Gas in Oil & Disappearing Fuel in Sight Glass

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T

Torque

Joined
Feb 27, 2008
Threads
74
Messages
262
Location
Dana Point, CA
I have a stock '81 FJ40 with an OEM carb. The truck has 114K miles and I don't know if the carburetor has ever been rebuilt . I'm guessing it has, but I don't know when.

The truck starts quickly and runs well, but just recently I noticed a gasoline smell in the oil. I drained the oil and had a sample evaluated by Amsoil. Sure enough there was a 2.5% level of gas in the sample. I consider this very high because I doubt if I had more than 100 miles on that batch of oil.

I went ahead and replaced the fuel pump thinking that was the likely culprit, but after reading some posts on iH8MUD I realized it might not have been. Just yesterday I noticed that the fuel in the sight glass will disappear within 8 hours of shutting down the truck. I'm guessing the fuel is leaking into the intake manifold and from there gets into my oil.

One other thing I've noticed about the carburetor is that if I use the choke when the engine is even slightly warm, the engine will idle fast, then slow and keeps cycling like this. Maybe this is normal? Anyway, I wanted to mention this in case it helps determine the problem.

Is my carburetor a "gonner"? Is there anything short of a rebuild I can try?

Thanks in advance!

John
 
The gas disappearing out of the carb bowl is either due to evaporation or capillary action siphoning it out the idle circuit. Try starting it cold to fill the bowl and then turn it off before the engine gets hot to see if it still dispappears. You could try a new O ring on the idle fuel solenoid to seal it better.

The idle speed oscillation is due to a problem in the idle fuel cut off circuit; either the manifold vacuum switch or the smog computer. If you ground the computer side of the switch it will go away until you find the problem.
 
Pin_Head,

Thanks for the information! My last test of the disappearing fuel in the sight glass was done with a cold engine. I ran it for no more that one minute. I'll pick up a new O ring and give that a shot.

If I was going to guess manifold vacuum switch for the oscillating idling problem, are you able to ID the part in the diagram below? Or, am I looking in the wrong place?

Thanks again.

John
47323668.webp
 
I think I found it on diagram 84-01. It appears as though both parts are no longer available. Grounding may be the (only) way to go.

John
 
Good tip. You're right, they do have both parts used.

Thanks.

John
 
Have you checked for gasoline in the oilpan since you've changed the fuel pump?
 
Not yet. All I have done since changing the oil is idle the engine for a total of two minutes. I wanted to first make carb adjustments/repairs before I do any more real driving.

John
 
Just wondering if your disappearing bowl gas could be as simple as a leaking float bowl bolt gasket?
 
I hope you don't mind if I piggy back on this thread.

I have a '74 FJ40 CA emmission carb with no smog attached, and the same empty bowl problem. I have yet to try the cold engine test, but I have noticed when I look in the sight glass right after shut down I see it bubbling and slowly draining. In total it takes over an hour to drain.

I will try the run and stop cold test in the AM.

I have just completed a carb rebuild and re jet and while it runns better, the bowl still drains.

Any suggestions on where to look next would be appreciated
thanks,
 
Thanks for the link, it is an interesting read. I like the delta T theory.

Since it is cold this AM I will run a few tests.
 
Current cold fuel level test parameters:
Engine cold over night
Garage temp ~ 80F
Removed coil wire
Used remote starter switch
Cranked with no spark till bowl was full
Since 0800 ( 4 hours ) zero movment in fuel level

When hot the bowel is empty in ~ one hour .

So when hot it is some how leaking into intake quickly with visable gurgiling.

Not sure what that means.
Carb fule level.webp
 
65swb45 said:
Just ported a base for someone in CO who also asked about it.
Click to expand...

That is a blast from the past. Since that time, I got two more rebuildable cores (I am collecting them to comply with the smog Nazis) and rebuilt them and checked to see if they also leak and they both did. One of them leaks faster than the other one. It doesn't have anything to do with engine heat because it will still leak out with the engine cold. I put some fluorescent dye (pyrene) in the bowl to track where it is leaking from and it is coming out of the idle port and pooling in the bottom of the manifold.

It still isn't clear why it leaks. It should not be possible to siphon out of the idle circuit because it is vented to the atmosphere by the air vent in the air horn and I verified that this air vent is open. A wild azz guess is that maybe it creeps out by capillary action (surface tension) and it seeps past the idle fuel cut off either past the O ring or the needle seat.
 
Just chiming in...

My 76 empties out also - I have not trouble shot it hot or cold nor checked how long it takes. I have simply noticed that it is empty after sitting.

I also was wondering about it washing oil from the cylinder walls but have not had the cruiser very long and am still working on bigger issues.

-just as extra data (that may or may not have any impact) The entire emissions system had a coat hanger abortion performed on it by the previous PO sadly I have hoses and wires dangling everywhere.
 
seeing is believing

So today I had to pull the air cleaner off of a 78 cruiser I am working on to get some elbow room while removing the booster and MC.

Cruiser has not been started for a week [while I was rebuilding the front end] so the only heat differential was the one between that of a engine which had been sitting under a closed hood vs the ambient air temp of about 90 at 2pm.

I looked down the barrel of the carb and saw gas sitting in the hole at the tip of the discharge nozzle in the secondary emulsifier. I gently blew into the carb to clear the tip............AND THAT WAS ALL IT TOOK! I watched in amazement as the emulsifier proceeded to completely drain the fuel bowl without the engine running!

Armandi [1975F40] was standing right there [actually, he was initially under the dash disconnecting the booster for me] and got to see the emulsifier dribbling out the entire contents of the carb.
 
There's always what appears to be a dried fuel stain in the bottom of my '78 intake manifold whenever the carb has been off. I've cleaned the manifold up a few times through the years for engine rebuilds and the like but the stain always comes back. now I know why. No real starting problems if the rig is run regularly.:meh:
 
65swb45 said:
I watched in amazement as the emulsifier proceeded to completely drain the fuel bowl without the engine running!
Click to expand...


This can't be siphoning because the outlet of the nozzle is above the level of fuel in the bowl (at least under normal parked orientations). The fuel bowl is not pressurized. That leaves capillary action or distillation (evaporation/condensation) as mechanisms.
 
Siphoning because of localized pressure phoneomenon and capillary action, oh man is this heading for chat..:) How about the interaction between all this and the float, I could imagine it bobbing up and down in harmony with drops being made pumping the fuel. When the draining is finished is there fuel left over in the bowl? Is there a different float available for the carb like a plastic one?
 
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