I have an old 307 in a Toyota LAND CRUISER. It Has a Carter AFB 500 cfm carb, Edlebrock Manifold,headers, Stock Chevy HEI, 9mm plug wires...etc...I have the timing set a 8deg. I am recently experiencing a backfire when i put a load on it at a low rpm. as i let out the clutch from a stop and ease into the second gear at a low rpm, if i lay into the gas (not too much) it will lag and then backfire... runs great once i get the rpm's up, I have looked at everything...timing, carb adjustments( set at 1 1/2 turns out), Distributer, plug wires, plugs....cant seem to fix it...also it seems like it does it more after it is fully warmed up at about 195deg...

Please...any suggestions.....HELP!!!!!!

OUT THE EXHAUST??

OR OUT OF THE CARB??

MY CAMARO BACKFIRES OUT THE CARB WHEN I LAY INTO IT AT A LOW RPM.
I DONT KNOW THE CAUSE BUT I THINK ITS TOO MUCH GAS,AIR.

Check your plug wires make sure you dont have any burned spots or tears on them. Check you dist cap and make sure it doesnt have any cracks in it. Hei or a point type dist?
How old is the motor? Adjust the valves?
Worst case= If you backfire through the carb I would say lobe going flat on the camshaft. Upon acceleration- timing, since you allready put a timing light on it did it change at all? check it again. I had a 350 the timing chain was shot and my timing was all over the place. Could be an exhaust lobe going flat if its through the pipes.

I am pretty sure it is backfiring through the carb...The motor is OLD!!! maybe 64 or so...the plug wires are almost brand new, HEI is in excellent shape, Timing chain is new, and the timing is steady at 8deg every time i check it, the only thing i can think of is the vaccume advance...are there different settings??? Since i have changed so much from the origional manifold, carb etc...should there be a different vaccume advance maybe....

Camshaft!

How 'bout an update YC ?

Running lean, timing off.:skull:

sounds like a flat cam to me also!

Hello people Its prob. the valves!

My Blazer was doing that for a while and it turned out to be valve related.

I might have to agree with valves or a flat lobe on the cam, BUT the I'm wondering if the module/wiring in the dizzy has taken a crap ? I just replaced my valves 3 months ago so I know that's not an issue for me.

My problem was- when I loaded up my 4.3, it started to backfire thru the carb. It would only happen in 4th/5th gear.
Then I found a frayed module wire inside (the white one).

Just for shits and grins I replaced the whole assembly b/c it was VERY worn-out.

Now it's just a question of setting my timing... which ain't gonna happen in this basterd 13F weather we've been having.

...and if YellerCruiser doesn't reply to this post I'll have to send him a personal :flipoff2:

Originally posted by imrtoy
Hello people Its prob. the valves!

Yea, thats what happens when an exhaust valve doesnt open :flipoff2: .

This post is "OLD"! So what was the outcome? What was wrong?