jet big enough. I went all the way to something like a 380 and it was still to lean. I ended up having FTZ drill some Alky jets to run gas. I never got it rich enough. Finally I bought a 35mm FCR and had no major problems tuning it.

If you suspect an air leak, grab a can of carb cleaner. Start the bike up and let it idle. Spray the cleaner around the intake, head, and carb. If the engine dies or revs up, you have an air leak.

 

The first thing I would check is for an intake air leak, like AlkyBurninX said, use carb cleaner or starter spray with the engine idling. Once you have satisfied yourself that there are no air leaks I would seriously consider spending $100 approx. and buy an "Exhaust Gas Temp Gauge", these things work marvellously. Your EGTs should never get above 1250 deg F for extended periods (white plug, piston meltdown) but the closer you run to that temperature the better power you will make.
The procedure is quite simple:
Find a long steady hill and start at the bottom and run up the hill in 3rd or 4th gear. Hold the throttle at ¼ to 1/3 until the EGT steadies out and record the reading. Now do the same thing at 1/2 throttle and then again at full throttle.
If the ¼ to 1/3 throttle EGTs is higher than 1250 open your pilot jet to make it richer, conversely close if the reading is lower. Lower temps being safer.
If the 1/2 throttle EGTs is higher than 1250 raise the needle in the carb, conversely lower it if the reading is lower. Lower temps being safer.
At WOT if the EGTs are higher than 1250 install a larger main jet, conversely if the reading is lower install a smaller jet. Lower temps being safer.
As you can see this is done on a trial and error basis but you will see the results of each change. Once done check the temps through the full throttle range to make sure the temps are where you want them.
I hope this is of some help to you.

 

just buy NEW JETS!!!!
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Try this CHEAP FIX! Reduce your slow (idle) jet, and keep the main jet fat (big). Also, how many turns out is the air screw? What mixture are you running?
My 250r ATC is @ 140main and 45 slow (idle) and its a little rich. Also I run a 50-1 mix. I have been playing with it for months, look at my post(s) [img]i/expressions/face-icon-small-smile.gif[/img] This seems to be the best at the momment. REMEMBER...tune it to YOUR riding needs, I learned that.

Ron