[Dick Boneske]

Of all the hundreds of Tri-Powers I've built, repaired, or restored, last week I encountered a new problem.

The car is a '58 Pontiac with a stock 370 engine. The carbs are Chevrolet type, with the large fuel inlets. I replaced the needle/seats, all gaskets, installed corrrect jets for '58, and sealed the end carb throttle plates with DAG213. The linkage from the front to rear and center to rear carb has been removed.

Engine starts well cold, idles well, has good throttle response. The end carbs are sealed well--putting your hand over the airhorn does not change idle. The end carb venturi area is dry at idle. Fuel pressure is 5 1/2 psi.

After the engine idles for awhile, and reaches 190 degrees, all is still fine. When the engine is shut down, there is no dripping inside any of the three carbs.

However, after 8 minutes, the venturi cluster in the end carbs only gets wet with gas, until after a few minutes, there is gas on the throttle plates for the end carbs only. Fuel pressure has now dropped to about 4 psi with the engine shut down.

Restarting the engine can only be done by holding the center carb wide open to clear the flooding. .

Has anyone seen a problem like this?

[carbking]

Dick - I don't know what is causing the issue (unless it is the Pontiac gods punishing you for putting Chevrolet parts on a Pontiac!)

But when restarting hot, try this method.

Don't even look at the footfeed, let alone touch it!

Crank the engine from 3~7 seconds (this is a trial/error thingy, each engine seems to have its sweet spot).

While still cranking, gently (so as not to engage the accelerator pump) push the footfeed down about 1/3 of its travel. The engine should start but run rough. Run at a high idle for maybe 10~15 seconds and you will be good to go.

I have been using this method because of the p/p used instead for fuel instead of gasoline for about 30 years. So far, the method has never failed me.

Jon

[Dick Boneske]

I have changed needle/seats in both end carbs with the original build, then twice since, with similar bad results. The front carb is worse than the rear. I neglected to mention that I put an entirely different carb in the front location with similar results.

A clue that something is wrong with the front carb was seen when I woriginally took that carb apart. The float was bent such that no gas could enter the front carb. Someone did that intentionally.

This is why I really dislike the use of incorrect carbs on any application. In this case, however, the Chevrolet carbs should have been OK. There are differences--fuel line configuration and accelerator pump diferences. Chevrolet does not use the second check ball under the pump. .

[Dick Boneske]

I have never had this issue in the hundreds of carbs I've restored. I will, at the owner's request, run a temporary fuel line to the center carb only, so he can drive the car. So far, I've not thought of a solution to the problem.

Remember, I completely changed the front carb to another unit with similar results.

[Kenth]

Some 25 years ago i had the same problem using a mech fuel pump.
I connected a fuel pressure gage and it showed over 20 psi a while after shut off.
Guess fuel standing in the line between fuel pump checkvalve and inlet valves expanded from engine heat.
Since then i´m using an electric fuel pump w/o checkvalve as a remedy.
Another benefit with an electric pump is it keeps the fuel bowls filled at WOT thru all gears.

[Cammer-6]

try a fuel filter with vent tube
rather than run a vapor return line
just plumb in a small gas can up front.
this will also let you monitor vapor vs steady stream of fuel.

[mgarblik]

I had a similar problem about a month ago on a customer's 65 Bonneville tri-power on a 389. This car has factory AC and the wrong fuel filter on it without the vapor return line. I rebuilt the front and rear carb, I did replace the brass floats with black foam ones. That took care of most of it but it still dripped a little after sitting and smelled like gas slightly. The final fix was replacing the in-line filter with the proper unit that has the 1/4" vapor line attachment on top. That took care of it.

[Dick Boneske]

Thank you for the feedback. Problem is not yet solved. As I said, the owner wants me to disconnect the end carb fuel lines so he can drive the car.

This brings up another question. Why doesn't the dripping occur on the center carb?

I did mention that the fuel pressure is 5.5 psi running, and it slowly dropped to 4 psi after shutoff--before the dripping begins. After about 45 minutes, the pressure was 2 psi.

I will consider using a vented filter. I have some other ideas to try before that, however.

[Formulas]

Is the fuel tank / system vented to atmosphere?

Simple test run it just like you do when there's a problem but take off the gas cap and see if this continues

Could be pressure is just building in tank pushing the needles off the seats

[mgarblik]

Originally Posted by Dick Boneske

Thank you for the feedback. Problem is not yet solved. As I said, the owner wants me to disconnect the end carb fuel lines so he can drive the car.

This brings up another question. Why doesn't the dripping occur on the center carb?

I did mention that the fuel pressure is 5.5 psi running, and it slowly dropped to 4 psi after shutoff--before the dripping begins. After about 45 minutes, the pressure was 2 psi.

I will consider using a vented filter. I have some other ideas to try before that, however.

The center carb not dripping is a head scratcher. The one I worked on with this issue was the same way though. Dripping ends, center bone dry. Only 2 things can cause this. 1. A siphoning effect pulling main metering fuel through that circuit. 2. Needle being pushed off seat flooding the bowl. There should be a siphon break in the cluster between the main feed emulsion tube and the main air bleed. The chance of all 4 being plugged seems remote. I assume you ultrasonic clean the carburetor parts. Wish I had a better answer. I will say the nitrofill floats I installed seemed to provide better control than the brass ones. But no science to back that up. Please let us know how you solve the issue. I am sure you will. It would be pretty easy to substitute a couple of known good clusters in those carbs. That would be an interesting little test.

[carbking]

Dick - I get 25~50 calls WEEKLY with folks having a similar problem. Rochester 2G, 4G, Q-jets, Carter WCFB's, AFB's, Strombergs, Zeniths, Holleys.

V-8's are more prone to leak than inline 6's, as the carb(s) is directly over the engine.

The post by Kenth (5) will help. Fiber insulators under all carbs will help; but some will still drip (it is the p/p called fuel).

The customer's location and the heat generated by the engine is more critical than the type of carburetor.

I have given up on trying to completely stop the drip. The secret here is to "unlearning" everything we were taught/learned about started a hot engine. Try the method I suggested in post (2). It works! I have had hundreds of customers call me back to thank me, as they could then restart a hot engine.

And in the "for what its worth" a.k.a. "not so useful trivia" category; folks in Colorado seem to have more trouble with this proportionately than most other locations. Absolutely (opinion) the worst fuel in the nation, and a lot of higher altitude.

By not opening the throttle, the engine is allowed to be an air pump, and pump out the overrich mixture (what holding one's foot on the floor used to do). The p/p sold today is so volatile, it continues to flood the engine if the throttle is held wide open.

Trying my method costs nothing.

Jon

[wbnapier]

I guess you could test this by filling the tan with real gas, and see if the problem is still present.

[Kenth]

What type of inlet valves are you using?
I have found the aftermarket disc style inlet valves are pure junk, they wont even hold a simple vacuum test w/o excessive force on them.
I would never install anything other than the original style .086" inlet seat and needle in the end carbs.

JMHO

[carbking]

Kenth - I don't believe the fuel valve is the issue here; Dick has posted when he has the drip, pressure is around 4 psi.

I think engine heat is pushing the fuel out of the main discharge nozzles.

We see it all the time in all kinds of carbs. The end bowl Holleys seem to have less issues (at least this issue) as there is an air gap beneath the fuel bowl on the end bowl Holleys.

Jon

[Dick Boneske]

Originally Posted by carbking

Kenth - I don't believe the fuel valve is the issue here; Dick has posted when he has the drip, pressure is around 4 psi.

I think engine heat is pushing the fuel out of the main discharge nozzles.

We see it all the time in all kinds of carbs. The end bowl Holleys seem to have less issues (at least this issue) as there is an air gap beneath the fuel bowl on the end bowl Holleys.

Jon

Why am I having this problem with this particular Tri-Power? I've used the same components to rebuild these carbs as hundreds of previous rebuilds. The fuel supply line with a vent such as the A/C cars use has been on a very small percentage of the rebuilds I've done. I appreciate the suggestion to use a vent line, but this would be a work-around rather than a fix.

I am going to try one other change to see if it remedies the problem--an entirely different style of needle//seat.

I will report on restults soon.

[JSchmitz]

Turn the carb upside down and test it with a vacuum pump. See if the needle and seat hold vacuum.

[wbnapier]

Any updates? I am curious.

[Dick Boneske]

I did not know that the '57-'58 small end carb's float levels are set differently than the later larger end carbs. The measurement is taken from the airhorn gasket surface to the TOP of the float, not the parting line as is done with the other carbs.

I reset the float level using the prescribed method. This results in float level about 1/4" lower than I had been setting it at.

Since resetting the float levels, the problem does not exist. The engine starts cold, hot, or anywhere between with no issue. The dripping from the venturi clusters has stopped.

FYI--I use the TOMCO one-piece needle/seats with the flat disc valve on all my restorations. Some of you claim they are junk, but I've had much better luck with them than conventional needle/seats. With conventional needle/seats, initial startup involves flooding of at least one of the three carbs in at least one out of four startups. This has not occurred with the TOMCO needle/seats in the 12 years I've used them. This inculdes hundreds of carb restorations done in that time period.