Backfiring help.

[RustyNailJustin]

Cruiser in question... 1976 FJ40, header.
So when I bought this thing the owner told me it had a back fire when shifting gears or when the idle droped quickly. I figgured no problem I can figure it out. Well After checking the timing and valve clearences I figgured it had a bad exhust valve. Pulled the head and took it to the machine shop they found a exhust valve that was not seating all the way. I had the head totally reconditioned. I put it all back together today, adjusted the valves and went out for a test drive. Guess what... the mother Fing pos still backfires! So I am a little irratated. On the up side I now have a new head gasket and a rebuilt head, but what is causing the backfiring? I did not install the headder the PO did and said the carb was re jetted. Where would you guys look next?

 

[skyshark186]

I would make sure your exhaust manifold/header is tight. Thats why mine was backfiring. Tightened up a couple loose bolts and whalla, it stopped

 

[desertdude]

isn't a backfire un burned gas in the cylinder ?

 

[RustyNailJustin]

I would make sure your exhaust manifold/header is tight. Thats why mine was backfiring. Tightened up a couple loose bolts and whalla, it stopped

I just had all that stuff off when I had the head off. Its tight with lock tight and a new gasket.

 

[skyshark186]

Mine was unburned gas getting into the exhaust, mixing with air from the leak, and combustion orcurring from the heat of the exhaust.

 

[RustyNailJustin]

How did you fix it?

 

[skyshark186]

My .02 would still be air getting in somehow. It cant explode/pop without oxygen, check they Y maybe?

 

[Romer]

Have you tried cleaning the carb with BGK44. It's hard to find but you can get it at NAPA and its expensive.

 

[skyshark186]

I just had all that stuff off when I had the head off. Its tight with lock tight and a new gasket.

Was it a toyota gasket? Ive heard of problems with non OEM type gaskets in this area.

 

[IDave]

Skyshark is right. Even if you think you are tight, headers, especially some certain brands, are notorious for leakage. You can spray carb cleaner around the rim/gasket and listen for a slowing of idle to help detect some leaks.

 

[desertdude]

so unburned gas somewhere between the cyl & exhaust... then finally sparking or burning. Bad wire? bad spark plug? check timing again? vacuum advance working? carb not to rich? Vacuum leak?

Maybe you have too many Fj's

 

[skyshark186]

Skyshark is right. Even if you think you are tight, headers, especially some certain brands, are notorious for leakage. You can spray carb cleaner around the rim/gasket and listen for a slowing of idle to help detect some leaks.

Ahhh....the first time ANYONE has ever said that. My life is now complete.

 

[RustyNailJustin]

Was it a toyota gasket? Ive heard of problems with non OEM type gaskets in this area.

No not toyota gaskets but good aftermarket type. I really dont think its leaking around the headder but I will look for sure.

 

[peesalot]

you might have a cam prob , did you measure the lift or at least check visually as you were doing the head and setting valves , did any valves adjust wierd?

 

[IDave]

Ahhh....the first time ANYONE has ever said that. My life is now complete.

And you can die happy? Wait until you're married. You'll remember this day for sure, cause it will never happen after that!

 

[RustyNailJustin]

you might have a cam prob , did you measure the lift or at least check visually as you were doing the head and setting valves , did any valves adjust wierd?

When I set them the first time cold they were chattering a bit but once I warmed it up and reset them hot. THey all set good and are quiet.

 

[IDave]

Not too tight then, are they? Shouldn't be quiet, but like a "Singer Sewing Machine" sound, as they say. To tight could cause your problems.

 

[Ian Rogers]

i look at the points, there is the 'nub' on the disy that opens and closes them, well one of mine wore down it would only backfire when hot, it took weeks to find. But in the end i got a new Disy and solved all of my problems. i would also do a good tune up on it, plugs, cap, roter, wires, points, condensor, coil.

 

[RustyNailJustin]

Not too tight then, are they? Shouldn't be quiet, but like a "Singer Sewing Machine" sound, as they say. To tight could cause your problems.

No they are adjusted correctly I promis.

 

[RustyNailJustin]

i look at the points, there is the 'nub' on the disy that opens and closes them, well one of mine wore down it would only backfire when hot, it took weeks to find. But in the end i got a new Disy and solved all of my problems. i would also do a good tune up on it, plugs, cap, roter, wires, points, condensor, coil.

Does it cold,hot,luke warm, it does not matter. Gotta be a air leak of some kind I think I just cant find the dam thing.