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Old 04-08-2010, 04:53 AM   #1 (permalink)
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302 rough idle, hesitation, backfire through carb.

I have a 1978 302 in a 1926 model T. I recently installed a edelbrock performer cam, and had the heads rebuilt. I have an edelbrock performer intake and 600 cfm performer carb. When I first start the engine it runs great, and idels in great. When I put the car in drive and get down the road 100' or so, it starts missing, and if I give it a lot of gas it backfires through the carb. When I come to a stop the idle is off, it almost feels like it is mis firing. As soon as i give it gas the engine responds correctly, but then starts missing/backfiring. I pulled the plugs, and for the most part the ones on the drivers side are clean, and the ones on the passenger side are fouled.

Chris
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Old 04-08-2010, 07:06 AM   #2 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

may be junk in the carb try removing the two mixture screws on the front of the carb blow some air through reinstall seat them lightly and back them out 1 1/2 turns.I had a similar problem worked for me.might also check ignition got good spark?
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Old 04-08-2010, 08:21 AM   #3 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

I will try cleaning out the screws. How do you check for good spark?
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Old 04-08-2010, 08:27 AM   #4 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

Vacuum leak is ONE of your problems.

Lean fuel mixture is ANOTHER of your problems... Like the guy's said, clean it out real good, back blow all the jets and orifices etc.

Check for proper fuel level.

Once other possibility is a leaky Vacuum advance bulb in your distributor.
Take Dist cap off. Put vacuum to the Dist nipple, watch the dist plate move when you apply vacuum and hold. If the plate starts to move when the vacuum is on hold or the plate don't move to begin with, that is one part to replace to start with.
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Old 04-08-2010, 08:54 AM   #5 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

With engine running I pull one wire at a time off of dist ,hold it a short distance from the spot you pulled it from ,a good spark will be bright blue and you will hear it arcing .be careful tho it can be a shocking experience lol
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Old 04-08-2010, 09:01 AM   #6 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

Just to add to the other things already said, if you just added the Edelbrock carbas part of the package, check the fuel pressure. Only needs 5 psi. Anything over that will overpower the needle and seat.
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Old 04-10-2010, 05:31 AM   #7 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

Thanks for everyones help! I checked for vacuum leaks and found two small ones on the carb linkage. I do not know if a little leak can make this big a differeance? I currently have 16 in. of vacuum. I do not know how to fix that except replacing the carb. The dist. vacuum advance is working properly. Missfiring does not happen on any one cylinder. Engine continues to get worse the more I adjust the carb and timing...very frustrating. I have adjusted the rockers but am getting a lot of lifter noise, and it changes/gets worse when I adjust the timing. Is anyone familar with limefire, or lakestyle headers? It seems my problems started when I installed them and have been getting worse ever since?
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302 with Edelbrock performer 600 cfm carb., performer cam, and permormer intake.
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Old 04-10-2010, 06:25 AM   #8 (permalink)
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A 78 302 should not adjustable valves unless the heads have been changed.
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Old 04-10-2010, 10:20 AM   #9 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

Are any of the plug wires touching the headers might have burnt through them.Just a thought
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Old 04-10-2010, 11:15 AM   #10 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

No vacum leaks from the manifold installation that could cause a lean condistion? MAybe the inatke was installed croocked or the carb has a leak in it .
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Old 04-10-2010, 12:50 PM   #11 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

Quote:
Originally Posted by bikingplumber View Post
I have a 1978 302 in a 1926 model T. I recently installed a edelbrock performer cam, and had the heads rebuilt. I have an edelbrock performer intake and 600 cfm performer carb. When I first start the engine it runs great, and idels in great. When I put the car in drive and get down the road 100' or so, it starts missing, and if I give it a lot of gas it backfires through the carb. When I come to a stop the idle is off, it almost feels like it is mis firing. As soon as i give it gas the engine responds correctly, but then starts missing/backfiring. I pulled the plugs, and for the most part the ones on the drivers side are clean, and the ones on the passenger side are fouled.

Chris
While you are troubleshooting, double check the firing order that came with your camshaft. Some camshafts require a change from a 302 to a 351W firing order. Also, check the wiring on your distributor, ignition switch wire should be on the + side of your coil, distributor wire on the - side of your coil.

Frank
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Old 04-10-2010, 06:16 PM   #12 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

I hate to bring this up, but you may have a cam lobe or 2 going flat. Hopefully that's not it, but I have had it happen with very similar results to what you're experiencing.
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Old 04-11-2010, 04:48 AM   #13 (permalink)
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Re: 302 rough idle, hesitation, backfire through carb.

I thank all of you for your input! I tried everything you all suggested, and I believe we found the problem. We found the engine was misfiring but only above an idle. We isolated the misfire to one cylinder, (no. 3), and identified the intake valve spring as being weak. I just had the heads serviced and am very upset that they did not check the springs, since this whole mess would have been averted. We are going to replace the one spring on Monday, and with any luck I will be up and running again!
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