Modern Vespa

Main Transfer port near to exhaust port, measured up to the top. Measurement should be someing like 46.50mm

Ok, exhaustport 32,6. Main transfer 46,8. Boost (?) 48,4 the pic shows the lowest position of the piston

And a gasket top 1 mm

Exactly how much of the piston edge is out the top of the cylinder with no base gasket fitted? I am guessing something like 0.5mm.

With 0.5mm of piston out of the cylinder the porting is just about ok. 124/184 Still a little too much but might just be ok with your narrow topped exhaust port.

The stock rings wear very badly when widening the exhaust port. I only know because I have done it too much before. How wide is your exhaust port at its biggest?

If you have less than 0.4mm of piston out of the top of the cylinder, then the cylinder will need to be shortened at least 1mm at the base or go back to a 57mm crankshaft. And there is always the option of a new cylinder and starting again

Its about 0.77 mm under the top as I remember...without no gasket under the cylinder. I have widening the port just as much as it were told in the german O-tuning guide.
And the question about the cylinder; My plan is to get either a pinasco 225 or a Malossi 220 this autumn . Witch one do you prefer? 8)

0.77 under means this cylinder is as you say 130/188. This will make power way to high to pull your gearing well and with the small size of the transfers and exhaust ports the power will not be so much (but still way more than stock). If it did rev out you will find it needs a bigger carb. It will run but going to under performing until Autumn.

Can you get hold of another stock cylinder that fits your piston? With your 60mm crank and skimmed head, we could make it go pretty well without too much work.

Most of the kits now are close to the limit of the Si carb. The Polini runs well on an SI and 60mm crank.

[quote="Jack221"]0.77 under means this cylinder is as you say 130/188. This will make power way to high to pull your gearing well and with the small size of the transfers and exhaust ports the power will not be so much (but still way more than stock). If it did rev out you will find it needs a bigger carb. It will run but going to under performing until Autumn.

Can you get hold of another stock cylinder that fits your piston? With your 60mm crank and skimmed head, we could make it go pretty well without too much work.

Most of the kits now are close to the limit of the Si carb. The Polini runs well on an SI and 60mm crank.[/
All right, I'll leave it like it is for now. But do I need to put a gasket for example 1,5 mm under the cylinder? Or doesn't that make any difference? Another question (sorry for harassment..) The engine is hard to start cold after I drilled the hole from trottelchamber to mainjet to 2,5 mm. Do you think it leaks fuel into the engine? (I left the fuel tap open overnight)

You only needed to dril 2.0mm but 2.5 should be ok. Try next time with the fuel off. Could be that the float needle is worn. Often just a badly set mixture screw.

If you put anything under the cylinder it will go worse. Already too high. Can't you get an old cylinder form someone or ebay?

Aha! My mixturescrew is 4 turns out. And I have ordered a new trottel house (Cosa). I'll look for another cylinder. Thanks for all feedback by the way!