Fuel Boiling In Pump?!? Engine Stumbles Under Load And Dies

THE VEHICLE
· 1964 Cj-5
· F134 Engine
· Glass dome style fuel pump (without vacuum ports).
· Solex Carb
· “Mr Gasket” in line fuel pressure regulator set to ~2lbs pf pressure.


THE PROBLEM
After warming up (about 20 mins of normal driving), the engine sputters and tries to die while under load. It only happens after a few miles of normal driving and once it starts, it happens every few blocks.

If I leave on the gas pedal for more than 5 seconds or so, especially if I’m flooring it and trying to get up to speed to shift into 3rd or 4th, the engine starts to sputter. If I feel it soon enough and let off the gas, it with catch itself and return to idle. Sometimes BACKFIRE and return to idle. Sometimes I don’t realize it’s happening soon enough and it dies while I’m rolling.

I can take it out of gear and usually fire it up while coasting or at the next stop sign and it starts up fine. The problem continues to happen if I’m anything but extremely gentle with the gas pedal.

Again, this is only when the engine is FULLY up to operating temp and when giving it steady gas pedal for more than a few seconds in a row.

It idles fine.


OBSERVATIONS
· While driving the fuel pump barely has ANY fuel visible in it. It even seems like bubbles are coming out of BOTH the inlet and outlet pump holes into the glass bowl.
· After shutoff, the glass bowl with start to slowly fill with fuel but the bubbles will continue to bubble up from the little pump valve holes almost as if the fuel below the screens or in the bottom chamber of the pump is boiling. Again, this is after shutoff.
· The fuel lines, the carb, the pressure regulator and the top of the fuel pump are all normal (hot but touchable) temp when running and just after shutoff. The BOTTOM half of the fuel pump, on the other hand, is super hot to touch. This part is attached to the engine so I would assume it would be a bit hotter but could it be hot enough to be boiling the gas while its passing through the chambers of the pump????
· I’ve checked the rubber fuel lines at the filter, before the pump for leaks. Nothing glaring. They are also only a few weeks old rubber hoses (rated for ethanol hoses).
· The TEMP gauge says it stays in the “middle” between hot and cold. I’m assuming that’s normal operating temp. After startup, I observe the temp gauge climb up to the ¾ mark where I assume the thermostat opens up, and then I see the needle move back to the middle area of the gauge where is stays during the rest of my drive.
· I’ve tried adding a new VENTED gas cap from napa. It finally keeps the fuel from spilling out of my tank but the main problem persists.
· I’ve tried cracking the gas cap and the problem also persists.
· I also thought maybe the fuel pressure regulator could be keeping too much gas from exiting the fuel pump so I cranked the fuel pressure setting on the regulator to the highest setting (well above what the pump itself is capable of) and the problem happened again within a few blocks.


RECENT SERVICES
· Freshly rebuilt and cleaned the Solex Carb.
· New Rugged Ridge/Omix radiator
· New heater core (rock auto)
· All new rubber hoses for cooling system
· Full cooling system flushed twice (blue devil followed by prestone “flush and wash”) Because the system was filthy with rust and crust. Rinsed it about 11 times in order to get the water to run clean before adding coolant and distilled water 50/50 mixture.
· Added 160 degree thermostat (PO had been running with NO thermostat)
· The fuel pressure regulator was recently added because the carb was flooding at 3lbs of pressure
· Cleaned the screen on the fuel pump
· Added metal “in-line” fuel filter and new rubber fuel lines (rated for ethanol) before the pump.
· Added heat shroud to the hard fuel line between pump and carb because it runs close to the exhaust header. Heat shroud is Rated for 500 degrees.
· Recently had a mechanic replace the distributor points (IAT) and set the timing. No idea what it was set to. I’m new at this stuff.
· They also fiddled with the carb adjustment screws to “set it” for me.

Here are pics of my setup:

 

The bubbles suggest an air (suction) leak. Boiling is very unlikely.

Could be one of your fuel line connections, or very possibly the gasket under the fuel pump dome.

 

I would try removing the fuel filter that's right before the pump.

Sounds exactly like what my 56 was doing when I first got it. couldn't even make it a few miles for the drive home after purchasing it. Acted like it was running out of fuel.

Mine had a fuel filter before of the pump like yours does. It was a clear filter, and wasn't clogged. Maybe there was a slight air leak, I don't know. But I did replac the hoses AND filter and the problem didn't go away until I simply removed the pre-pump filter. I removed that and only kept the filter infront of the carb, and that fixed the issue.

 

https://www.youtube.com/shorts/6gnH59leR4g

https://www.youtube.com/shorts/4tgdKu7_aXs

Here are a couple vids I shot. The crazy Thing is they continue after the vehicle is shut off. Also, Wouldn't there be fuel spewing out from the fuel line somewhere since its under pressure if there was an air leak? Again, Its most noticeable in the OUTLET side of the pump. to the carb.

The bottom half of the fuel pump get super hot to the touch.

Ok I'll try bypassing the filter and see if anything changes.

 

That filter is in a very hot location next to the exhaust. I thought the glass bowls had a filter screen but I preferred my filter after the pump on the vertical run in front of the rocker cover.

I wouldn't be surprised if a plastic filter were to deform if placed there.

 

That looks like the inlet side of a poppet valve, not the outlet side. Bubbling from residual vacuum in the pump?

Be careful of making assumptions and jumping to concussions. One step at a time. Prove each step.

 

http://earlycj5.com/xf_cj5/index.php?threads/133267/#post-1439237
See how the fuel lines run? Run them like its supposed to and then see what happens. Your fuel filter is way above the pump and the pump has the fuel lines that need switched.

 

there's usually markings on which side is the inlet, they can be clocked, so his may not be wrong. fuel lines going up farther than the pump and back down is probably a good call though, no clue if that would be a problem, but it certainly can't hurt to make the lines lower down.

My 46 has a diesel with a mechanical pump that pulls fuel up and out of a fuel cell mounted in the back of the jeep on top of the floor, fuel lines go at least 2 feet higher than the pump as the lines leave the tank, so I know mechanical pumps will pull up a hill like that, but keeping the lines flatter probably is better.

 

I just deleted the in-line fuel filter and I’m gonna do a quick run around the neighborhood just to see if anything changes. Figured I would tackle the easiest bit first and then move on from there.
If that doesn’t work, next will be rerouting the fuel lines.

 

Just got back from my drive. Almost made it home from about 5 miles or so and it happened again. Stumbled and almost died when giving alot of gas pedal. The interesting thing is, it only happened once this time vs every few blocks once warmed up. hmmmmm.
After shut off, bubbles still fizzing up from the output valves in the outward bound side of the fuel pump. Fuel level still not even high enough to cover the screen in either chamber while running and after shutoff.

Looks like there's crap in my tank because there's some rust crumbs on my screen in the pump now. Will be reinstalling my fuel filter asap.

I'll need to clean the pump now anyway so I'll take it apart and check to see if there's anything glaring going on inside.

How would I check to make sure the gasket and or the o rings on the pump were good beyond just rebuilding the pump or buying a new one? Anything I can try or look for while i've got it open for cleaning the screen?

Once cleaned, I'll reorient the inlet/outlet ports so that the hoses can be rerouted per that link. The PO had it backwards so I just went with that orientation when I made my new fuel line. Lesson learned.

I really hope this cures the problem.


Questions in the meantime:
Could this be distributor/timing related?
Could this be vapor lock?
Any reason to think it could be the new KN air filter I'm using now instead of the oil bath? Maybe too much air coming into the carb?

hahaha. Im grasping. But I have no idea.

Thx in advance!

 

"Questions in the meantime:"
Could this be distributor/timing related? No
Could this be vapor lock? Not likely
Any reason to think it could be the new KN air filter I'm using now instead of the oil bath? Maybe too much air coming into the carb? No

When I see a bunch of rubber fuel lines and clamps I cringe. I think air is getting sucked into the line. Proper fuel line is hard line from tank to frame rail opposite pump, a proper flex line from there to pump, a hard line from there to carburetor, and I like to put a fuel filter at the carburetor. Rubber hoses clamped to hard lines is an easy way to have air infiltration, and I think that is where your bubbles are coming from.

 

I'd love to see a few pics of your setup.
Can you elaborate on what makes a "a proper flex line from there to pump"? do you mean a braided steel line? If so, how are you attaching the two?
"I like to put a fuel filter at the carburetor." How are you attaching the fuel filter? Do you have a link for a good filter that screws into a hard line system? All I've been able to find are "clamp-in" ones that bring back the need for hose/clamp connectors.

Would the air infiltrating into the system make a difference in whether or not the engine is hot at running temp when it stumbles? Also, Nothing is happening at idle. Just when giving steady gas pedal at highish rpms. Could it be high speed jet related in the carb?

Thanks! Just trying to piece all of this together to make sense of it.

I totally understand the need for hard lines but am still learning how to make them/ run them.

Also, The whole temp thing really throws me off.

 

Check for a clogged line. Consider disconnecting it and draw from another fuel source.

 

I don't see a brass screen in the fuel pump. Does the bowl have a center divider? If it does then be aware that unless the divider is squarely centered on the gasket, it will give you issues. I'm not a fan of that design. Also, as noted by Oldpappy, I too cringe when I see single clamps on rubber hoses. The worm drive clamp, when tightened, causes the rubber to bunch up and leave tiny gaps through which air is sucked in. You won't see any gas leaks from these spots. NAPA sells a clamp, in various sizes, that most closely follows the original design of a full-wrap clamp that, when tightened, won't cause gaps. Click the link. NAPA. As well, running any fuel line within a couple of inches of a heat source, exhaust, and radiator hose, will cause the gas to boil in the line. The factory routed the metal fuel line low and under the water pump for this reason. The factory, as also mentioned, routed the main fuel line along the frame with a rubber cross-over (anti-vibration) to the pump. These tubes are available from any of the Jeep Parts dealers.
And now, please forgive me but I feel compelled to express my thoughts on the air filter setup you have. Please go back to the oil-bath air filter with the correct tubing. Yes, it is a little messy doing the annual cleaning. But it is more efficient and less expensive than what is currently installed. Especially if you run in a dusty environment.

 

As mentioned, the flex line from the hard line at the frame to the pump is available from just about any of the suppliers. The link shows one for a M38A1, not sure if your Jeep is that or a CJ5 painted to look like one.

https://quartertonparts.com/product/m38a1-m170-fuel-line-to-pump-hose-8331933-g758/

I like to use a Carter filter with the ceramic element, I think it is the best fuel filter design ever made, and they last forever because you can clean the ceramic element in solvent when needed.

When I can't find a Carter ceramic, I use an AC style with the replaceable paper element. These are easier to find than the Carter filters because good reproductions are made for the old Chevys and sold by the suppliers for mid fifties Chevys.

The outlets and inlets on either of these accept standard flare fittings.

Were I setting one up on your Solex I would install it where you have the regulator, and move the regulator down closer to the pump.

I recently found a NOS Carter ceramic on Ebay, and that will be going on my CJ5. They can be found, but they are not cheap.

Napa stores have racks of different length brake line with flared fittings. I make my hard line from pump to carburetor using a piece of that about three feet long, and while I have made the supply line from the tank I usually buy a preformed hard line from Walcks or QTM which runs along the frame to the front where that is clamped down to the frame and the flex line goes over to the pump.

Very nice looking engine bay, everything clean and tidy, but I also would rather have the oil bath air cleaner with the vent hose from the oil pipe routed to that rather than just a hose hanging there with a filter hanging down low.

 

The only picture I have handy of a filter installed at the carburetor is on my CJ2A, which is a rough old Jeep I use to run around the farm with, but it shows an AC paper element filter installed.

 

Just possibly crud blocking the tank end is aggravating the suction situation, and encouraging an air leak.

Does the line flow free if disconnected low in the engine bay? Can you blow it back easily and hear bubbling in the tank? Does that then mitigate the stalling for a while?

But this is only a slight possibility - still pay attention to the other suggestions.

 

This is what I think is happening too. If the fuel pickup is clogging, you will be pulling more vacuum on the line from the tank and hence the bubbles. IE, incipient vapor lock. If the inlet is clear, even an electric pump for EFI has enough suck to pull gas from an opening in the top of the tank.

 

There's a steel screen on the inlet side of the pump chamber. Yes theres a center divider. I assume the gas gets pumped in and falls through the screen before getting pumped over to the exit side which has no screen and out to the carb.
I just took it apart and what I thought was rust crumbs from my short run was in fact a bit of rubber hose that had chunked off when I was taking the previous hose off.

I still see a tiny bit of rust flakes at the bottom of my tank so I blew through the hose from the engine bay and heard it gurgling in the tank. I assume if there were anything in the line it'd be back in the tank now.
I have to look into how to clean the tank out before trying again. It's a newish tank so it probably doesn't need the whole cleaning and sealing shebang but I prob should get those crumbs out somehow.

I see what your'e saying though if the line was clogged that would make everything work that much harder to draw fuel etc.

Turns out..... I actually HAVE ONE of those flex lines sitting in a box! It was an accidental order and was scheduled to be shipped back to kaiserwillys HAHHAA.. Everything happens for a reason I guess! I just didn't know what It was till you showed me that pic!!!

The flare end of the fuel line from the tank had been chopped off by the PO so I'll make a new flare and attach it later today!

I live in LA so its not dusty at all here generally. I just put on the KN filter this last week because in attempting to clean the oil bath, I accidentally stripped the paint off because I was using engine degreaser like a genius. Then, I took it to a local speed shot and they "tanked" it overnight but even afterwards I could still shake out small seeds of some sort that an animal had buried in there years ago. I spent half a day trying to vaccuum, blow, and shake out the seeds but I got freaked out by how many kept coming and threw on the KN filters just to be able to get around in the meantime while I figure out how to proceed. I Have two oil baths btw. The other one is missing the nipple for the dipstick to air cleaner hose. They are both seemingly impossible to get 100% clean.

Totally get it. Hopefully after a cleaning, the tank can be checked off the list of suspects.

I went ahead and tore down the fuel pump this morning. All looks good inside and actually looks relatively new. The springs and rubber gaskets all look new and don't have any tears in em. The diaphragm, however, has some sort of grey/white crud under the lip (see pic). I can only assume it's a bit of loctite 567 that I hadn't let cure enough on the npt fittings before adding fuel.

Maybe it had worked its way into places it shouldn't have and is keeping things from sealing? I checked and there was a tiny glob of it in the brass screen at the inlet of the carb too.

 

Maybe then possibly also in the float valve, or other carb passages, restricting flow? Not familiar with Solex carbs, that's another whole kettle of worms...