Toyota ASIN Carb. Rebuild; Float Bowl drains after shutting off engine

Can anyone offer a solid-knowledgeable and proven solution to the fuel draining problem?
Fuel puddles in the intake manifold beneath the carb.; especially when hot and causes hard starting. This is a very slow drain.
The carburetor has been expertly rebuilt (several times) and about every imaginable solution has been tried.
This appears to be a common problem with ASIN carburetors and I have scoured the internet without finding the proven weird and unknown solution. Many people have simply given up but I am determined to find the unknown solution.
Tried unsuccessful solutions:

All ball checks have been gently reseated (including the supposedly inaccessible spring and check-balls under the 2 pressed in caps covering the accelerator passages).

All lines to the carburetor disconnected when engine is shutoff

Non-ethanol fuel used
Needle and Seat sealing confirmed
Changing the carb. tilt (front to rear) using a 5-degree wedge plate,
New fuel pump and pressure checked
And other solutions given on all of the websites I have looked at. I have exhausted the list.
I, and a friend (both knowledgeable in automotive), are completely stumped and this has become a challenge we choose to not give up on.
1985 Toyota Pickup> 22R 2.4L (1981-1990) TOYOTA TRUCK PICKUP-HILUX 2366 cc > ZT5

My only experience is with small engine carburetors. You’re saying when you shut it off the fuel left in the bowl ends up in the intake manifold some time later when you come back to start it up again?

Is the place where the fuel is settling higher or lower than the bowl?

Thanks for your reply but his problem is far beyond small engine carburetors. The ASIN carb. along with the smog system on the '85 Toyota is very complex and the solution is far beyond normal solutions. Very elusive, frustrating and weird!
The float bowl level lowers over hours. The fuel bowl has a sight glass and normal/desired float level marked.
I don’t want to appear as a “Know it all”, which I am not, but I have a background that includes mechanics including carb. rebuilding on small engines, outboard motors, marine engines, racing engines and OEM automotive engines.
I do appreciate your response and thanks.
Stumped in Eagle, ID

I have nothing to add but searching memory banks from 40 years ago, seems carb problems as they tried to deal with pollution controls were problems when new. My bil installed fuel injection on his 62 fairlane so that might be the best option if possible or put a fuel shut off on the line and run the fuel out at the end of the day.

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Is this a new problem? It was fine last summer in the heat?

Another question- does it drain out if the carb is off the truck on the workbench? If it’s only when the carb is in the truck and hot, then it could be fuel boiling.

Do you think if you pointed a small fan at it to keep it cool after parking that it would affect it?

how recently?

unless things have changed since last time I rebuilt a carb (10+ years ago,) I used to have issues with the ethanol in fuel eating the carb rubber innerds.
I was having to rebuild the carbs on my Ford vans just about every year.

You are definitely right about that carb’s complexity. I presume you’ve read how it works in an aftermarket repair manual for your car. It’s pretty well explained in my Haynes manual for my fuel injected Corolla, which also covers earlier model carb years.

The only idea I can offer is this has something to do with the carb’s evap emissions system. It’s supposed to prevent fuel in the bowl from evaporating into the outside air when the engine is off. Some sort of vent path is provided to allow the vapors to go somewhere, presumably into the evap canister, after the engine is turned off and the latent engine heat evaporates the bowl fuel. You might try disabling that system for a test, allowing the fuel bowl to vent to outside air. If that solves the problem at least you know the cause. The fix is anybody’s guess … lol

I had a similar problem on my 50 year old Ford truck. Difficult starting showed fuel bowl empty, intake manifold surface wet w/gasoline. Removed carb from engine and put it over a container, filled fuel bowl, not a drop leaked out overnight. So decided fuel must be getting heated up and forced out through the idle or venturi or accel pump pathways into the intake manifold. Removed vent hose, problem solved. Vent hose later shown to be clogged.

This will sound silly, but have you tried a thick insulated spacer between crb and manifold?

If your question is for me @PvtPublic , truck came originally equipped with that spacer, and remains. I presume OP’s carb configuration is to the oem spec, when the truck was new. If not, that’s the first suspect.

Been a problem for nearly a year and it has become an obsession to find th root cause-solution.

Websites I have gleaned information from with no success.



Good suggestion, I have but will do so again.


Yes and thanks.


Strip all the emissions crap off the truck, bolt a Webber on it and take up a new hobby.

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He did say that this bowl draining is a very slow process, so it continues to drain long after the engine has cooled off. There has to be some passage that it is leaking through then. What else could it be?

Hairline crack in the bowl one thought.

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Thanks. Used dye to check it out and didn’t find any cracks.


Suspect it’s a siphon or capillary action but can’t determine why!



Considered that but I’m on a mission to find the root cause.