1976 FJ40 hesitation and backfire (1 Viewer)

[Mean One]

Mine was a little piece of rubber that came off when changing the fuel filter

 

[65swb45]

Starvation.

Try running the truck off a gas can instead of your tank.

Tip from my Chinese cousin:Lo Tec.

 

[samatulich]

I was going of trying that too @65swb45

 

[samatulich]

Just an update. I did find a vacuum leak coming from the base of the carb. I pulled the carb off, had a good look through it, replaced the screen at the fuel inlet, checked the jets, and did a good once over. Everything had been dipped in carb dip last year, so I just sprayed the ports with air or carb cleaner and inspected what I could. I put everything back together and installed carb only to find a second vacuum leak where the primary barrel butterfly shaft went through the far side of the carb base. So I pulled the carb a second time and swapped bases out with a spare that I had. Installed everything again and this time I had a vacuum leak at the carb base again. I went through my carb rebuild kits and found a two barrel carb base gasket. I was under the impression that the carb base did not need the gasket, but I installed it anyway. This took care of the vacuum leak so I am happy.
Went for a test drive today, I was able to get up to 65mph with out the backfiring a few times on the drive. Periodically I would get a backfire out the tail pipe, but not nearly the same as before. I’m not out of the woods yet, but I’m feeling much better about the setup.
BTW, I continued on with the desmog process and only have the charcoal canister hooked up to the manifold vacuum via the VSV. I have the carb base vacuum port run to the inside vacuum advance on the dizzy. The power valve is hooked up to the throttle positioner. I need to buy some 3mm vacuum hose to replace the lines that I currently have. Some are nice and tight and others not so much.
Also noticed that the 2F is not getting up to 180*, more like 130*; so I’m thinking the thermostat my need replacing. Figured I need to get the engine up to temp before doing a valve job and dialing in the carb.
Thanks again guys for the input and suggestions.

 

[1911]

Also noticed that the 2F is not getting up to 180*, more like 130*; so I’m thinking the thermostat my need replacing.

Or it may be that the upper rubber gasket (that goes on top of the thermostat) was not installed previously. That will act like a bypass if the gasket is not there.

 

[65swb45]

Just an update. I did find a vacuum leak coming from the base of the carb. I pulled the carb off, had a good look through it, replaced the screen at the fuel inlet, checked the jets, and did a good once over. Everything had been dipped in carb dip last year, so I just sprayed the ports with air or carb cleaner and inspected what I could. I put everything back together and installed carb only to find a second vacuum leak where the primary barrel butterfly shaft went through the far side of the carb base. So I pulled the carb a second time and swapped bases out with a spare that I had. Installed everything again and this time I had a vacuum leak at the carb base again. I went through my carb rebuild kits and found a two barrel carb base gasket. I was under the impression that the carb base did not need the gasket, but I installed it anyway. This took care of the vacuum leak so I am happy.
Went for a test drive today, I was able to get up to 65mph with out the backfiring a few times on the drive. Periodically I would get a backfire out the tail pipe, but not nearly the same as before. I’m not out of the woods yet, but I’m feeling much better about the setup.
BTW, I continued on with the desmog process and only have the charcoal canister hooked up to the manifold vacuum via the VSV. I have the carb base vacuum port run to the inside vacuum advance on the dizzy. The power valve is hooked up to the throttle positioner. I need to buy some 3mm vacuum hose to replace the lines that I currently have. Some are nice and tight and others not so much.
Also noticed that the 2F is not getting up to 180*, more like 130*; so I’m thinking the thermostat my need replacing. Figured I need to get the engine up to temp before doing a valve job and dialing in the carb.
Thanks again guys for the input and suggestions.

Don’t wait: do two valve adjustments. One now, another after you sort out the cooling. You’re chasing your tail if you can’t drive the truck long enough to warm it up because of backfiring.

 

[DougAustinTx]

Probably not your problem, but my 79 2F which normally runs like a top started missing, popping and spitting last weekend and was almost unable to make it home up a couple of the hills we have here. I checked the resistance on my Toyota plug wires and they were good. Checked the rotor and cap in the dizzy.. good. Turns out that the two bolts holding the coil bracket to the fender were not getting a good enough ground to reliably fire the ignition. How can two bolts fail to ground a bracket?? Took the coil/ignitor assembly off and looked at the bracket. Apparently the PO had painted the bracket the exact shade of an unpainted zinc bracket. The threaded nuts in the fender were clean and unrusted. I have no idea why it took 6 years of driving for the problem to show up. Cleaned the paint off the bracket and problem was solved.