VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 1935 chev fuel percolation problem still happening

Hi there,
The Story so far:-
went on a reasonably long club run yesterday, usual hot day 35 deg Celsius,and on the way home the fuel percolation problem happened again.
I experienced very rough running for about a minuet, I turned on my newly installed 6 volt electric fuel pump hoping that it would clear the fuel and push more through the line.
It did nothing to help the matter and I pulled over th the verge, ran the engine on tick-over, it was OK.

When revved, it ran so roughly, that I decided to stop the engine running. It would not restart until it had cooled down , 2 hours later.
The fuel pipe from the mechanical pump to the carbie is wrapped in an exhaust bandage to help insulate it from the heat in the engine bay!
I wonder if this modification is actually keeping the heat generated IN the pipe, instead or OUT?

The new electric fuel pump from the filling station is designed to rum in tandem with the engine pump and has a filter installed near to its installation position as per instructions. I also have another filter installed just after the fuel pump ( as per original configuration before the electric pump installation) ......Is 2 filters in the line one to many?

Has anyone re routed the fuel line to a different position that is cooler than the present one, I was thinking that maybe taking the fuel line backwards to the bulkhead and up and over the rocker cover and then forward to the carburettor??

Is there any special insulated pipe that can be used for the fuel line , forward of the mechanical pump?

Or perhaps a shield that can be fabricated to deflect heat in the engine bay , away form the vital organs of the pump and pipe?

Clutching at a straw now....a refrigeration unit to cool the fuel as it make its way to the carburetor?

any ideas or thoughts on this matter , greatly appreciated.

Peter

I suspect the eletric pump is not pumping.
Remove the fuel line from the carburetor and stick it in a container . With the engine NOT running turn on the eletric pump and see if it is pumping gas.

The front of the engine nearest to the radiator is the coolest. Even though the air coming through the radiator is heated by the coolant coming from the engine it still does additional cooling as it flows past the HOT engine. Also the lower part of the radiator is cooler than the top. The hottest place under the hood is the exhaust manifold and next is the engine near the firewall. I suspect that your fuel line eventually gets hotter with the insulating wrap as the engine is run for an extended period of time. Heat will travel from the fuel pump down the metal line and without any air flow to help cool it keep getting hotter. The flow of gasoline inside the fuel line will help cool it but particularly at low flow rates (lower engine speed) that becomes of little consequence.

I agree with Gene. Make sure that the electric booster pump is operating properly.

As you suspect each fuel filter increases the resistance to fuel flow and the potential of gasoline boiling between the tank and fuel pump.

I would agree, check the electric pump operation.

I have always had relief, with vapor lock, by flipping the switch to the electric pump.

Same here....an electric fuel pump has always cured my vapor lock problems. However, the less filters that you run the better because of the extra restriction.

Peter
Of the number of fuel pipes I have muffler bandaged this is the 1st I know of that continued to have problems. I have not fitted a electric pump in tandem so wont comment on the benefits though there is probably lots.
Another chat member rerouted the pipe straight up from the pump between spark plugs over rocker cover to the carburettor. This will keep it away from the thermostat housing and exhaust manifold. The shorter length may well help as well.
Tony

hi there all,
thank you all for your interesting reply.
If the car has been standing for a week or so I turn on the electric pump to prime the carburettor and on the 2nd push of the button she bursts into life. It makes a ticking sound like the one on my series one 52 land rover....

Previously, before the electric pump installation, I had to repeatedly crank over the the engine to mechanically pump the fuel up to the carbie, and that severely drained my 6 volt battery.

So I am pretty sure that the electric pump is fully working, but, I will disconnect the fuel line from the carbie and see what happens as Gene suggested.

I will also monitor the flow and then disconnect one of the filters after the pump. Then thirdly remove the heat insulating wrap to the pipe and leave it bare and go for a run, maybe....if I am that brave.

Peter

A thought: why dont modern cars get vapor lock?

The major reasons modern cars don't vapor lock is: fuel pump located in the tank where gasoline keeps it cooler and fuel injection under pressure instead of atmospheric carburetion.

It is rare to have vapor lock between the pump and carburetor.

hi there chipper,
regarding vapor lock...
today I checked the flow of the new 6 volt petrol pump located down near the tank and filmed it too.
I was not overly impressed by the flow, but then I have nothing to compare it with! I did expect it to be more vigorous as stated in my comments. Can someone with a 6 volt pump do the same test and then we would have a comparison of flows?

http://vid1083.photobucket.com/albu...t%20pump%20test/PC082493_zpsw4wnyvsd.mp4

I also removed the fuel filter in the line after the manual pump and reconnected the hose, the flow was the same.

Peter

Peter
With a open fuel line like that clip showed that flow would be sufficient to run 3 engines the next test is pressure, I think someone else posted 2 or 3 lb is the standard to look for.
Tony

I watched the clip and was not of the same opinion as Tony so perhaps some of the more experienced folks will chime in. The last time I did a similar test was probably 50 years ago and I had the line inserted in a quart soda bottle. The stream flowed all the way to the rear of the bottle with good force.

Hi there Steve,
now thats an interesting observation, that means that it had vigorous pressure in my book.
I sent an email to the manufactures in New Zealand explaining what the problem was and also the video clip that I posted on here. I am waiting for a reply.
I haven't tried the same test using the mechanical pump, thinking that just cranking it over would not produce a full flow test?
but that might be interesting too!

Tony:- the pump is rated at 2/3 lbs pressure, but I have no idea what that looks like when coming out of a pipe?

Peter

There two pump tests.
Onw is for pressure at cranking speed.(3 pounds)
The other is for volumn. That is one pint of fuel in one minute at cranking speed.

I recently had a similar problem with my '37. I had purchased a fuel pump with a glass bowl to add "character" to the engine compartment.

Thru most of the summer it never seemed to run right. It would idle okay but would buck after it warmed up, especially if I went on highway trips of 55 mph.

During one such trip I noticed that the fuel filter bowl was only 1/4 full (running) and there appeared to be air bubbles coming from the fuel pump. So I bought an electric 6 volt fuel pump to add to the system ( my fuel system from tank to carb is all new material ) thinking this would cure the problem.

So before I install the electric fuel pump, I took a page from my drag racing days and decided to add a fuel pressure gauge to check the fuel pump. The gauge was registering 1 1/4 lbs of fuel pressure at idle. The shop manual says that it should be 2 lbs -3.5 lbs of fuel pressure.

I removed that fuel pump and reinstalled the original fuel pump and the pressure registered on the gauge as 2 3/4 lbs. at idle. 2 1/2 lbs at 40 mph.

What a difference in the way the car drove. From that point on taking the car on long trips became fun. Good power, nice idle, smooth operation. ( have not had to add the electric fuel pump as of yet)

Talked with the person I bought the pump from and agreed to look it over. Got it back a couple of days ago and plan to reinstall it and check the pressure as I have not removed the adaptor for the fuel gauge.

Also, the "carb type pump" generates 3 lbs of pressure, while the F.I. pump generates 55 plus lbs.

hi there Gene,
the only problem with doing the "one pint of fuel in one minute at cranking speed " is that it would run my 6 volt battery flat as a tack, so that test is not very practical for me.
In reading other reply's , I suspect that either the 6 volt pump is not functioning properly and possible the mechanical pump is suspect, with regard to pressure. ( but that has a new kit through it last year ,the mechanical pump )I could try to send the 6 volt pump back to the filing station, the postage could be $60 plus or more , for a replacement, but the same luck-luster performance may be evident again?
Guess I'm between a rock and a hard place.

Peter

hi there Dave,
thank you for your interesting reply.
I think that you are onto something in your writings.
Pressure is all important with the fuel system and I'm starting to think that mine is suspect.
My new 6 volt pump may be a duffer but I will have ti find a way of proving it good or bad.
I glad that you solved the problem, it must be so nice to go out for a run and to know that one is going to make it home in the afternoon?

Peter

If a 1935 chev engine is running at normal operating temperature and the mechanical fuel pump is operating correctly and the car is being driven under normal conditions then there is no need for an electric fuel pump or to wrap the fuel line to the carburetor It is also very unlikely that the fuel will percolate. My thoughts are that you probably have an obstacle or debris either in the carby, fuel line or fuel tank that moves around and occasionly blocks off your fuel supply. I suspect the fuel tank. I am not sure in your video if the electric pump is pulling fuel from the tank but if it is and you have a partial blockage then that may explain why it is not pumping as it should

What most people are not aware of 35 degrees CELCIUS is around 100--110 degrees FAHRENHEIT . that's REALLY HOT and can be a contributing factor to the fuel percolation possible problem.

mike

Have you contacted the "teck. advisor" at the Filling Station via the net to see what the pump that you bought should be doing? I am sure it has some specs.

I should give credit where credit is due....In the '37-'42 forum I posted about this problem and Chevgene pointed out that any vapor lock problem is confined to the area starting at the fuel pump out-put to the carb. Thus my reminder of checking fuel pressure. ( Thank you Chevgene for the heads up )

This is what prompted me to add an adaptor at the carb inlet to check the fuel pressure with the "character" fuel pump and the inline glass bowl filter.

After I had replaced the fuel pump, but before I started the engine I removed the inline fuel filter with an adaptor pipe. After taking the reading I replaced the inline fuel filter and found that the filter had a 1/4 lb of fuel pressure restriction.

I have been toying with the idea of adding a return line to the fuel tank instead of adding my electric fuel pump.

My thought was that if I "T" into the fuel line between the inline fuel filter and the carb with an 1/8th inch line back to the tank the restriction of the smaller line and it's length would not have a substantial affect on the fuel pressure but allow for a constant flow of "cool" fuel to the carb.

Any thoughts ??

Hi there,
In talking to a friend about this problem, we both came to the concussion that there may be some type of restriction at the tank end, inside the tank.This was before I read this post!

I had the tank cleaned many years ago, the end was removed and the internals cleaned. but that was years ago.

We are going to drain and remove the tank and have a look inside. I cant remember if there is some kind of gauze filter over the outlet?
Before we do that, I am going to remove the hose from the line and activate the pump directly from the tank into a container to compare the flow to the previous test.

Mike in Canada:- 35 deg celcuis is hot as you say, last week in the car-park at the local shopping center I pressed the temperature button in the car, and it was 39 deg C with a hot wind, now that's definitely HOT, everything you touch is hot, trees, timber and even your wallet!

Peter

Peter --

Just gonna ramble on a bit here. As stated above, the addition of a "Y" connector and a return line to tank may help also. My old 75 AMC Matador with the 258 six in it has this set up and also have had others set up that way also. Always pumping fresh cool gas to carb that way. Another thing, if you could find an early 50's Pontiac flathead six or eight in it and you will see a plate under carb that helps with carrying heat up and away from carb to help with vapor lock?? Just a couple of thoughts here.

Jim.

Peter and Mike, 35 deg celsius equates to 95 degrees fahrenheit.Peter, you were probably a little upset on the day of the run as the temperature was in fact 26 deg in your area or 78 fahrenheit. I still think you have a blockage problem and not a fuel boiling one.

I also am thinking about a fuel blockage problem. Put an air hose on the fuel line after removing both ends and see what blows out into a bottle! Both fuel lines to and from fuel pump! Wear safety protection!