Problems with 65coupe misfire at wot

Kaden Alwazzan

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I recently bought this car. It fell on its face around 3500rpm and I diagnosed it as secondary’s not oppening which I was proven correct after I took the bowl off and found 10 year old black fuel all in it. Replaced the entire carb with a Holley 670 and initial drive felt decent and didn’t Baugh down. While trying to adjust mixture screws I gave it a blip in throttle and it backfired out the carb. Since then it idles rough and I believe misfires at WOT and does not stop until I lift the throttle. Since then I have replaced the power valve and plugs Checked the plug wires all seems to be good but still misfiring I am very new to these old cars and could use some help
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decipha

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usually backfiring through the carb is due to being lean, prob best to put a new fuel filter on it and verify your fuel pressure doesnt fluctuate, then its a matter of dialing in the pump shot if your jetting and all else is correct
 

john11gt

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The timing needs to be checked at idle and above 3-4000 rpm because of the vacuum advance.

With the timing it’s at, it may idle fine but once it’s at wot the vacuum advance will cause to advance too much and cause a misfire.
 

Kaden Alwazzan

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The timing needs to be checked at idle and above 3-4000 rpm because of the vacuum advance.

With the timing it’s at, it may idle fine but once it’s at wot the vacuum advance will cause to advance too much and cause a misfire.

The timing is set to 6°. At higher rpm I have no way to check because the ballencer is only marked to 12°

I just find it weird that the car ran good and the backfire seems to have killed it. I’ve changed the gaskets. Plugs. I’ve re adjusted the mixture screwes. It runs beautifully but as soon as you’re wide open it jerks and rumbles horribly.


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john11gt

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You can try cleaning the plugs up, and take it for wot run and immediately shutting the engine off and reading the plugs. White would be lean, black rich obviously.

You can buy timing tape from summit or amazon for a few bucks to solve the issue with the marks on the damper, i had the same issue.

Does it start to break up at wot while it’s in neutral or driving or both?

Do you have a fuel pressure gauge?

You can buy a small fuel pressure gauge from auto zone and run a line to near the cowl so you can watch fuel pressure while driving temporarily.
 

Kaden Alwazzan

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You can try cleaning the plugs up, and take it for wot run and immediately shutting the engine off and reading the plugs. White would be lean, black rich obviously.

You can buy timing tape from summit or amazon for a few bucks to solve the issue with the marks on the damper, i had the same issue.

Does it start to break up at wot while it’s in neutral or driving or both?

Do you have a fuel pressure gauge?

You can buy a small fuel pressure gauge from auto zone and run a line to near the cowl so you can watch fuel pressure while driving temporarily.

It breaks up only while under load


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john11gt

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I had an issue similar. It was fine while cruising but wot above 5k and it would break up. I thought it was going lean also but it ended up being the timing.
 

Papaw

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Sometimes a backfire through the carb can cause damage to the power valve on the metering plate. If the problem persists after trying a fresh set of properly gaped plugs I would look there.
 

cj428mach

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Let me help you out.

efi_kits.png


I have one on my 69 Mach 1. Other than the braided feedline you can't even tell its there. This pic was before I cleaned up the wiring at the starter solenoid and hid my alternator fuse.
 

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Kaden Alwazzan

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Any updates?

It dropped a valve lmao Update on the misfire and backfire was bad fuel. Local station was leaking water from snow into its tanks and I filled up. It all was going well after I figured that out until it dropped a valve. Come to find out the rocker arms were hitting on the keepers instead of the valve stem


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Papaw

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Make sure you have the correct kind of rocker arm for the valves you are using. The more common "rail" type of rocker needs the valves with extended valve stems.
 

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