Fuel flow problem on 67.5

[Habitat.pat]

I'm still trying to get my newly rebuilt SPL to be reliable & the latest problem is that the fuel system is not up to par.

I have all new lines from tank to carbs, new fuel pump from Dean, carbs gone through by ZTharapy, gas tank was cleaned by a shop & new (temporary) clear fuel filter. The car will start up & run fine for a about 5 miles, then starts to stumble. To start with the fuel filter has been close to full but when it stumbles the filter is almost empty. If I let the car sit for an hour of so the fuel level in the filter will be close to full again. I added a tee into the fuel line before the filter & added a vacuum gauge to see if it would show the problem. The needle didn't move, at least in the few minutes I ran the engine in the shop. I've checked the fuel cap by putting it on a spare filler neck & I can blow through it just fine. If I disconnect the fuel line from the filter & blow into the fuel tank, fuel comes out of the hose though I can't see how much but it appears to be clear. I put the vacuum gauge on the line into the fuel pump (no tee) & the pump is pulling a good vacuum. With everything hooked up, blowing into the tank does not cause any leaks, so I don't think the problem is an air leak before the pump.

Anyone have any ideas with this?

Peace, Pat

[fj20spl311]

I would guess the pump is not working when its hot
add a pressure gauge on the "high" side of the pump to make sure your getting 2-4 lbs of pressure.
does your vacuum gauge show pressure also?

[tjp]

Maybe a slight clog in the tank's outlet that is just open enough to allow fuel to flow at idle but not enough flow at speed ???

[redroadster]

Do you have the vacuum pump with canister/ bottle ?
It's a quick good way to test the tank flow it should fill the bottle quick 2,3 pumps , if not it's going to struggle , also do you have the tank
1/2 full ,
it's recommended to have the slight restriction in the line ,a up and down loop on the interior back ( under car ). for in case of a wreck it's to stop the line from siphoning out the tank on the ground beneath
The 180 bend is a bit smaller than the reg size of F line ,to work

[SOUPY]

Pat, Have you tried pulling choke out when it starts stumbling? Could it be a float issue, even tho you had carbs reworked, between shipping and installing carbs something happened? Does it start acting up just running in driveway or while driving under load?

[bajaroadster]

I have read that if the car starts and idles well initially, but then stumbles at operating temp that it may indicate one or both of the carbs are running rich. Z Therapy carbs are generally set very close to specs and only need very little adjustment , if any, so it seems unlikely that this is your problem. I had similar symptoms and pulled all plugs to visually check color. The plugs indicated that the rear carb was indeed running rich. Leaning it out slightly seems to have resolved the issue.

[Habitat.pat]

Thanks for all the suggestions, I'll try to get to them tomorrow.

I have a vacuum pump but the canister disappeared a long time ago so I ordered a new one that is due tomorrow.

My fuel lines are all new stainless, so if I wanted to put a loop up for safety I'd have to cut the line & add a loop. The fuel line attaches to the tank @ the top of the tank, so there is already a bit of a loop because the fuel line is a couple inches above the top of the tank.

I am also considering adding an auxiliary fuel tank (squeeze mustard bottle with vent hole) to feed the pump directly. That will tell me if the problem is before the pump or not.

I suppose it is possible that even though I had the tank cleaned that there is cruft in the bottom of the tank that blocks the pickup when running that drops off after the suction goes away allowing me to blow through it.

Peace, Pat

[spl310]

The fuel refilling in the filter tells me that you have a piece of trash in the tank that is partially blocking the pickup. The pump creates a vacuum which keeps the draw going. When you stop driving, it has time to vacuum fill the filter.

[Gregs672000]

Good suggestion to check spark plugs for differences between 1/2 and 3/4 as it will narrow down if it's carbs or before. If after all this fuel related effort it still does the same thing AND you have a points distributor, I'd swap out the side condenser as they will cause similar running issues as they warm up.

[Cahhh68]

My 68 1600 had a similar issue short time back. Turned out it was a hidden hairline crack in the fuel line in the turn immediately before the front carb. While loosening and inspecting the lines at the carbs, fuel filter, and pump, I must have opened the hairline crack a bit because after refitting and starting it was easy to smell fuel whereas I had smelled very little and intermittently before. Replaced the line from pump to front carb and all is well now.

[Habitat.pat]

Well, I thought I’d found the problem, but $700 later, it’s still there.

I connected an electric fuel pump directly to the 1/4” fuel fitting on the tank with a clear reservoir in line & got lots of air in it. I assumed that the fuel pickup line in the tank had a pinhole in it, allowing the air to fill up the filter. New tank installed & there is no change!

My original tank was from a 70, it had a carbon canister on it that was capped off, as well as the 5/16” fuel return fitting. The only line connected to the tank is the 1/4” flair fuel line. My new tank is for a 69, so it has 2 fittings for the fuel line & return. I capped off the 5/16” & connected the fuel line to the 1/4”. Can anyone verify that the fuel line is really the 1/4” flair on the tank?

I’m getting ready to Jack it up again & run the test directly on the tank again.

If I didn’t already have gray hair going in, I’m sure it would be gray after weeks of troubleshooting!

Peace,
Pat

[Habitat.pat]

Oh, no gas cap on, so it’s not pulling a vacuum.

[Sup3rsak]

Pat, here is my recent experience. I got a used gas tank and evaporust the bottom half for a day. It looked clean but I bought it off Ray and he said to evaporust it anyway and good thing because I think a rat made a nest. In the fill neck and baffle was blocking the debris in there and I strained out the crap but it was eventually clean. Blew out the fuel lines so everything was clean and dandy.

My experience sounded like yours everything is fine and I would drive it and he engine would bog down to no fuel and the fuel filter had no gas in it. No suction from the tank into the filter. I would setup an auxiliary gas tank ( plastic bottle ) directly into the fuel filter bypassing the tank to make it home. So I know its a tank pressure issue? But I would do what you did and blow air into the gas tank dislodging whatever was in there. This kept happening but I assume its whatever left over crap was collected and after 3 fuel filters everything seems fine. I assume the gas was dissolving whatever it was and the fuel filter was catching it. Drove to Solvang last weekend without any issues and that trip had a few fill ups.



To help troubleshoot what is consistent when the car will have no fuel? Can you let it idle and sit with the car for 15 minutes and see if it is fine? then take it for a drive and whether you idle at 15 minutes or not at all will the car be starved of gas consistently?

use the vacuum test at different stages of the line to check for an air leak. plug and isolate different parts and see if it can hold pressure. ( tank to before filter, filter to carb, cut down each location to isolate and find if there is a leak and which specific component.

[Habitat.pat]

Ok, it’s been awhile since I updated, sorry.

I connected a clear reservoir to the outlet of the fuel tank that fed an electric fuel pump, then into a gas can. When I turned the pump on I got a lot of rather small bubbles in the reservoir. I pumped almost a full tank & it didn’t decrease so I ordered a replacement tank & the air coming out of the tank was gone but I still had air entering the fuel filter. I then broke the fuel line @ the union & connected the reservoir & pump, no air but when I connected it to the steel fuel line @ the filter I had air. A very close inspection of the new stainless fuel line double flair @ the filter showed that it wasn’t “quite” right. I had tightened it down tight but I just tightened it more & the air stopped!

I filled the filter just because I like it that way & went for a “spirited” drive, about 10 miles. About half way through the trip I checked the level @ it was very low, but not empty. I’ll look in the morning to see what it looks like but I suspect I’ve found the problems —-at least for now. I hadn’t expected 2 separate problems! My troubleshooting needs more practice!

Life is getting better!

Thanks to everyone for their input on this, this list is great!


Peace, Pat

[redroadster]

I found a sock screen that fits the pickup