C-60 engine .60 over pistons Fuel

[oldiron29]

When you guy build C-60 engine with .60 over pistons, Do you need to rejet the carb? I have it running with half choke. I have cleaned carb and ran wire through jets. Just thinking it might need more fuel to run with .60 over pistons?

[Cecil]

No I've done a couple with those oversized pistons. You have some kind of fuel issue.

[oldiron29]

Cecil, What metering jet have you used .030 or .035 ? It is an F cub engine with out style carburetor.

[Cecil]

To be honest I don't remember. If you have a .35 use it. Also check for a vacuum leak. If you need half choke I'm pretty sure it's fuel.

[MiCarl]

It's not .60, it's .060 - makes very little difference to the displacement.

[jckengr]

When I did my cub engine (.060 over pistons, .030 head mill) I opened up the main fuel jet diameter 1 letter number and function was very satisfactory. You may not be aware that the cub tractor engine manifold intake bore is approx. .125 smaller than the carb throat diameter. I used a cub power unit manifold which matches the carb throat diameter. I found the cold weather starting performance greatly improved and the power increase noticeable. I have wondered about cooling effects, however mowing with a 5 foot belly mower has not shown any overheat situation.

John K

[John *.?-!.* cub owner]

Loosen the gas cap to see if that makes a difference, also if you have an inline fuel filter it needs to be for a gravity flow setup. Also check for debris obstructing fuel flow from tank inlet or sediment bowl.Remove the bottom plug from the carb and see if you have a good steady stream, drain out a good teacup ful to make sure something is not restricting fuel flow. The .060 oversize is such an extremely small displacement difference it will not make any difference if carb is correct, no leaks in intake manifold gaskets, etc. What else has been done besides boring engine? Do not overlook a bad coil or burned points, I have seen them mimic fuel starvation, though it does not happen very often.

[oldiron29]

John, I just put it back together. was .060 when I got it I, put out really good smoke screen. I never saw ring worn so bad.
I honed it new aluminum pistons new rings, new valve, guide and ground seats. Just started it and check oil pressure 40lbs. I know it had been run on 12 volt I don't know for how long, so I am sure points are burnt. I will get everything checked and adjusted see if I can get it straightened out.