Idle problem & jet needle question?

anyone messing with carbs. and or jetting would do themselves a huge favor by getting Sudco's "Mikuni Tuning Manual." it's a clear and understandable manual on how your carb. works., how the changes to any give part effects it. any bike shop that vends out of Sudco can get it. it's an awesome book.

What did the reeds look like?

I don't think its the jet needle clip position that is affecting your problem - the needle is connected to the slide and fits itself inside the main jet - the main jet isn't part of the circuit at idle and therefore the needle won't have an impact - as you turn the throttle the slide moves up and in doing so the needle moves up and out of the main jet - the taper on the end determines the amount of fuel that is drawn up into the barrel of the carb. All of this happens from 1/2 throttle and up. Go to Eric Gorr's site and read the 2 stroke tech article about jetting - it may make it a bit clearer (eric-gorr.com). Now lets go back to your problem...if I remember you correctly, we all convinced you that you needed a new top end to get the bike running...now that it is running, you are having some fine tuning issues....assuming you replaced the piston/rings/gaskets, etc the bike should run fine...some exceptions - if you are having problems with the idle you may have an air leak somewhere -- the reason I say this is the wandering idle issue and the fact that you are choking off the air screw to "force" the bike to run better...my first guess - bad ignition side crank seal. I'm not saying this is 100% - just a thought....tell me what the OLD piston looked like? simply worn out? or burned up somewhere (hole in the crown maybe? or a melted ring? Or the top melted into the ring?). If so, you've got an air leak that is letting extra air into the combustion chamber and thereby leaning the fuel/air mixture out...since fuel aids in cooling the cylinder this can cause overheating and a fried piston. I would pull the left cover to expose the flywheel - and with the bike running try to spray some carb cleaner right at the seal...if the idle jumps up, you know you've got it. if not check around for other leaks - between the carb and intake, the base of the cylinder, the head, etc in the same manner). Another possbility would be to start the bike up - get it warm and then ride it a bit....not too long just enough to get it warm and see if the idle catches....if so you may have excess piston to cylinder clearance and until the piston expands after warming up, your seal in the combustion chamber is not sufficient...also as I said before, check the reeds...keep in mind a 2 stroke works from changing pressures - so if you have a leak or bad seal somewhere its not going to run right....there are more things I can tell you but start with these. Good luck

yeah - melted rings - sounds to me like a lean condition caused the overheating. not a problem for the help!!

well well well.....hmmmmmmm.....I really thought you'd have nailed it with an air leak....have you gotten the chance to look at the reeds? now i'm not even sure that is the problem....And then you had the float needle sticking closed...could that be hanging up and starving the bike's fuel supply? you know when a two stroke runs out of gas, it starts to rev UP real high? check the reeds...then ride the bike...see if the problem still persists. if you don't have any air leaks and your top end is new - the carb is really the only thing left. you do have the air filter cleaned and NOT overly oiled? just thinking anything at this point.

OOO just thought of something else - can you turn the idle up a bit and get it to idle steady?

the compression test done warm will give you a better reading for sure.

sounds like your float is 100% sticking - at least we know when starting - and it could be what's making your idle jump - I hate to be captain obvious and send you into the carb for the umpteenth time but you need to go in there and see what's up.....scratch the float needle with your finger nail - does some whitish dry stuff flake off? same thing for the fuel inlet (where the needle it going up into) - push the needle jet up there and see if it stays. If so you've got to clean that out - and add a little carb cleaner to there where you re-assemble - the wetness will aid its movement when the first rush of gas comes in. The float is floating right? I think we confirmed that. your inlets and vents are NOT clogged correct? have you blown compressed air through the inlets on the carb?

The air filter isn't likely to be the cause even with 2 stroke oil on there (I would use motor oil in a pinch - a little thinner and less goopy but if you put it on thin, it should be fine).

Is the float mechanically moving ok? meaning there isn't something in its way? Or its not bent and such? the arms where it gets pinned are not pinched hindering its movement are they?

I'm doubting its the reeds now too - and BTW the reeds sometimes come off with the gasket intact to one side of the assembly - I've taken them on/off many times w/o having to replace the gasket so don't stress over that.

no lunch necessary - the bike is for you grandson, right? As long as he's happy, I'm happy.

JT2Fast4u I am going through the same thing with a friend's kid's bike. He put a new top end in it and the exact idle symptoms you mentioned are happening here. I dont have the manual for this bike, but I was wondering if you could send the float height measurment and where you measued it from. I did all the air leak checking, carb cleaning also, and was going nuts trying to figure it out.
Thank you very much !!!!! Rick