Hard starting when hot By pcdj64 (Read 499 times)

[pcdj64]

i have a 2012 Motofino MF50QT-6, it has a 100cc BBK with naraku touring cam, 41mm crankshaft, naraku carb with #85 main and #36 pilot jet, performance cone air filter and performance exhaust, also has performance coil and CDI with NGK iridium plug.
i installed a high torque starter and 7 amp battery so i wouldn't have slow cranking issues with the BBK.
it does not burn oil or smoke, the valves are set at .03 intake and .04 exhaust, it runs great and has lots of power.
starts up cold no problem and the idle comes down after it warms up, if i go for a long ride and then shut it off it will not start unless i hold full throttle and hold starter, it tries to start, you can hear the starter get faster as the engine is trying and then it will catch and run, it runs great once it starts and will stay running as long as i want it to, the spark plug is not white or black.

anyone have an idea of why it is hard to start hot?
it does it every time after a long ride, if i let it cool it will start up fine.

[Bashan]

My first thought is the valves are set too wide. I would knock that down to .002 on both, or .002 intake and .003 exhaust. I know it's a BBK but they can be hinky on the valve gap. See if that makes a difference, if not we can try something else.

[pcdj64]

Thank you for the reply, i adjusted the valves and it does seem to start up a lot faster and easier.
i will keep you posted.

[cdoublejj]

Jul 20, 2013 4:14:23 GMT -6 Bashan said:

My first thought is the valves are set too wide. I would knock that down to .002 on both, or .002 intake and .003 exhaust. I know it's a BBK but they can be hinky on the valve gap. See if that makes a difference, if not we can try something else.

This was trick a buddy of mine taught me to get a teeny tiny bit more lift off the cam. People always say to set wide gaps when in reality they don't even know what the gap is for. He once tested weather or not the gaps get smaller when something gets hot and he found the gap got bigger.

I think i set mine to something like .002 intake and .002.5 exhaust. The only time i have hard start is in the middle of winter when i leave it outside over night.

[pcdj64]

setting both at .004 which is the smallest on the feeler gauge, it started up without holding the throttle, it would tick once it got hot but still ran good.
the 139QMB can't really handle a 100cc kit very well on a Motofino, the engine made a clunk and then started dumping oil out from the bottom while it was running.
i have no idea what caused the noise but it did stop for a second when the clunk happened then started turning again, it runs fine but i can't use it anymore because of the leak.
the gaskets are dry, it is coming from the bottom of the casing somewhere by the swing arm bolt on the right side, it doesn't leak when th engine is off.