Choosing a carburetor for an open class without limits?


Not sure where animal came in . My understanding was a clone type engine .
still high compression and advanced timing is hard on rod bearings .
The OP's stock compression ratio (8.89:1) should not damage the bearings. There are thousands of stock engines run on gas everyday and, as mentioned in another forum here (L206), some last 9 seasons on the stock components. I agree that the timing is fairly high. The prolong over rev beat the piston to death and I am sure the rod felt every pounding.
The Animal I mention is just for reference for a OHV motor running on gasoline.


I read in another post that you are using gasoline / petrol for your fuel?

In the other thread post, you state that your ignition timing is 30 btdc. I think that is too much. On the Briggs Animal, on gasoline, we found best timing was around 26 or 27 btdc with 87 pump octane.

add that to the engine specs and your actual (calculated) C/R is 8.89
bore 70mm, sweep volume 208 cc, head 18cc, head gasket(.010 thk) 1cc, piston dish 1cc and piston clearance (down the bore)3.4cc
From what I read between the two posts is:
you do not have "too much" compression - a 72mm flat top piston & .010 head gasket would be a nice 9.71:1. with a .020 head gasket, 9.28
you have too much ignition timing
you are running at too high of sustained RPM. The rod might take it but the piston won't (see your picture with the detached piston top ring set)
you may need slightly thicker oil -10w40
Thanks for the advice, I'm trying to find a 72mm piston. I also have 2 heads with different combustion chambers. I have to collect all the parts together and then I will understand what compression ratio is obtained. Now the motors are disassembled. We use gasoline with an octane rating of 100, which is 93-94 by US standards.