Carb float bowl drains overnight (1 Viewer)

[Spanky Pete]

I know others have had this same issue. On a recently rebuilt Aisin carb (still smogged..Portlend DEQ goes back 30 years), the float bowl is draining down to the bottom of the sight glass overnight. Does not appear to be from sight glass gasket or drain plugs. Appears to be gas pooled in intake manifold, so it is not from evaporation. Takes at least several hours to notice slight drop in level, then completely down to bottom of sight glass by morning, so it does not appear to be from boil-over.

Any new thoughts, developments, or fixes out there regarding this pesky thing.

Other than this, I have finally got this rig running like it was new!

 

[inkpot]

Does your oil smell a lot like gas? It should if your getting that much fule draining that way. Or, is it being drawn back into the fuel tank? My Piggy does that. John

 

[Michael Hanson]

Hi, Your underhood fan working? Could it be evaporating after you shut it down do to heat? Mike

 

[Spike Strip]

I had a conversation with Mark A. about this very subject, since he had encountered it a few times before.

He posted about it in the 40 section: https://forum.ih8mud.com/40-55-series-tech/102886-float-bowl-leaking.html

There are other threads, about it also ... Never seen a difinative answer, though.... But since you've got gas pooling in the intake, it's probably coming out the idle or primary circuit. Vent could be clogged. How's the O ring for the sight glass ?

Maybe try and Oklahoma Rebuild ?

 

[Spanky Pete]

Carb fan is working. It is grounded to the body, so it runs for 20 min no mater what, so the carb is definitaly getting blown

 

[Pin_Head]

I had this problem on a couple of carbs and I gave up on trying to fix it.
On mine:
It drained even without running the engine or getting hot.
It drained out the idle circuit (I added a fluorescent tracer to spot it).
The air vent for the idle circuit was open and not plugged.
Replacing the idle fuel cut off solenoid o-ring did not stop it.

I suspect that it is creeping out of the bowl into the idle circuit by surface tension and seeping past the needle in the idle fuel cut off solenoid. Polishing the idle fuel circuit hole to cut down on surface tension and replacing the idle fuel solenoid would have been my next moves, but I threw in the towel.

 

[Michael Hanson]

Does the cruiser idle and run well? Mike

 

[Spanky Pete]

Mike, it runs great. It idles perfectly. It just requires some revving during cold start ups to get the float bowl filled with fuel again.

There is the case where on occasion a hot start (with float bowl full) results in crappy idling where it wants to stall unless I feather the gas. revving the engine a few times usually gets this to dissapear. During these instances (several times it has happened now) my vac gauge behaves as if the rings are bad, or the oil is contaminated. This caused my concern about the float bowl draining, possibly thining the oil. I haven't noticed any rising oil level or strong gas smell. I can smell faint gas on the distick, but not enough to rule out it just being my imagination.

 

[ntsqd]

I ran into a similar situation with a carb'd domestic vehicle. Do you smell raw fuel after a hot shut-down? Does it do this with any brand of fuel? I found that one particular brand was the worst offender and quit buying it.

I suspect that US fuel is now formulated for EFI and will boil off more readily in a carb than fuel of old. There may not be a cure.

 

[Spike Strip]

I suspect that US fuel is now formulated for EFI and will boil off more readily in a carb than fuel of old. There may not be a cure.

This is very true ! Modern fuels are formulated to fully vaporize at much lower temps than previous versions.

 

[Michael Hanson]

Are you running a 10 percent eth. blend? Go to no eth.. MIkel

 

[Spanky Pete]

I have been running E10 blend, and didn't even know it! I started checking various stations around the neighborhood and they all have E10. Finally talked to a knowledgable gas station attendant (yes we have gas pump attendants in Oregon), and he says all of the stations in the portland metropolitan area have gone E10. He thought I would have to go pretty far out to find pure gasoline...what next!

I will see what happens next time I can find a tank of the pure stuff.

 

[Michael Hanson]

You will need to change all your carb. seals to work with the newer E10 fuels. MIke

 

[TobyB]

I suspect that US fuel is now formulated for EFI and will boil off more readily in a carb than fuel of old

I was thinking the same thing.

One way to test it would be to get some race fuel. It'll have a much higher
flash point. Do get the unleaded, though. I forget the local supplier
in the Portland area... Competition Motorsports, I think is one.

I would, of course, never use AVGas or anything like that!

t