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backfire out the carburator ??????

Discussion in 'Ford Trucks' started by SCAPEASAURUSREX, Nov 29, 2001.


    from NJ
    Messages: 196

    Never had this problem before ?? What do you think causes the truck to " backfire " through the carb when you shut the truck down ??? It just started happening today, It's also been real hard to get started.. ( thank GOd for dual batteries ) LOL... Thanks ...
  2. CT18fireman

    CT18fireman Banned
    Messages: 2,133

    Common cause is timing is off.
    Could also be a carb out of adjustment
    Try these first

    If not think
    Timing Chain has jumped.
    Valves out of adjustment or bad.

    How does it run once started? Any recent work done? Tell us tthe age, motor? etc?
  3. I agree with the fireman, most likely your timing is out. Lots of potential causes. Sounds like a good time for a tune up.

    Be aware that the timing being off can cause overheating also. It may not always be present, and will be most noticed under a load (or plowing).

    Another indication of timing problems is preignition, or what is commonly called spark knock. (The rattling you hear when you step down on it going up a hill). If you have noticed this lately then there is a good chance that that is it.

    Some people move to a better grade fuel to ease problems like this. It helps for a short time and costs them alot in the end.
    Hope you find your problem. Bob

    from NJ
    Messages: 196

    Thanks Guys,

    Heres the details.... Its' a 1985 F150 with a 351W, 4 spd tranny, 4x4, 2bbl carb...

    I have done a tune up ++++ The timing was done not too long ago.. And I prior to that had replaced the timing chain and water pump ( so I hope It didnt' skip a tooth.. ) Recent work... Ughhh What havent I done, or replaced... Even the carb was rebuilt in the spring.. new radiator, hoses, gas tanks, alt, smog pump, gaskets, exhaust manifold, eshaust pipes, wiring, plugs, cap, rotor, wires, filters, all fluids, window, bumpers, and so on. I have been trying to do a full resto on this thing , But its' one thing after another.. Ughhh..But at least its a strong truck.. Has the high GVW package, So its like a base 250..

    I dont see that it is running hot as per the temp gauge, but it acts like it is running hot..

    Also , Once I get it started and running it runs great, lots of power no pinging or anything.. The only time the probs occur is when I start it up ( hard starting ) and shut down, ( backfire out carb ) ..

    Thanks again...
  5. thelawnguy

    thelawnguy PlowSite.com Addict
    Messages: 1,011

    If its got that VV carb you wasted your money rebuilding it, either spend the 1000+ on a new one or swap over to older carb/ignition system.
  6. New_to_plowing

    New_to_plowing Junior Member
    Messages: 10


    All the above replies are things I would check for also. You may have an ignition module going bad as well. I had one going bad in my old truck (88 f150 converted to carb) it would get real hot and hard to start. When I tried to start it, and it didn't want to, I'd start pumping the gas.....which would flood the carb. Excessive gas, along with the choke can cause backfires, but not usually....of course mine did, and blew the seal along with the backfire! Also make sure all your wiring to the coil, module, and distibutor are good. Hope ya figure it out.
  7. DaveK

    DaveK Senior Member
    Messages: 420

    Since most parts have been replaced. Runs good after started (and warmed up - my assumption). One possiblity is the choke not operating properly. It is also possible that the EGR valve is stuck open. This won't always give these symtoms. But I have seen it. Usually you will get somewhat of a rough idle when the EGR is stuck open, unless the idle is set higher than normal. After you verify that both ignition and valve timing are correct, I would check the choke first.

    from NJ
    Messages: 196

    WOW.. Great replies guys,,, Thanks

    I am going to mess with the truck this weekend, tried tonight but it still is raining here..

    The idle is smooth once it warms up.. So I'm thinking now.. choke, timing, EGR valve.. Or ignition Modual.. Huh.. Guess I'll be busy checking it this weekend.. I did manage to get the cap off and that seemed OK.. the contact tips were white.... But not warn... Usually they are black ? at least that I have noticed in the past... Changed them anyway.. just to rule it out.. Let you know what if anything I come up with ..

    Thanks again...

    from NJ
    Messages: 196

    Ohhh Boy...

    Found a few problems... First of all the choke was not working... No voltage going to it..?? wire must have broke somewhere.. ?? Also found a few vaccuum lines off one of which was the one to actuate the EGR valve... I am going to replace all the vac lines. they are very dry and brittle.. a few were cracked..

    Thanks again for all the help guys..