Rejetting

[JMiller]

I think my trike is running a little rich, how should I rejet the carb? Should change the pilot jet, main jet, both or what?

[Tri-Z Pilot]

Where is it running rich? I.E. 1/4 to1/2 throttle? 3/4to full throttle?

[JMiller]

smokes and loads up while ideling and low throttle

[Tri-Z Pilot]

That would be your pilot jet, check and see if your pilot passage is clogged, or try adjusting your idle mixture. Is the carb dirty?

[Tri-Z Pilot]

Forget what I said about a blocked passage, I was thinking lean. Is this a bike that you just bought, or is it new?

[JMiller]

I've had it @ 1 year. Just rebuil the engine,(crank bearings, crank seals, all other seals, piston, & rings). The carb is spotless.

[Tri-Z Pilot]

Did it act like this when before you rebuilt it?

[JMiller]

Yes it did.

[JMiller]

The carb has stock jetting.

[Tri-Z Pilot]

Hmm, could just be the climate where you live, have you tried adjusting the idle mixture to lean it out? Make sure you do jetting changes when the bike is warmed up.

[JMiller]

The only adjustment on the carb is the idle screw. Could be the climate.

[Tri-Z Pilot]

You mean the one on the left side with the spring behind it?

[JMiller]

right side

[Tri-Z Pilot]

There should be a tiny screw somewhere on the carb which adjusts the idle mixture. If it is on the front of the carb (motor side) turn it clockwise to lean the mixture, but if it is on the back of the carb (airbox side), turn it counter clockwise to to lean the mixture. What kind of carb is it?

[JMiller]

Mikuni

[Tri-Z Pilot]

Ok, I am looking at a mikuni flatside carb that I have, is the choke a knob on the leftside that pulls up, right by the letters T.M. ?

[TimSr]

smokes and loads up while ideling and low throttle

You rarely have to monkey with the pilot jet from the factory size unless youve done major changes, such as big bore kit or something. The pilot jet only affects idle, and ALL two strokes load up at idle. Your best bet for improvement in it loading up at low RPMs, provided carburetion is fine at the top end is to drop the needle, by raisng the clip. I typically drop my needle to the lowest setting. Running lean at midrange is not a major concern as long as you are rich enough at the top side. Ive never heard of anyone melting a piston at midrange. Too lean at mid range is not desireable, but if yours is loading up that bad, I doubt youll have a problem. You need to take some top end and some mid range plug readings. Make sure top end is okay before proceeding elsewhere.
The air screw is adjusted for best throttle response off of idle.

[JMiller]

Thanks for the info Tim :D

[200Xtreme]

I have seen MANY 2- strokes, melt pistons in the 1/2 to 3/4 throttle range. If it is running rich at idle, and low throttle settings, I would check for a heavy float, and or misadjusted float level. If you do move the clip position, only go one at a time and do plug chops to check progress. I used to have an old polaris 400 snowmobile, and the previous owner had melted four pistons in it. Every time he would put another piston in it, he would put a larger main jet in it. when I bought it , it had 400 main jets in it (240's are stock). I put a heat gauge on it, and it was running at 1200 degrees at 1/4 throttle, and about 850 wide open. I dropped the clip one position( this brought my midrange down to 1000 deg.) then I started dropping mains, and got down to 260's and it ran great. Come to find out his wife was riding it and melting pistons in the midrange!!! sorry about the long story, but just be very careful, and know exactly what you're doing, when messing with 2- stroke jetting!! (especially when leaning them out)

[slippy4]

i dont get why it runs lean at midrange with a bigger jet. youd think it would flood out or run rich? i dont know about jetting and trying to figure it out. can you shine some light on it for me?

[Tri-Z Pilot]

The main jet has very little to do with the midrange, mid range is mostly affected by jet needle taper, and the jet needle clip setting, and I think the throttle valve cutaway plays a small part in it too.

[Tri-Z Pilot]

This is a little schematic I drew, that shows which jets contribute to what throttle position you are at, it should help a good bit.

[TimSr]

The main jet has very little to do with the midrange, mid range is mostly affected by jet needle taper, and the jet needle clip setting, and I think the throttle valve cutaway plays a small part in it too.

The main jet has everything to do with the entire range, other than at idle. At idle the pilot jet bypases the main jet. As soon as the throttle is cracked the fuel is coming through your main. When the throttle is wide open, you pull the needle out of the hole, and the only thing limiting flow is the size of the hole in the man. When you back off the throttle, the needle drops in, and how far its in affects fuel flow. If you raise or drop your main jet size, it will affect the entire range, other than idle. If you raise or lower the needle, it will not affect the upper part of the throttle because its not being used.

The needle adustment is limited to two nothes in either direction. In spite of the statement that 200xtreme has seen "many of them melt at midrange", (and I have no snowmobile experience) Ive never heard of it on dirt bikes or ATVs, because if your main jet is correct, the needle doesnt give you enough adjustment to accomplish meltdown. If your main is lean, Id agree that you could probably move the needle enough to melt it at midrange, and I would agree that there is certainly nothing wrong with moving it one notch at a time, and doing the proper plug checks.

The main and the needle will handle about 99% of carburetion issues on a stock carb with a mostly stock motor, or ones with only external modifications (pipes, filters etc.) Its rare to have to monkey with the other settings unless you get into big bore kits, (not an overbore), strokers, and major porting which is normally combined with other exhaust and carburetion modifications anyways, and other major engine modifications.

[Tri-Z Pilot]

I guess that I didnt think about that part, while you are getting fuel through the mainjet, the needle probably affects the midrange the most, but If the main cant give the needle jet, and jet needle enough fuel, you would be lean, thanx for the heads up timsr.

[JMiller]

I moved the clip on the needle up two notches, I havent taken it out for a ride yet. If it still runs rich. could it be possible that my needle or seat is worn?