Backfiring Carb
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
gunrackgirl,
I would bet money on this one but, I'll pass and just tell you 99% chance that it's The unlead fuel curse, you need new harden exh. seats. Take a compression test. My 2 cents
orich
I would bet money on this one but, I'll pass and just tell you 99% chance that it's The unlead fuel curse, you need new harden exh. seats. Take a compression test. My 2 cents
orich
Senior User
Joined: Sep 2002
Posts: 306
Likes: 0
From: United States
Mine does the same thing. Irritating isn't it?
OK, what I do to 'fix' mine is:
- Make sure the timing is advanced as much as possible. Mine's at about 12 before but I have to use premium gas.
- Trickle (and I mean trickle slowly) water into the carb while revving about 2 grand. If you put too much in too fast, you could hydrolock a cylinder. That's not good. What you are trying to do is knock any carbon buildup off the valves.
- Change the plugs (even if you already changed them), thay are bad.
I haven't determined what is the root cause but these three steps make the truck run good again for a few weeks.
Larry
OK, what I do to 'fix' mine is:
- Make sure the timing is advanced as much as possible. Mine's at about 12 before but I have to use premium gas.
- Trickle (and I mean trickle slowly) water into the carb while revving about 2 grand. If you put too much in too fast, you could hydrolock a cylinder. That's not good. What you are trying to do is knock any carbon buildup off the valves.
- Change the plugs (even if you already changed them), thay are bad.
I haven't determined what is the root cause but these three steps make the truck run good again for a few weeks.
Larry
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Larry
That's a good old trick of getting the built-up carbon out.
A lot of people think that if there older vehicle runs ok on unleaded gas so why use the unleaded Additive, right. What, I was told is that the lead that was in gas worked as a lube and a cushion that reduced heat at the exh. seat and over time by not using the unleaded gas Additive the seats over heat and slowly
burn away and since there so hot when you put your foot in the carb. when you are under a small load it pops back in the carb.
because when the intake valve opens the exh. seat is so hot it does a flash back as like a glow plug. And this condition gets worse in warmer weather. I used the additive in my truck and it did help, but with a camper on it in hot weather it would start to pop back when going up a hill trying to pass a big slow truck on vacation and my old truck went slower and slower until that big truck passed me. The same has happen to my ex-father inlaw 2 trucks. And a few other guys, I know. The big fix was to do the head job with harden Exh. valve seats and all is well again!!
Ps, I had to set my timing at 2* degrees BTC and always used the high octane gas and The Unleaded Curse still got me.
1996, I had to get the harden seats and that was the end of the poping back. I still use the additive, and with 9.3 compression
I gota run that high 91 octane gas and that's a must for me..
My 2 cents
orich
That's a good old trick of getting the built-up carbon out.
A lot of people think that if there older vehicle runs ok on unleaded gas so why use the unleaded Additive, right. What, I was told is that the lead that was in gas worked as a lube and a cushion that reduced heat at the exh. seat and over time by not using the unleaded gas Additive the seats over heat and slowly
burn away and since there so hot when you put your foot in the carb. when you are under a small load it pops back in the carb.
because when the intake valve opens the exh. seat is so hot it does a flash back as like a glow plug. And this condition gets worse in warmer weather. I used the additive in my truck and it did help, but with a camper on it in hot weather it would start to pop back when going up a hill trying to pass a big slow truck on vacation and my old truck went slower and slower until that big truck passed me. The same has happen to my ex-father inlaw 2 trucks. And a few other guys, I know. The big fix was to do the head job with harden Exh. valve seats and all is well again!!
Ps, I had to set my timing at 2* degrees BTC and always used the high octane gas and The Unleaded Curse still got me.
1996, I had to get the harden seats and that was the end of the poping back. I still use the additive, and with 9.3 compression
I gota run that high 91 octane gas and that's a must for me..
My 2 cents
orich
Senior User
Joined: Sep 2003
Posts: 184
Likes: 0
Gunrackgirl, I had a backfiring problem on my '67 and it turned out to be the wire connections onto the Coil (primary and ground). The stock 90 degree gripper thing-a-mabobs were worn and the connection was loose. Every now and then the electrical connection was broken and the coil wouldn't fire for a split second. Then it would connect, and I would get one of the worst backfires you can imagine. I put on new screw-eye ends and then puts nuts on the coil connectors (primary and ground). That solved my problem.
