smallblock Timing question

[james_se-r]

truck runs poor when it warms up if the timing is not advanced past the standard 6-8 degrees at the distributor. the engine will back fire up through the carb? If the timing is advanced it seems to run better? any ideas of what is going on and how to fix it??? thanks

[amac209]

what year is your truck?? if it's an older carb engine it should be set at 8 degrees btdc while the vacuum advance is disconected and plugged. when you rev the engine it should advance to about 30 degrees at around 3000 rpm if it doesn't the centrifugal advance is sticking. the vacuum advance should be conected to a ported vacuum source so it applies vacuum when the throttle is opened. check the vacuum advance diaphram on the distributor it might be leaking. should hold vacuum, try to blow through it. give me a little more information and i can be more specific

[bduff509]

Back firing through the carb could mean that your timing set jumped a tooth. Does your mark dance around when checking the timing? You can get your timing mark to line up & be a tooth off on your valve timing. If you think it might be your timing set replace it quick. Stock heads typically have a lot of valve clearance but bad valve timing can destroy your motor fast.

[calgary_redneck]

Check to make sure the balancer hasn't slipped to

[bduff509]

Good point. Stock balancers are not that expensive. If you've been horseing your engine much remember they're only rated for 4500 RPM. I raced one (per class rules) for 3 yrs. at over 6000 RPM 'til I noticed it wobbling. I replaced mine & the next week another guy had his blow apart. It would be difficult to tell if it slipped. You might be better off just replacing it.