The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by brajaboy, Mar 9, 2020.
But why is the fuel line getting sucked dry too?
A fairly simple test that might be helpful:
If you have access to a portable fuel tank (outboard motor or other), add an electric pump, and hook it directly to the carburetor. Don't forget to disable you existing fuel system. Start the engine. If it runs for a period of time with this set-up, you have fuel delivery issues. If not you have carburetor issues.
I would use a fuel bladder & the mechanical pump....not a fan of electric pumps on old mills myself
thanks for the replies. So to clarify, it is with three different carbs (2 brand new) 3 different fuel pumps (2 brand new), 2 different pick up tubes (tank has 2 locations) , 1 new fuel tank. I will try an external fuel tank today. The crazy thing is that as soon as the the carb is taken out the equation then the fuel flows strong and freely. The minute it is hooked back up the flow greatly diminishes but does flow enough to keep fuel in both filter and bowl. As long as you don"t get on it while driving it will keep up (very slow dribble). But you get on the gas and it cant keep up builds pressure in the line and sucks it dry till pressure is released by taking line off carb then fuel flows again perfectly. If the pickup was having something sucked into then it would not let fuel pass no matter what, no? it seems no matter what carb is on it as soon as its hooked to it flow dies to an almost nothing. Enough to keep idling but not enough to drive. and if you suck it dry you must release pressure before it sill fill filter and bowl, then the cycle starts all over again.
So have you tried, as several have mentioned, removing the fuel cap?
Many vehicles were originally vented through a hole in the gas cap. Someone in government decided long ago that this was a bad idea, and newer caps do not have the vent hole.
The tank MUST have a vent to allow fuel to escape past a certain point; at which time the tank will have a vacuum, and fuel escaping the tank is impossible until the vacuum is relieved.
yes if you read first post I stated cap on or off does not matter still does it
What’s the fuel pressure?
where’s the pump?
it’s possible to have flow but no pressure. You need some pressure to get fuel past the needle valve
some pics would help the eagle eye dudes spot some clues.
Is there a float bowl air vent that is blocked ?
Get you one of these and hook it to the fuel inlet on your carb. Pump it, if it builds pressure your needle is sticky or you have a vent issue in the carb. My .05 cents. I raised my labor rate
I'm betting fuel tank related. When you remove the fuel line and have built up pressure the pump is doing its job. The fuel supply is not getting to the pump. Do as others have suggested and try a portable tank even a Jerry can.
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I had a somewhat similar problem when I started circle track racing. I could make a couple of laps then the car would die. Pull to the infield, wait a couple of laps and it would restart. I fought this problem till the end of the season. Next year I changed engines and found a small piece of gravel in a fitting going to the fuel pump. The gravel acted like an orifice and only allowed a small amount of fuel to the carburetor. Gave me enough gas to make just a few laps but that was it.
I can see it being a tank vent issue if it stops pumping after a few minutes. Bet it's cheap on gas though
When replacing the hose lines was it fuel injection hose, I was told not to use it in a old car with mechanical pump because it was made for pressure not suction.
I don't know but it might collapse easier than other hose
The pumps have a inlet and a outlet. Is the fuel going into the outlet?
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Not sure if this is even possible —- can the electric pump be wired backwards and run in reverse?
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Well I hooked up a jerry can in the back and right away the flow was better. Took it out and got on the gas and did not display the symptoms. Now I have not taken it on the hwy yet and that will be the true test up even the slightest of grades. So so far it looks like the pickups in the tank are the problem. The weird thing is that one of the pickups broke off while i was pushing it down when it looked like it was not below the fuel level but i could not see properly. I forced it to much and it broke off so fished it out. It was as clean as a whistle. So something blocking it? Maybe but i think I would see something in the tube... maybe not. But the other pickup that I hooked it to was flowing perfectly (siphoning) before the pump. But start it up and again pressure build up and a trickle flow. So must be a a poor design or something even though its brand new... ill get on freeway and update.
Pickups in the tank,,,,plural ?
Also,,,,you mentioned you broke one of them off ?
That is valuable information to know,,especially now,,,,,it might have helped more at the beginning ,,,,LoL.
I suspect it is something to do with the “new “ fuel tank like you mentioned earlier.
That is kind of useful info I think
I busted the pick up tube off and I’ve got a wired fuel delivery problem. Any ideas
Sounds like the tank is set up with two outlets, one for fuel out, the other for a return line like a FI system would have. If you had both of them hooked together for supply, when the shorter return one hit air, it would cause a starvation problem. I'd only use one of them, the one that goes closer to the bottom of the tank, and plug the other off as it's unneeded unless you are running a return style regulator or filter.
Hell I'm just happy somebody came back and gave an update on their issue! I'm still waiting to hear about that 283 that wouldn't fire a few months ago sounds like you're on the right track brother
If you read the post this happened (meaning i broke it) after I was trying to diagnose not before, the problem already exsisted, so not sure what you talking about.
yes two outlets as i stated before and tried both separately with same results. Never had them hooked together for one feed.
Sorry ,,,,I read the post,,, wasn’t clear when it happened .
Just took it for granted it had already happened before .
As i said if you read the post I said I was trying to figure out the problem as it already existed before and the pickup looked like it may not be below the fuel level so I pushed it down hard and it broke. So no it was not useful info in the beginning. I may not be that smart but I'm for sure not that dumb.
That's a very weird way to tap into the tank. The pump is having to pull the fuel up through whatever gooseneck is inside the tank, like sucking on a soda straw. Any time the fuel sloshes away from the end of the pickup, a column of air will get drawn in and cause the same effect as vapor lock. More so if the fuel bowl is small in that 1-barrel. What makes this doubly suspicious is the tank is about the only thing you haven't addressed.
I'm only recently back to messing with vehicles that have mechanical fuel pumps so if I'm off point about what one will do in your circumstance, I defer to those who do know for sure.
I gave up after not getting an answer to
- what’s the fuel pressure ?
Where’s the pump ?
Despite how crystal clear you believe the information is it’s not that easy to follow, you have people trying to help and you keep giving them attitude.
Why did you have to force the pickup back in? Was it maybe too close to the bottom of the tank? Maybe some pictures would help us figure out what you have going on.
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Nobody here has a special incantation to evict mechanical demons. The liquid fuel is doing exactly what it is supposed to do, trust me it’s not defying any physics or laws of fluid dynamics.
I also believe you that the fuel is not doing what you want it to do. That’s because there’s some unknown and non belonging “thing” along the fuels path and the fuel is listening to that certain “thing”.
It’s your job to stop assuming and start proving. The sooner you can remove from your thinking the idea that “new” means “Good” and replace it with “new means hasn’t proven itself yet” you’re be way better off.
Thats what I am saying. I did do that to everything but the tank. In trying to figure it out I followed exactly that. I replaced 3 different carbs, 2 new fuel pumps. all new rubber and metal lines new fuel filter. the only thing I did not replace but was new when I bought it was the tank. So to the suggestions of others to run a aux gas tank to see that's where I figured out it is something in the tank. It runs better than it ever did before now I could never go full throttle and have it last it would always almost die from starvation. I am going to take it out on the hwy to prove it because that is really where it has a problem. If it does it again then we know there is still that demon. but right now its looking like the tank. will update.
I dont have a fuel pressure guage so I do not know. But the fuel pump is below the tank as stated. I believe I stated that in a reply. if not sorry as someone asked that same question.
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