Backfiring through the carb. Wait there's more....

[71massbronco]

I am a little confused on what to do next.

Setup: 302, Weiand Intake (not sure what model) Carter AFB 9000 carb electronic Mallory Electronic Ignition, all was installed by somebody else before 2008.

This truck Sat since 2008 and probably was the last time it ran.

Here is what I know. The casting on the engine block is D1 hence a 71 which is the year the Bronco was manufactured. It was running a little rough lately so I started to investigate it more. I took all the spark plug wires off and re installed them according to the 14526378 and no fire at all, an occasional backfire through the carb but not starting at all. I hadn't checked the engine block yet. So I thought maybe I have an HO. So I rewired it to that which is the 1372.... order. Boom it starts but backfires through the carb a little and then as it idles out seems to go away. But under acceleration it kind of does a popcorn in the maker sound until I hit a decent rpm seems to go away. Then let off and it popcorns some more as it idles. And it is making the motor vibrate and shake like the harmonic balancer has torn loose.

This is the point where I get under the truck to check out to see what I actually have under the hood. It is a 71 non HO or so I assume. So I put the the plug wires back to the 1452 and all I get is a back fire.

Things I have done so far. I checked with a timing light and number one seems to be at number one on the distributor. I am at about 12*
I also removed the sparkplug to make sure I was at TDC. (But not at the compression stroke) I assumed it was there because the HB was spot on. What are the chances of it spinning exactly 180*? Knowing my luck 100 percent

I also ordered a rebuild kit for the carb. I pulled out the mixture screws and one seems like it was passing gas like a grandpa but the other seemed a little corroded like it is not seeing any liquid. That's one of the problems.

When it comes to these issues, I am ok, but I know that there are nuances that I don't know about these trucks and carburetors. Especially Carters so any help is appreciated because I am sure I missed something.

 

[langester]

Old firing order should be 15426378, not sure if you had a type error or not. I just went through what you are describing, make sure you are not 180 out as well.

 

[71massbronco]

Old firing order should be 15426378, not sure if you had a type error or not. I just went through what you are describing, make sure you are not 180 out as well.

That is exactly what was happening. I fixed it. I had to remove the distributor and turn the rotor 180. I am going to leave this post up just in case anyone else has the same problem. Hear is a fun fact: your truck will run (albeit very rough and backfire a lot) with the H.O. firing order and if your rotor is 180 out of phase. %). Back to life now.

 

[Seventee]

A shortcut for a 180 out situation is to place the #1 plug wire on the cap where #6 normally goes. Then place the remaining wires in the correct order from there. I would normally just go ahead and reset the dizzy but you could use this as a test.

Also make sure you are going the correct direction (CCW). I had an instance where someone wired the cap CW and was having similar symptoms.

Edit: nevermind, sounds like you figured it out!

 

[langester]

Had the exact same problem, I tried everything I could think of and finally got it right. Glad you got it fixed.
Have a good one!

 

[triracer67]

Same thing when I purchased bronco, PO had wired as HO. Man, it backfired bad. Swapped to non-HO and ran perfect.