The Ford Barn

Daba · 09-30-2020, 06:54 PM

I have a 31 three window four-door with a B motor the car runs great up until 45 miles an hour anything over 45 it starts to pop through the carburetor any suggestions would be grateful. Carburetor adjustment? Timing adjustment? fuel mixture adjustment? drive the car off a cliff ?? Lol
Thanks again Daba

31 three window four-door deluxe with B motor
31 slant window four-door deluxe

GRutter · 09-30-2020, 08:39 PM

I would check point gap setting to be sure that there is enough dwell angle to allow coil to build back it's field.

As point rubbing block wears, the points ride closer to the cam, holding them open too long. Then as speed increases, you get to a point where the points are not closed long enough to build up a full field in the coil. A weak spark results.

Chuck Sea/Tac · 09-30-2020, 10:34 PM

It sounds lean to me. Have you opened up the GAV when it starts popping to see if it runs a little better? Be sure to let us know what the solution is.
Have you played with the timing recently?

Certimafied · 10-01-2020, 12:45 AM

I would guess lean mixture as Chuck Sea/Tac said or timing is off for that engine rpm and load.
I recently had a Porsche ( I know way different beast hear me out though) that had some surging and backfiring problems at cruising speed . I ended up finding the intake valves way too tight and a series of small vacuum leaks. Adjusting the valves cleared up a lot of issue and fixing the vacuum leaks cleared up the rest.

johnbuckley · 10-01-2020, 03:06 AM

yep often a symptom of a weak mixture/fuel starvation, ... so easy things first ... check the flow of fuel from tank to carb and the various stariners filters etc.. then move on to other stuff.

Daba · 10-01-2020, 06:22 AM

Sponsored Links (Register now to hide all advertisements)

I’ll give the GAV a shot today and check back. Can I use the new timing wrench I got for my other model A on a model B engine ?

John · 10-01-2020, 06:46 AM

It sounds like it is time to get that 'B' carburetor cleaned out.

Patrick L. · 10-01-2020, 06:52 AM

Good info, but, loosen the fuel cap and take it for a drive. The vents are known to plug.

rocket1 · 10-01-2020, 08:36 AM

Intake valve hanging up try MMO in the gas tank.

johnbuckley · 10-01-2020, 11:06 AM

Quote:

Originally Posted by Patrick L.

Good info, but, loosen the fuel cap and take it for a drive. The vents are known to plug.

Yes, Thanks Patrick.. I'd forgotten about that one ..... That's another one that has caught me out!

Patrick L. · 10-01-2020, 11:58 AM

Quote:

Originally Posted by johnbuckley

Yes, Thanks Patrick.. I'd forgotten about that one ..... That's another one that has caught me out!

John, with our age and what we have rolling around between our ears its easy to forget where we put all that info in that grey matter.

Daba · 10-01-2020, 03:37 PM

I tried the gav no difference then the timing much worse. I used the New timing wrench I got for the model a apparently the timing is slightly different. It moved about a quarter of a turn more than it was to start I think I’m going to go back to that point and try again.

Daba · 10-01-2020, 06:08 PM

I opened up the points and BINGO it did the trick. Thanks again for all your suggestions.
Daba

GRutter · 10-01-2020, 09:25 PM

Glad to see that fixed it for you.
George

shew01 · 10-02-2020, 03:28 PM

Quote:

Originally Posted by GRutter

Glad to see that fixed it for you.
George

Love the graphic. Yup, I’ve definitely had that feeling after finally getting the car to start when it was broken in the past. [emoji23]

Sent from my iPhone using Tapatalk

09-30-2020, 06:54 PM	#1
Daba Member Join Date: Jun 2020 Location: Orange Massachusetts Posts: 75	Carburetor backfire I have a 31 three window four-door with a B motor the car runs great up until 45 miles an hour anything over 45 it starts to pop through the carburetor any suggestions would be grateful. Carburetor adjustment? Timing adjustment? fuel mixture adjustment? drive the car off a cliff ?? Lol Thanks again Daba 31 three window four-door deluxe with B motor 31 slant window four-door deluxe

09-30-2020, 08:39 PM	#2
GRutter Senior Member Join Date: Sep 2017 Location: Mint Hill, North Carolina Posts: 386	Re: Carburetor backfire I would check point gap setting to be sure that there is enough dwell angle to allow coil to build back it's field. As point rubbing block wears, the points ride closer to the cam, holding them open too long. Then as speed increases, you get to a point where the points are not closed long enough to build up a full field in the coil. A weak spark results.

09-30-2020, 10:34 PM	#3
Chuck Sea/Tac Senior Member Join Date: May 2010 Location: Between Seattle & Tacoma Posts: 2,354	Re: Carburetor backfire It sounds lean to me. Have you opened up the GAV when it starts popping to see if it runs a little better? Be sure to let us know what the solution is. Have you played with the timing recently?

10-01-2020, 12:45 AM	#4
Certimafied Member Join Date: Aug 2020 Location: Belmont N.C. Posts: 85	Re: Carburetor backfire I would guess lean mixture as Chuck Sea/Tac said or timing is off for that engine rpm and load. I recently had a Porsche ( I know way different beast hear me out though) that had some surging and backfiring problems at cruising speed . I ended up finding the intake valves way too tight and a series of small vacuum leaks. Adjusting the valves cleared up a lot of issue and fixing the vacuum leaks cleared up the rest.

10-01-2020, 03:06 AM	#5
johnbuckley Senior Member Join Date: Jul 2010 Location: United Kingdom Posts: 1,441	Re: Carburetor backfire yep often a symptom of a weak mixture/fuel starvation, ... so easy things first ... check the flow of fuel from tank to carb and the various stariners filters etc.. then move on to other stuff.

10-01-2020, 06:22 AM	#6
Daba Member Join Date: Jun 2020 Location: Orange Massachusetts Posts: 75	Re: Carburetor backfire Sponsored Links (Register now to hide all advertisements) I’ll give the GAV a shot today and check back. Can I use the new timing wrench I got for my other model A on a model B engine ?

10-01-2020, 06:46 AM	#7
John Senior Member Join Date: May 2010 Location: Richmond, VA Posts: 189	Re: Carburetor backfire It sounds like it is time to get that 'B' carburetor cleaned out.

10-01-2020, 06:52 AM	#8
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Carburetor backfire Good info, but, loosen the fuel cap and take it for a drive. The vents are known to plug.

10-01-2020, 08:36 AM	#9
rocket1 Senior Member Join Date: Mar 2014 Location: Midland Park,N.J. Posts: 1,108	Re: Carburetor backfire Intake valve hanging up try MMO in the gas tank.

10-01-2020, 03:37 PM	#12
Daba Member Join Date: Jun 2020 Location: Orange Massachusetts Posts: 75	Re: Carburetor backfire I tried the gav no difference then the timing much worse. I used the New timing wrench I got for the model a apparently the timing is slightly different. It moved about a quarter of a turn more than it was to start I think I’m going to go back to that point and try again.

10-01-2020, 06:08 PM	#13
Daba Member Join Date: Jun 2020 Location: Orange Massachusetts Posts: 75	Re: Carburetor backfire I opened up the points and BINGO it did the trick. Thanks again for all your suggestions. Daba