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235 adjustments
#1249717 Sat Jan 06 2018 04:14 AM
Joined: Jun 2015
Posts: 293
I
Shop Shark
235 backfiring through carb and jerking and missing, especially under load, what do I need to do? Is it timing?


Stovebolter -- the Next Generation
(I'm 20)

1941 Chevy 1/2-ton pickup
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Re: 235 adjustments
Ian Ring #1249719 Sat Jan 06 2018 04:21 AM
Joined: Dec 2001
Posts: 15,150
Boltergeist
This very thing happened recently to a bolter. I believe his turned out to be in the distributor....a good place to start. The thread is not very old so maybe a few topics down you will find it.


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Re: 235 adjustments
Ian Ring #1249733 Sat Jan 06 2018 11:31 AM
Joined: Jun 2006
Posts: 759
T
Shop Shark
Timing can do it, but so can a lean condition. Lean (insufficient fuel) can also cause a miss. A lean mixture burns slower which means combustion can still be underway in a cylinder when the exhaust valve opens. This ignites the charge in the intake manifold intended for the next cylinder in the firing order - and you get a backfire through the carb. So check your distributor/timing as suggested, but also look for something that is causing a lean mixture (clogged jet, low float level, etc)

Re: 235 adjustments
tomctomc #1249817 Sat Jan 06 2018 11:46 PM
Joined: Dec 2017
Posts: 771
D
Shop Shark
I am a start with the basics kind of guy. Pull the plugs and make sure not fouled or cracked. Just for giggles, do a compression test. See if anything is all of the sudden way out of wack. Next, I would bring the motor up to top top dead center or where ever the spec is for no. 1 to fire on your motor. Trace the no. 1wire to the distributor cap tower and put a chalk mark under the no. 1 wire tower. Remove the cap. The rotor should be pointing at the chalk mark or pretty darn close. Check the cap, make sure it’s not all gummed up or filthy or just plain worn out. Check the point gap. How old is the coil? Vacuum advance is next, make up a little adapter and rubber hose arrangement so you can sort out whether the diaphragm is bad. If it is, you have both a bad vacuum advance and a vacuum leak. You might also pull the valve cover and just make sure no bent push rods, broken push rod cups, of flat cam lobes (no lift on one or more valves.

Last edited by Dragsix; Sat Jan 06 2018 11:48 PM.

Mike
Re: 235 adjustments
Ian Ring #1249823 Sun Jan 07 2018 12:45 AM
Joined: Feb 2004
Posts: 20,608
H
Boltergeist
Do a valve adjustment, then a compression test.
Jerry


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Re: 235 adjustments
Ian Ring #1249832 Sun Jan 07 2018 01:25 AM
Joined: Jan 2014
Posts: 1,373
J
Shop Shark
Ian, I know the engine was relatively “new” to your truck. Did it run fine for a while? Or has it acted like this since installed?

Re: 235 adjustments
JW51 #1249868 Sun Jan 07 2018 05:44 AM
Joined: Jun 2015
Posts: 293
I
Shop Shark
It ran fine for a while and then past few days it got cruddy, I played with timing but that didnt a lot, replaced coil so that's fine. I thought my next thing is to check for a vacuum leak and I dunno what else


Stovebolter -- the Next Generation
(I'm 20)

1941 Chevy 1/2-ton pickup
"Lucy"
In the Stovebolt Gallery
More pix on Photobucket

1967 Ford Mustang - "Sally"
Re: 235 adjustments
Ian Ring #1249928 Sun Jan 07 2018 05:53 PM
Joined: Mar 2005
Posts: 141
R
Shop Shark
Have you checked your fuel tank, line, fuel pump, fuel filter and carburetor for sediment? My truck behaved similarly, I even had to tow it home once, as it would not pull even a modest hill for missing, bucking and backfiring. Even a tiny amount of rust, or sediment in the system can cause symptoms you describe.

Re: 235 adjustments
RdsLessTaken #1250021 Mon Jan 08 2018 09:55 AM
Joined: Jun 2006
Posts: 759
T
Shop Shark
Originally Posted by RdsLessTaken
Have you checked your fuel tank, line, fuel pump, fuel filter and carburetor for sediment? My truck behaved similarly, I even had to tow it home once, as it would not pull even a modest hill for missing, bucking and backfiring. Even a tiny amount of rust, or sediment in the system can cause symptoms you describe.


this is what i think happened. it explains the sudden onset of symptoms.

Re: 235 adjustments
Ian Ring #1250099 Tue Jan 09 2018 12:21 AM
Joined: Jun 2015
Posts: 293
I
Shop Shark
When I changed the engine I didn't put a fuel filter, back cause my fuel pump has a screen in it, I'll put a filter in a see it that helps


Stovebolter -- the Next Generation
(I'm 20)

1941 Chevy 1/2-ton pickup
"Lucy"
In the Stovebolt Gallery
More pix on Photobucket

1967 Ford Mustang - "Sally"
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