Fuel Delivery Issue (carb gurus needed!)

[RWrightPhotog]

Have a small problem....

After installing a used but rebuilt Motorcraft carb on my Jeep I am having a "surging" I guess you'd call it issue. When going up a hill or if I just floor it and hold the gas down it runs fine and fast for about a minute them stumbles like its out of gas. If I keep my foot on the gas it'll try to cut off, but if I take my foot off the gas and let it idle for a moment it'll continue....

It almost seems like the bowl is going dry.

It starts fine and fast every time, it's just driving it up hills or if I just hold down the gas, which of course I am holding down the gas going up hill.....

I'm just lost on how to trouble shoot it or what I need to adjust.... That being said I haven't adjusted the carb. It was a remanufatured carb that I got from a guy a while back bolted to a 360 intake and I just bolted it on my motor. Looks new on the outside and relatively clean on the inside, so it's not too old of a rebuild.

[mineral co]

It almost seems like the bowl is going dry.

That is very likely exactly what is going on.

If you care to confirm it, create the situation and then immediately shut off the engine (don't accidently lock the steering when turning off the key!). Pull the top off the carb and see how much fuel is in the bowl.

If the bowl really is going nearly dry, it is a fuel supply problem, i.e. fuel pickup in tank, fuel lines, fuel pump, external fuel filter, or the small internal filter in the carb (if it still there).

Somebody made a post recently of a nearly identical problem, and it turned out that the line to the carb was connected to the wrong port on the fuel filter! The carb hose should be connected to the larger of the two ports on the end of the filter with two ports and the fuel return line should be connected to the smaller of the two.

Why did you replace the carb? What problem(s) were you having that led to that?

[RWrightPhotog]

It had a Holley carb on there that didn't had an unhooked up manual choke (sucked for starting) and the Jeep didn't feel very powerful. This carb gave it back some power and a choke!

The fuel lines are hooked up the same as the other carb.... I will have to check the internal filter though.... Fuel pump was working fine before of course I know how these things go....

[mineral co]

Keep in mind that more power requires more fuel. Any fuel supply component could have been marginal and possibly have kept up with more minor fuel demands, only to be beyond its abilities with the replacement carb, i.e. assume nothing, check everything.

[serehill]

Step one replace the filter & check all fuel lines for cracks. If you didn't have any starvation issues before the carburetor change then it is connected incorrectly or the float is set wrong. I would be more willing to bet you have a fuel delivery problem. Unfortunately this will need inspection all the way to the tank. Also make sure all of you fuel lines are as far away from the exhaust as possible.

[RWrightPhotog]

Well there's not /that/ much more power... Just a quicker response and seemingly runs smoother, right carb for motor y'know. Cuz the Holley was by no means a small one....

That being said, I believe it is definitely a fuel delivery issue.... It's definitely not getting to the engine like it should. I will change the filter ASAP and check for any kinks or anything.

Yeah, had no issues before change.... I was actually leaning towards the float maybe being set wrong.... As I have never been it one of these how do I check that and adjust it?

Fuel lines are clear of exhaust, checked them for cracks and everything when I was under it last. Fuel lines under the hood are new-ish.

[letank]

The easiest way would be to let the engine die during the test that you mention... pull in a safe spot, and remove the carb air horn to visually check your fuel level.... then either adjust the float level... or may be your fuel line is either plugged or rusty at the pick up assembly on top of the gas tank which allow air in the line, the sock is collapsed, or the fuel pressure is not up to specs, this last part is best dealt with a fuel pressure gauge before the fuel filter...

START WITH THIS : of course talking about fuel filter is the return line at 12 o'clock -the small nipple should be on top- which could cause starvation if it is not at 12 o'clock.

[tgreese]

There is a spec in the TSM for fuel delivery. It shows both pressure and volume, and how to test. At 1J-8 in my '82 manual; that manual is available online at http://www.oljeep.com They show a fancy tester, but you can do it without the tester.

You can either feed the carb from a can on the cowl while doing your test, or run on the fuel in the float bowl. The engine will run for long enough to test on what's left in the float bowl.

Comment - broken rubber fuel lines are likely the primary source of under-hood fires. If you have not, replace all the rubber lines. Cheap, cheap insurance. Change them every time you replace the filter, fuel pump, whatever. And leaky lines will prevent your fuel pump from working - it's like trying to suck soda from a straw with a hole in it.

[mineral co]

I had another thought about this last night.

Now, I think valid trouble-shooting procedures are always appropriate as that's the only way to avoid a guessing game, and running the vehicle until the problem develops and then cutting it off and checking the fuel level in the float bowl is a very good initial test. Let's say you did that and the float bowl was still full.

Then, I think there is only one really likely source of trouble and that is the power valve. Were did you connect the power valve to? Power valves seem to be a not-uncommon problem on 2150s, so it might just be bad even if it is connected properly.

[tgreese]

I had another thought about this last night.

Now, I think valid trouble-shooting procedures are always appropriate as that's the only way to avoid a guessing game, and running the vehicle until the problem develops and then cutting it off and checking the fuel level in the float bowl is a very good initial test. Let's say you did that and the float bowl was still full.

Then, I think there is only one really likely source of trouble and that is the power valve. Were did you connect the power valve to? Power valves seem to be a not-uncommon problem on 2150s, so it might just be bad even if it is connected properly.

Vacuum holds the power valve closed. Disconnect the hose and you'll have too much fuel.

[RWrightPhotog]

Where is the power valve nipple? Not to sound like too much of a dumb*** because I just went and looked at the carb and it looks like I only have two vacuum lines hooked up to it. Distributer and PCV.

There is a vacuum nipple on the back with a cap on it that I just noticed! Perhaps this is my problem.... I used the same lines that were hooked up to the Holley on there.

(Starting to feel like a dummy if thats it. )

[tgreese]

Where is the power valve nipple? Not to sound like too much of a dumb*** because I just went and looked at the carb and it looks like I only have two vacuum lines hooked up to it. Distributer and PCV.

There is a vacuum nipple on the back with a cap on it that I just noticed! Perhaps this is my problem.... I used the same lines that were hooked up to the Holley on there.

(Starting to feel like a dummy if thats it. )

Front underside on a 2150. What year? The 2100 used on earlier models has an internal passage, so no hose.

[RWrightPhotog]

I'll have a look, I'm not sure... I didn't see one. I'm honestly not sure what year it is, I believe it came off of a newer 360 manifold, but of course that doesn't which it is. Could be a 2100 I guess, where are the model numbers...

Whats the nipple on the back then?

This is my first Motorcraft carb to deal with, like I said before I had the Holley and before that carbs on 60's Chevy I-6 motors....

[RWrightPhotog]

Found the power valve..... Definitely wasn't hooked up, was capped... Hooked it up to stock location on manifold.

But no difference. Created the situation, pulled top of carb off. Bowl has a little under 1/2 inch of gas in it. Shut it off at first "surge."

[mineral co]

Well, that doesn't make any damn sense!

Under normal circumstances there is no way that hooking up a power valve that was not previously connected could have no effect. If it was working right, while disconnected, you should have noticed better running as more load was applied.

Makes me wonder what else is going on with that carb, starting with the power valve.

A half-inch of fuel in the bowl is too low, but not so low as to cause the engine to act like it is running out of fuel. At this point it seems likely that there is more than one problem or that carb is not built correctly, or both.

I'm always reluctant to advise somebody that is not well versed in carbs (I don't know what your knowledge level is! No offense intended) to get into something more challenging, but that power valve circuit needs to be looked at very carefully as is seems to be doing nothing. Also, I still think the fuel supply needs to be looked at carefully.

[letank]

Fuel level is measured from top of carb body, depending on carb, between .9 to .7, measured a 1/4 from the edge to compensate for edge effect. Different chart seems to have different numbers.

Connecting the power valve to the intake manifold vacuum resulted in no noticeable differences.... Hummm.

As for the fuel pressure, may be time to borrow or buy a fuel pressure gauge $25ish. Put a T before the fuel filter... 4 to 6 psi is expected, it will run on 2 psi but not very well - my experience-

Did you check the fuel filter return line position at 12 o'clock....

Remember that the cheapest fix is usually the solution... I know too many who have replaced radiator, water pump.... For a defective $7 thermostat.

Reading post... The cap on the back of the carb is the hook up for the pcv system... Should be connected to carb and the pcv orifice in the back passenger side of the intake manifold, next to the egr valve, the pcv valve is modulated by a vacuum line connected to the charcoal canister as well as one of the carburetor ports... At this point.... How much emission do you have connected! Is the the 82 or the 7*

May be a few pict of your carb and surrounding areas.

[RWrightPhotog]

Power valve did cause idle to smooth and it seemed that it lasted for longer before starting to cut out, but not a HUGE difference. It just didn't cure my problem.

It was about a 1/2 inch from bottom of bowl, and it was when it first started to choke out that I shut it off and coasted it down the road into my yard.

Fuel filter is in correct position!

edit: It's the 82. Almost no emission stuff is on the Jeep.

[tgreese]

Whats the nipple on the back then?

Going to the air horn? Choke clean air feed. Should connect to the choke stove in the manifold.

There is also a large diameter connection at the base for the PCV.

[tgreese]

Look at this:



The nipples at the base of the carburetor should be in these positions. There is also a nipple from the air horn that goes to the choke stove, not shown here. "PV" should produce no vacuum when the engine is running - it is connected to manifold vacuum. "E" and "S" are ported vacuum, that goes to zero when the throttle is closed.

[mineral co]

Okay, so the power valve did have some effect. Checking fuel deliver is still high on the list of things to do.

And it's also possible for some symptoms to be very misleading. I'll relate a quick story on my truck, which I resolved only just now. I've noticed over the last several days that my truck felt like it was running out of fuel under heavier loads. Climbing steeper dirt roads with the throttle in the 2nd half of its travel, or jumping on it out on the highway resulted in poor running and roughness. I was really thinking the power valve in the carb wasn't working correctly. Backing out of the throttle improved the situation quite noticeably.

So I started looking at it. The dang choke wire was disconnected at the choke! How the heck did that happen? The choke was sitting only half open. I reconnected it, and it runs like a champ again.

It wouldn't be your only problem, but do make sure that choke is actually opening all the way when the engine is warmed up.