here I am again hopefully for the last time with my questions. I had a mech. do a leak down test and the front cyl. was 155 and the rear was 140psi.he said it was leaking past the intake valve.of course he wanted to take it apart right away. the bike finally runs great starts up fine has plenty of power.I said not yet.here is my question the carb pops at highway speeds every so often (throttle steady)and when I roll the throttle real slow she pops( usually when the engine is cold) could this be becouse of the leaking valve? or do I have an issue with the carb adjustments. the plugs are brown with a little black around the edges. the mech said it was the leaking intake valve I'm not so sure about that. when the bike is warm it goes. thanks larry

 

Hey Larry...
If the intake valve is leaking now, it will get worse in time. 155 front and 140 rear sounds pretty good to me.
If the bike starts easy and runs good once it is warmed up, it does not need anything except to be ridden and enjoyed.
Any ironhead Sporty will run like crap when the engine is cold. You have to give them a chance to warm up fully before you go tearing off. I do it this way:
Start it up with choke if you need it (most do) and let it set there and idle for three or four minutes. Then ride off nice and easy for another two or three minutes below 35 mph. You're not in that great a hurry. After that the engine is at operating temperature.
From the sound of it the popping may be in the carb rather than a valve 'leaking'. A leaking valve is the result of warpage and/or a degraded seat which causes loss of compression of course. I don't think you are there yet.........pg

 

Did you check the pushrod adjustment? A little tight and your valve will leak.

 

My '81 had the exact problem and after replacing the rubber seals and clamps between the intake manifold and heads the problem went away.

 

Definitely check the push rod adjustment. Adjust them cold. As the engine warms up they loosen up from expansion.

 

my 1980 did this come to find out my battery level was low.