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backfire thru the carb ...solved

73azbronco

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Nov 11, 2007
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7,796
google this, some good ideas out there:
backfire through carb

Did it do this before you swaped all the parts or after?

What is your idle vacuum?
 
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Ethansdad73

Ethansdad73

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Apr 8, 2008
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it was not running for about 4yrs and it was in WA state prior...In WA there were no issues with this, but i was not able to drive it as much as i have here.. I think i may just bite the bullet and have it tuned at a shop.
 

broncnaz

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Joined
May 22, 2003
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24,341
Swap your t stat back out for a 189 or 195 that 160 is opening and staying open thats why its heating up so much.
Shouldnt matter a bit that the engine is not original as long as it has the bronco balancer(timing pointer on the drivers side) the timing will read correctly. the hesitation can usually be fixed with a accelerator pump adjustment.
As for it missing at 3000 rpm it could be lean, to much timing advance or valve issues. hard to say. Have you checked to see what color your spark plugs are after a good run? If they are still white its to lean if black might be to rich.
What dist do you have? is it a dual diaphragm ie 2 vacuum hook ups? or a single. The singles are better suited to modified engines. if you have the dual it can be replaced with a single.
I have another method for timing that works well when I dont have a timing light you might want to try it see if it works for you. With the engine fully warmed up loosen the dist start engine, rev to 3000 RPM and hold it there then turn the dist until you find the smoothest running spot then tighten it back down. readjust idle if needed take it out and drive see if it runs how you want with no pinging. This usually works out to abot 12 degrees advanced when I check it with a timing light.

Different timing settings do affect the idle quality once timing is set you usually have to readjust the idle mixture screws then set idle speed and possible adjust the idle mixture screws again.
 
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Ethansdad73

Ethansdad73

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ok i have it set about 6-8 degress right now and i just ran it for about 20+ min and it seems to be running better... Only when i manually down shift (c4) do i get the backfire (not under throttle) but its not thru the carb out the pipes so at least it sounds cool. The temp ran about 170-200 and does not go above that. I then checked it with the engine of and the ingition on and it stayed at 200 and did not go higher.... I do think that it may be running rich and the idle is a bit low, but over all i think its better... I am tuning between work and picking the kids up from daycare so the weekend will be the real test. I did also notice i am missing half a blade on my fan....sure that does not help the heat issues.
 

broncnaz

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May 22, 2003
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Change that fan out before the rest comes apart and destroys your radiator. Sounds like you could be a little on the rich side with that exhuast back fire.
 

1970mule

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Joined
Dec 20, 2007
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1,515
i haven't read all the post but i have read that backfiring thru the carb maybe a vacum leak from the intake manifold, spray some starter fluid arond the intake mani and if it reves up then you have a leak.
 
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Ethansdad73

Ethansdad73

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Took the bronco out for dinner with the family and we went thru town and it was rush hour...so i hit a lot of lights. It started to get hot. Was running about 210-220. On the way home we went out to the hwy and it ran about 170/ I checked the temp when we got to dinner and when we got home and the temps did not change when the engine was off. I know that the timing is just a few degress off, but would it effect the temp that much from stop and go to hwy drive. It seems that i have a low speed cooling issue? I am thinking i should swap in a new fan ( bc bronco has one that looks good. Move the trans cooler from in front of the radiator and maybe a water pump hi flow. I will be in the future swaping a 351w in and these parts should be interchangeable right?
 

broncnaz

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May 22, 2003
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Yep the parts will interchange. A hi flow pump would be my last resort. A new fan and moving that cooler should help a bunch since you seem to be haviing low speed cooling issues that tells me not enough air is moving through the radiator at low speeds. A hi flow water pump will only compound the problem by moving the water through the radiator even quicker so it has even less time to cool off. I would also consider flushing the radiator real good if it hasnt been done in a while.
I dont think that timing would cause that big of a swing in temps but I could be wrong.
 
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Ethansdad73

Ethansdad73

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i do have a shroud. Looking a getting a fan and cooler then and go from there.. Thanks again.
 

NYLES

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Aug 13, 2004
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I had that cooling fun during OCBR added trans cooler and fan, didnt help got home added shroud didnt help.......spoke with my machinist "if it aint getting over 220 dont sweat it!" sitting still or put puttin itll get to 215-220 as soon as you hit hwy speeds right back to thremostst temps.
 
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Ethansdad73

Ethansdad73

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ok back to the same issue... i got a new fan as it was missing a blade, got a good one from BC and a shroud as well. I also moved the fuel filter above the above the power booster to get it off the manifold. Truck runs a constant 175-180 degrees idles fine at 190.

Had a ASE certified freind help with the timeing at my house with just a timing gun and i have new Manifold and carb gaskets and i still get the back fire when i have been driving for a while and or under load, but not all the time. I can not duplicate the event. I need to upgrade to disc brakes so i shift manually my automatic transmission from time to time and it pops a lot when decelerating.

The timeing may be off by just a hair, but that just does not seem like it would cause that much of an issue? Any ideas?
 

nosaj2k

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Dec 19, 2008
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226
Loc.
Green River, WY
I would STRONGLY recommend replacing the distributor. I had the exact same backfire through the carb issue with an old F-150. I had a worn 360 that I decided to upgrade to a fresh 390. Much to my dismay, it really didn't run any better than the old worn 360. Long story short, I discovered the bushings were worn in my old distributor - I replaced with a new unit and the difference was like night and day :eek:
 

broncnaz

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May 22, 2003
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Have you checked the spark plugs yet to see if its running rich or lean? popping in the ehxuast can be caused by a few things rich condition, due to jetting or wrong timing or theres a leak in the exhuast that lets cold air in.
 

12-Pack Jeff

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Sep 10, 2009
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Loc.
La Mirada, Ca
I skimmed the thread pretty good, I agree a worn out dizzy can cause much grief throwing multiple intermittent problems which can lead to wild goose chases. New (rebuilt), OEM replacements arent too expensive from your local parts supplier. Will work fine in stock and slightly modified engines. Also, you mentioned your carb is new, what kind of carb did you replace? Is your manifold designed for use w/ the carb your using? I know its an odd question, and generally people say.. well it bolts up, so it must work. But back in high school we swapped a carb... like q-jet to edelbrock.. it bolted up, but took a lot of major adjusting to run even halfway decent, and still popped and stuff.. turns out the carb didnt fit the manifold completely and there was a sliver of air leaking in under the base gasket. To solve it we had to use a special metal plate like a heat dissipater between the manifold & carb... More on the carb, I didnt see how many CFM it is, and after you installed it was it tuned for the engine? most likely the carb isnt CAUSING the problem, but if its grossly mis-adjusted it will definitely amplify the problem. Dont read too much into my previous statement though as it mainly applies to GROSSLY MIS-ADJUSTED carbs... (i.e. it took LOTS of fiddling with after installed) While I dont think this will solve your problem, it could help isolate it a bit more. Good Luck.
 
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Ethansdad73

Ethansdad73

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i dont remember what carb i swap from but the manifold is a street dominator, holley? I could not tell you if its single or dual plane but " the carb just bolted up" I would not be suprized about the distribator, as i replaced the ingnition a few thousand miles ago...which was at least 7-10 years ago...wow where did the time go. I also think i may have some bad fuel or water in the tank as the reserve tank produced more back fire. I have not tuned the carb since i pulled it out of the box as it drives the socks off my old one and i only drive it on fridays and weekends on small errands. I have disc brakes up next then my lift goes on. So i guess i may have to squeze a dizzy in too.. grr
 

broncnaz

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May 22, 2003
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The holley street dominator should be a dual plane really about the same as a edelbrock perfromer manifold.
If the gas is old and suspect that may be 90% of the issue.
 
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Ethansdad73

Ethansdad73

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well issue solved. metal fuel filter... first it was directly over the manifold, so i moved it to the fender but still under the hood, and i still had the problem... so i got a clear plasic one and mounted to the underside by the tank valve. bye, bye problem. Still have hard start after driving for a while ( by hard start i mean more the 4 turns of the engine to start, cold its one) but that is liveable for now.. header wrap, and venting should solve the rest in time... Thanks for all the help and advice in trouble shooting it.
 
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