The Stovebolt Site Forums The Shop Area Engine Shop Fuel seep at throttle plate

I think I have seen this asked before (maybe even by me!), but it has been a while and I do not recall the advice. I have a Carter on my 56 235 and after shut down this morning I noticed a strong odor of fuel. Upon checking the engine, I found fresh fuel on the base under the throttle plate pivot area. My guess is some excess fuel from the bowl dripping on to the plate then running out the shaft. My question is, is there something I can do to either stop the fuel from dripping down (maybe the float level is too high?), or keep it in the throat and not running out the shaft. Or do I not need to worry about this.

Thanks,
Lee

Your float level is possibly set too high.

Take the top off and adjust the float. It can be done on the vehicle if you're careful.

I would also recommend adjusting the float level slightly lower AND check fuel pressure/volume.

A float tends to get higher with use from the constant upward thrust of the float against the needle valve. Even if it was set right when the carb was assembled, its position can change over an extended period of time. This is more common with Carter carbs, as Rochesters usually don't run long enough between rebuilds for that to happen!
Jerry

The following is copied from the "Troubleshooting" section of my website:

"FUEL LEAK BY THROTTLE SHAFT(S)



A common complaint today is fuel dripping out of the throttle body by the throttle shaft AFTER the engine is switched off. While a number of issues may cause this problem, by far the most common issue is the volatility of modern fuel. Mechanical fuel pumps have a check valve which prevents fuel from moving back to the fuel tank. The problem is as follows:



(1) After the engine is switched off, heat from the engine heats the fuel in the fuel line.

(2) The expanding fuel (increased volatility) creates pressure in the fuel line from the pump to the carburetor.

(3) The check valve prevents the fuel backing up through the fuel pump.

(4) The pressure increases to a point the float/fuel valve combination in the carburetor cannot withstand the pressure.

(5) An amount of fuel (usually from a teaspoon to a couple of tablespoons) flows into the fuel bowl of the carburetor.

(6) This raises the fuel level in the bowl above the main discharge nozzle(s).

(7) Fuel flows through the main discharge nozzle(s) and drips onto the throttle plate(s) which is/are closed, and exits out beside the throttle shaft(s) dripping onto the intake.



Possible solutions:



(1) IF POSSIBLE, AVOID ETHANOL LACED FUEL! Sometimes you can buy real gasoline at a marina

(2) Buy the lowest octane name-brand fuel that does not ping or detonate in your engine (the higher grades often have more ethanol)

(3) Install a “vapor return line” (take a look at return lines used on many factory air-conditioned cars)

(4) Learn to live with the issue."

END OF QUOTE

Jon

Insulate the fuel line where its closest to a heat source might help. My 250 had a fuel line the went around the front of the motor between the thermostat housing and valve cover, I always had restart issues if I didn't wait long enough for the fuel to dry out. I suspect it was caused just by what Jon mentioned above. I have since rerouted the line straight up out of the pump and over the valve cover right into the carbs, eliminating quite a bit of line and avoiding the heat of the thermostat housing. Starting issues are way better now, and with a lot less fuel odor.

An example of a return line such as Hot Rod Lincoln CarbKing suggests is how I fixed my fuel percolation issue. Even though my '57 is modern compared to your I6 one bbl., the theory is the same. I have steel filter located pre-pump that has three nipples, I placed a flare tee at the carburetor so I could then run a 1/4" tube back down to the filter, this accomplished two things, it reduced the fuel pressure at the carburetor, and it allows pressure to bleed off when the engine is not running. I don't have a fuel percolation problem any longer.

Edit by moderator correcting source of info

Could the issue be reduced by after shutting the engine down, mash the throttle pedal to the floor? That would activate the accelerator pump and reduce the level in the float bowl. Also the gas discharged into the carburetor would go down into the intake manifold since the throttle plate would be open. I guess that would be part of carbking's possible solution #4.

Thanks for all the good ideas everybody. I will check the float level and make sure that is properly adjusted, and try the accelerator pump idea and see if that corrects the issue too. I recall my old Mustang had some kind of insulating wrap around the fuel line at the carb, maybe I can get a similar product to wrap this line with. The only starting issues I have are when the OAT is high and the engine is hot; then it sometimes takes a bit of cranking to get it started.
Thanks again to all.

Clothespins???

I run non ethanol gas in a YF carb. It still does this throttle shaft weep thing.

I’m not terribly worried about the weep. I have thought about adding a bypass regulator or vapor bypass fuel filter for some other reasons.

Ol' Roy only uses regular unleaded deathanol 87 octane and has never suffered from this malady in 4 years/11,000 miles.

It would be very simple to fabricate a T fitting to put into the fuel line to the carburetor with a small Holley main jet or something similar to relieve the pressure buildup in the line, plumbed back to the fuel pump inlet. About a 1/32" or slightly smaller orfice would be plenty.
Jerry

I had a 66 Buick Special deluxe with A/C which had a three nippled fuel filter. The tiny nipple was for the bypass hose which went to somewhere between the gas tank and inlet of the fuel pump.
I don't what the availability of this filter is in the aftermarket, but its function does lay creedence to what Hotrod is suggesting to solve the problem.

Probably this one:

www.ebay.com/itm/374966621309?

Jerry

That is the type of filter I use and included in my explanation a few posts back. I probably don't have an AC Delco but my local old style parts store had it in stock.