danthedirtguy

Hello, all,

I am helping a buddy with a timing issue, I put it to spec and it back fires when accelerated...could it be timing chain jumped?

1970cs

How many miles are on the engine? You could go back to basics and pop the cap and check for excessive slack by baring the engine backwards and forwards and see how much lag when the rotor moves back the other way.

Also while you got the cap off, bring up #1 on TDC and see if actually pointing directly at #1 on the cap.

Pat

oldcutlass

Is it backfiring through the carb or exhaust?

MDchanic

And of course all the other questions:

Stock compression?
Stock cam?
Stock distributor?
Stock emissions setup?

What "stock timing" have you set it to?

Have you verified that the balancer mark hasn't "walked"?

- Eric

danthedirtguy

Its back firing through carb.....set initial timing to 6 degree ( yes with vacuum advance line disconnected and a cap in end of line) it would barely run..so i timed it by sound to get it running decent and it was not even on the timing tab.

Pat, I was thinking i will do your idea and check tdc and where the rotor lines up to.

My buddy just bought the car so i have no idea of specs other then holley carb,header, edelbrock intake and supposedly rebuilt.

Thanks all for replying...

Octania

If the technician is capable, timing "by ear" can sometimes be better than "by spec" - I know a guy who does not have a timing light, he sets it to as much as it will take w/o detonation. If the timing mark is off, then going "by spec" is pointless.

oldcutlass

Sounds like plug wires are swapped. Remember firing order is CCW.

MDchanic

In that case, I would recommend starting from scratch - verify that the timing mark on the balancer is correct, that the cam timing is right (to the best of your ability), that the spark plug wires are in the right order, that the dwell angle is set correctly.

- Eric

danthedirtguy

All good advise....gonna go back to basics and check plug wires and check tdc.

Eric, when you said check cam timing what do you mean?

MDchanic

Well, ideally, if you know what cam it is, you can use a degree wheel and a dial indicator to check lift at X degrees to be sure the cam is set right.

It gets stickier if you don't know the specifics of the cam.

Unless you have an innate sense of proper valve timing (and I suspect a few here do), you would have to remove the timing cover and get a look at the chain and gear to check alignment. Ordinarily, if you were told that an engine had a "new cam," you would think you could believe that the chain and gears were fine, but if you look here, you can see that even a fairly new timing set can have a hellacious amount of slack if it was cheap crap to begin with.

If you really have no idea what's in there, it may be worthwhile to check.

- Eric

danthedirtguy

Thanks Eric, thats what i thought you meant