When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
If your motor runs strong at wide open throttle, and what you are experiencing at a normal cruising speed ,can be described as almost imperceptible , only felt by the driver, the passenger unaware of anything abnormal. If that's an accurate description,if while driving you're not always sure yourself it's there and sometimes have to concentrate on it to feel it, then there is a good chance there is a restriction in one of the main carburetor jets
Something as small in length and diameter as a human eyelash, is enough to cause the exact condition described above
I have a Carter/Edelbrock on mine so I can just turn the two screws on the front of the car to Richen it up some and that is what I did. As others have said by looking at your plugs it does appear you are a little bit Lean.
That will only richen up the idle (and possibly a bit on the transition circuit). It won't richen (or lean out) the primary or secondary systems.
What type of carburetor is on the engine, does it have threaded air bleeds. How long have you been experiencing this surge condition and what rpm does this usually occur.
Raising the float level will start the main circuit sooner that may be why you noticed a change.
I pulled and plugged the dist. Hose, couldn’t really tell if there was much of a change. What does that mean? It’s noticeable in all speed and rpm except full acceleration, more noticeable at a steady, low end range.
The carb is a Holley 4779-9.
Ehh - probably could use some new plugs although that may not be the direct cause of your missing issue. I would check it in the dark for spark plug wire leaks. Do you have points still in the distributor - although I don't think burnt points or mis-gapped points would behave as you are describing? Also, do you have any idea what the timing is set at?
Ehh - probably could use some new plugs although that may not be the direct cause of your missing issue. I would check it in the dark for spark plug wire leaks. Do you have points still in the distributor - although I don't think burnt points or mis-gapped points would behave as you are describing? Also, do you have any idea what the timing is set at?
No, it’s HEI. The timing is set at 12 deg. Tonight I’ll check the wires.
I'd put a new set of plugs in that plug and see if that miss goes away. Next step is to find out why your new set of plugs will shortly look like the ones in your pictures.
Ehh - probably could use some new plugs although that may not be the direct cause of your missing issue. I would check it in the dark for spark plug wire leaks. Do you have points still in the distributor - although I don't think burnt points or mis-gapped points would behave as you are describing? Also, do you have any idea what the timing is set at?
Just got back from checking, absolutely no leaks at all, even at 2000 rpm.
I'd put a new set of plugs in that plug and see if that miss goes away. Next step is to find out why your new set of plugs will shortly look like the ones in your pictures.
i can try a new set of plugs, but I don’t think I need new wires (see post). Have we eliminated the carburetor?
i can try a new set of plugs, but I don’t think I need new wires (see post). Have we eliminated the carburetor?
Is that the same set of plugs shown in your first photos? Maybe it's just the camera angle and lighting? In general, it looks like the tips are burning hot/clean with heavy deposits on the ground electrode?
Doesn't look like a carburetor problem to me. Looks like oil to me on some of them but maybe an expert has a better slant on things.
I installed new spark plugs last year, they still look good. And a new HEI module last spring. It probably could use new spark plug wires though.
Leaking HV is not the only failure mode possible wrt plug wires. What about the cap and rotor too? Looks to me like some holes aren't getting full spark. If it was a fuel problem wouldn't all the plugs look more or less the same? A compression test would not hurt.
MikeM called it..... Those plugs are clearly "hot" enough to burn through some cruddy build up....the tips of the electrodes are clean but the rear of the top electrode is cruddy in almost all cylinders, along with the ring at the top of the threads. Something is going on....here are the plugs from my 61 - note the difference..
Last edited by Frankie the Fink; 10-12-2018 at 08:03 AM.
I installed new spark plugs last year, they still look good. And a new HEI module last spring. It probably could use new spark plug wires though.
Don't overlook the wires. After chancing down a miss with my motor last year, it turned out to be 3 of the wires were not making a good connection at the spark plugs. A new set of wires fixed the miss.
Leaking HV is not the only failure mode possible wrt plug wires. What about the cap and rotor too? Looks to me like some holes aren't getting full spark. If it was a fuel problem wouldn't all the plugs look more or less the same? A compression test would not hurt.
I ran it when I pulled the plugs. Here are the results.
Cylinder Compression Test
#1 - 140, #2 - 152, #3 - 145, #4 - 143, #5 - 140, #6 - 145, #7 - 146, #8 - 140
Running along at about 60 mph, I feel the car jerking or a miss (don’t know the technical name) ever so slightly. It was worse until I adjusted the front Holley float but it still does it. How can I tell if it’s electrical or fuel related?
Update! Went for another drive, it’s really a lot more noticeable at 40mph, 1500 rpm. Same whether dist. Is plugged or unplugged.
Let me give you my experience with my 65 327/365 corvette. I had issues early on with the engine breaking up around 3000 rpm. I sent the carburetor and eventually the distributor out for Eric Jackson to be rebuild. Both came back but after installing the carburetor, I notice a slight surging. I thought it was the distributor as I was still experiencing the high rpm breaking up. After replacing the distributor. I noticed that when the choke was on and/or driving the vette it still had the weird issue while driving.
After 1 1/2 years of experiencing the weird surging I replaced everything possible electrical related during that time. What was replaced - spark plug wires, new coil, new ballast resistor, spark plugs (twice), distributor springs, vacuum advance canister (three times), distributor cap (twice)... Everyone I talked to or who worked on the car said it was electrical related. I did change the jets on the carb as well as the pump discharge nozzle.
What I was experiencing after 1 1/2 years of trying to figure out the issue - vette would pop (after fire) out the drivers side exhaust when around 1100 - 1500 rpm while choke was on. I also experienced the trailer hitching around 1000 - 15000 rpm at 35 - 40 mph's. I had taken the car to several places and had several people look at the car. They either said carb or distributor was the issue. Finally, while trying to adjust the fuel mixture on the carburetor, the fuel mixture screw on the drivers side would not adjust out.
Finally after 1 1/2 years of frustration, I called Chicago Corvette and tried to order a restored 2818-1 carburetor. They actually told me they felt it was the distributor as well and not the carb and talked me out of buying the carburetor. Went back out to the vette, tried to adjust the carb as well as put the original springs in the distributor. Still had the issues of the 1100 - 1500 rpm popping/surge. I call Chicago Corvette and told them to send me the carb. After replacing the carburetor, the engine ran like a champ. No more issues. Issue turned out to be the rebuilt/restored carburetor.
I wouldnt rule out the carburetor as I have had what appears to be the same symptoms that 59BlueSilver is having.
What I learned from this (frustrating) experience, just because your carburetor was rebuilt/restored by what was supposed to be the best rebuilders in the country, doesnt mean it was rebuilt correctly.
Last edited by Kelly Burnside; 10-14-2018 at 11:26 AM.
Reason: added other quote
Okay, I’ve replaced spark plugs, wires, and HEI module, can’t think of anything left electrical. Took a friend for a ride and after getting on it hard on the interstate, it bogged down, backfired, and engine quit. Friend said it was fuel starved. Restarted and returned home and float level was pretty low on both primary & secondary. Reset float level on Holley 4779-9. Today I’m going to change the fuel filter, it’s a year old. I’m also using a Holley red electric fuel pump. Before I got on it, it was still surging slightly.
Its a long shot but check the distributor clamp bolt for tightness, and maybe the bulkhead connectors for corrosion, burnt, missing or bent pins/wires, etc..
Floats don’t change level by themselves, especially both. Surging at midrange is almost always a lean condition which is confirmed by your plugs. The five biggest causes are (in order of easiest to fix):
1. Float level too low
2. Clogged filter (either external filter, brass filters at fuel input of carb if equipped, or both)
3. Clogged carb passage(s)
4. Vacuum leak
5. Low fuel pressure
This assumes that the carb is tuned properly with jets and air bleeds properly selected and idle mixture and choke properly adjusted.
10-08-2018, 04:58 PM
