Aisan carb observation... (1 Viewer)

[e21pilot]

I know my 1980 running on its 1996 rebuilt original Aisan carb has some problems so I am planning on a rebuild/replacing of the carb soon.

However, I noticed today that when I park it on a level surface, I can see fuel in the float bowl through the sight glass, but if I check it at periodically at 6 hour intervals, the level slowly drops until I see no fuel in the bowl. I wonder why this happening? When I go to start it, I have to crank the engine several times just to get enough fuel in the bowl so that I can them pump the gas to get it running. Is there a simple fix to this issue?

 

[unklwedy]

I know my 1980 running on its 1996 rebuilt original Aisan carb has some problems so I am planning on a rebuild/replacing of the carb soon.

However, I noticed today that when I park it on a level surface, I can see fuel in the float bowl through the sight glass, but if I check it at periodically at 6 hour intervals, the level slowly drops until I see no fuel in the bowl. I wonder why this happening? When I go to start it, I have to crank the engine several times just to get enough fuel in the bowl so that I can them pump the gas to get it running. Is there a simple fix to this issue?

 

[Pin_Head]

Is there a simple fix to this issue?

No.

It is apparently due to the increased surface tension of oxygenated, "reformulated" gasoline. The fuel creeps out of the bowl due to capillary action.

 

[navarch]

Having been educated by Pin Head's very helpful carb rebuild videos on youtube I hesitate to chime in something different from a more knowledgeable guy than me, but I had the same problem when I first bought my 78 FJ40. In my particular case, it was due to a leaking fuel pump diaphragm that allowed fuel to gradually drain out of the float bowl and down the fuel supply line until it reached equilibrium with gas in the tank. Like you, I would have to turn it over a few times to get fuel to the bowl if my FJ40 had been sitting for more than a day or 2. Unfortunately, being new to both FJ40's and carburetors in general, I did not identify my problem until the diaphragm deteriorated enough to clog the carb (I did not have a secondary fuel filter between the pump and carb). I could've saved myself some trouble had I known to replace the fuel pump which is easy enough to do even for a beginner like me.

 

[Pin_Head]

The fuel inlet is at the top of the carb, so it is impossible for the bowl to drain back through the fuel line.

 

[sggoat]

There may be some evaporation issues also--the OEM carbs are not nearly as open to atmosphere as some others(eg Webers) but they are still open. Do you have the OEM exhaust manifold?-and do you have a heat shield on the intake?

 

[navarch]

Pinhead, you must be right - I had thought that the head differential between the carb and fuel tank had caused a sort of siphon effect that was no longer restricted by a perforated pump diaphragm, but that no longer makes sense to me given your point about the elevated location of the fuel inlet. I haven't experienced an emptying float bowl since then but, in hindsight, it's difficult for me to identify cause and effect since I replaced the entire fuel system at that time.

 

[e21pilot]

I should have provided more details...I have the stock carb and intake with after market header and a "heating plate" under the intake that heats the intake using hot water circulated from the back of the engine. There is also a cooling fan that blows air at the carb for several minutes every time I turn off the engine.

Interesting thing is I have had this same setup since 1994 and didn't have this problem till a few years ago and it has been getting worse.

I've never changed the fuel pump in all the years I've owned it but I assumed it's fine because it runs great once I get it started.

I live in California though and I know they have been changing the formulations of the fuel in recent years. If it capillary action as suggested, I'm not sure a carb rebuild will solve this.

 

[Pin_Head]

For sure, it wicks out of the idle fuel circuit. I tracked it by adding a fluorescent dye to see where it was coming out of. It is designed to not siphon out, because there is a tiny air vent hole to prevent this at the top. I suspect that it also depends on corrosion/oxidation of the aluminum. You might try polishing out the idle fuel hole or drilling it slightly larger for the top couple of millimeters.

My carb would empty overnight even if it was never started, so it is not due to engine heat. Also, if I filled it with a low surface tension liquid, like paint thinner, it wouldn't empty, so it seems related to surface tension. California has the highest levels of oxygenates in fuel, so it may be worse here.

 

[BrowardDet]

Try non-ethanol "recreation" fuel. It's tougher to find in some places, but less alcohol = "thicker" fuel, more surface tension in the bowl, I'd maybe try that.

 

[e21pilot]

I would be willing to give a tank a try. Where can you find such fuel? I have heard of a few stations selling high octane racing fuel but I don't know if this has ethanol in it or not. On the polishing, are you suggesting that the rough surface might make it easier for the fuel to work it's way out of the bowl? Is it going into the intake or back into the fuel line or..?

 

[GA Architect]

I would be willing to give a tank a try. Where can you find such fuel? I have heard of a few stations selling high octane racing fuel but I don't know if this has ethanol in it or not. On the polishing, are you suggesting that the rough surface might make it easier for the fuel to work it's way out of the bowl? Is it going into the intake or back into the fuel line or..?

Click here: Pure-Gas

 

[Landpimp]

all my old stuff(and small engines) gets non ethanol fuel, some that get driven more in the summer I cheap out and run costco, but if its going to be sitting very long, non ethanol is the way to go.

 

[e21pilot]

On this theory of ethanol in the fuel and capillary action being the culprit, is there any fuel additive out there that might mitigate or even correct this problem? If there was, it would help in the medium term as I won't get around to rebuilding the carb for a few months.

 

[Nottajeep]

Not sure if my problem is related. But I drove 150 miles round trip today and the truck really started stuttering and hesitating on the highway speeds. Sometimes would die when I came to a stop. A few times, I killed the engine and pulled over. Carb bowl looked empty.

Gas cap did not give me the vapor lock sound.
Stock carb rebuilt by Jim and a recurved dissy. Running only non ethanol.

Signs of a bad fuel pump??
Thoughts?

 

[e21pilot]

Sounds like a fuel pressure problem to me. Could be the fuel pump. Maybe even something as simple as the fuel filter is plugged up. You might want to do a fuel pressure test to know for sure.

 

[Nottajeep]

Fuel filter is new. And this only starts cutting out 30 mins or so into a highway trip.

How does one test fuel pressure?

 

[e21pilot]

The last time I tested fuel pressure on a carbureted vehicle, I went to the local auto parts store where they rent out special tools and gauges. I was able to get a fuel pressure test kit that had a collection of T fittings that allowed me to T the gauge into the fuel line between the pump and the carburetor. Once I had this in place, all I had to do was start the engine to measure the pressure. I liked this setup so much, I ended up putting a permanent gauge under the hood just after the filter so I could easily read the pressure any time. I didn't do this on my FJ40 however because I've had a fuel pressure problem with it.

In your case, you might want to take a reading when the engine is cold and then again after it starts to sputter. This would provide some interesting data points.

 

[Greasyfingers]

Hope nobody minds me jumping in but I need to ask pinhead where I can get the carb rebuild manual he was using in his vidio. I Found a 1981 aisan for my fj40 and bought a rebuild kit from SOR.
After watching his vidio I don't think I would try without a good manual or a copy. The problem is the price . I got a frame and chasse for a couple of bucks but the originals are a lot more. I can't locate a copy of a carburetor rebuild manual.

 

[Coolerman]

Fuel filter is new. And this only starts cutting out 30 mins or so into a highway trip.

Sounds more like you have debris in the gas tank that is sloshing around. After a while it covers the fuel outlet resulting in the truck stumbling. When the truck sits for a while, it settles to the bottom unblocking the outlet. This allow you to start and run for a while before it again covers the outlet.