Bronco Hut  
 

   Ford Bronco Parts - Classic Vintage Early Bronco Parts   Toms Bronco Parts   BC Broncos
Community
 Message Forum
 Photo Gallery
 Event Calendar
 Book Reviews
 Bronco Wallpaper
 Bronco FAQ
 
 600+ Bronco Links!
 
Search all Bronco Links
Buy / Sell
 Classifieds / Want Ads
 Vendor Forum
Rust Bullet
Bronco Tech
Recent Tech Articles
 •Holley Carb Tips
 •Aussie Locker
 •C6 203 205 Doubler
 •4 Link
 •Clutch Replacement
 •Early Turn Signals
 •C4 Improvements
 •Threaded Dipstick
 •NV3550 5 spd
     More Tech...
Bronco Auctions

Welcome to the ClassicBroncos.com Forums.

You are currently viewing our boards as a GUEST which limits your access to viewing only. To take advantage of all the forum features please take a moment to register. Registration is fast, simple and absolutely free so please, join our community today!

If you have any problems with the registration process or your account login, please contact contact the admin. If you've lost your password click here.

Go Back   ClassicBroncos.com Forums > Archives > Bronco Tech - Archives

 
 
Thread Tools
Old 11/21/10, 02:49 PM   #1
Blue71
Contributor
Bronco Guru
 
Blue71's Avatar
 
Broncos Rule!

Johnson City, TN
Joined: Aug 01
Posts: 4,542
Backfiring trough the carb?

'70 Bronco with an aftermarket carburated 1987 302 motor. Someone has put an Edelbrock intake and an Edelbrock 4bbl on it. It ran and idled good a few days ago after purchasing it, but now it will barely idle. Id did set for a while bu it has new ethanol free gas in the tank and a new fuel filter. When you try and rev it up...it backfires through the the carb and runs rough then dies. Sometimes shoots a small flame or two out of the carb too. Wahoo!

Guide me.

Thanks,

Blue71

'69 Half Cab
'70 Wagon
'71 Stroppe Baja
'73 Sport
'74 Sport
'75 Wagon
'76 Explorer w/ Four Wheel Pop-up Camper
'77 Wagon
'77 Original Ranger, 76,000 mi

"Yes I Know, But When Do I Get To Drive That Thang"
Blue71 is offline  
Old 11/21/10, 02:54 PM   #2
Explorer
Contributor
Bronco Guru
 
Explorer's Avatar
 
Raphine, Virginia
Joined: Mar 08
eBay: gfw1985
Posts: 4,238

My Gallery
Garage
Backfire thru carb usually indicates timing. May need to adjust to the new gas mix.

66 half cab 203ci I6, Classic Inlines aluminum head and intake, DSII, Holley 390 cfm 4V, Isky cam, Keith Black flat top pistons, ARP studs, balanced, 9.7:1 compression
Explorer is offline  
Old 11/21/10, 03:52 PM   #3
SDlivin
Sr. Member
 
SDlivin's Avatar
 
San Diego
Joined: Feb 10
Posts: 763

My Gallery
X2 on timing.
when I changed my cam / intake, it took me quite a bit to get the correct timing down. when it was incorrect, I would get the backfire through the carb etc....
Not sure on the gas though...

Check timing and Vacuum.
Should have around 8-12 BTDC for timing at idle, and 15-20 vacuum pressure @ idle.
Results, may vary accordingly....

-Robert
Mostly '70 bronco. 351w, gt40 heads, msd 6al, expl serp, chevy disc front, manual 3 spd, d20, 3.5" SL, 2" BL, 35" mt, l/s rear and front, d44, .......
SDlivin is offline  
Old 11/21/10, 05:43 PM   #4
77bronco_ed
Contributor
Bronco Guru
 
77bronco_ed's Avatar
 
Michigan
Joined: Jul 04
Posts: 1,579
If after checking and setting timing if this happens again it could be timing belt?

77 Bronco-All glass, 456 locked x 2
74 Bronco-Stock
77 Bronco streetrod project begins...
77bronco_ed is offline  
Old 11/21/10, 08:38 PM   #5
oldiron
Sr. Member
 
oldiron's Avatar
 
Gaze upon the light and see that it is blue.

Chattanooga
Joined: Jul 05
Posts: 527
No timing belts on 302's.
Other options for backfiring through carb:
Waaayy to lean, check for fuel enrichment (power valve on a holley)
Vacuum leak (could also explain the rough idle)
Burnt valve (could also explain the rough idle) easy to check with a vacuum guage.
Clogged fuel filter (again, causing poor idle quality and overly lean condition)

Need more info to be more accurate, such as how long did it set, driven much. etc,etc.
Greg

'74 wagon 302/c4 (new project)
Build, break, repair, repeat.....
oldiron is online now  
Old 11/21/10, 08:55 PM   #6
El Kabong
Contributor
Sr. Member
 
El Kabong's Avatar
 
Workin' On It

Pasadena, CA
Joined: Oct 09
Posts: 641
Also double check the firing order & condition of the wires. Reversed wires or crossfiring can cause backfiring by lighting the mixture while the intake valve is open.

-Rough 73, cut, 400, np435, d20, 35s.
-90 xlt, 351w, e4od, bw1356, 35s.
El Kabong is a cartoon horse from when I was a kid in the the 60s. No bong was used in the selection of this user name.
El Kabong is online now  
Old 11/21/10, 08:58 PM   #7
DirtDonk
Contributor
Bronco Guru
 
DirtDonk's Avatar
 
San Jose, CA
Joined: Nov 03
Posts: 17,232
And speaking of ignition, are you sure you're getting enough current to the ignition? I ask because you're running into all those other wiring issues right now.

Paul
DirtDonk is offline  
Old 11/21/10, 09:19 PM   #8
Blue71
Contributor
Bronco Guru
 
Blue71's Avatar
 
Broncos Rule!

Johnson City, TN
Joined: Aug 01
Posts: 4,542
Quote:
Originally Posted by DirtDonk View Post
And speaking of ignition, are you sure you're getting enough current to the ignition? I ask because you're running into all those other wiring issues right now.

Paul
Hey Paul..Me? Wiring problems? .I should be fine on the current. This is on another Bronco that I picked up a few days ago. Its a '70. That '75 is the booger with the starting issue we talked about before. Will double check though.

Thanks,

Andy

'69 Half Cab
'70 Wagon
'71 Stroppe Baja
'73 Sport
'74 Sport
'75 Wagon
'76 Explorer w/ Four Wheel Pop-up Camper
'77 Wagon
'77 Original Ranger, 76,000 mi

"Yes I Know, But When Do I Get To Drive That Thang"
Blue71 is offline  
Old 11/21/10, 09:25 PM   #9
bax
Contributor
Giant Member
 
bax's Avatar
 
smokin 37's

Melbourne.
Joined: Aug 05
Posts: 11,288

My Gallery
Do I need to come pick it up from you?

1971 U15 Hunter 289/435/20/ 4,11. 1968 U15 - EFI 408C/C6/205/4.88/37's/hi9/ARB's/hydro-boost/full cage/4wdisk/PS/powerasswipe/bla-bla-bla!
bax is offline  
Old 11/21/10, 09:25 PM   #10
Blue71
Contributor
Bronco Guru
 
Blue71's Avatar
 
Broncos Rule!

Johnson City, TN
Joined: Aug 01
Posts: 4,542
This Bronco sat for a few months. But ran fine for the past several days. Really strong 302 and idled well. Just the last day or so its giving these problems.

El Kabong- Firing order should be fine since it ran great a few days ago and nothing has been changed. Will check condition of wares again, but looked in good shape, even on the ends.

Oldiron- Might possibly be a valve. It did set a few months so will go back and double check fuel filter. If I can get her to idle..will check vacuum too.


Would there be any reason that the timing would be off since the other day? Haven't messed with it since it ran good. Might have jumped time possibly??? Really seems more like a carb issue. It is like it almost loads up or something.

'69 Half Cab
'70 Wagon
'71 Stroppe Baja
'73 Sport
'74 Sport
'75 Wagon
'76 Explorer w/ Four Wheel Pop-up Camper
'77 Wagon
'77 Original Ranger, 76,000 mi

"Yes I Know, But When Do I Get To Drive That Thang"
Blue71 is offline  
Old 11/21/10, 09:30 PM   #11
Blue71
Contributor
Bronco Guru
 
Blue71's Avatar
 
Broncos Rule!

Johnson City, TN
Joined: Aug 01
Posts: 4,542
Quote:
Originally Posted by bax View Post
Do I need to come pick it up from you?
Bax..drive up and help me fix this baby

Andy

'69 Half Cab
'70 Wagon
'71 Stroppe Baja
'73 Sport
'74 Sport
'75 Wagon
'76 Explorer w/ Four Wheel Pop-up Camper
'77 Wagon
'77 Original Ranger, 76,000 mi

"Yes I Know, But When Do I Get To Drive That Thang"
Blue71 is offline  
Old 11/21/10, 10:55 PM   #12
gumbydood
Jr. Member
 
Joined: Jul 09
Posts: 81
A broken valve spring might also cause this problem... i had some serious backfiring/misfiring issues with a broken intake valve spring, and it could be a "fine" one day and "bad" the next. Just a thought...
gumbydood is offline  
Old 11/22/10, 02:58 PM   #13
Blue71
Contributor
Bronco Guru
 
Blue71's Avatar
 
Broncos Rule!

Johnson City, TN
Joined: Aug 01
Posts: 4,542
Ok...I did get it runng bnetter today. Found a vacuum hose off behind the Carb on a vacuum tree fitting on the manifold. There was also another open port on a back there as well on that same tree. Doesn't appear to go to anything. Vacuum advance vacuum hose is in good shape and it comes off the front of the carb. Can't see any more vacuum leaks. Now she will idle fine. Revs up pretty nice and strong too. I took her for a spin, and first run was pretty good with a small bit of back firing from the carb, but not to bad and she ran strong. The next run down the street...it started out strong in the throttle, but would fall on her face in the mid range. Also seemed to fall on her face while pulling up hills too. Tried this several times and same thing happens. Timing seems to be pretty close too according to throttle response and starting. Brought her back in the garage and reved her up hard and no bumbles now. Just seems to do it mainly when driving.


Thanks,

Blue71

'69 Half Cab
'70 Wagon
'71 Stroppe Baja
'73 Sport
'74 Sport
'75 Wagon
'76 Explorer w/ Four Wheel Pop-up Camper
'77 Wagon
'77 Original Ranger, 76,000 mi

"Yes I Know, But When Do I Get To Drive That Thang"
Blue71 is offline  
 

  ClassicBroncos.com Forums > Archives > Bronco Tech - Archives

Thread Tools

Forum Jump


All times are GMT -6. The time now is 08:03 PM.


Bulletin Board Software by: vBulletin
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Garage Plus vBulletin Plugins by Drive Thru Online, Inc.


This site created, owned and maintained by Jon Hanna
Copyright 1996-2014 All rights reserved. Privacy Statement
ClassicBroncos.com is not affiliated with Ford Motor Company