Ignition or Vacuum problem?
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Ignition or Vacuum problem?
Great forum and thanks in advance. I've got a rebuilt 73 302 that my mechanic talked me into replacing the edelbrock with a 600 Holly because it was running really rough and there was no way to hook up the kick down gear to the Edelbrock. It now runs horribly when starting out or when cruising around 15 - 35 mph or whenever there's not much load on the engine. He pointed out that he thought there was a vacuum leak in the intake and that maybe it wasn't the right one for that engine. Then he pointed out that there are three plug wires that are sparking but when disconnected from the distributor- it doesn't effect the sound of the engine at an idle. It seems to me that it's an ignition problem. Like those cylinders aren't firing in the first place if you can remove the fire and there's no difference. Is this right? Also, I've noticed in the past that I can smell gas in the exhaust although I haven't really checked since the switch. Thanks for any advice y'all might have.
Trent
Trent
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Ignition or Vacuum problem?
If you can disconnect 3 spark plug wires, and it doesn't run worse big time, those 3 cylinders are dead! That explains gas smell through the exhaust, 3 cyl. pumping raw gas out the pipe. By "sparking" did you mean that those 3 could spark a spare plug hooked up external to the engine, showing that they were live?
Check firing order vs. how the plug wires are connected. Swap wires and plugs from good cylinder to bad and vice-versa, to see if problem moves with the parts, or stays with the same cylinders. If the same cylinders are dead, maybe time for a compression test, recent rebuild or not.
Check firing order vs. how the plug wires are connected. Swap wires and plugs from good cylinder to bad and vice-versa, to see if problem moves with the parts, or stays with the same cylinders. If the same cylinders are dead, maybe time for a compression test, recent rebuild or not.
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Ignition or Vacuum problem?
Why did you let anybody talk you into ditching an Edelbrock? If you have a vaccuum leak, there's not a carburetor on earth that can help you. Pour something foamy on your intake, and run the engine to find that leak, and fix it. I agree, reference your manual to research your firing order, and check your timing. Also take your wires to a DC multimeter to test resistence through them. you can do the same for the cap and rotor. The Holley is definately not makinng the problem any better. The good thing is that testing Ignition peices is easy and cheap, but please fix the vacuum leak, or none of this will really help. Good luck, John
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Ignition or Vacuum problem?
Thanks for all the great advise. I did check the firing order and it seemed to be ok. I hope it's a matter of plugs and wires. I'll check them. What I meant by them firing is when I pull the wires off of the distributor, and hold them close to the socket, I can see and hear a spark. So, I guess that the juice is getting to the plug at least. I'll see about the vacuum leak in the intake too. Thanks!
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