Hesitating engine

[Rackarboda]

I have been having these problems with a studdering and coughing 383 since I bought the car a year ago. If I put a little effort on the pedal it almost sounds like it’s going to die before it makes a loud sneeze in the carb and pulls off a little. Feels like maybe 100 bhp. Flooring the pedal doesn’t make it either, hesitation at first, a cough, the engine revs and eventually coughs some more. At idle it sounds quite ok, but when cruising it feels like small hic-ups every now and then.

When I bought the car it had an Edelbrock 750 that I fiddled with a little before trying two other Holleys, and finally bought a restored Carter just to be sure. Nothing. Tried to adjust the mixture screws without any luck, if I screw them inwards the idle decreases around a turn from the bottom, but when unscrewing I can go on forever without any result. Changed the sparkplugs and wires, switched to a Pertronix ignitor and coil and swapped the distributor cap. I have checked the firing order maybe 10 times.

Finally took out the engine and had it apart. Cleaned everything, swapped timing chain and gears (looked like crap), fuel pushrod, and had the heads/valves renovated. Really hoped it would make a big difference, but absolutely no luck. Cleaned the fuel lines and even connected the hose directly to a small dispenser just to try. Checked for vacuum leaks.

It’s starting to get really frustrating and I’m running out of options. My last resort in mind is to try with an electric fuel pump, or else I have no idea what to do next. Any opinions?

 

[texas69bee]

Timing and A/F???
Here's an article that fits your description .
http://www.badasscars.com/index.cfm/page/ptype=product/product_id=95/prd95.htm

 

[oldbee]

Yup after 4 carbs& no difference I'd be playing with timing.

 

[747mopar]

I'd double check your timing as well. That many carbs doing the same exact thing sounds fishy. Try to think of what hasn't been changed, it sounds like a lean burn situation with the air screws being able to be turned that far. Where's your timing set right now, have you watched it with a timing light?

 

[PurpleBeeper]

All of you are thinking what I was. #1 fuel mixture or carb issue, #2 timing chain getting worn, #3 vacuum leak. Geez...you've worked on all those. Coughing out of the carburetor is what I've always assumed is an intake valve a little bit open (for whatever reason....long push rod, junk on the valve seat, timing off, etc.) so that the spark in the combustion chamber could ignite the air/fuel inside the intake.

747's idea of taking a really close look at your timing curve is a good one...maybe a weight fell off or spring broke?

 

[69 GTX]

Vacuum advance maybe stuck.

 

[NOSTRT980]

check push rods and rockers

 

[Bill Monk]

I'm leaning toward timing for sure because any backfire through the carb is usually either timing, a miss or a lean condition but we have already swapped carbs. We need to eliminate the miss first. I agree with 69gtx on checking to make sure the vacuum advance isn't stuck. Take the cap off and while you're at it check that for cracks, and suck through the hose. Also check your plugs, they will tell you a lot about what's going on in the engine. This will help: http://www.4secondsflat.com/Spark_plug_reading.html

 

[mmissile]

Timing jumped?

 

[Rackarboda]

I'd be damned if I hadn't checked the timing issue, but I put it through the scope a couple of times to find some answers. What I did forget though, was that when I lined up the gears, the timing mark at the harmonic damper was approximately 5° off (see picture). I think I need to put on a timing tape to get the correct values, the stock one only goes to 15 and I can't get a correct advance value.

Btw, I've checked the advance in the distributor, seems to be working fine. I will check the sparkplugs as well and see what's going on in there. Thanks for all the help, I'll get back!

 

[gtxno1]

check fuel pressure make sure supply line at the tank is not cracked

 

[383MovingViolation]

My 440 Roadrunner does the same thing. Mash it real quick and it will sputter stumble and cough before it takes off. I have checked many things also, timing, new metering jets in the Edelbrock carb, adjusted jets etc. Starts great and idles great. Runs fine at cruising speed so ??????????...don't know.

 

[Lionized]

Compression check? Vacuum leak(s)?

 

[Rackarboda]

check fuel pressure make sure supply line at the tank is not cracked

I tried connecting the fuel pump directly to a small bottle without any luck, but I am quite curious about the fuel pressure. The plastic fuel filter fills up nicely (sometimes), but I don't know if the carb needs a constant pressure?

Compression check? Vacuum leak(s)?

I've checked for vacuum leaks, but still need to make the compression check.

 

[miller]

Seeing your balancer, might also check TDC, to make sure the balancer outer ring hasn't slipped.
Put #1 piston at TDC, and see if the balancer timing mark lines up with 0.

 

[Bill Monk]

Miller is right on checking TDC. Once you establish true TDC and mark it, use a good advance timing light, you wont have to fool with the timing tape.

 

[PurpleBeeper]

Vacuum advance maybe stuck.

Good point 69

 

[PurpleBeeper]

Seeing your balancer, might also check TDC, to make sure the balancer outer ring hasn't slipped.
Put #1 piston at TDC, and see if the balancer timing mark lines up with 0.

Another good point. Very rare, but it has happened to me

 

[PurpleBeeper]

I'd be damned if I hadn't checked the timing issue, but I put it through the scope a couple of times to find some answers. What I did forget though, was that when I lined up the gears, the timing mark at the harmonic damper was approximately 5° off (see picture). I think I need to put on a timing tape to get the correct values, the stock one only goes to 15 and I can't get a correct advance value.

Btw, I've checked the advance in the distributor, seems to be working fine. I will check the sparkplugs as well and see what's going on in there. Thanks for all the help, I'll get back!

View attachment 431643

Wow..... I had the same issue (5-degrees) with an old purple 292/509 cam. I put in a 4-degree advance bushing in the timing gear (old-school way, offset bushing), so I never ran the cam 5-degrees retarded. "Maybe" that's the issue? It would be sort of like a timing issue you couldn't adjust for...sort of.

 

[AMX364]

"putting it through scope" is not the same as checking the timing and advance. It can show the firing pattern and find a bad plug or wire. Check your timing static, vacuum advance and total and post the results along with rpm for mechanical advance. There are some smart people on here and should be able to help.