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Discussion Starter #1
I have a new (rebuilt) 302 with a holly carb that barely runs. The engine backfires terribly through carb and even catches Fire in the carb. Pretty sure the timing is at least close and firing order is correct. Even verified the firing order by removing the valve covers. Any help would be appreciated. When it does run, it shakes pretty good.
Thoughts?
Thanks Mike
 

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hmmmm. If you've confirmed firing order, I'd suspect ignition. What are you running for ignition bits Mike? You sure it's an HO 302 and not marine?
 

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Newly built 302. Could it be timing gear is off or even 180 deg. off on distributor. What kind of fuel pressure do you have? Are you using correct firing order? Mike
 

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Backfiring through carb is definitely timing or firing order. You could always try the other firing order to see if its better or worse. Get a timing light on it if you can get it to run long enough and you may be way off even though it runs. Let us know the outcome once you figure it out.

Mike
 

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This happened when I started my motor and it was timing. After I get rid of the backfire I had to put in new power valves. The new carbs are protected for this but mine were ruptured.
 

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I could never do the finger-over-plug-hole to determine TDC but here is something I came up with that works well if you have a compression checker like this:



Remove the gauge and just using the hose, screw the hose adapter into #1. Take a small square of electrical tape and put it over the opposite end and press it firmly on the small OD of the adapter. Prop it up vertically and you can use both hands to turn the engine and watch for a little bubble in the tape to confirm TDC when timing mark is at or near zero. Works great.
 

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Valve adjustment. If they are tight it will shoots flames out of both ends.
 

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Firing order:

302 HO/351W firing order is 1-3-7-2-6-5-4-8
Small Block Ford 260, 289, 302 order is 1-5-4-2-6-3-7-8

Verify the firing order shown above is correct for your engine and that the dizzy is not 180* out.
 

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I'll Admit To It...

On my first [email protected] replica, I had a 390 that I did the rebuild on, and had excessive back firing on my initial start-up. I found that I had guessed the rotation of the rotor wrong and had the wires in "reverse" order. It took a few minutes to figure it out but when I did it ran fine from then on.

Regards, Rick.
 

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Discussion Starter #14
My firing order is 1-3-7-2-6-5-4-8 counter clockwise. Confirmed this by watching the valves open and close too. I checked the valve tightness on the passenger side. I can rotate the pushrods by hand. I will check the driver side today. I am using an all in one distributor from MSD. It was what came with the engine. Standard 5.0 coil. It takes forever to start. Once it does it runs ok but still back fires out the carb. Eventually it just dies and will not restart. I have spark the whole time as checked with a timing light.
Mike
 

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Make sure the coil you have is compatible with your MSD dizzy.
 

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I had a similar issue. Check your valve cover / rocker arm clearance.

The valve covers I was using didn't provide enough clearance...which I initially didn't identify, so i adjusted the timing (way out)...complicating the issue. Switch to different valve covers, reset the timing...now running great.

Good Luck!
 

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My firing order is 1-3-7-2-6-5-4-8 counter clockwise. Confirmed this by watching the valves open and close too. I checked the valve tightness on the passenger side. I can rotate the pushrods by hand. I will check the driver side today. I am using an all in one distributor from MSD. It was what came with the engine. Standard 5.0 coil. It takes forever to start. Once it does it runs ok but still back fires out the carb. Eventually it just dies and will not restart. I have spark the whole time as checked with a timing light.
Mike
Being able to rotate the pushrods doesn't tell you much, assuming hydraulic lifters. The fact that it dies and won't restart also supports the idea that the rockers are too tight. Are they adjustable or pedestal? If you're confident in the firing order and timing, I'd start by re-checking the valve adjustment. :beer:
 

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Hi Mike

Is it a roller cam or flat/hydraulic................. maybe a cam going flat?

Even if the break-in is done correct it has happened where a cam can still can still go flat.

Just a thought.

If not that I am in the Ignition/Coil/Timing/Firing Order camp.
 

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I bet million dollars you are 180 degrees out. At your TDC keep turning the engine and see if the exhaust valve starts to open. Ive done this a bunch of times.
 

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Discussion Starter #20
I set TDC by sticking my finger in plug hole number 1. I can feel the pressure coming out. I will check it again though.
Mike
 
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