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Mar 9, 2003 | 02:03 AM

SumoBronco

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New User

Joined: Mar 2003

Posts: 3

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From: Albany OR

Backfire

Anybody want to give the new guy some help?

I have a full-size '86 Bronco with 4.9L 300 I6 w/ 1bbl carb.
Last fall, it starts backfiring, right before hunting season. I took it to a local shop, and the guy says its the thermactor valve. As a temporary fix, he takes off the belt that runs the thermactor. It ran without backfiring, but gave off really dirty exhaust and started stalling out at idle.

Finally got the part put in, but it starts backfiring again. I bring it back to the shop and they adjust the carb. He says it is still running too rich, but he can't adjust any lower. Also says carb should be replaced ASAP. It is still backfiring, when decelerating in gear, or even just going downhill slowly in gear.

My plan is to rebuild the carb (will be my first time for this) because I think this might be the problem. Any suggestions on things I might have missed that would cause this problem?

Mar 9, 2003 | 03:45 AM

79 posi

Senior User

Joined: Feb 2003

Posts: 277

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Backfire

Totally a guess here, but could timing be an issue?

Mar 9, 2003 | 01:22 PM

Vampiro

Cargo Master

Joined: Sep 2001

Posts: 3,135

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From: Canada

Backfire

if it backfires the timing isnt set right. time it first

Mar 13, 2003 | 02:24 PM

SumoBronco

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New User

Joined: Mar 2003

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From: Albany OR

Backfire

Thanks! I'll start with the timing and save the carb for later.

Mar 18, 2003 | 08:00 PM

kcw12

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Joined: Jan 2003

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From: Indiana

Backfire

Speakin of timing. where are the marks for the timing and would timing make valves clatter.

Mar 19, 2003 | 02:50 AM

GeneStoner

Posting Guru

Joined: Aug 2002

Posts: 1,493

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From: Great NW

Backfire

As you are looking down to your engine, the timing marks are next to your harmonic balancer on the left. NOT, on the cover of your timing chain.

Mar 22, 2003 | 03:03 PM

cypress_303

Junior User

Joined: Feb 2001

Posts: 72

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From: Canada

Backfire

If your six is equipped with the polution control recirculator pump, and all the junk that goes with it, that can be the cause of back firing, that was cause of mine, every time i'd grab 3rd it sound like i was doin a drive by shooting. If it's the kind where the whole polution control starts out right above each exaust port, (kinda looks like old school fuel injection) the rail that all the ports feed into can wear and rust out due the fact it's thin material, you can pull all that junk right out, pump included and plug the holes with a stard NPT pipe or hydraulic fitting, I think it's 3/8 NPT but not totally sure any more it's been a while since dealin with that delema. Hope this pertains to you in any way and maybe helps.

~Ben