She's running rough and backfiring....HELP!!
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Laughing Gas
Joined: Jul 2001
Posts: 849
Likes: 14
From: Fayetteville, NC
She's running rough and backfiring....HELP!!
Ok...here's the deal. I let my truck set for a week to fix the rear end. Started her back up and she ran like crap. Idled rough and backfired going down the road. I checked the timing and it's not jumping around and is set at 30 BDC with the advance hooked up. The other day before I left work I changed the plugs and then it wouldn't even run. It just kept backfiring really back. I got it home and done a complete tune up. You name it it's been replaced, retorqued whatever. It runs a little better now but it's still running rough and backfires a little. Does anyone have ANY idea what's causing this??? Im' half tempted to pull the timing cover and check the chain and all. I have another set in the garage I was saving for a complete rebuild in the future. What do you think....
Senior User
Joined: Apr 2003
Posts: 221
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From: Greater Cleveland Ohio
She's running rough and backfiring....HELP!!
Hello,
Check your vacuum connections. Particularly at the manifold tree and carburetor. Also listen when its running for any swishy sucking noises. I would pay close attention at the carb/manifold area. If that doesn't turn up a suspect, try the timing.
Advance the timing a bit. See what happens at 10 degrees BTDC, then try 0 degrees TDC (both with advance vacuum plugged). I don't know if you have a Cleveland, M, or 400, but the hot rodders have set timing as far as 42 degrees advanced.
Unfortunately, if it backfires too much, the power valve in the carburetor is prone to malfunction. Hopefully its not too late.
Have you done any work like removing the carb?
Check your vacuum connections. Particularly at the manifold tree and carburetor. Also listen when its running for any swishy sucking noises. I would pay close attention at the carb/manifold area. If that doesn't turn up a suspect, try the timing.
Advance the timing a bit. See what happens at 10 degrees BTDC, then try 0 degrees TDC (both with advance vacuum plugged). I don't know if you have a Cleveland, M, or 400, but the hot rodders have set timing as far as 42 degrees advanced.
Unfortunately, if it backfires too much, the power valve in the carburetor is prone to malfunction. Hopefully its not too late.
Have you done any work like removing the carb?
Lead Driver
Joined: Nov 2000
Posts: 6,628
Likes: 345
From: Albuquerque
She's running rough and backfiring....HELP!!
30 degrees is too much initial timing, way too much! However if you chain jumped I would expect to see retarded timing. (I could be wrong there). With the backfiring it's possible the balancer broke loose and the outside ring turned giving you false readings.
Power valve on a Holley?
Distributor sheared the pin?
Stuck mechanical advance?
Power valve on a Holley?
Distributor sheared the pin?
Stuck mechanical advance?
Thread Starter
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Laughing Gas
Joined: Jul 2001
Posts: 849
Likes: 14
From: Fayetteville, NC
She's running rough and backfiring....HELP!!
Guess it would help if I told you what I had. Sorry. I'm running a 351M. I just found out the previous owner had it bored .030 the other night (after having the truck for two years). Edelbrock 600 carb and Performer intake. Stock distributor with single vacuum advance. I pulled the distributor at work and the gear wasn't broken nor were there any teeth missing. I think I'm going to check the balancer like you said bear. The only three vacuum lines I have are one for the brake booster, the vacuum advance and one I have no clue what it's for. Just goes from the intake to the front right side of the carb next to where the PCV line plugs into. Just out of curiosity...would a pickup coil cause this kind of problem?
Thread Starter
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Laughing Gas
Joined: Jul 2001
Posts: 849
Likes: 14
From: Fayetteville, NC
She's running rough and backfiring....HELP!!
Ok....after a little observation of the motor running and turning it off this is what I noticed and hypothosize. The driver's side head has always had a little tick to it even after I had the heads redone. For quite some time I've noticed that when I turn it off there is a little knocking sound coming form the head like something is still moving. So I pulled the valve cover off and found that the sound is coming from one of the rocker arms. I put my hand on it and it feels like it is moving very slowly almost as if there is a problem with the lifter (such as it it either sticking or something). After about 30-45 seconds it stops. Now...my hypothesis is either there IS something wrong with the lifter or the timing chain has stretched enough to allow the cam to turn just slightly when it stops. I don't know if you guys follow my thinking or not, lol, but what do you think? Is this a possibility?
Posting Guru
Joined: Aug 2002
Posts: 1,214
Likes: 2
From: Minneapolis, MN
She's running rough and backfiring....HELP!!
It's normal for the lifters to bleed down slowly after the engine is shut off. That's what you felt and are probably hearing.
30° timing might be OK with the vacuum connected but you should check it with the vacuum disconnected and plugged. That way you have a stable reference to refer to. If the vacuum changes, the timing changes. Another thing to check is the total timing/advance. Look for about 38° to 40° total.
As for the missing/backfiring. I'd first check the firing order and make sure squirrels haven't set up housekeeping in the tailpipe. If that's right, then do a compression test. It's possible that the timing chain has stretched/jumped and the timing has been reset to compensate. Try rocking the crank back and forth to determine the slack in the chain. Just a little is normal. You'll feel it if there's a lot of movement.
Hope this helps and good luck.
Greg
30° timing might be OK with the vacuum connected but you should check it with the vacuum disconnected and plugged. That way you have a stable reference to refer to. If the vacuum changes, the timing changes. Another thing to check is the total timing/advance. Look for about 38° to 40° total.
As for the missing/backfiring. I'd first check the firing order and make sure squirrels haven't set up housekeeping in the tailpipe. If that's right, then do a compression test. It's possible that the timing chain has stretched/jumped and the timing has been reset to compensate. Try rocking the crank back and forth to determine the slack in the chain. Just a little is normal. You'll feel it if there's a lot of movement.
Hope this helps and good luck.
Greg
