IT 125 erratic idling

[Fringo]

Hello, I've just joined this forum and I hope that someone can help me out with some issues with a 1981 IT 125 that my 13 year old son just bought. When he bought it, it was running rough and was really hard to start. I took the carb off, cleaned it and replaced the needle valve assembly with a new one, next, I adjusted the air mixture screw in totally and out 1 3/4 turns, I also cleaned the petrol tank and mixed some 91 octane petrol with good quality oil (approx 32:1), I also put a new spark plug in. The bike fired right up and was running a lot better, but only with the choke on, when I try to put the choke off the engine revs crazy. I have tried to adjust the idle screw out but it does no good. When the choke is on, it revs a little high, the idle screw does not affect this either except if I screw it in the revs will increase. We did notice as well that the engine flooded when we tried to start it a couple of times. I hope that someone can help with this choke problem, Thanks

[Airhead]

Crank seals need replacing ?

to prove...spray WD40 through the slots in the magneto rotor when the engine is racing away (choke off) aiming at the crank seal of course you may see / hear something...a change in engine speed or tone etc

[Fringo]

Thanks, I'll try that at the weekend when I get a bit of time.

[Fringo]

OK, so I went out and started the bike as you said and sprayed WD40 through the slots, I didn't notice a difference in tone apart from the motor dying out. I started it up again and done the same with the WD40, the motor died again, is this a sign of the crank seals being worn? and if so, can they be replaced without the motor being torn apart, also, if this is a major job, would he be able to ride the bike like this until the end of the season without doing any major damage to something else. Don't think that I said before, when we kick the bike over, if it doesn't start right away and starts to flood, the petrol pisses out of the exhaust manifold. Thanks for the help

[Airhead]

how do you know about petrol pissing out the manifold? surely you have an exhaust on the bike!

as for the dying thing, yes this could well be an indication the seal is gone, in effect you maybe starving the motor of the air it need to burn with the fuel, and so it dies. Probably the carb throttle adjustment is turned to fully shut the throttle because of the fast idle caused by the seal leak and so when the WD40 plugs the leak...voilla it dies!

Can be changed easily with engine in the frame, you will need a flywhheel puller...i think they are usually 27mm (check) I understand if two small holes are drilled into the seal at opposite sides and then self tapping screws are threaded into the holes....This gives something to grasp with molegrips and pull out the seal, best done when the engine is warm, maybe use a hot air gun to warm the case around the seal area

[Fringo]

Thanks, that sounds painless enough, about the manifold thing, the original pipe is on the bike and not in very good cond. the head pipe has many dents and previously repaired (but not very well done so) areas. When the bike is running there is an exhaust leak and when the bike floods, petrol pisses out those same holes. I am looking for a used original pipe for it but they are not readily available(at least not for a decent price),I don't think the DT is the same pipe but I wonder if it would work ok,? there are certainly alot more of those around. You didn't say, do you think that it would do any damage to ride it with the crank seals worn and choke on. Thanks again.

[Airhead]

Try starting it by turning the fuel on and then off again, only turn it back on after it has run a while (before the bowl empties)

as for running with choke on this will affect performance and add to the flooding, might as well get the seal ordered and fitted ASAP i think.

Come to think of it if you get it started leave the fuel off for the first time until it dies, this way any excess fuel in the crankcase will be expelled...then go for the starting method of OFF wait then ON

[Fringo]

Thanks, I'll stop at the Yamaha dealer on the way home tomorrow and order the seals, he'll be using the bike this weekend so I'll try to do the job next week. He's only learning and is still a bit nervous so the bike won't get any kind of abuse from him riding it too hard. Thanks again, I really appreciate the help, I've only ever owned two, two-strokes, a KH 250 that I took in a trade for a CB 550 and a DT 250 that I bought in London and two weeks later straight swapped for a much older XT 500 (one of my favorite bikes), so I'm not too educated about the blue smoke spewing monsters but with guys like you helping out, It makes it almost easy.

[Cynic]

If there is no proper seal on the exhaust then the engine will suck air in instead of the charge from the expantion chamber and go lean sending all your carb settings out the window.

Add the float height being all to heck and the crank seals its hardly suitable for your lad to get to grips with. Surely your better to fix it and then hand it over.

[Fringo]

It definitely would be better to fix it first, but this being Canada and our riding season coming to a close, I just want him to get the most use that he can before the weather breaks. He only gets to ride it on the trails up north at our cottage on weekends and I work fairly long hours during the week so I'm just trying to get him something to practice on until I can get a bit of time during the winter when hopefully all of the issues can be resolved. Do you think that an expansion chamber from a DT would work, I have ordered the crank seals today and I think that I need to address the exhaust leak next. Thanks for the input.

[Airhead]

yeah for what you want it for a DT pipe would work sure it would, the difficulty though is getting any other pipe but the original to mount right on the bike...