Rebuilt R5 Engine break in

[R5HiFive]

Hey again,

All the advice I've gotten here has led to me now starting my 71 R5 and breaking in the fresh top end. Wiseco pistons and bore.

Problem is that the left cylinder is overheating.  Running 32:1 premix. New vape ignition with key way to set ignition.
 
All went well for two start ups and slow undulating revving of the engine. I go for the third start up after letting the engine cool till warm and the rpms climbed higher and higher to 5k without touching the throttle. So I killed the engine, started again, and the same thing happen. I tightened the carb boots, started again, and it stayed around 2.5k.  The left cylinder got really hot quick and the right cylinder was warming up normally. 

Any guidance to fixing this issue would be greatly appreciated!

Thanks for reading,
Tommy 

[rodneya]

Did you do a leakdown test after assembly?

[dgorms]

New crank seals? You're sucking air somewhere.

[R5HiFive]

Didn't do a leak down test.  The engine was running fine before the rebuild so I guess I figured the crank seals were still good. 
Will do one and report back

[m in sc]

if you dont know when that seal was replaced, just do it. will probably take less time than doing a leakdown test. you dont need to split the case to do it.