Speedster 657x, port engine hard to start when hot

[jagilbert]

Port engine starts fine when cold but is very hard to start when hot.

• This is a "new" 657x shortblock from SBT. I moved my old carb, intake, rotary valve cover, etc from the old to the new engine. Installed and timed new rotor valve, new plugs, new lines from oil pump to rotor valve cover. The old rotary valve cover was kinda scored, but I polished it as best I could and got rid of any burrs.
• Have not made any adjustments to carb since moving it to the new engine.
• Still running double oil during breakin: 50:1 premix in the tank, plus oil injection.
• Once its running, it runs great just like the other engine, cold, warm or hot
• It cranks over just as fast hot as cold (i.e. its not acting seized)
• Choke doesn't help to start when hot
• The only way to start it when hot: No Choke & 3/4 throttle. After several seconds it will sputter and struggle to life, then run fine.
• Compression Mag: 132, PTO:135
• The other engine starts and runs great, cold, warm or hot.

Any ideas?
Thanks!

Jeff

 

[Waterluvr]

Your needle and seat are leaking fuel, effectively negating any real pop off. A service kit including a new needle and seat and cleaning should have you back in business.