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1978 Toyota pickup backfires on warmup when letting off gas between gear shifting

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1978 Toyota pickup backfires on warmup when letting off gas between gear shifting

Old 01-17-2019, 06:15 AM
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Iíd put the Weber on if I had the time and space to do it. The Weber was good on the Ď69 Landcruiser I had. The mechanic is asking for all original so he can hook it back up to original specs. So Iím leaning toward a rebuilt AISAN. Iím looking into a place called carb-x.com (anybody used them?)only because I think they have one ready to go and Iíve been without a truck for two weeks now and I need it. I might regret it later. I hope not tho!
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Old 01-17-2019, 07:50 AM
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Originally Posted by 83 View Post
National is the place I tried, too, because they do have good reviews. I got a carb I couldn't tune, so I took it to a specialty shop and they couldn't tune it. The carb shop showed me how there was a huge vacuum leak at the...man I think throttle arm but it's been a while now. Sent it back to National and they did their fancy "live engine test" ( ) and told me nope, everything is perfect with this carb and sent it back to me. It ended up in the trash and a Weber ended up on my truck. This was during the countdown (days, literally) until I moved into my camper and hit the road. I couldn't mess with it any longer. Ordered a Weber shipped two-day, installed it with a friend the day before I moved out of my house and hit the road.

But that's just one persons experience.
83 -

That's really strange, because they always replace the throttle arm bushings so there is no slop or vac leak there. Gotta say that's the 1'st time I've ever heard of there being that problem from them. Maybe they rebuilt it on a Monday or a late Friday?
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Old 01-18-2019, 04:15 PM
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Could be!
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Old 01-24-2019, 07:21 AM
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Update: new carb installed from carb-x.com. My Mechanic says the main accelerator pump is sticking possibly because the carb had been sitting for a while. Ugh! truck hesitates on slow acceleration. Carb-x said they engine test them before they send it and to check the egr valve. So Iím stuck in the middle of this plus the truck still has small backfires when cold! Mechanic is trying to give me the truck back like this with a huge bill.

Im still looking for that TVSV 9092502060. Does anyone have one or have a source for one? I found an eBay part that might work 9092502057 and 9092502056. Were these the same spec function and thread size? That is do they operate at the same temperature and fit in the same position on the truck?

Thx
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Old 01-24-2019, 07:32 AM
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I don't know if you've tried this, the thread is getting a bit long to keep track. But the hesitation and continued backfiring still makes me wonder about a vac leak.
I believe you have a vac advance diaphragm on the distributor. Is is hooked up? Is it good? To test it apply suction by mouth to a hose connected to it to verify it holds vacuum.
Then plug the hose back to the carb or intake and again apply suction while the engine is running to confirm idle changes. If it's the dual diaphragm type can, test both.

Last edited by Melrose 4r; 01-24-2019 at 07:33 AM.
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Old 01-25-2019, 08:37 AM
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Yep. Again, one man's experience, but that's my experience with rebuilt carbs from internet providers. "We engine test them. It tested fine. Problem must be on your end". Which is, most likely, true a lot of the time. I mean these trucks are old. But...
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Old 02-11-2019, 05:08 PM
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so I wanted to give a final update. It turned out to be the TVSV or lack there of since it never had one installed. Considering the history of the vehicle and the fact that it was stored with only 12,000 original miles when I bought it and currently has about 25,000 miles it turns out that Toyota Incorporated the TVSV later on as a fix for backfires as discovered through an old bulletin from the company.

Since the backfires damaged the fuel jets on the old carb, I bought a rebuilt carb from www.carb-x.com Which turns out to have a bad accelerator pump diaphragm that when warm hesitates in first gear. So every time I take off from a stop sign etc I have to double tap the gas And then let off the clutch. Otherwise it stalls out because there isnít any fuel being delivered.

So Iím currently seeing if the diaphragm will straighten itself out over time after soaking in gasoline for a while and being used. I doubt this is going to work. If anyone has any ideas throw them at me. Otherwise Iím hoping that carb-x will Send me another one for free and Iíll send back these two bad carburetors. Itíll probably cost me another hundred or $150 dollars or so to have a new carb installed. Ugh.

thx everyone
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Old 02-12-2019, 04:19 AM
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Lots of good work tracking down what was causing the problem. Kinda strange about the TVSV. Maybe it was an early build that didn't get the full smog package treatment? My "78 had one on it, which I have now replaced with a plug & eliminated it entirely. Perhaps a previous owner or mechanic removed it? Might never know. Mines been running fine without any of the smog equipment onboard, except for the vapor canister.

I'm not too sure about the backfiring damaging the fuel jets, since they are just pieces of brass with a hole in the center, but backfiring or "pop-backs" thru the carb are known to damage the power valve. That one has a spring & check valve in it that can be damaged beyond repair. Only fix for that is a new power valve. Also if the accelerator diaphragm is boogered up, it's not too likely to come back on it's own.

Also not too sure about Carb-X sending you a new carb. I checked their warranty section online & they say it's limited to their rebuilding/repairing the carb they sent you. Plus their core charge is DOUBLE what National Carb charges ($100 vs $50).

So what to do? Keep trying to get Carb-X to make it right. Failing that, use one of their failed carbs as a "core" & get another carb from National.
http://www.nationalcarburetors.com/l...partnum=toy387
I got mine from them & have been very pleased with it.

Or, get a carb kit & fix/replace the accelerator pump & power valve yourself, or have a carb guy do it.
https://www.rockauto.com/en/catalog/...epair+kit,5964

Only hitch in that plan is that it takes a thin wall deep socket (10mm if I remember correctly) to remove & install the power valve. There is no room in the carb body for a regular wall deep socket to fit in there, & it can be hard to find a 10mm thin wall deep socket in the stores, which is why a carb guy may be a better idea in this case; he has the special tools.

Also, just me, but no way I am paying $100 to $150 to have a carb installed. If your skill or confidence levels aren't up to doing it yourself I get that, but it's not that difficult for anyone with a brain & common sense, both of which I think you possess.
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Old 02-12-2019, 08:01 AM
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Originally Posted by 13Swords View Post
83 -

That's really strange, because they always replace the throttle arm bushings so there is no slop or vac leak there. Gotta say that's the 1'st time I've ever heard of there being that problem from them. Maybe they rebuilt it on a Monday or a late Friday?
This is sort of old and beside the point now, but what the carb guy thought was not that it was a simple fix like the bushing. Of course National replaced those. He thought that years and years of use, possibly even used for a time with worn-through bushings by a previous owner, had actually formed a bit of a groove in the metal, so that replacing bushings would not be able to seal the leak.

Glad to hear you're figuring it out! Sorry to hear it's still not resolved.
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