over revving

[dylan]

hi all new rebuild li 125 s3 starts up second kick every time i can get gears no probs tickover not good stalls if not revving but when i seem to stop at a junction etc and go it to fisrt or neutral it revs like mad when i set of again runs like a dream just noticed slight leak bottom ov the petrol tank any ideas please cheers

[Scooter Paul]

Be careful. Could be a number of things but an air leak will give these symptoms and air leaks can be expensive such as holed Pistons.

Paul

[St George]

I agree with Paul, that engine is getting air from somewhere via a leak : )

[dylan]

Thanks forgot to mention if it helps it's just come to me the scooter didn't do it on first 20 miles the engine was cutting out then on a run even when changeing gear so a friend messed with tick over I think but still doesn't tick over good with out revving the engine but when running no probs what so ever until it revs like mad as I'm pulling up now and again at junctions iv done 45 miles running engine at the moment 25 mile with this problem

[MickYork]

Is it a Jetex carb'......

[davla]

Maybe the exhaust manifold has come loose from the barrel?

[dylan]

Dellorto I think

[Donnie]

Is it a Jetex carb'......

Bit unfair to jump immediately to the jetex when the op has put a mate has "messed with carb"

I don't think it'd matter what carb, jetex, mikuni or delly if the people trying to fix it don't actually know what they are doing, as evidenced by the original post for help.

I'd say you need to be checking over several things, including getting some history on the engine as the scoots new to you.

But yea, Id be checking the basics for air leaks first, ie carb, manifold, exhaust and cylinder head. Following that a strip and check what jets are in the carb would be a good next step.

[Donnie]

Also dylan, where are you in the country as there may be someone local can have a looksee?

[MickYork]

Is it a Jetex carb'......

Bit unfair to jump immediately to the jetex when the op has put a mate has "messed with carb"

I don't think it'd matter what carb, jetex, mikuni or delly if the people trying to fix it don't actually know what they are doing, as evidenced by the original post for help.

I'd say you need to be checking over several things, including getting some history on the engine as the scoots new to you.

But yea, Id be checking the basics for air leaks first, ie carb, manifold, exhaust and cylinder head. Following that a strip and check what jets are in the carb would be a good next step.

My experience with Jetex carb's cost me 2 holed pistons in 2 months (different carbs). They were correctly set-up but caused the mixture to run lean at irregular intervals. The general suspicion was that the casting was slightly porous and caused the problems.

I appreciate some Jetex carbs run fine but i'm sure i'm not the first to question the Jetex's reliability.

[Donnie]

Your not the first and im sure not the last, but this problems obviously air leak related most likely is all im saying. Going straight to something generic like blaming a jetex could lead him down the wrong path completely.

I've had 3 jetex's and several mates with them, not a single one's had a problem in 8 years. OK, one, but that was after the fella had fitted a blasted and sprayed petrol tank and not washed it out, then did 600 miles from Bedford to Kelso and back and it only started having problems the last 50 miles. Of course his mugello needed a complete replate too!

[dylan]

My friend is out of the country for 2 week he knows lambrettas was just wandering if it's safe to run it in with this problem as I can do 15-20 miles per day round indust est based in pontefract

[Scooter Paul]

I wouldn't. A holed piston is a messy affair. Not just a case of replacing it. The debris goes everywhere into the crank area, ports etc.

Paul