Backfire with Weber 32/36...any ideas?

[PhilC64]

The last couple of weeks have been quite a headache. While driving on the highway, I started to experience a backfire through the Weber 32/36 DGV carb on my 74 F motor. I pulled the air cleaner and seen it occur. Manual choking the carb does not cure the condition. I know this backfire is a result of a lean condition thanks to several searches here in the forum.

Here's what I've done to try and resolve the issue.

Rebuilt the Weber completely with a kit from Redline. New accelerator pump, new power valve, thoroughly cleaned the jets and emulsion tubes, blew out all orifices with Gumout and then canned air. Reassembled and brass float set per the Haynes Weber Manual with all specs verified through web searches.

Stock distributor has new cap, rotor, points and condenser. Points were gapped per spec to a tight 18 mm. Timing was set with the new rubber vacuum advance line off and plugged. The BB timing mark floats a bit but stays within the window.

Electric fuel pump is new along with a regulator set at 3.5 psi, new clear tube filter was also installed.

Since I tore apart the Weber 3 times already, I'm pretty danged sure the carb is clean. What else can I do with the carb that I may have over looked?

Since the BB timing mark floats in the window, would my distributor need to be rebuilt/ replaced? Would this be cause of the backfire? Prior to replacing the cap and rotor I observed serrations inside the cap caused by the rotor possible floating up and down witin the cap. Since I replaced the cap and rotor, I have not noticed any serrations in the cap.

What else should I do short of replacing the carb and distributor?

 

[Poser]

Is this a new carburetor?

Is this a new to you carburetor?

Is this a carburetor that you know the history of?

Is this a carburetor that was working fine on your Land Cruiser for years and all of a sudden it started acting up?

 

[65swb45]

Vacuum reading.

Compression test.

Adjust valves.

Second compression test.

Second vacuum reading.

Report back.

Best

Mark A.

 

[Texx]

The last couple of weeks have been quite a headache. While driving on the highway, I started to experience a backfire through the Weber 32/36 DGV carb on my 74 F motor. I pulled the air cleaner and seen it occur. Manual choking the carb does not cure the condition. I know this backfire is a result of a lean condition thanks to several searches here in the forum.

Here's what I've done to try and resolve the issue.

Rebuilt the Weber completely with a kit from Redline. New accelerator pump, new power valve, thoroughly cleaned the jets and emulsion tubes, blew out all orifices with Gumout and then canned air. Reassembled and brass float set per the Haynes Weber Manual with all specs verified through web searches.

Stock distributor has new cap, rotor, points and condenser. Points were gapped per spec to a tight 18 mm. Timing was set with the new rubber vacuum advance line off and plugged. The BB timing mark floats a bit but stays within the window.

Electric fuel pump is new along with a regulator set at 3.5 psi, new clear tube filter was also installed.

Since I tore apart the Weber 3 times already, I'm pretty danged sure the carb is clean. What else can I do with the carb that I may have over looked?

Since the BB timing mark floats in the window, would my distributor need to be rebuilt/ replaced? Would this be cause of the backfire? Prior to replacing the cap and rotor I observed serrations inside the cap caused by the rotor possible floating up and down witin the cap. Since I replaced the cap and rotor, I have not noticed any serrations in the cap.

What else should I do short of replacing the carb and distributor?

I set my fuel regulator at 2, although my weber is now on a 22R rather than a land cruiser. Doubt it'd make any difference in regard to backfire, just a little probably worthless info. Chances are, your distributor is toast.

 

[PhilC64]

Is this a new carburetor?

Is this a new to you carburetor?

Is this a carburetor that you know the history of?

Is this a carburetor that was working fine on your Land Cruiser for years and all of a sudden it started acting up?

I bought the truck this past October and was unsure of anything on it! I got it running and the carb performed decently. The backfire issue never reared it's head until I was driving it on the expressway when I last drove it. The truck never ran until I got it running.

Vacuum reading.

Compression test.

Adjust valves.

Second compression test.

Second vacuum reading.

Report back.

Best

Mark A.

I'll get those numbers later today after work and give you the results. I'm pretty certain it's not a manifold or vacuum leak since spraying it with ether does not raise the rpm's at all when I sprayed the exterior of the carb and manifolds with it. There is only 1 vacuum line from the carb to the dizzy, all other vacuum ports have been blocked off.

I did play with the regulator pressure setting as well. It ran he same from 2 psi to 5 psi.

 

[OLDNSLO]

Quit pissing in your gas tank Phil

 

[Pin_Head]

If the backfiring is through the carb and it is accompanied by bucking and surging while the engine is under high load, then it may be a fuel deliver problem with dirt in the fuel tank or a clogged filter, etc.

A more detailed description of the problem and the circumstances under which it occurs might lead to a better guess.

 

[JohnnyC]

1) did you clean out the filter in the carb?


2) is the dissy advancing?

 

[jtoro]

Same problem here. I solved it rebuilding the dizzy and correctly setting the spark. At the beginning I thought it was caused by a lean condition, cleaned and jetted the carb without any significant improvement. If your bb is floating and the dizzy is not loose, it could be caused by a "not so straight" dizzy shaft or irregularly worn angles on the thingy that opens the points.

 

[PhilC64]

If the backfiring is through the carb and it is accompanied by bucking and surging while the engine is under high load, then it may be a fuel deliver problem with dirt in the fuel tank or a clogged filter, etc.

A more detailed description of the problem and the circumstances under which it occurs might lead to a better guess.

While under load it did not buck or surge. It backfires if I stab the gas pedal. I can ease the throttle but it eventually backfires before the secondary's kick in. I get back fire under load as well as while in neutral. This problem reared its head when I was at a constant highway speed and continues regardless if under load or not.

The fuel pump is new and known good with a regulator set at 3.5 psi. I also set the regulator in stages from 2 psi to 4 psi and it still backfires. All hoses from the hardline to the filter, to pump, to regulator, to the carb are new. The glass fuel filter is full with no debris in it at all.

1) did you clean out the filter in the carb?


2) is the dissy advancing?

The small mesh filter in the carb was replaced when I rebuilt. The older one was tarnished but didn't have any debris in it.

The dizzy advances when I put a vacuum pump on it. I'll recheck for advance again as well.

I'm heading out to the garage now. I post up later after I check vacuum, compression, adjust the valves and recheck those after the adjustment. I'll check for vacuum advance as well while I'm out there.

 

[PhilC64]

Same problem here. I solved it rebuilding the dizzy and correctly setting the spark. At the beginning I thought it was caused by a lean condition, cleaned and jetted the carb without any significant improvement. If your bb is floating and the dizzy is not loose, it could be caused by a "not so straight" dizzy shaft or irregularly worn angles on the thingy that opens the points.

You posted while I was writing my reply.

I have a similar concern since the bb floats even after new tune up parts were installed. When I initially set the dizzy a few months back the bb was steady.

 

[SevenTwo]

Check for vaccumm leaks.

 

[PhilC64]

First I want to thank all of you for your excellent replies! As usual a fresh set of eyes on an issue usually does the trick!

Following Marks advice, I took vacuum and compression numbers and was getting the feeler gauges ready to adjust the valve train. I popped off the valve cover and found, much to my dismay, that the #6 intake and exhaust rocker arms extremely loose. The reason they were loose is that the rocker arm shaft pedestal and rocker arm shaft were broken in two! I was effectively running on 5 cylinders!

I have a few decisions to make regarding this situation. Do I fix this F motor's valve train, go with the SBC conversion route, or say screw it and get a Prius?

Thanks again folks! You guys as usual are a great source of info!

Some broken cruiser porn for you!

 

[JohnnyC]

i vote fix the f ....but...if you go with a sbc...i see knothin

 

[PhilC64]

I've started to price out crane rentals to swap the head. I figure myself and a crew of 8 laborers could have it swapped out in a couple of hours.