Massive backfire- HELP
Thread Starter
|
Senior User
Joined: Sep 2002
Posts: 110
Likes: 0
From: Calgary Alberta
Massive backfire- HELP
My 1970 f100, w/ 302, 3 speed manual has recently started backfiring, REALLY loud. It never used to do this. I have changed two things. One; I tweaked the idle screws on the carb to get a little more rpm out of it at idle.
Two; I purchased a new gas cap, (because I lost the old one, oops). The reason I suspect the gas cap might have somthing to do with the problem is because it seals really well, and when I take it off after driving around for a while I get a whoosh of air being sucked into the fuel tank.
The backfire occurs when decellerating, and occasionally when lugging. It is an exhaust backfire. The truck accellerates really nice after adjusting the idle screws, so I dont know what to figure.
Any help would be great, I dont want a noise violation ticket, I have already been pulled over by the cops once but he was laughing so hard he couldnt write the ticket out. (Apparantly he had been getting reports of someone firing a firearm off while driving and he had been searching all day for the culprit, I guess he had a sense of humor)
Thanks Scott
Two; I purchased a new gas cap, (because I lost the old one, oops). The reason I suspect the gas cap might have somthing to do with the problem is because it seals really well, and when I take it off after driving around for a while I get a whoosh of air being sucked into the fuel tank.
The backfire occurs when decellerating, and occasionally when lugging. It is an exhaust backfire. The truck accellerates really nice after adjusting the idle screws, so I dont know what to figure.
Any help would be great, I dont want a noise violation ticket, I have already been pulled over by the cops once but he was laughing so hard he couldnt write the ticket out. (Apparantly he had been getting reports of someone firing a firearm off while driving and he had been searching all day for the culprit, I guess he had a sense of humor)
Thanks Scott
Posting Guru
Joined: May 2003
Posts: 1,011
Likes: 0
From: South Dakota
In my mind to have an exhuast backfire you are really loading up the system with unburnt fuel, then BANG! With the cap to tight you would not be able to idle well and may 'run out' of power when passing due to not enough fuel delivery. When you decelerate and it backfires this is because the throttle plates close to tight. I would check the dashpot that keeps the throttle from closing to tight. this is a monentary unit but if not set right can cause backfires or to high an idle. Your having to adjust up the idle circuit is because the vent on your tank is plugged or kinked shut. You will need to correct it or install a vented cap.
An old trick with sticks was to go about 30mph, shut off the key, pull the choke or stand on the gas. Release choke or gas and turn the key on. KAWHOOM. Got me pulled over once.
An old trick with sticks was to go about 30mph, shut off the key, pull the choke or stand on the gas. Release choke or gas and turn the key on. KAWHOOM. Got me pulled over once.
Thread Starter
|
Senior User
Joined: Sep 2002
Posts: 110
Likes: 0
From: Calgary Alberta
Thanks for the replies, I am going to check out the exhaust leak possibility, I have headers and a dual exhaust system- could be a bad collector gasket?
I am also noticing poor mileage, so the possibility of running too rich and flooding the system with fuel is another possibility.
The adjustment screws near the base of the carb- are they for adjusting idle or mixture and do you turn them in or out to make the mixture leaner?
I am running a 2bbl carb torn off a 1979 LTD that I had rebuilt.
I am also noticing poor mileage, so the possibility of running too rich and flooding the system with fuel is another possibility.
The adjustment screws near the base of the carb- are they for adjusting idle or mixture and do you turn them in or out to make the mixture leaner?
I am running a 2bbl carb torn off a 1979 LTD that I had rebuilt.
New User
Joined: Feb 2003
Posts: 21
Likes: 1
Trending Topics
Senior User
Joined: Sep 2003
Posts: 184
Likes: 0
I had this problem on my truck. Just like 68Torino said, when your engine continues to spin and the plugs don't ignite the fuel charge, you pump explosive vapors into the exhaust system. It doesn't take much to make it explode. My problem was that one of the connectors to my coil had worn loose. It was one of the stock type that kind of snaps on. Anyway, it would get loose enough without coming off to break the conductivity for a second or two, then it would vibrate and make contact and--KABAM. It would scare the crap out of me. Long story short, check to see how tight your connectors are, maybe that's the problem. I put on new round-ended connectors so I could bolt them tight.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
Thread
Thread Starter
Forum
Replies
Last Post
Scott Yager
1973 - 1979 F-100 & Larger F-Series Trucks
23
Sep 5, 2016 04:11 PM
shanes66charger
1987 - 1996 F150 & Larger F-Series Trucks
2
Nov 3, 2013 08:18 AM
68f10059
1967 - 1972 F-100 & Larger F-Series Trucks
34
Oct 15, 2013 11:06 AM
areoseek
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
26
Sep 25, 2013 05:30 PM
DarkWolf40
FE & FT Big Block V8 (332, 352, 360, 390, 406, 410, 427, 428)
7
Jan 2, 2006 09:15 PM