Drivability problem....Ideas please?
Thread Starter
5th Gear
Joined: Aug 2006
Posts: 5
Likes: 0
Drivability problem....Ideas please?
I have a seldom driven 66 with the 327. Began running rough last year, problem still there this year. Symptoms: Won't idle, bucks when driving under steady throttle, but pulls well, runs just fine under acceleration. It is not an intemittant miss; constant put-put exhaust sound at fast idle. Me thinks it is a fuel/air mixture problem; if a spark problem should be most noticable under hard acceleration. No black exhaust, I think it is running lean.
Here's what I have done to trouble shoot so far:
Put Techron carb cleaner and Sta-bil in tank before storing for winter last year. Looked for an air intake leak: sprayed carb cleaner all around the base of carb and intake manifold, no perceptable change. Pulled and plugged all vacuum lines one by one, no change. Removed the idle adjusting screws and sprayed carb cleaner in there, no change.
Any other trouble shooting ideas before I pull and rebuild the carb? Even if I rebuild the carb, I don't have confidence that I can completely clean all internal passages.
Thanks for any ideas you may offer.
Jay
Here's what I have done to trouble shoot so far:
Put Techron carb cleaner and Sta-bil in tank before storing for winter last year. Looked for an air intake leak: sprayed carb cleaner all around the base of carb and intake manifold, no perceptable change. Pulled and plugged all vacuum lines one by one, no change. Removed the idle adjusting screws and sprayed carb cleaner in there, no change.
Any other trouble shooting ideas before I pull and rebuild the carb? Even if I rebuild the carb, I don't have confidence that I can completely clean all internal passages.
Thanks for any ideas you may offer.
Jay
Instructor
Joined: Aug 2007
Posts: 122
Likes: 0
From: St. Louis MO
I would suspect one of the following:
Burnt valve: Test with equipment like % leakage tester, compression tester, etc.
Carb: If it idles well enough to see if the mixture screws work, that is a pretty good test of the idle circuits. Engine should slow when the screws are in to far or out to far.
Vacuum leak: not much vacuum stuff on that but something worth looking at.
Burnt valve: Test with equipment like % leakage tester, compression tester, etc.
Carb: If it idles well enough to see if the mixture screws work, that is a pretty good test of the idle circuits. Engine should slow when the screws are in to far or out to far.
Vacuum leak: not much vacuum stuff on that but something worth looking at.
Drifting
Joined: Nov 2007
Posts: 1,513
Likes: 34
From: columbus ohio
run it at night in the garage with the lights off. see if there is a spark
at plugs and along the wires and out side the distributor. i had a miss
and found it this way. had a bolt on ign shield go thru the plug rubber.
good luck jim
at plugs and along the wires and out side the distributor. i had a miss
and found it this way. had a bolt on ign shield go thru the plug rubber.
good luck jim
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Racer
Joined: Aug 2004
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From: California Missouri
Hook a vacuum gauge to it and report back
I would hook a vacuum gauge to it after you check your power valve. See if its pulling a steady vacuum at idle. If it is let the guys know how much.
If its not and the needle flopping around like a windshield wiper in a huricane, you have valve or valve spring problems, and air is being pushed passed the valves back up into the intake. However you state it runs strong, so this probably isn't the problem because it wouldn't run strong with a burnt valve or broken valve spring, I wouldn't think.
If its not and the needle flopping around like a windshield wiper in a huricane, you have valve or valve spring problems, and air is being pushed passed the valves back up into the intake. However you state it runs strong, so this probably isn't the problem because it wouldn't run strong with a burnt valve or broken valve spring, I wouldn't think.
Thread Starter
5th Gear
Joined: Aug 2006
Posts: 5
Likes: 0
Thanks everyone for the replies, BUT....
I have to say that I discounted most of your ideas. Most of you seem to have missed what I think is the telling symptom. Poor running condition is only under steady throttle / idle. PULLS STRONG, RUNS WELL UNDER ACCELERATION. Doesn't that tell you that the problem is not anywhere in the ignition system, because then poor performance would be most noticable under hard acceleration? Wouldn't that also be true if problem was a burnt/open intake or exhaust valve? Wouldn't that also be true if problem was carburatur power valve, poor performance would show itself under acceleration which is not the case here?
When running poorly at fast idle, dramatic improvent noticed when I spray carb cleaner down the throat of carb. I am still thinking problem is that it is running lean, which then is compensated for by the enriched mixture during accelertation. But I don't know how to find the source of the lean condition. I have checked and can't find any source of air infiltration at the manifold or vacuum lines. So now I am down to thinking it is internal to the carburator.
Still would appreciate any other ideas, or rebuttals to my ideas, you can offer.
Jay
When running poorly at fast idle, dramatic improvent noticed when I spray carb cleaner down the throat of carb. I am still thinking problem is that it is running lean, which then is compensated for by the enriched mixture during accelertation. But I don't know how to find the source of the lean condition. I have checked and can't find any source of air infiltration at the manifold or vacuum lines. So now I am down to thinking it is internal to the carburator.
Still would appreciate any other ideas, or rebuttals to my ideas, you can offer.
Jay
Instructor
Joined: Feb 2008
Posts: 131
Likes: 13
From: Urbanna Va.
My 2 guesses are
I think it could be 1 or both of these...
1. Check the secondaries in the carb.. They may not be completely closed, and/or have some gunk on them that don't allow them to comptel seat. With the car idlling press on them to insure the are closed and see if it resolves the problem...
2. Have you done anything with your vac advance or timing?? Running way too advanced can cause eratic problems that go away under load...
I have experienced both of these problems..
BK
1. Check the secondaries in the carb.. They may not be completely closed, and/or have some gunk on them that don't allow them to comptel seat. With the car idlling press on them to insure the are closed and see if it resolves the problem...
2. Have you done anything with your vac advance or timing?? Running way too advanced can cause eratic problems that go away under load...
I have experienced both of these problems..
BK
Race Director
Joined: Jan 2003
Posts: 17,659
Likes: 3,666
From: Central Arkansas
I have to say that I discounted most of your ideas. Most of you seem to have missed what I think is the telling symptom. Poor running condition is only under steady throttle / idle. PULLS STRONG, RUNS WELL UNDER ACCELERATION. Doesn't that tell you that the problem is not anywhere in the ignition system, because then poor performance would be most noticable under hard acceleration? Wouldn't that also be true if problem was a burnt/open intake or exhaust valve? Wouldn't that also be true if problem was carburatur power valve, poor performance would show itself under acceleration which is not the case here?
When running poorly at fast idle, dramatic improvent noticed when I spray carb cleaner down the throat of carb. I am still thinking problem is that it is running lean, which then is compensated for by the enriched mixture during accelertation. But I don't know how to find the source of the lean condition. I have checked and can't find any source of air infiltration at the manifold or vacuum lines. So now I am down to thinking it is internal to the carburator.
Still would appreciate any other ideas, or rebuttals to my ideas, you can offer.
Jay
When running poorly at fast idle, dramatic improvent noticed when I spray carb cleaner down the throat of carb. I am still thinking problem is that it is running lean, which then is compensated for by the enriched mixture during accelertation. But I don't know how to find the source of the lean condition. I have checked and can't find any source of air infiltration at the manifold or vacuum lines. So now I am down to thinking it is internal to the carburator.
Still would appreciate any other ideas, or rebuttals to my ideas, you can offer.
Jay
Having said the above I think you have some other problem from your description that it won't idle and the put-put sound. I think you need to get a vacuum gage and see what it shows - how much and how steady. Also check your point dwell and timing. Closed up points can make it run rough. You may be due a carburetor rebuild kit.
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
don't know what to suggest to you but as you describe the symptoms:
symptom 1. - idle problem
symptom 2. - bucks under steady throttle
observation. - runs fine under acceleration
Seems to only have problems under conditions of high vacuum (idle and steady throttle driving) and drives fine under conditions of low vacuum (acceleration).
Either or both of the two symptoms could, as one possibility, be related to the vacuum advance on the ignition system.
symptom 2. - bucks under steady throttle
observation. - runs fine under acceleration
Seems to only have problems under conditions of high vacuum (idle and steady throttle driving) and drives fine under conditions of low vacuum (acceleration).
Either or both of the two symptoms could, as one possibility, be related to the vacuum advance on the ignition system.
Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,357
From: Santa Ana CA
Could even be a problem with the float level in the carb.
If the floats have become "waterlogged" or gotten out of adjustment, excess fuel could be running down the carb into the manifold. This could manifest itself at idle and steady state.
But when you tromp on it, the car needs all the fuel it can get and the level in the bowls drops anyway so all is good.
If the floats have become "waterlogged" or gotten out of adjustment, excess fuel could be running down the carb into the manifold. This could manifest itself at idle and steady state.
But when you tromp on it, the car needs all the fuel it can get and the level in the bowls drops anyway so all is good.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
Advance the timing and then reduce the idle because it should increase as the engine cleans up.. Idle screws should be 1 1/2 turns out as a start. Close the butterflies to a recommended limit depending on hydraulic or solid cam.
