250r Keihin 34mm Carb Problems

[TrikeMike]

I'm still having problems with my 34mm PJ carb (At mid to high RPM it flattens out and sounds like its either rich or starving) Someone had suggested that I do a plug chop and look at the plug for possibly being too rich??? I did this and the plug looks OK. No carbon fouling or excess fuel/oil. I bought this from a guy in Georgia. I'm in Michigan and it's COLD. Could this have an impact on the setup? The carb was setup in warmer weather and now that it is cold there's not enough fuel for the motor? Does that possibly mean that when it gets warmer it might run better? Any help is appreciated!!!

[mbubbac]

yes it probly the weather. when dealing with 2 strokes the weather effects that alot more than 4 strokes and theres more tuning involved, tune it a lil richer in the winter cuz when theres cold air its more dense and more air is going in but not as much fuel and then when its warm out the air is less dense and the air is pull the right amount of fuel in

[TrikeMike]

Thanks. On the Keihin PJ carb, is the adjustment on the choke (turn clockwise or counter-closkwise) the idle or does that affect the rich/lean?

[sandpuppi101]

Yep,This good old Michigan weather gives you lots of practice tuning a 2-stroke in.I have a 85'R and if I don't rejet for the cold then it starts hard and runs really rich.You need to lean it out a bit.I suggest getting some jets bigger/smaller and look in your R manual for settings.Or ask the gang here,they are the real pro's,cause we all have trikes.Another thing would be to play the spark plug game,meaning running a hotter plug and checking it periodiocally ,looking to get the right color on the plug,But I suggest caution because you can easily have a meltdown in your cylinder if you don't do it right!Where in Mich.are you?

[Dammit!]

tune it a lil richer



You need to lean it out a bit.


I haven't lived in a cold climate in so long I can't even remember which of these is right.

The real question is though, how did you do the plug chop and what color was the plug? All you said was there was no fuel or carbon build up but it's the color that tells you what's going on. If it's a nice tan color, it's spot on. If it's more light gray or white, it's lean (lean = DANGER WILL ROBINSON). Obviously black is too rich. How you did the plug chop is important because different fuel circuits are active at different throttle ranges. It might be jetted fine at low or mid throttle and then too rich at full throttle or any other variation.

Answer those questions and you'll get more help.

[TrikeMike]

This is what I love about this forumn. Every question I ask yields 3 more (which is good). I am hell bent on learning this 250r carb game (86 250r) and you guys are always there to help. The plug seemed to be on the gray/medium gray side. Also what does the twisting of the choke lever control. Is that just idle? Does anyone have a manual or setup for the Keihin 34mm PJ, I feel bad peppering you guys with questions all the time. I can't seem to find one searching the internet. Thanks.

[Dammit!]

That is in fact just the idle. The mix screw is on that same side towards the bottom.

You didn't answer HOW you did the plug chop though. Here's what I would do.

With a clean plug and after the bike is warmed up sufficiently, get it wide open, hold it for a few seconds then pull in the clutch, let off the throttle and kill the engine all in one motion. Coast to a stop and check the plug. This will tell you what your Main jet is doing and if it needs to be bigger or smaller. Do the same thing at Half open throttle. This is mainly needle position and taper controlling fuel flow. If it's lean, Lower your needle clip (this INCREASES fuel flow by actually raising the needle, more fuel flow = richer). If it's rich, do the opposite.

Also, read this thread (http://www.3wheelerworldforums.com/showthread.php?t=26242). There's a lot of good info there.

[TrikeMike]

That thread link should be MANDATORY reading for anyone troubleshooting 2-stroke carbs. Thanks. I will give some of this a try and check results.
Thanks again!

[sandpuppi101]

Hey Dammit you bring up a good point that I really did,nt even think about.Being in the warm Arizona climate{I'm very jealous} you would,nt have to rejet for temp.so much ,but how about altitude .Do you notice changes when riding at different elevations or do you not ride in the hills.Sounds like you play the plug game also!I love doing that ,it's like exactly how far can I go.But it took me awhile to learn plug color vs octane vs needle position vs main ,all that fun stuff.All main factors,when playing the so called plug game!It's all fun and games till you have a meltdown.LOL Beware white plugs!!!

[Dammit!]

All the places I've been to so far have been roughly the same elevation so I haven't had to make any changes for that yet. This summer I plan to check out some of the places north of the valley like Cinders (which I think is like 7000 feet!). I still have my stock 34mm carb so I was planning to use that one and get it jetted for that elevation when I get up there and then switch back to my 38mm when I'm down here. Easier that way maybe.

I'm admittedly FAR from an expert on carbs and jetting. You'll see me asking for help occasionally too. There's a few guys here that are way better at it than me that helped me out when I needed it so I try to pass along what I can when I can in return. Funny you mention octane because that's something that I've been pondering lately. Might have to start another monster thread on it to go with the carb thread. :D

[sandpuppi101]

The thing about it is there are so many ways to go about doing ,say you carbs if there stock or oversize or your exhaust if its stock or aftermarket,just so many things.We could go on and on and on,but like I said before in a thread somewhere,we all have trikes so we are all teachers and I at times am a pupil also,and that is what is so great about conversing with everyone on here.Yeah octane is very important too,and I gotta tell you it would be a good thread too,I would be interested in hearing other views and experiences on that subject.