Ok so here goes. I am 16, just got my license a few days ago. Before then, I had received a non-running 1986 F150 off a friends grandparent's farm. It is rough, but it has a title and it was free. For a first truck I couldn't complain. Well I got it home and all it took to get the old 300 six running was a mechanical fuel pump. fired right up. After that I did basic tuneup items. Cap, rotor, plugs, etc. Well after driving it around the property for a few days, it suddenly stopped running. A bunch of gunk from the gas tanks had made its way up into the carb. I rebuilt the carb and put it back on (after cleaning the fuel tank) and it wouldn't run right. I kept fiddling with the carb, must have taken it apart 10 times. In the end, I got fed up with it and bought a new carb. The link to the carb I bought is:
https://swperformanceparts.com/162-C...hoC1lsQAvD_BwE
While I was waiting on the carb to come in, I pulled the intake and exhaust manifolds off and replaced the gaskets, just because. I also removed and plugged the holes for the EGR tube, because it was damaged when I took off the manifolds. I put the new carb on and it has some funky issues. I dont think I have vacuum lines hooked up correctly, or something of the sort, I'm not sure. Basically what i've confirmed. The engine is getting gas, I can watch gas squirt into the throat of the carb when the throttle is opened. It is getting spark, I checked each plug individually while the motor was cranking. each had spark. I turned the motor to TDC on the compression stroke and set the distributor to plug #1. I also did a compression check and each cylinder was between 145 and 155 psi. But that truck will not start to save its life. Sometimes itll get a little off starting fluid, but very seldom. I have found that sometimes, if I disconnect the fuel line from the carb, the carb will push gas out of the inlet for a split second and then the motor will run just about perfectly until it drains the carb. I don't understand. Any help at all is appreciated, I need this truck on the road ASAP. Thanks y'all!
Some information about the truck
1986 F150
4.9L (300) L6
4-speed NP435 Tranny
Came with dual 19-gallon tanks
Has the TFI style (distributor mounted) ignition module

I don't know what else you guys might need, but let me know! I'm open to share anything about the truck if it helps me get it on the road.

P.S. The truck's name is Bull. Just thought I'd include that.

 

When you have the fuel line hooked up, and trying to start it, do you see fuel dripping into the carb? If so, it's overflowing and flooding the engine. I would replace the fuel pump. All that gunk that came from the tanks has also ran through the fuel pump, might have messed it up and now it has too much fuel pressure for the carb.

That is the wrong carb for your truck by the way. But once you get it running and driving, you can address that problem later. You have several wires that plugged into the carb that have no place to go right now correct?

 

DaveF that is not the wrong carb he is just half way done with going from feed back to a DSII system
But yes some wires cant be hooked up but that should not keep it from running.

Un-till you are 100% sure the tanks are crap free I would take them out of the picture and run it off a small gas can set on the fender and long hose to the fuel pump.
Yes that new pump could be the cause of it is putting out too much psi because of crap stuck in it.
What you can do is pump gas into a container and see what it looks like might tell us what is going on.

When you installed the new carb other than bolting it on did you do any other adjusting to it?
Out of the box they should run enough to get up to temp so you can make adjustments like idle speed & mixture.
Dave ----

 

I agree about getting it to run off a seperate gas can sitting off to the side. Once its running from a gas can, I would disconnect the 2 rubber fuel lines going into the tank selector valve (under the drivers side, halfway back) from the tanks and install two (one for each line) in-line fuel filters. I would also disconnect the rubber hose from the other side of that selector valve as well as the hose going into the fuel pump, with both ends open, blow out the line with an air compressor to make sure it is free of debris.

I will add this, my truck (82 4.9) ran like crap for the longest time. I was going to replace the carb until I noticed there was a hot air pipe supposed to go from exhaust manifold to the carb. My truck had an "electric" choke so I didnt think that stove pipe was required. Turns out my "electric" choke was an "electric assisted choke" and once I put that stove pipe on the truck runs like brand new. Your setup may be different, and that wouldnt cause it to not start, but thought i'd throw that out there.

 

Thank you guys for the suggestions! I have already replaced the gas tank with a single tank, and ran a single fuel line to the pump. I put a clear filter just before the fuel pump, and there is no gunk in the filter. I also replaced the fuel pump after the gas tank issues. All the electronics off the old carb hooked up to the new one with no issues. The fuel pump does seem to have a lot of pressure compared to what it should, but I cant be sure, just pure speculation.

 

You must have gotten a different carb than the one in the link. I don't see the fuel solenoid or the throttle position sensor on the carb in the link. I just see the choke hook-up.

 

No, that's the carb I got. I had to take all the mounting brackets for the electronics off the old carb and put everything on the new one, as all the holes were there for everything. Everything was the same from old carb to new except for the new one had one less vacuum line.

 

That has to be a new one as I did not think you could get feed back carbs with out all the electronics.
How would the place selling the carb know if you had issues like you do if it is the carb or the old un-tested electronics?
Also know if the TPS is not installed as per spec, cant just be bolted on, this will cause run and maybe start issues.

Any way you can take a picture or 2 of this carb and the vacuum & wire hook ups?
We may spot something that is not right that could help.

As for the fuel pump putting out to much PSI you can pick up a vacuum / fuel PSI gauge from the auto parts store or HF for cheap. You will need this to make adjustments to the motor once you get it running.
Dave ----

 

That sounds the fuel pressure from the pump is too high. It's overwhelming the carb float valve, overfilling the float chamber, and dumping raw fuel into the intake manifold. This in turn wets the spark plugs and they won't fire. That explains why starting fluid barely works, but the engine runs just fine (although only briefly) with the fuel line disconnected. The other possibility is the float valve is misadjusted or simply stuck open. That would cause the same symptoms.

As others have already suggested, get a mechanical pressure gauge. It's cheap, maybe $15 or so. Get a good brand, as you will use it the rest of your life. It's one of the primary tools needed for basic troubleshooting. I've had mine for over 30 years, still going strong.

If the pressure at the carb inlet is too high, your new pump is bad. If within specs, it's probably the float valve acting up.

From the Unsolicited Advice Department:

Be careful not to do too much at once. It's WAY to easy to unknowingly induce a new fault while trying to fix another. That becomes a troubleshooting nightmare. I do not care to discuss how I know this...

Your saga began with a truck you had running fine, and then it suddenly quit. I had to cringe when I read about the new manifold gaskets and messing with the EGR tubing. Even if bad, a problem there wouldn't make the engine suddenly quit. For all we know, maybe one of the bolts bottomed out on crud in a blind hole. The bolt may feel tight, but really isn't, and you've just added a new massive vacuum leak. That's just an example of what can happen when fixing something best left untouched for the moment while chasing an active fault.

Not trying to bust your butt, just trying to keep from adding new problems to the root cause.

 

I know I really overdid it on doing new things at the same time, I just thought "as long as ive got this stuff apart, why not replace the gasket!" I completely agree with what youre saying there. I wont have access to the truck until sunday when I go back to my dads for a week. I will try to get some pictures and get a fuel pressure guage hooked up to it. Thanks for all the helpful advice you guys, I sure need it.

 

I'd look at the float first. How can gunk passing through the fuel pump up the pressure?

 

Not sure that it could. But look at post #5. If I read that correctly, he replaced the fuel pump again. Perhaps this new one is bad from stock, putting out too much pressure.

Heck, if purchased from the same source, the pump replaced in post #1 could have also been from the same bad batch. Don’t know. A quick check with a mechanical gauge will make sure the present pump is within specs.

Check the float or pump first? Personal preference, I suppose. I’m lazy, would probably check the pump first because it seems like less work.

 

While we are on the topic of the float... How level is the truck? You haven't done one of those silly things kids do and squatted the truck have you? Or there's not some suspension issues and the front is down or anything like that? Or you wouldn't by chance be working on the truck in one of those driveways that go uphill in both directions would ya? You get what I'm saying? Truck pretty level and on flat level ground?

 

Truck being level doesn't matter unless you are actually adjusting the float setting. And the fuel pump does have a regulating mechanism inside it. The only thing I am hanging onto was the comment that it ran fine once he took the fuel line off till it ran out of fuel. That indeed could be a float adjustment also. I have heard a lot of horror stories about "rebuilt" and even "brand new" carbs.

 

Id say it depends on how unlevel it is. My truck has a pretty aggressive rake currently and it's enough to affect the fuel gauge. I spent some time looking into mechanical fuel pumps last night and looking at different diagrams. Couldn't see any obvious way they're regulated. Looks more like pressure is more a function of volume and line diameter. Also couldn't find a single mention of one ever increasing in pressure.