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!

Several years ago a group of us were heading to Dayton, Ohio for a Central Meet on a 95 Deg. day and we were running between 45-50 MPH. We pulled into a rest area for a 'potty stop' and as we were about to leave, my
'35 Std coupe refused to start! A quirt check showed there was spark, so it had to be fuel. The fuel line from the pump
to the carb was so hot you wouldn't keep your hand there very
long! One of the people we were traveling with had some ice cubes in a cooler. I took a couple of ice cubes and with them
wrapped I got a napkin I rubbed them up and down the fuel line the ice cubes were all melted.
The coupe started immediately and I never had a vapor lock problem again!
It was very hot, and we were pushing them a little bit. So,agreeing with a previous poster, vapor lock is most likely to occur in the line between pump and carb, especially since it is routed so
close to thermostat housing

Don't anybody remember taking a spring loaded clothes pin and attaching it to the fuel line ( sometimes more than one). Seriously it sounds more like a clog in tank. Are you sure someone didn't maybe put a foreign object in the tank ie( ping pong ball or ladies pantyhose, knotted. Jay

Some may think this is sematics only, but here goes:

Vapor lock is defined as vapor in the fuel pump. The fuel pump is designed to pump liquid, and while it will pump vapor (gasoline in a gasous state), it does so quite inefficiently.

Vapor CAN develop in the fuel line from the pump to the carburetor, but think about this - if the carburetor is out of fuel then the fuel valve (needle and seat) in the carburetor is open, and (assuming there is fuel in the fuel pump), the fuel pump will pump fuel into the line forcing the vapor out of the line into the carburetor. Since the vapor is lighter than what fuel may be in the carburetor bowl, the vapor will be forced out of the carburetor bowl vent. This is called "hot fuel soak" or simply "hot soak".

What happens with hot soak is the air entering the air intake of the carburetor is saturated with fuel, and additional fuel (or vapor) entering the system through the carburetor just makes the mixture richer, in fact, so rich that it will NOT burn. So basically, there is too much fuel, rather than too little fuel which is the case with vapor lock.

The link below describes a method that generally works starting a car with a hot fuel soak issue:

http://www.thecarburetorshop.com/Troubleshooting.htm#Hardstarthot

The good thing about hot soak is that (assuming the owner in frustration does not run down the battery) hot soak will disappear in an hour or so once the engine has cooled off.

Jon.

Jon gives the best advice. A real KING.
Read all of his suggestions.

Jon,
Hope a bunch of folks copy, read and digest your information. The hot soak problem is very common in downdraft carburetors particularly those with the intake manifold bolted to the exhaust manifold.

Good going buddy.

This is good interesting information especially the part about hot starting. I noted that fuel percolation seems to come about after the engine has been turned off. Like Phil Lipton I have experianced fuel percolation under pretty much the same cicumstances as his.I guess the problem is that you dont know you have it until you hop back in the car, PUT YOUR FOOT ON THE ACCELERATOR and then try to start the car. A couple have mentioned using an electric fuel pump to overcome this problem but unless I am missing the point I cant see how that could help given that Jon says that the fuel is already too rich to burn. In Peters original post I am of the impression he was driving when the car cut out. I have never had a fuel percolation problem while driving down the road but maybe others have.

Dad had that problem. As a boy I saw his quick fix was to put clothes pins one after the other along the fuel line. Seems he added "wood" insulation on it! Ha. Ha. But it did work.

that must have been acting like a heat sink?
not sure how clipping clothes pegs to a fuel line helped hot fuel in the lines, but hey, if it worked for your dad, thats great.
Peter

Yes, my problem started when actually driving the car. It started spluttering and I pulled over, having experienced it before.
It ran OK on tick-over , but when revved, got worse so I turned the car off.
In reading the information from Jon, I did the wrong thing. His advice on restarting is good advice indeed and I guess most of us would have floored the peddle and flooded the best.
Next time I will try the "Jon" method.
Indecently, I removed all the plugs to inspect and all were very black and sooty, indicating an over rich mixture, and that checks out with the " JON" story.
I haven't had time to check the fuel lines for blockage or the tank, but will get around to it very soon, hoping for a cool day in the shed...

Peter

Never heard of the clothes peg idea before. Makes me wonder if you were to lightly wrap some copper mesh around the fuel line between the the pump and carburetor whether it would work like the fins on a radiator and disapate the heat. I guess someone has tried it.

I think it would attract the heat as the heat is coming from an exterior source (the engine) and not inside the fuel line.

There is no "magic" in the clothes pins. Wood is a good insulator. If enough of the clothes pins are placed on the fuel line, they will cover a certain percentage of the line surface area, and thus slightly reduce the heat.

A much better solution (although one gets fewer comments at the car show ;)) is to wrap the line with a high-temperature reflective modern insulation.

An even better solution (if the vehicle is a "driver", not a show car) is to install a three line fuel filter right at the carburetor, and connect the "vapor" line to a new fuel line that runs completely back to dump into the top of the fuel tank.

Take a look at newer vehicles with air conditioning and their vapor return line. The factory engineers solved the issue.

Jon.

Dad did not have those fancy insulation things in those days. They used what they had. Times were simple. It will be intersting to see what "low teck" will do. It gets 124 degrees Farenheit during the Summer here in the South (America). Place the pin squeese together parts away from the fan, so the air flow will remove transfer heat off the pins. They will tend to "float" in the air removing even more heat.

I find that ethanol blend gasoline causes many of these problems. I never had vapor lock or percolation until it was introduced.

The reason the electric fuel pump might help is that it would
raise the pressure slightly; raising the pressure also raises the boiling point, just like with your cooling system. The
problem is that raising fuel pressure too high may cause it to
overload the carb needle and seat and cause the carb to flood!
I think maintain 3 1/2 to 4 1/2 psi of pressure would be within specs to function with flooding!

Hi there,
It takes time to sort out these problems and mine are no different.
I have now removed the petrol tank and had it cleaned, nothing unusual was evident..

The fuel gauge was not working properly so I ordered and installed a new fuel sender 30 ohms device from the filling station.

I blew compressed air through the existing fuel line from the tank to the fuel pump and no evidence of a blockage or obstruction was found.

So later this week I will refit the fuel tank and see what happens. I have made a new fuel line from the mechanical pump to the carburetor without any filter this time. So that is the only thing that has changed. All that remains now is to test drive the car on a hot day ans see if the fuel percolation problem still gives trouble.
I need a new box of straws, all donations gratefully received

Peter

In my estimation nothing was done to prevent heat percolation.

I hope that fixes it. But as you know it is a hobby. Good luck.

Hi guys; What does Peter mean when he said he needs a box of straws. Did I miss something? I'm not real sure but do they have ethenal( nuts, can't spell it) gas in the down under? Thanks Jay

Jay,
I think he has grabbed all the straws out of his last box.

Chipper...maybe that is what is missing in my engine bay, Straws and clothes pegs, must go down to "Supercheap" and see whats on special this week...

Peter

Hi Guys;. Well now I understand about the straws. But I think I would end up with the short one. Thanks for explaining that , Chipper. Thanks Jay

In an effort to help our Aussie Buddy, I have one last thought. When it 'vapor locks', just out of curiosity, try
loosening the fuel line at the carb, place a container under
the line and turn the engine over. If fluid gasoline comes
out, it's not percolating between the pump and carb! Make sure
there is an insulator between the carb and the intake manifold, if not, install one! The other thing no one has mentioned, is a stuck heat riser in the exhaust manifold! It
could be diverting constant heat under the carb, causing it
to overheat and causing the fuel in the carb bowl to percolate. It's a remote possibility, but at this point, I feel it's worth a try!

I think so, too. Look between the engine and manifold. The counter weight is there where it is hard to see. Also see spring attached. You should be able to move it. If not it is stuck. If it is closed you are O.K. but if stuck in the "cold" possition you got to move it.