Air in the fuel line

[soth122003]

I have a question about the mechanical fuel pump. Can the mechanical pump pump air into the line to the carb? My P-15 died on me last week going to get take out. Wouldn't start again.  Primed with the electric fuel pump and hit the accelerator a couple times and it would try to start and then stumble and die. Pulled the air filter and could see the accelerator pump, pump fuel into the intakes. I sat there for about 30-40 minutes waiting for a friend and when he showed up we dinked with it some more but it would stumble and die after the start. 

 

Towed back home and trouble shot the next day. It started with no problem and ran fine. Then I noticed that the fuel filter (K&N glass) just before the carb had air going through it. Not a lot, just like the treasure chest in an aquarium, about every 40-50 seconds when running at idle or every 15-25 seconds at about 2000 rpms. Troubleshooting suggested that 

 

1. Vapor lock from air into the line but I have an electric fuel prime pump and it still wouldn't run on the day of the shutdown.

2. crack or split fuel line sucking air into the line causing a low fuel supply at speed. Again the electric fuel pump should over come this because it is supplying fuel from back at the tank and pressurizing the fuel line. The amount of bubbles suggest a pin hole.

3. Mechanical fuel pump is going bad and pumping air into the system, but can a fuel pump do that? and at a very low amount of air, just about five to ten bubbles about 1/8" in size every 30-40 seconds.

4. I have two problems thinking I had one. Crud in the carb that blocked both the idle and run circuits and a pin hole leak some where.

 

The crud either pushed through during the last attempt to start or fell back and broke up on the tow home. The next day I pulled the top of the carb and the inside looked good and clean. Had my grandson hit the prime pump and the carb filled normally and the float shut of the flow just as it was supposed to. I did not see anything floating around in there so I put the top back on and we started the car and presto, it started fine and ran great. Parked it as it was Easter and we had dinner to go to. 

 

The next day I put a fuel pressure gage on at the carb and started and ran the car. Gage said the Mech pump was putting out 6 psi. The prime pump when the engine was not running was at 3 psi. At this point I thought crap in the fuel line or carb had stopped the car. Started the car and then noticed the air bubbles coming through the inline filter (I hooked the pressure gage up after the filter but before the carb) I then ran the car for about 30-40 minutes and no problem except for the bubbles in the fuel filter. 

 

I'm fixing to go out and put the car up on stands and inspect the fuel line and see if there is a pinhole some where in it. While I'm doing that I just want to see what you guys think about this problem or problems. Can the mech fuel pump be going bad and introduce small amounts of air into the system to cause it to shut down or is it a crud issue and a pinhole leak at the same time? Any thoughts comments or tips are greatly appreciated.

 

Joe Lee

 

 

 

[Los_Control]

My first thought, a pinhole in the line can cause issues ..... the electric fuel pump should point it out quickly. .... I'm not positive a electric pump will overcome a leaky line to make it run ..... it should show the leak though.

 

I'm going to throw a different idea out of left field. ..... When was the last time you got fuel and when did the issue happen?

If you have water in your fuel, it is heavier then gas and goes to the bottom .... then you drive and you mix it all together and it gets passed into your carb ..... It might look like a air bubble coming through the glass filter? .... Just a idea .... It will cause issues that are hard to describe. .... It has been known to happen that a gas station gets fuel delivered with water in it ... by accident, and then there is condensation and other things that could cause it.

 

We used to be able to buy a bottle of HEET at the local gas station for $1, pour it in the gas tank and it enables the heavy water to mix with the gas and it just runs through the system as a lower grade fuel .... then the next time you fill up you have no water and quality fuel ..... In theory.

 

I fought a strange issue for a long time and spent many hours and $$ trying to fix it ..... a $1 bottle of HEET was the cure in the end 6 months later.

If you drain gasoline into a white coffee cup and let it sit. If it has water in it, it will look like a air bubble sitting in the bottom of the cup.

It is possible that is what you are seeing passing through the fuel filter .....

 

Just saying it may not be your issue ..... I see now they switched up the bottle and now is $3 ..... it just wont hurt to try it.

 

[Ivan_B]

If you see the accelerator pump squirting fuel into the intake, I would suspect that you had enough fuel in your carb bowl and the car should start and run for a while even if there was no additional fuel input from the pump. Are you sure you are dealing with a lack of fuel condition? Is it possible that it was just overflown with gas and then aired-out? I would also not completely rule-out other potential culprits. Did you check for good spark when the car would not start?

[soth122003]

6 hours ago, Ivan_B said:

If you see the accelerator pump squirting fuel into the intake, I would suspect that you had enough fuel in your carb bowl and the car should start and run for a while even if there was no additional fuel input from the pump.

That was my thought exactly! Except that it wouldn't start. That's why I thought that something had blocked the idle and run circuit of the carb. 

 

7 hours ago, Los_Control said:

If you have water in your fuel, it is heavier then gas and goes to the bottom .... then you drive and you mix it all together and it gets passed into your carb ..... It might look like a air bubble coming through the glass filter?

That is a great thought Los. I haven't had water in the fuel of a car in a loooong time. But now that you brought it up... I'll pull the fuel sender tomorrow and have a look. I fill the tank about every 3-4 months  and with a full tank, moisture or condensation is low, but with the tank setting at or below half for about a month or two and not being driven very far (like about 10 miles a week)  here in FLA. condensation can be a problem.  A cup of watery fuel can stop a car in its tracks.

 

The checking I did today found no pinholes in the lines or bubbles in the filter either. Thinking back with water as a possible problem, the drive to the Taco place was straight for about 2 miles, Then a stop sign and a fairly tight S-curve then another stop sign, turn right and then 50 feet later the car quit. That S-curve and the stops must have mix the water and the 1/4 full tank just enough to kill it. Then when it was home and sat over night the water settled car works fine.

 

I remember in 89 I was on call for the Panama invasion and got the call at 3am. Went to start my vette and it wouldn't crank. This was Dec 24 and the temp had dipped to about 28 degrees that night. Got my flashlight and look in the tank of the vette and there was about a 1/4" of ice on the bottom of the tank at the fuel pick-up. Got a ride to deploy and when we didn't go, got back to the house at about 2pm and used a stick to break up the ice and Heet to evap the water.

 

These things happen so rarely that we usually don't think of them till way down the trouble shooting line. I'll check the tank tomorrow and get back to you guys then.

 

Joe Lee

[soth122003]

WINNER WINNER CHICKEN DINNER Thanks for tip Los.

 

I pulled the sender and measured the gas level, it was at 2 1/2" in an 8" deep tank, which matches the fuel gage reading of about 1/4 tank of gas. Looking in the tank from the sender hole I couldn't see any water, but it was probably back by the tank drain, and the drain plug is stuck and I can't remove it. The one thing I didn't do last fill up was to put Stabil in the tank. It keeps the gas good and also helps with condensate. 

 

When I measured the gas level, I stirred the gas in the tank then I smelled the gas. It didn't smell bad, but it smelled weak. The strong smell wasn't there. It smelled lite, like half of the normal gas smell. I have new fuel filters on the way to replace the one before the prime pump at the tank and the one before the carb and when I change them, I'll take another crack at removing the drain plug and hopefully know for sure about the water in the tank.

 

So tune in next week for another exciting episode of "As the Wheel Turns".

 

Joe Lee

[Los_Control]

Glad you may have it figured out.  Or think you do.

I once rebuilt a carburetor for my Uncle 7 years ago. And when I opened it up I saw terrible looking goo. It looked like water in oil .... A chocolate milkshake.

 

85 year old Uncle complained because the carburetor had just been rebuilt and that did not fix it. I just never seen gunk like that build up in a carb.

It was obvious to me the problem was coming from the fuel tank .... the 1979 Dodge truck had sat for years .... then revived and put back on the road.

Uncle claimed he put $20 worth of gas in it every 6 months, but it was always adding fresh gas to old gas .....

 

Modern fuels to pass regulations today simply do not last more then 1 year .... just turns to goo.

While it may be water in your fuel system, it could just as easily be old gas that has gone bad sitting in the tank.

17 hours ago, soth122003 said:

3-4 months  and with a full tank, moisture or condensation is low, but with the tank setting at or below half for about a month or two and not being driven very far

I'm only suggesting, thats what my Uncle did .... just kept adding new fuel on top of old. .... Ended up with a pile of goo.

My understanding, modern fuel starts to  deteriorate after 1 year. .... It simply turns to goo. ...... I have seen no evidence that adding new fuel on top of old  rejuvenates it.

I personally will drive the fuel out and then add more fresh fuel.

 

Back in 1970's, Grandpa went and filled up every gas tank in his wrecking yard because the gas would last a long time ....

Modern fuel is designed to implode on itself to help with evaporation. 1 year is considered it useful age and needs to be removed and replaced.

 

Either way, drain the tank and flush the system may be a good idea here.

 

[Ivan_B]

Couldn't you just siphon everything out of the tank and replace with new gas? If you really get water in there, it should be trapped by the good-old bowl filter.

[soth122003]

17 hours ago, Ivan_B said:

Couldn't you just siphon everything out of the tank and replace with new gas? If you really get water in there, it should be trapped by the good-old bowl filter.

That's the plan. Trouble with water is it don't stay in one place while driving and tends to mix with the fuel and run right along with it to the carb. Hence the small bubbles visible in the fuel filter. Only thing that will really stop it is a water fuel separator. Got the filters in today but will wait since I'm going to order the square pipe plug socket set and try to impact the fuel tank drain plug out (very carefully).

 

Joe Lee

[Sam Buchanan]

4 minutes ago, soth122003 said:

That's the plan. Trouble with water is it don't stay in one place while driving and tends to mix with the fuel and run right along with it to the carb. Hence the small bubbles visible in the fuel filter. Only thing that will really stop it is a water fuel separator. Got the filters in today but will wait since I'm going to order the square pipe plug socket set and try to impact the fuel tank drain plug out (very carefully).

 

Joe Lee

 

Just use a torch to get the plug red hot....that oughta bust the rust loose.................   😲 🤣

[Ivan_B]

Come on, now, let's not go crazy here. Siphon pump works just fine 🥲

[Sam Buchanan]

On 4/13/2024 at 4:06 PM, Los_Control said:

My first thought, a pinhole in the line can cause issues ..... the electric fuel pump should point it out quickly. .... I'm not positive a electric pump will overcome a leaky line to make it run ..... it should show the leak though.

 

I'm going to throw a different idea out of left field. ..... When was the last time you got fuel and when did the issue happen?

If you have water in your fuel, it is heavier then gas and goes to the bottom .... then you drive and you mix it all together and it gets passed into your carb ..... It might look like a air bubble coming through the glass filter? .... Just a idea .... It will cause issues that are hard to describe. .... It has been known to happen that a gas station gets fuel delivered with water in it ... by accident, and then there is condensation and other things that could cause it.

 

We used to be able to buy a bottle of HEET at the local gas station for $1, pour it in the gas tank and it enables the heavy water to mix with the gas and it just runs through the system as a lower grade fuel .... then the next time you fill up you have no water and quality fuel ..... In theory.

 

I fought a strange issue for a long time and spent many hours and $$ trying to fix it ..... a $1 bottle of HEET was the cure in the end 6 months later.

If you drain gasoline into a white coffee cup and let it sit. If it has water in it, it will look like a air bubble sitting in the bottom of the cup.

It is possible that is what you are seeing passing through the fuel filter .....

 

Just saying it may not be your issue ..... I see now they switched up the bottle and now is $3 ..... it just wont hurt to try it.

 

 

 

HEET is 99% iso-propyl alcohol and would most likely be useful only if using non-ethanol gasoline. If the tank has ethanol-laced gasoline in it, the ethanol is already absorbing moisture that is in the gas (that is why ethanol-contaminated gasoline is nasty stuff....corrosion city). The amount of ethanol in a few gallons of E10 is far more per volume than what is in the red plastic bottle.

 

It does work well with gas-fired camp stoves, however. 

 

Update: Since last fall my TR6 has been stored in a temporary enclosed garage (Harbor Fright) and this spring it has presented a couple of yips which I have wondered might be due to water condensing in the tank because of the outdoor storage. Los Control got me thinking about this, so why not. I added the appropriate ratio of HEET to the tank just in case there was still some moisture in the tank. Yep, a sniff test confirmed HEET is good ol' alcohol (no taste test...). I figured it wouldn't hurt anything to add it since the tank already has E10 in it.

Edited April 15 by Sam Buchanan