backfiring, poor throttle response

[cwb]

Here's the story on my '87 60: Rebuilt head, rebuilt carb (by Jim C), surfaced manifolds, desmogged completely (ecept for charcoal canister). Got it back together, finally. I've adjusted the valves, looked high and low for vacuum leaks, checked fuel flow, and I think the timing is good. But it's got a slight backfire and has poor throttle response. It starts decent and idles fine. But it's still a bit rough, backfires just a bit (not any big booms or explosions), and doesn't pull itself very well.

I'm thinking the timing must be off. But does anybody have any other thoughts? I feel like I'm sooo close...yet so far away.

Suggestions?

 

[hj60]

It's most likely timing.
Get a vacuum gauge and a timing light with a dial. Use them to tweak your
timing. 7° is the best place to start, but you may need to play with a
degree or two.
Plus, the vacuum gauge will tell you if you put everything back together
right.
Good writeup on it here: http://www.ih8mud.com/tech/vacuum.php

 

[60wag]

Do you have the carb spark advance hooked up correctly? What altitude are you at? If you chopped the High Altitude Compensator out of the system, you might need to advance the timing another 7-8 deg and lean out the carb a bit.

 

[cwb]

I'm only at about 1500 feet, so I don't think the altitude compensation is the problem (I'm planning to put it back in, though). I think the best bet is the timing, which I plan to check today.

Thanks for the help.