fuel boiling in carb

[Dmcbrass]

I have a problem with my GT and its 32/36 weber. This problem has existed for 4 years but is getting worse. When I shut the engine off and let it set for a few minutes, the fuel begins to boil in the carb and spill over into the intake. This requires me to then start the car as though it is flooded (accelerator pressed to the floor and crank forever). The problem used to happen in hot weather (greater than 85 degrees F) but is now happening all the time. The other day I ran the car for 30 minutes in 65 degree weather and shut it off. I came back a few minutes later and you could hear the gas boiling. The Engine temperature appears normal and I'm not loosing any coolent. The car is also beginning to run poorly after extended drives, hesitation when accelerating (not when the second barrel is open) (it accelerates fine when the throttle is completely open) and missing at high speed. I've replaced the points and plugs and set the dwell (currently running 48 degrees). Does this make sense to anyone out there?

[First opel 1981]

Originally Posted by Dmcbrass I have a problem with my GT and its 32/36 weber. This problem has existed for 4 years but is getting worse. When I shut the engine off and let it set for a few minutes, the fuel begins to boil in the carb and spill over into the intake. This requires me to then start the car as though it is flooded (accelerator pressed to the floor and crank forever). The problem used to happen in hot weather (greater than 85 degrees F) but is now happening all the time. The other day I ran the car for 30 minutes in 65 degree weather and shut it off. I came back a few minutes later and you could hear the gas boiling. The Engine temperature appears normal and I'm not loosing any coolent. The car is also beginning to run poorly after extended drives, hesitation when accelerating (not when the second barrel is open) (it accelerates fine when the throttle is completely open) and missing at high speed. I've replaced the points and plugs and set the dwell (currently running 48 degrees). Does this make sense to anyone out there?

Do you have the heat shield installed between the carb and the intake manifold? Do you have the spacer installed between the heat shield and the carb?

If no to either of those questions, then you have found the first possible reason for your problem.

[Gary]

Check out this thread:
http://www.opelgt.com/forums/afterma...m-problem.html

[wrench459]

Somewhere around this time of year. The gas companys switch over to the summer blends of fuel. Problem is there is no one easy fix that works on all Opels.
Anything you can do to lower the carb temps helps.
This includes
Heat shield
Splitting the intake from exhaust manifold
Blowers across the intake
Lower T-stat
Raising the fuel pressure (with a return line)
Even a rubber spacer or phenolic block between the carb and intake.
HTH

[tomking]

This is one reason I separate the intake manifold from the exhaust manifold on my engines. You dont need that heat all the time. I am running two welded up, home made sprint manifolds.

[Dale .D]

Personally I would eliminate the current exhaust manifold & replace with one of the new headers from OGTS

Originally Posted by Dmcbrass I have a problem with my GT and its 32/36 weber. This problem has existed for 4 years but is getting worse. When I shut the engine off and let it set for a few minutes, the fuel begins to boil in the carb and spill over into the intake. This requires me to then start the car as though it is flooded (accelerator pressed to the floor and crank forever). The problem used to happen in hot weather (greater than 85 degrees F) but is now happening all the time. The other day I ran the car for 30 minutes in 65 degree weather and shut it off. I came back a few minutes later and you could hear the gas boiling. The Engine temperature appears normal and I'm not loosing any coolent. The car is also beginning to run poorly after extended drives, hesitation when accelerating (not when the second barrel is open) (it accelerates fine when the throttle is completely open) and missing at high speed. I've replaced the points and plugs and set the dwell (currently running 48 degrees). Does this make sense to anyone out there?

[opelbits]

I fought the fuel percolation problem, too, including the drivability problems after an extended run.

I tried all the recommended fixes (heat shield, phenolic spacer, checking and rechecking the carb condition and settings, electric fuel pump, F.I. (sprint) manifold, everything) and while they helped, they just lessened the problem.

The only thing I found that made a substantial impact was rerouting the fuel line. My electric pump is in the back, but even if you are running the mechanical fuel pump, rerouting should still work just fine.

I ran the fuel line down and across the back of the suspension crossmember, then came upon the far side, keeping the line away from all the radiator hoses and the engine block.

The major problem I have found is that running the fuel line up over the front of the engine is possibly the biggest contributing factor to fuel percolation and vapor lock. Think about it, it's high up where all the heat goes and it's two nearest neighbors are the hot engine and the upper radiator hose.

Oh, and make sure the fuel inlet to the carb is away from the engine, not the one closest to it.

I will virtually guarantee this solution, like maybe 95%.

[hrcollinsjr]

Since these cars ran fine for years without this problem, I'm going to jump to the conclusion that the gas we now use is the main culprit. Would running a higher grade help any?
All of the suggestions I've seen look like viable solutions. Probably no single one is going to cure the problem by itself. The last choice on my list would be a lower temp T-stat. Lowering the temp beyond a certain point causes increased engine wear and lowers the engine efficiency.

JM2CW,
Harold

[Dmcbrass]

There is no return line on my car. Is that a problem?

[First opel 1981]

Originally Posted by Dmcbrass There is no return line on my car. Is that a problem?

As far as I know only the 73 had a fuel return line. That return line did clear up many of the vapor lock issues since there was always a positive flow through the fuel line. Your problem isn't a vapor lock. Your problem is a hot intake issue. Though you won't be hurt if you had a return line, adding one won't solve your problem.

[Tru-Craft]

I made myself a simple 38DGAS carb/header tube heat shield today.
Took a piece of 1/16 Aluminum and bent as shown.
Removed the back two nuts on the carb base and removed the needle.
Hopefully it will help keep the heat away from the carb and manifold.
The air gap should help a little.
At least now I can adjust my carb without burning my fingers. Use a dime as a screw driver to adjust.

To reduce the carb boil over problem:
*Electric fuel pump.
*73 fuel tank with return line.
*Re-routed fuel line.
*High temp Plastic carb spacer, 5/16" thick.
When I shut off my motor, the fuel level in the float bowl will still drop "boil/evaporate" when really hot.
But less than before.
Lyle

[wrench459]

Back in the middle 80's Chrysler had a major problem with vapor lock/fuel foaming. They came up with several different kits to combat the issue.
See TSB-180486 dated Feb. 1986. Also look into reed vapor.
Recall that around the same time frame the fuel changed to include a 10-12 percent alcohol content. Humm sound familiar?
Now they used a fuel separator to reroute the hot fuel back to the tank.Along with an electric pump.
It was a simple canister bottom hole inlet ,middle hole outlet and the top hole with a fixed orifice return. Worked great on 95% of the cars. Lets not talk about the other 5%. First thing that came to mind after typing that was "Lemon law"
Lyle I liked your shield. I'm sure it was made in stainless.

[opelbits]

A return line would be nice, but needs a little figuring. The return line and rerouting the existing fuel line both help with the basic issue of the fuel heat soaking. Move the line out of the 2nd hottest spot under the hood and keep the fuel moving. At idle the fuel is hardly moving in the line and since idle is usually while stopped, like in traffic, the heat from the radiator and the exhaust manifold is just accumulating under the hood. Nevermind that when the car is not moving and without a stock airsnorkel to block the hole as it draws air from in front of the radiator, sitting still the hot air behind the radiator could be pulled back around thru the snorkel hole and back thru the radiator and getting even hotter.

Try rerouting the fuel line from the pump to carb firstwithout trying anything else. It's just the cost of a piece of hose and while as HR says, all of these solutions are worth investigating, the single biggest improvement for me was rerouting.

[West Coast GT]

I haven't experienced the hard-to-start syndrome until yesterday. It wasn't even a hot day. Once I got the GT started again I was apprehensive about shutting it off while I ran the remainder of my errors.

Since the GT has an electric fuel pump, with on/off switch, I started shutting it off a few minutes before arrival at each destination. This worked well.

The only change made in the last several weeks leading up to this flooding problem was to play around with the ignition timing.