Bad fuel, dirt/sludge in tank, fuel filter, accelerator pump diaphragm leaking?

 

Thanks for all the comments and suggestions.

The compression test was done with the carb off.

I am also suspicious of the front cylinder readings but it was consistently the same every time and I ran it front-rear three times. Even so, the connections could have leaked. I'm thinking I need a better way to connect to the front cylinder or lift the tank up and out of the way.

here's what I think is NOT the problem so far...

the carb has been completely rebuilt and thoroughly gone through three times
it is getting a good supply of fresh gas
the intake gaskets were replaced and leak checked
the exhaust pipes were pulled, inspected, and the exhaust gaskets were replaced and leak checked
the ignition module, coil, plugs, and wires have been replaced with new performance parts
the valve train looks like it is working just fine...both valves are opening and closing and the cylinder is making pressure...

I cannot think of anything else so I guess I am pulling the head tomorrow.

 

Come on man; 90/120 CCP? New the TC88 will make 155-160 all day; even at 65K miles CCP should not be much below 150psi. Those CCP readings would have me doing a leak down test and anticipating a top end rebuild. You could have broken a ring on the front cylinder. Time to do the big bore.

 

I am back on the road again...the ignition module was the problem all along...then there was my screwup.

After I had gone through the carb and replaced the exhaust and intake gaskets without any luck, I was sure the ignition module was the only other thing that would cause this kind of problem when I ordered the new SE performance kit. While I was waiting for it to come in (it was weather delayed for a week) I started doing other things and just made things worse. When I second guessed myself and went back through the carb again, I got the needle jet in upside down when I put it back together. Although I pulled the carb and opened it up and looked it over again yesterday, I didn't take out the main jet or needle jet holder and since I could see the needle jet sticking up in the carb, I just "assumed" that it was in right and did not physically take it out and make sure it was all in correct. Sooooo....when I put the new module and coil kit in it had a whole new problem and it really did run worse. Before it was backfiring and stumbling but I could run it down the street, but after I replaced the module and coil, it was really AFU with that needle jet in backwards.

I pulled it all apart today getting ready to pull the head and as I was looking over the carb for the umpteenth time, I saw the jet was in upside down...embarrassing, but easy fix. Put it all back together and tuned the carb and it runs great. I put the old module back in and verified that it was the original problem.

From the beginning, the problem seemed to be classic carb/vacuum symptoms. I kept telling myself that and kept going back through the carb only one time too many and got complacent. The only thing I found that I can positively say was bad was the leaking rear exhaust gasket. That wasn't much of a leak but it was enough to make it start running lean.

The compression test setup I used was an auto parts store rental unit and the connections were flaky. I bought one this morning and ran the cold compression test several times again with the new gauge and the front just makes 120 and the rear is slightly more. According to MoCo, that is the minimum. It also means that it is time for a top end and I just so happen to have one laying around here.

Thanks for all the suggestions and advice.

 

Cool ... Glad to hear you found that gremlin !!

 

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Thanks for following up on your topic.