272xp got me not stumped.

[Okie294life]

Bought it with a scored top end, work done so far:
1. New crank seals
2. New piston/cylinder non oem
3. Rebuilt carb

- When i start it up it won’t idle at all, and only will start after choked. If will run at full throttle, but is screaming like a demon and not smoking at all. I cranked around on the hs jet some to see if it would calm down after cranking the hs jet open, didn’t really seem to make much impact. This is with both jets set one turn out. I tried to pressure test it but had cork in the intake as a spacer, and it was leaking. I got up to about 5psi and no leaks from the crank seals or the head so I feel pretty good about it at least beginning this process without any air leaks. Where to start? I’m bumfuggled.

 

[cscltd]

Fuel line, fuel filter?
Should pressure test before ripping it apart
Fixing it before knowing cause can result in same thing happening again or lots of unknowns.

 

[Gord404]

well if everthing else checks out ( vac test is very important and that wasn't done)- sounds like you have an air leak in carb block or carb gasket between the two or your carb has got other problems that just a rebuild won't solve it- another thing is the gaskets you use on either end of your carb block should be oem or at least not the chineese black ones, need I say they are not up to sealing properly,so do a by the book vac and pressure test- you can put a piece of innertube with a couple of bolt hles in it and put it between your carb and manifold- block off the exhaust the same way and pump through your spark plug hole

 

[singinwoodwackr]

Bought it with a scored top end, work done so far:
1. New crank seals
2. New piston/cylinder non oem
3. Rebuilt carb

- When i start it up it won’t idle at all, and only will start after choked. If will run at full throttle, but is screaming like a demon and not smoking at all. I cranked around on the hs jet some to see if it would calm down after cranking the hs jet open, didn’t really seem to make much impact. This is with both jets set one turn out. I tried to pressure test it but had cork in the intake as a spacer, and it was leaking. I got up to about 5psi and no leaks from the crank seals or the head so I feel pretty good about it at least beginning this process without any air leaks. Where to start? I’m bumfuggled.

Try 7-10psi. Sure sounds like an air leak.
You need better test plates to find air leaks than a cork…
Did you test the carb?

 

[Cantdog]

You didn't list the o-ring that seals the oil pump to the case. That would be my first guess.....as said ....a pressure and vac test will show the issue or at least rule out an air leak.

 

[singinwoodwackr]

You didn't list the o-ring that seals the oil pump to the case. That would be my first guess.....as said ....a pressure and vac test will show the issue or at least rule out an air leak.

And, you can’t do the test with the clutch removed.

 

[Gord404]

And, you can’t do the test with the clutch removed.

272 it doesn't matteras long as the oil pump is on which contains the seal and big o ring- 372 it's a must- doing a 61 right now myself- most are the same setup as the 272

 

[J D]

Check impulse isn't leaking or partially blocked (saw & carb)... that would cause lack of fuel leading to the symptoms you describe.
A defective fuel pump diaphragm, fuel line, or fuel filter would cause similar symptoms too