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Yamaha V80 2 stroke not running correctly

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Hi folks.

Just wondered if anybody could help...

I rebuilt a Yamaha V80 engine (same as PW80 if that means anything to anyone) as i bought it on ebay as a runner, but the case got cracked in transit, not ideal.

Anyway, i stripped it down and used the cases from another engine and rebuilt the engine. All seemed ok with build, i used Threebond to join the halves together as recommended on forums (no paper gasket).

Anyway, it doesn't run properly. I feel i have fooled around with everything trying to get it sorted.

Basically, in stock form, carb, autolube, air filter etc) it just doesn't run well. It bogged down massively and wouldn't allow for any road speeds.

I attached the carb to air filter rubber pipe from the original engine (v50) which has approx 50% diameter reduction and it ran really quite well, getting up to 50mph easy enough. The air filter was old, so quite restricted and the reduced pipe meant that air getting in via the filter would be a lot less than intended by Yamaha, which meant i must have been masking a fault.

I can not get away from the thought that i have an air leak somewhere, but i just need some ideas as to where it could be from and whether there is anything else to consider. When i rebuilt the engine i replaced crank bearings and seals.

Things i have done to try and solve my issue:

Put sealant on the base gasket and reed set (no difference)

replaced carb with a brand new one (worked worse than original, Chinese crap)

changed the jets and fitted a K&N that i had bought during the rebuild (terrible effect obviously, but i'm hoping to use once it's working properly)

adjusted and played with most configurations of needle height and idle jet screw

checked compression and was at 120 which is ideal

The exhaust is the same Fuego exhaust i fitted before the removal of the 50cc engine, but the 50 and 80 engines have exactly the same exhaust (diameter etc) so can't see that the exhaust would cause an issue as it worked fantastically well on the 50 compared to the standard one.

I am at a point where i may have to re-fit the 50 as i need to use the bike, but it was really too slow and would give me less chance to fault find whilst on the road.

So, can any 2 stroke folk help with my problem, i know there are a few of you on here!

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Why do you think thers a airleak,? are the revs not returning to idle when engine hot . if this is the case ,spray WD40 or carb cleaner at suspect areas, should be a reaction to revs in the problem area,

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Aye up,

The only reason i think air leak is because the bike doesn't run with the standard set up, i have to restrict the air in to get it to run.

Like i said though, i'm open to any other suggestions that could cause the problem.

The bike currently struggles in third gear, the original air filter has broken up today amd you can't buy them anymore, hence why i bought the k&n before.

It pulls ok in 1st, a bit restricted in second and doesn't pull in third. I can get it to 30 in second but it wheezes up to only around 38 in third.

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