Fuel leaking from carburetor bowl

I have an 87 V6 Dakota with a Holley 6280 carb, similar to the 2280
except it has an O2 feedback solenoid operating the supplemental fuel
jet rather than vacuum control.

Here is the problem. The fuel escapes from the float bowl after the
engine has been shut down and allowed to sit for period of time. The
fuel level sinks down to the top of the main jets, about 3/8" from the
bottom of the bowl. I am not sure how long this takes, but overnight
will do it.

Is this normal? Would the heat of the engine after it is shut down
cause the fuel in the bowl to evaporate out the bowl vent?

I just removed the top of the carb and cranked the engine without
starting it to raise the fuel level to where it shuts off the inlet
valve. I covered the bowl with plastic and I am waiting to see if the
fuel escapes from the bowl when the engine is cool. Temperature
outside is about 60 F.

While I am waiting to see what happens, I thought I would check with
anyone who might know if it is normal for the fuel level in the float
bowl to drop after a hot engine is shut down and allowed to cool off.

Thanks,
Jack

On Apr 8, 6:31 pm, "jack6128" > wrote:
> I have an 87 V6 Dakota with a Holley 6280 carb, similar to the 2280
> except it has an O2 feedback solenoid operating the supplemental fuel
> jet rather than vacuum control.
>
> Here is the problem. The fuel escapes from the float bowl after the
> engine has been shut down and allowed to sit for period of time. The
> fuel level sinks down to the top of the main jets, about 3/8" from the
> bottom of the bowl. I am not sure how long this takes, but overnight
> will do it.
>
> Is this normal? Would the heat of the engine after it is shut down
> cause the fuel in the bowl to evaporate out the bowl vent?
>
> I just removed the top of the carb and cranked the engine without
> starting it to raise the fuel level to where it shuts off the inlet
> valve. I covered the bowl with plastic and I am waiting to see if the
> fuel escapes from the bowl when the engine is cool. Temperature
> outside is about 60 F.
>
> While I am waiting to see what happens, I thought I would check with
> anyone who might know if it is normal for the fuel level in the float
> bowl to drop after a hot engine is shut down and allowed to cool off.
>
> Thanks,
> Jack

There were indeed engines where the carb would get heat soaked when
the engine is turned off in the summer, and boil away some gas.
Frequently what happened is that the pressure was raised in the float
chamber, and that pressure was high enough to exceed the pressure head
between the bowl and the jets, and the fuel was forced into the
manifold, causing hard starting when the engine was hot.

This was after the float chambers were sealed from the atmosphere.
With earlier carbs, the pressure in the float bowl could not build up
because it was vented directly to the atmosphere, and hence was at
same ambient pressure as throat where jets were.

jack6128 wrote:
> I have an 87 V6 Dakota with a Holley 6280 carb, similar to the 2280
> except it has an O2 feedback solenoid operating the supplemental fuel
> jet rather than vacuum control.
>
> Here is the problem. The fuel escapes from the float bowl after the
> engine has been shut down and allowed to sit for period of time. The
> fuel level sinks down to the top of the main jets, about 3/8" from the
> bottom of the bowl. I am not sure how long this takes, but overnight
> will do it.
>
> Is this normal? Would the heat of the engine after it is shut down
> cause the fuel in the bowl to evaporate out the bowl vent?
>
> I just removed the top of the carb and cranked the engine without
> starting it to raise the fuel level to where it shuts off the inlet
> valve. I covered the bowl with plastic and I am waiting to see if the
> fuel escapes from the bowl when the engine is cool. Temperature
> outside is about 60 F.
>
> While I am waiting to see what happens, I thought I would check with
> anyone who might know if it is normal for the fuel level in the float
> bowl to drop after a hot engine is shut down and allowed to cool off.
>
> Thanks,
> Jack
>

That would be normal and can happen in my Jeep engine according to the
book and experience. (couldn't find a 2 outlet filter when on a trip
once)

They call it vapor lock and put in a fuel return line from the filter to
the tank to prevent it. This way when the vapor appears, it can blow
back to the gas tank leaving the float bowl full.

If you don't have a return line to address, you might want to reroute
the gas line away from heat or insulate it.

You also should have an air vent for the float bowl. This is likely a
charcoal canister that has a $2.00 air filter on the bottom of it that
most folks forget to change with every tune up... Changing the first
one is a bear to dig it out, but then they just tuck in and out.

I have also heard of cracked bowls...

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

On Apr 9, 7:23 am, Mike Romain > wrote:
> jack6128 wrote:
> > I have an 87 V6 Dakota with a Holley 6280 carb, similar to the 2280
> > except it has an O2 feedback solenoid operating the supplemental fuel
> > jet rather than vacuum control.
>
> > Here is the problem. The fuel escapes from the float bowl after the
> > engine has been shut down and allowed to sit for period of time. The
> > fuel level sinks down to the top of the main jets, about 3/8" from the
> > bottom of the bowl. I am not sure how long this takes, but overnight
> > will do it.
>
> > Is this normal? Would the heat of the engine after it is shut down
> > cause the fuel in the bowl to evaporate out the bowl vent?
>
> > I just removed the top of the carb and cranked the engine without
> > starting it to raise the fuel level to where it shuts off the inlet
> > valve. I covered the bowl with plastic and I am waiting to see if the
> > fuel escapes from the bowl when the engine is cool. Temperature
> > outside is about 60 F.
>
> > While I am waiting to see what happens, I thought I would check with
> > anyone who might know if it is normal for the fuel level in the float
> > bowl to drop after a hot engine is shut down and allowed to cool off.
>
> > Thanks,
> > Jack
>
> That would be normal and can happen in my Jeep engine according to the
> book and experience. (couldn't find a 2 outlet filter when on a trip
> once)
>
> They call it vapor lock and put in a fuel return line from the filter to
> the tank to prevent it. This way when the vapor appears, it can blow
> back to the gas tank leaving the float bowl full.
>
> If you don't have a return line to address, you might want to reroute
> the gas line away from heat or insulate it.
>
> You also should have an air vent for the float bowl. This is likely a
> charcoal canister that has a $2.00 air filter on the bottom of it that
> most folks forget to change with every tune up... Changing the first
> one is a bear to dig it out, but then they just tuck in and out.
>
> I have also heard of cracked bowls...
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
> Canadian Off Road Trips Photos: Non members can still view!
> Jan/06http://www.imagestation.com/album/pictures.html?id=2115147590
> (More Off Road album links at bottom of the view page)

Thanks for the feedback, Don and Mike. I think it might just be heat
related. With the engine cold, I popped the top off the carb and
cranked til the bowl was full and then covered it with a plastic bag.
The next morning, the gas level was down some, but not nearly as much
as sitting overnight after the engine was fully warmed up. I have a
spare carb with a loose throttle shaft, but the bowl and top look
okay. I'll rebuild the carb and use the throttle section of the one
and the bowl/venturi section and the top from the other and see what
happens.

Thanks again guys.

Jack

On 8 Apr 2007 16:31:01 -0700, "jack6128" > wrote:

>I have an 87 V6 Dakota with a Holley 6280 carb, similar to the 2280
>except it has an O2 feedback solenoid operating the supplemental fuel
>jet rather than vacuum control.
>
>Here is the problem. The fuel escapes from the float bowl after the
>engine has been shut down and allowed to sit for period of time. The
>fuel level sinks down to the top of the main jets, about 3/8" from the
>bottom of the bowl. I am not sure how long this takes, but overnight
>will do it.
>
>Is this normal? Would the heat of the engine after it is shut down
>cause the fuel in the bowl to evaporate out the bowl vent? <snip>

It's normal. Due to the volatility index of contemporary fuel, the
evap. system will adsorb (NOT "absorb") a lot of the fuel in the bowl
overnight into the charcoal cannister. That's why, after you crank
for awhile to get fuel up to where it'll hit the venturis, then you
get a momentary "run rich" condition after the coolant temp allows the
cannister to purge. Very common on any 6280 equipped V6 or 318. If
your vent solenoid plunger is stuck to the air horn casting, you'll
wind up with the fuel boiling over into the manifold, getting the same
symptom, but a "rich" start.

Carburetors are obsolete. Get used to it. Now that gasoline is on
its way out, it'll get worse, not better.