Dieseling, surging - is it time to dump this carb?

[rt-man]

Long-time member, haven't posted in a while. Older enthusiast. Having fuel issues. Question is, fix what I have or slap on a new carb (which I have)?
Car is a '73 Satellite Sebring Plus. Motor is a rebuilt 360, ported heads, 340-spec cam, HP exh manifolds. Engine has about 3-5k on it.
Carb is a Summit 600 vac sec, which I understand is a Holley knock-off. M08600VS. About two years ago, noticed after I accelerate hard (opening the secondaries) and take my foot off the accelerator, the car would surge for about 2-3 seconds. Still does it. Recently, I stopped for fuel, when I shut off the car, the motor dieseled for about 15 seconds. Never did that before. Are the issues related?
About 18 months ago, I bought a rebuilt Edelbrock AVS2, 650cfm w/ electric choke and the tuning kit from National Carburetor. On my previous Mopars, I've always sought out rebuilt Carter AVS carbs to run on the 440s in my '70 Charger and '72 Satellite. Have not put the Edelbrock on the car...yet.

Decision point: car is going to a local classic car dealer for some service next week (unrelated). Should I have them slap on the Edelbrock and tune it or sort out the Summit carb?

Fire away.

 

[R413]

How much money do you want to spend here? Can you install the AVS2 carb yourself? It may run good out right of the box and save you hundreds of dollars. Shop rates are not cheap.

Dump that summit carb, money pit POS.

 

[Rusty knuckles]

I don't know anything about that specific carb but it sounds way out of tune or your distributor has come loose. Slapping a new carb on it isn't necessarily going to fix anything.

 

[69 Sleeper Bee]

I just put that same Edelbrock AVS2-650cfm on the Sleeper Bee and it ran great out of the box, aside from a slight fuel-air & throttle adjustment.
Without knowing about the summit carb you may need the edelbrock-1481 adapter bracket for throttle / kick down hookup.

 

[ruffcut]

I agree with others that a carb change may not fix your problems completely. It may resolve the surging after WOT, but the dieseling is more likely to be resolved with a timing adjustment. JMTC

 

[R413]

I don't know anything about that specific carb but it sounds way out of tune or your distributor has come loose. Slapping a new carb on it isn't necessarily going to fix anything.

If you've never been around a Summit carb then how can you say this. The carb is the top culprit at this point. The timing came be easily changed to see what that does.

Dieseling is the carb throttle plates not backed down to idle or dripping more fuel into the mix at idle.

 

[RR Fan Dan]

Long-time member, haven't posted in a while. Older enthusiast. Having fuel issues. Question is, fix what I have or slap on a new carb (which I have)?
Car is a '73 Satellite Sebring Plus. Motor is a rebuilt 360, ported heads, 340-spec cam, HP exh manifolds. Engine has about 3-5k on it.
Carb is a Summit 600 vac sec, which I understand is a Holley knock-off. M08600VS. About two years ago, noticed after I accelerate hard (opening the secondaries) and take my foot off the accelerator, the car would surge for about 2-3 seconds. Still does it. Recently, I stopped for fuel, when I shut off the car, the motor dieseled for about 15 seconds. Never did that before. Are the issues related?
About 18 months ago, I bought a rebuilt Edelbrock AVS2, 650cfm w/ electric choke and the tuning kit from National Carburetor. On my previous Mopars, I've always sought out rebuilt Carter AVS carbs to run on the 440s in my '70 Charger and '72 Satellite. Have not put the Edelbrock on the car...yet.

Decision point: car is going to a local classic car dealer for some service next week (unrelated). Should I have them slap on the Edelbrock and tune it or sort out the Summit carb?

Fire away.

Yes Edlebrock.

 

[Geoff 2]

If you have the AVS [ Edel or Carter ], use it. It is a better design....for many reasons. One benefit is that the primaries are smaller, which gives better throttle response & mileage. Then, when you want power, you have the larger secondaries.

 

[Geoff 2]

Dieseling. Probably not a carb problem per se, but can be. Usual cause is a big-ger cam, which requires a higher speed. Also aggravated if the engine runs hot, or spark plug heat range is too hot [ should be 5's, if NGK ].
If auto trans, simply switch off the engine with car in gear.

What cam?
Idle speed?
Ign timing?
Etc.

 

[Rusty knuckles]

If you've never been around a Summit carb then how can you say this. The carb is the top culprit at this point. The timing came be easily changed to see what that does.

Dieseling is the carb throttle plates not backed down to idle or dripping more fuel into the mix at idle.

Well you kinda make my point. If the carb is out of adjustment then a couple minutes with a screwdriver should fix it as long as the throttle cable and kick down isn't hanging up.

But the dieseling indicates timing issues. Which can do the same surging when you let off the throttle. 90% of carb issues are ignition issues.

 

[R413]

@rt-man tell us more about this, answer 10 questions please:
what is the idle vacuum?
What is the idle speed?
Does the exhaust smell or burn your eyes?
How old is the fuel in the tank?
When did you last add new fuel?
Has the car sat for extended period before now?
Have you recently changed anything under hood fuel or ignition related?
What ignition system?
What coil?
How old?

Well you kinda make my point. If the carb is out of adjustment then a couple minutes with a screwdriver should fix it as long as the throttle cable and kick down isn't hanging up.

But the dieseling indicates timing issues. Which can do the same surging when you let off the throttle. 90% of carb issues are ignition issues.

A screwdriver won't fix a leaking needle & seat or float level too high, or throttle blades too far open at idle because this are to far open to compensate for plugged idle circuit. Close the throttle and car dies.

Surging is also lean AF mixture. Can be from wrong calibration on carb or gummed up innards.

Ignition could be bad, we don't know what is on this car yet.
How about I swap the carb for a reliable design, and if I can't fix it that way then you fix the ignition? LOL

 

[Orig69]

It sounds like when the secondaries are closing they're dragging on the bore walls.

 

[khryslerkid]

A lot of carbon build up in the cylinders can cause run on also, along with a dripping/rich carb. Timing is mostly related to pre detonation, pinging.

 

[oldbee]

Well, you have a good replacement carb in the wings, but first thing that came to mind with your story is what about sticking counterweights in the distributor? That’ll sure cause some dieseling from higher idle speed.

 

[rt-man]

I just put that same Edelbrock AVS2-650cfm on the Sleeper Bee and it ran great out of the box, aside from a slight fuel-air & throttle adjustment.
Without knowing about the summit carb you may need the edelbrock-1481 adapter bracket for throttle / kick down hookup.

I've got the adapter bracket. Didn't think it was relevant to the original question. Thanks.

 

[rt-man]

I agree with others that a carb change may not fix your problems completely. It may resolve the surging after WOT, but the dieseling is more likely to be resolved with a timing adjustment. JMTC

Thanks.

 

[rt-man]

@rt-man tell us more about this, answer 10 questions please:
what is the idle vacuum?
What is the idle speed?
Does the exhaust smell or burn your eyes?
How old is the fuel in the tank?
When did you last add new fuel?
Has the car sat for extended period before now?
Have you recently changed anything under hood fuel or ignition related?
What ignition system?
What coil?
How old?


A screwdriver won't fix a leaking needle & seat or float level too high, or throttle blades too far open at idle because this are to far open to compensate for plugged idle circuit. Close the throttle and car dies.

Surging is also lean AF mixture. Can be from wrong calibration on carb or gummed up innards.

Ignition could be bad, we don't know what is on this car yet.
How about I swap the carb for a reliable design, and if I can't fix it that way then you fix the ignition? LOL

All very good questions, R413. a few answers off of the top of my head:
idle vacuum: will have to throw my vacuum gauge on it
idle speed: 500-800rpm
exhaust smell: recently runs rough when cold, low idle, as if the electric choke is not functioning.
Fuel age: recent, less than a month
Sitting: no more than a week at a time during the Spring/Summer/Fall
Recent changes: Long story, but a different shop doofus recently (6 weeks ago) messed with the timing, which pissed me off. I "think" this could be a contributing factor to a few things, or just a coincidence. They said they reset it, but I have my suspicions...dieseling happened after that
Ignition system: electronic
Coil: I forget
How old: the car or me?

The dieseling/run on is a brand new issue and just happened the one time. The surging after WOT has happened continuously for 2-4 years, hence why I bought the Edelbrock carb. The car is a cruiser but I'd like it to run well (duh, who doesn't?) Based on your inputs, I think the timing needs to be reset and the carb swap is a personal choice, of course. Holley vs the world. In my time, my preference is the Carter/Edelbrock AVS, but to each his own.

Thanks, everyone

 

[Geoff 2]

Post #14 has a good suggestion & should be investigated. Check ign timing engine cold, & idling. Then check timing when it is dieseling. If timing has increased, it would indicate sticking weights inside the dist.