No-load Misfire Puzzle

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howco4

howco4

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I'm running a fairly stock 383 in my 70 Swinger. The carburetor is an Edlebrock 600 cfm, on a single plane Wieand manifold. I'm using the stock Mopar electronic ignition. When running at speed, under light load conditions, a regular misfire, or hesitation occurs. The engine performs fine under load and hard acceleration. My take: It's not ignition, but a fueling problem. Anyone????
 
Carb has not been apart, but has been in storage for a couple of years before usage.
 
Also, no change to the ignition. Seemingly, an ignition problem would show up under load.
 
I used to tear down my holly carbs on a regular basis. Never been into an Edlebrock. Trying to get some second opinions before do it.
 
howco4 said:
Carb has not been apart, but has been in storage for a couple of years before usage.
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Tear it apart and give it a good cleaning and check your adjustments. Could be a float hanging up. To much fuel at light load will show up as a popping in the exhaust.
 
go with a smaller primary rod.jmo

surge at cruise=lean

fine at wot=main jet seems within or close to good, but check spark plugs color.

what/how much total timing are you running cause the other side would be that you have too much vac advance timing or mech timing and my need to tune it out some take 4* out of it by means of a lil allen wrench into the vac canister nipple or turn the distributor clock wise to retard it 2*-4*
 
All the hoses are connected. I am running a elderly, (old), distributor. I could do a check by plugging port and running it, to see if it makes a difference.
 
I've never done it myself (well, tear down an edelbrock lol) but i've been told it's real ez compared to a holley. it's two-piece and the top horn comes off while the carb is still on the intake if you so desire...the eddy manual has step by step in it...:read2: http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf it takes a minute to download but it should be all there!!!
 
Demon 408 said:
As wild&crazy said, check timing. Timing first, then carb. Especially if you have not checked intial, vaccum and total timing.
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I 100% agree with you Demon, but if the carb is not right from the get go (it was in storage) won't it throw the timing off or something?? Not claiming to be an expert or anything, just wondering?? :-D
 
I've always timed my engines by ear. Maybe I should try a timing light this time, if I can find the damn thing.
 
MarPar said:
I 100% agree with you Demon, but if the carb is not right from the get go (it was in storage) won't it throw the timing off or something?? Not claiming to be an expert or anything, just wondering?? :-D
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Carb won't throw off the timing. And when starting from a completely unknown point you should do timing first. Once he checks his timing is good then he can move onto the carb, keeps you from chasing your tail. To much or to little vaccum advance can affect light load cruise.
 
If it is surging at light throttle openings cruising down the road it is running lean.....make sure you don't have any vacuum leaks. Spray a can of carb cleaner around the base of the carb and the intake manifold. If you have a vacuum leak the cleaner will get sucked in the the rpm will change..I had the same issue and the carb base gasket was blown out about 1/4 inch. I just rebuilt my Edelbrock carb with a kit from Summit, piece of cake.
 
Will pick up some carb cleaner tomorrow. Will also round up my vacuum gauge, and timing light. Weather in Renton has been in the 90"S, and will dictate my level of activity. Beer may prevail.
 
Timing too far advanced. Same thing happens to my 440 if I pull it too far advance. You can probably dial it out by adjusting the vacuum advance can. Quick test is to unplug the vacuum advance and try it like that. If the misfire is gone, you found the problem.

George
 
I would check the timing.Set initial,then rev up to see what rpm total is being achieved.Try to get total all in by 2500 rpm and she should respond. I have never ran an edelbrock carb so my experience with them is zilch.Hope ya find out whats ailing her.
 
As was mentioned... Timing will affect carb, carb will not affect timing. So you set the timing first. If this is a points distributor, timing affects dwell, dwell does not affect timing, so again, timing first. If everything is connected including the vacuum advance can, for purposes of diagnostics disconnect and plug the hose at the vacuum advance. If the surge goes away, you need to adjust the vacuum advance. As far as a base generic timing settings.. If the engine is stock to mild with iron open chamber heads I'd use 14° initial, 38° total, plus the vacuum. Get a set of Mr gasket light advance springs and replace the near-solid stif one with the lightweight one. Then see if it still surges. If it does, plug the vacuum advance line and drive it. If it goes away, post, and we'll tell you how to fix that. I highly doubt it's the carb. Possible, but generally never start with a carb. Start with timing, and timing by ear is like cooking by waiting for the smell of smoke. use the light. That's what they invented it for...
 
I guess technically, I can't defend "seat of the pants timing". There have been a couple of times, when running aftermarket components, I've timed per spec, and still had to reset my timing, while doing a driving shakedown to get my best performance. I wasn't dealing with this kind of a problem however. There are some good ideas listed in these postings, and I will do a follow up. It's over 90 degrees here again today, so will wait til weather cools down a bit to mess with it. I'm going to try to combat the heat, with a glass of beer and tomato juice.
 
moper said:
As was mentioned... Timing will affect carb, carb will not affect timing. So you set the timing first. If this is a points distributor, timing affects dwell, dwell does not affect timing, so again, timing first. If everything is connected including the vacuum advance can, for purposes of diagnostics disconnect and plug the hose at the vacuum advance. If the surge goes away, you need to adjust the vacuum advance. As far as a base generic timing settings.. If the engine is stock to mild with iron open chamber heads I'd use 14° initial, 38° total, plus the vacuum. Get a set of Mr gasket light advance springs and replace the near-solid stif one with the lightweight one. Then see if it still surges. If it does, plug the vacuum advance line and drive it. If it goes away, post, and we'll tell you how to fix that. I highly doubt it's the carb. Possible, but generally never start with a carb. Start with timing, and timing by ear is like cooking by waiting for the smell of smoke. use the light. That's what they invented it for...
Click to expand...
Always set dwell first.
 
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