Engine Issue 427/425
My engine with less than 5K miles appeared to be flooding out. I had the carb (numbers correct) rebuilt. Issue continued and I installed two other correct rebuilt carbs on engine with no change. Valves were adjusted and ignition system checked to the best of my ability with new plugs installed. Distributor had been rebuilt at Specialty with all ignition parts coming from them. After checking complete ignition system and following several discussions with Dave at Specialty I installed points distributor that had once been on the car. Condition remained the same. Engine starts but runs rough. There is blue smoke coming from sidepipes and the gas fumes will burn eyes when running. Checked all cylinder compressions which were OK. Vacuum at throttle plate is 7 at idle and remains around 7 as you accelerate thru 1800 and reaches around 11 at 3000 RPM's. Visually checked everything I can. You can clean or install new plug and they all will be black with gaseous smell after start up. At this point it appears the problem would be internal. Possibly hole in intake port of heads, valve problem, vacuum leak, etc. Any suggestions?
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Re: Engine Issue 427/425
did you check all the plug wires?
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are there plugs of the eight that are in worse shape after a startup/run?
Are they just carbon fouled and dry or wet gas soaked?
Bill -
Re: Engine Issue 427/425
Fuel pump pressure too high?Comment
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Re: Engine Issue 427/425
Have not changed wires as they are not old and my problem is every cylinder. Plugs are carbon fouled and wet.Comment
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Re: Engine Issue 427/425
Who rebuilt your carb? When Lars did mine a few years ago, he warned me that the current batch of offshore needle and seats are garbage (he won't use them), and can't take anything more than 5 PSI. I ran into this same problem on my son's truck with the original Q-Jet. I got a rebuild kit off of ebay and sure enough, as soon as I hooked it up after rebuilding the carb, it started flooding. I checked the pressure and the stock pump was putting out 8 PSI, well within the original specs for the GM pumps, but way too high for the Chinese garbage needle and seats. I installed a Holley low pressure regulator (down to 5 PSI) and no more flooding.
EdComment
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Re: Engine Issue 427/425
The idle vacuum is low...........even for this engine. Could this low of vacuum activate the carb power valve?? What power valve was installed in the carb?? There are a few different ones with different vacuum settings. Typical is 6.5 in HG.
The comment about high fuel pump pressure is also a good one to check.
LarryComment
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Re: Engine Issue 427/425
With the stock 427 solid lifter cam, the manifold vacuum should be about 14 inches at 800 to 900 rpm regardless of fuel richness. Walter referred to "vacuum at the throttle plate". Perhaps he was measuring venturi vacuum rather than manifold vacuum, since I think the distributor of a 66 L-72 uses venturi vacuum .Comment
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Re: Engine Issue 427/425
Haven't checked FP. Is there a way a pump could start producing more preesure?Comment
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Re: Engine Issue 427/425
Two Holley's rebuilt by same individual and I know he used Holley parts. When both produced the same results I took a Holley 800 that had been on the car for 10 years and the car ran equally as bad. I did not rebuild that carb but I did take it apart to make sure it was clean.Comment
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Re: Engine Issue 427/425
Walter,
Did you adjust the emulsion screws at hot engine idle and how far are they turned out? Post the heat range of the spark plug that's in the engine. How far is the idle speed screw turned in to idle the engine, what I am getting at is that if the transfer slots are over exposed the engine idle will get rich plus the emulsion screws will not make any difference when trying to fine tune the idle mixture.
Another thing could be the power valve gasket, I believe it's torque something like 100 inlbs. and if it leaks fuel can be drawn into the engine where you can't see it under the throttle blades. Do you see any fuel drip looking into the carburetor throat when hot, if so turn the float adjustment down six flats and lower the fuel level. Don't go by the sight hole.Comment
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Re: Engine Issue 427/425
Patrick - That's a good point about the OP possibly checking vacuum from the ported source and may be contributing to those low numbers. My neighbor has a 427/425 66 Coupe and when we were getting it initially fired up, noticed that the best way to check manifold vacuum was to 'T' in to the choke unloader hose.Mike T. - Prescott AZ.Comment
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Re: Engine Issue 427/425
Have you tested the power valves? A ruptured power valve allows more gas. The way I test my power valve when it is suspected to be ruptured is to put a finger over the fuel bowl vent, if the car dies I replace the power valve.Comment
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Re: Engine Issue 427/425
I will try today but I have put 3 carbs, two which had been rebuilt with new power valves, on the engine with same results.Comment
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Re: Engine Issue 427/425
If your true engine/intake manifold vacuum is 7 IN HG as you stated earlier, the power valve may be okay, but still opening in response to the low vacuum. This is unwanted at idle or low RPM.
Is your engine/intake manifold vacuum really 7 IN HG, or were you reading the "ported" vacuum number as Pat Boyd questions??
Again, you need to check and verify the fuel pump pressure as well.
LarryComment
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Re: Engine Issue 427/425
I don't have technical knowledge to answer if vacuum is the manifold or "ported". I took the vacuum reading from outlet on throttle plate in correct 4150 Holley carb. where you would connect hose from distributor. Consistently getting 7 in. reading at idle.Comment
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