engine and carb rebuild

[waynekemp]

can anyone help i have had my li125 engine rebuilt and i have changed all gaskets etc on dellorto 18 carb when i come to kick over air/fuel mixture is coming out of air intake and not going to cylinder thank you

[grandpa]

Hi Wayne
Remove air bellows and place hand over carburettor you should feel suction when you kick engine over with throttle open Do you have good compression?
Could be ring stuck,head gasket leak,air leak piston in wrong way round inlet manifold leak
Good luck
Grandpa

[waynekemp]

hi i have removed bellows and air fuel mix is being blown out under pressure[ you say the piston could have been put in wrong way round ] is that possible wayne

[grandpa]

Hi Wayne.
Yes the piston can be put in back to front,the arrow or 'S' stamped on the piston always faces exhaust port.However ,I have no personal experience of whether that would cause air to blow out rather be sucked in.Perhaps an Adult may come along and comment.If you haven't got a manual you need to buy "the complete Spanner's manual Lambretta second edition by Martin "sticky" Round.
Certainly air needs to be sucked in,(Induction) for it to run.Its a pain, but if no-one comes along with a better idea you may have to remove head to check that the arrow is facing down towards the exhaust.No need to take engine out....Rear shocker off bump stop off cowl off then head off!
good luck
Grandpa

Come on chaps 108 views and no comments

[holty]

normally mixture being expelled out of the carb would be down to too much inlet duration, in other words the inlet being open for too long, there are 2 main causes, inlet port too big, or piston skirt shortened too much. you say the engines been rebuit, is it a new piston, did you compare to the old one, if shorter that could be your issue, or has the barrel been butchered by a diy tuner? the suggestion about piston wrong way round is worth a check but dont think it would cause it to blow out the way you suggest, who rebuilt the engine and what knowledge of the engine do you have ?
holty

[waynekemp]

thanks for info i have bit the bullet and ordered a new i50 cylinder and piston kit so i know all parts the same by the way the piston was in the right way thank for help

[hullygully]

does it only happen when your fuel tap is turned on?

[byron]

...Yes the piston can be put in back to front,the arrow or 'S' stamped on the piston always faces exhaust port.

... generally the rule, but I have known pistons to have the arrow stamped incorrectly... check the transfer cutouts line up, and the ring peg position is also a clue