Mechanical fuel pump going bad?
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Mechanical fuel pump going bad?
My newest project, a 79 Lincoln Continental, is acting up on me. I rebuilt the carb, new fuel filter, and new plugs. It runs great around town. Out on the highway it will buck and chug almost every time you hit about 60-65 mph. It does fine at lower speeds even at full throttle. I noticed today a couple times it was hard to start hot.
I've never had a mechanical fuel pump go bad other than leaking. Is there a way to diagnose it for sure? Any other ideas? Thanks for your help.
BTW, it's got a 400 and 2 barrel Ford carb.
I've never had a mechanical fuel pump go bad other than leaking. Is there a way to diagnose it for sure? Any other ideas? Thanks for your help.
BTW, it's got a 400 and 2 barrel Ford carb.
Last edited by brown 4x4; Jun 11, 2007 at 10:16 PM.
MSEE
Joined: Apr 2004
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From: Austin, TX
It's possible, but first I would check the float height. If the float height isn't too low, I would suspect the fuel pump as well. One way to check the fuel pump is to take a look at the oil. When mechanical fuel pumps fail internally, they often pump gasoline into the crankcase. Check the oil and see if it is suspiciously overfull or if it smells like gas.
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I'm fairly certain I've got it fixed. Put a new fuel pump on it this afternoon (even easier than on a pickup BTW). Drove it a few miles on the highway and it never acted up. I'll have more time tomorrow and take it on a longer drive.
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I wanted to update and ask another question on my problem.
The fuel pump fixed the problem for about a day. I finally figured out it was the float/needle/seat causing the problem. When I installed the carb kit I noticed the new needle and seat were quite a bit different but installed them anyway thinking maybe they were just redesigned. After messing around with the float level and having no luck I put the old float, needle, and seat back in. Runs perfect now.
I've still got one problem though, and it did this with both needle/seats and floats. When I shut it off gas will continue to flow down the throttle bores flooding the engine. I took the top of the carb off and blew through every hole. It's my understanding there's supposed to be an air bleed to prevent this from happening. I don't remember this happening before the carb kit, but I also didn't drive it much then.
The fuel pump fixed the problem for about a day. I finally figured out it was the float/needle/seat causing the problem. When I installed the carb kit I noticed the new needle and seat were quite a bit different but installed them anyway thinking maybe they were just redesigned. After messing around with the float level and having no luck I put the old float, needle, and seat back in. Runs perfect now.
I've still got one problem though, and it did this with both needle/seats and floats. When I shut it off gas will continue to flow down the throttle bores flooding the engine. I took the top of the carb off and blew through every hole. It's my understanding there's supposed to be an air bleed to prevent this from happening. I don't remember this happening before the carb kit, but I also didn't drive it much then.
MSEE
Joined: Apr 2004
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From: Austin, TX
If there is enough gasoline flowing down the venturis that you can physically see it, then as far as I know, the float is set too high and you're flooding out. I personally don't know of such an air bleed. If your carb is a '79 then I imagine there is a vent valve but I believe that's for evaporative purposes. Gasoline sits at the same level in the fuel bowl. The float acts like a regulator, to maintain this level - high enough to provide enough fuel during high demand, but low enough to keep the engine from flooding during low demand. There is nothing in the system that makes the fuel overflow when the engine is cut off - the fuel will still stay at the same level.
I wouldn't reuse the orignal needle and seat either - I'd install the new ones and adjust the float tang accordingly to acheive the required height.
I wouldn't reuse the orignal needle and seat either - I'd install the new ones and adjust the float tang accordingly to acheive the required height.
Last edited by fmc400; Jun 23, 2007 at 08:50 PM.
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I agree about not reusing the needle and seat, but the new ones simply didn't work right. Maybe the kit had the wrong ones accidentally put in it. I had the float set to spec. I do plan to install new ones. I drove a 77 F-150 once with the float set too high and it would flood so bad sometimes it would die when you hit a large bump or hit the brakes too hard. Mine doesn't do this at all, but I guess that's not too good a way to diagnose a high float.
The air bleed I was referring to is just what I learned all carburetors have "built in" to prevent fuel from siphoning out of the bowl down the throat after the engine is shut off. I have no idea where it is or even if it really exists. It's not flooding when it's running and fuel mileage isn't suffering, it's just annoying and embarrasing when I restart the engine.
The air bleed I was referring to is just what I learned all carburetors have "built in" to prevent fuel from siphoning out of the bowl down the throat after the engine is shut off. I have no idea where it is or even if it really exists. It's not flooding when it's running and fuel mileage isn't suffering, it's just annoying and embarrasing when I restart the engine.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Ah, I see. Well, I did a little more reading into some diagrams and now I think I'm up to speed. It seems that in the venturi assembly, there is an "anti-siphon" passage. I really don't know if that's related to your problem, because I haven't run into this issue before. The trouble is that those passages will probably be full of gas at this point, so I'm not sure how you would check it out. I really don't know if that would lick the problem - some debris in there is the only thing I could imagine being wrong with it.
There is a website floating around the internet (the guy who made it used to be on these forums) that has some helpful diagrams of the 2150. Here is a link to the page that mentions "anti-siphon." http://home.earthlink.net/~bubbaf250...b/carb02b.html
There is a website floating around the internet (the guy who made it used to be on these forums) that has some helpful diagrams of the 2150. Here is a link to the page that mentions "anti-siphon." http://home.earthlink.net/~bubbaf250...b/carb02b.html
Last edited by fmc400; Jun 23, 2007 at 10:49 PM.
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