Carb size for 80cc open transfer piston ported engine

[radiatedmocha27]

So I noticed that my bike is running lean and I decided to upgrade to a piston ported open transfer cylinder using a 48 and 1/2 mm high hole piston on a 40 mm long rod crankshaft The cylinder is an LD80 with stock ports, at top dead center the bottom of the Piston skirt just barely clears the intake port and I have about one and a half to 2 mm of overlap at bottom dead center for the piston I'm curious as to what the best carb sizing is for performance using this configuration?

 

[DieselTech]

19-21mm will be plenty of carb for a performance build.

 

[radiatedmocha27]

So I noticed that my bike is running lean and I decided to upgrade to a piston ported open transfer cylinder using a 48 and 1/2 mm high hole piston on a 40 mm long rod crankshaft The cylinder is an LD80 with stock ports, at top dead center the bottom of the Piston skirt just barely clears the intake port and I have about one and a half to 2 mm of overlap at bottom dead center for the piston I'm curious as to what the best carb sizing is for performance using this configuration?

The overlap is on the exhaust port BTW, negligible given I run with an open header

 

[radiatedmocha27]

So I drilled out my carb jet just a little bit because it was running lean this is the new plug/ole plug

 

[radiatedmocha27]

I also adapted an LD80 open transfer cylinder to the 40 mm crank and no there is no piston clearance issues due to the help of some extra gaskets

 

[Chainlube]

I also adapted an LD80 open transfer cylinder to the 40 mm crank and no there is no piston clearance issues due to the help of some extra gaskets

Does the piston come above board at TDC? Two head gaskets will create an air leak.

 

[radiatedmocha27]

Does the piston come above board at TDC? Two head gaskets will create an air leak.

Actually running extra base gaskets and so far no leaks and the ports line up near perfectly, however I HAVE doubled up top gaskets in the past with no issues

 

[Chainlube]

Actually running extra base gaskets and so far no leaks and the ports line up near perfectly, however I HAVE doubled up top gaskets in the past with no issues

If the piston comes up flush with the deck, or a bit less, then a second head gasket is only going to lower your compression. I've sanded my head gaskets down in the past to raise my compression, it probably wasn't a lot, though. What can you expect for a 6:1 compression engine?

 

[radiatedmocha27]

I actually had to throw on 3 base gaskets on the bottom because the piston did clear top dead center quite a bit to the fact that I couldn't even bolt down the head properly without binding up the rotating assembly, Don't judge me because this was only a $30 cylinder and piston kit and I wanted to experiment to see if it was possible there are three base and three top gaskets, all stainless steel on top and the nice hard tan ones on the bottom which are sealing absolutely amazing I've gone through three tanks of gas and so far the three top gaskets are holding up and I've checked inside the cylinder and so far there's been no damage or air leakage, I simply added one until the squish clearance was made it took three gaskets on the bottom to get the port timings to line up and they line up great, I'm sure if I took the time to modify the head I could have made the clearance without having to add the top gaskets which is something I may do later in the future lol, but it'll still pull a comfortable 36 mph uphill on a 28 tooth sprocket

 

[mony0_3]

What's your top speed with that 28t sprocket?