I am by NO means an expert on such things, but just as a food for thought/planting a seed sort of thing (and curious about all this, as well)...Do you have a fuel pressure regulator attached to the fuel line (probably right near the carb)? A Weber without one may act funky, and one installed without the fuel return line properly addressed seems like it could also make things sad panda in there. The above is the first thing that came to mind when I read your post, and though I doubt it'll save the day I do hope it helps on some level with troubleshooting.

 

The fuel return line was designed to run back to the gas tank. If you are lucky, the PO left the line under the Jeep and all you have to do is hook it back up.

As far as Vaporlock goes, you need to insulate the fuel lines from heat. One trick I have heard of is to put WOODEN clothes pins on the lines. Don't how or why that works but I hear it does.

 

If the return line was hooked up it shouldnt vapo at the pump. also is the bowl vented to the carbon can? not being vented would vapo the bowl.
the return line is hooked to a fuel filter that has an extra line (two in one out to carb). Might need a pressure reg on the line to carb but not sure. Mine doesnt have reg.

search vacuum diagrams for venting bowl and hooking up carbon can.

 

the return line that goes back to the tank should split off from the fuel filter. You mentioned you had a clear one which makes me think you have one inlet and one outlet. We had the same issue with my buddies CJ-7 and 258 4.2L. We put a Weber on it and found an open return line from the PO. We put a new fuel filter and fuel pressure regulator on it and plumbed the return line back in and it seems to work fine. My bet is you need to get the correct fuel filter (or just incorporate the correct one with the clear one) and hook the lines back up.

 

Hmm. The 'cap' on the return line is actually a fuel filter installed to keep junk out of the return line while providing a vent effect for the sealed tank.

The filter has an input and two outputs. I tried routing the input from the mechanical pump to both the input to the carb and the output to the tank but it's starving for fuel (cutting out) at 45 MPH and up on a constant run.

I'm thinking the return 'vapor' line is now routing fuel back to the tank (bad?).

I bought an electric pump tonight, blaming vapor lock (the same reason for not starting except under full throttle when hot?) but the pump only installs near the gas tank and I'm going to research more before doing that as it would be way easier to have a pump mounted up front.

Summary-

Starts great cold.
Starts hard after a few miles (or have to wait a while) almost every time I stop and restart within 10 minutes the fuel filter is empty and no start.

The fuel pump and filter are new.

Any time the vehicle reaches 50 MPH the engine loses power.

All hoses and lines good.

Thanks in advance, Guys.

 

I tinkered with it some more tonight and added a fuel pressure regulator. The fuel return line is still hooked up, and the Jeep is running GREAT around town.

Still though when I get to 45 -50 MPH or under hard acceleration, she just cuts off completely. Just shuts down. If I'm quick about letting off the gas I can keep her running but only at lower RPM (less speed / power).

:-(

 

see if your tank is venting right! with only a 1/2 tank pull the cap off then try to go on the hiway if the problem goes away you are having a venting problen if problem prosisest you got a pumping problem.

 

see if your tank is venting right! with only a 1/2 tank pull the cap off then try to go on the hiway if the problem goes away you are having a venting problen if problem prosisest you got a pumping problem.

Just got done with a rewire under the hood, now back to the fuel issue.
I'll try taking the gas cap off on the way home from work this evening. I was thinking since the fuel system has a return line the system is supposed to be pressurized but I guess air has to come from somewhere to replace the used fuel.

 

I pulled the cap on the way home yesterday, issue still persists. This one is frustrating!

 

Can you identify the carb.

Reads as though it is fuel starvation... not because of the hard start which is most likely the screws settings at fault but because of the limited rpm coupled with hesitation at the hard accel, which ironically could be the settings as well, a clogged jet, float setting or even timing.

If it is a real Weber the series and size will be stamped into the body mounting flange at the end that is 180* opposite the choke assembly.

 

I'll check that when I get home and report back.

 

This is what's on the side of the carb... Hope it makes sense!

 

Any thoughts?

I was going up a long steep hill today, started out at 50 and was doing 25 at the top with my hazards on, bucking like a bronco. I have to let off the gas until the engine catches again, just like its running out of fuel or something.

 

Last bump... I'm counting on you guys but I hate over bumping.........

 

Well, I've learned a lesson I won't soon forget.

Reads as though you're running low on fuel which is either the float, the screws settings, supply blockage or pump failure.

Number one thing to do for the time being is to eliminate the FPR and restore the dual outlet fuel filter and the fuel return line.

Then once the engine is fully warmed shut it down so you can back out the idle speed screw counting the number of turns until its tip clears whatever it stops against, then return it to that same position.

Then run the two mix screws in until they are lightly seated... counting the number of turns of each, then reset them to the same position.

Tell me what you find for those three screws.

During what may only be a temporary FPR removal would be an excellent time to test the fuel pump output. Disable the start by pulling the coil to dist. wire. Fit a tube to each of the dual outlet fuel filter outlet nipples long enough to reach a container held a safe distance clear of the cooling fan. Cranking the engine for thirty seconds should generate 1 pint of fuel.

 

Awesome information, mcmud.

It has been raining almost constantly here for days, as soon as I can get out to the Jeep I'll do the things you suggested and post the results.

 

OK. I'm back on the Heep thing after riding the MC for a couple of weeks. The screw settings are as follows..... The Idle screw is 4 turns out, both side screws are 3/4 out each. There are additional screws on the back of the carb, the PO may have adjusted them too.

 

I am having the exact same problem. Engine seems to be starving under acceleration and loses power going up hills. 4.0I6, Weber carb and electric fuel pump. It all started when the redline fuel pump that came with the weber carb failed. The new one called for a filter before the pump. I added an inline filter. The filter between the pump and regulator has the dual outlet and the smaller one is connected to the fuel return line. The Jeep starts and idles just fine. The new fuel pump is 5-9psi but I cannot get more than 2psi. Interesting - if I squeeze the return line I can get up to 6 psi at the carb. Seems gas is going back to tank rather than to the carb. Did you ever get this figured out?

I am not using the optional bowl vapor outlet or the charcoal canister.

 

So - because this setup worked fine with the Redline Weber fuel pump, I am assuming the problem is the O'Reily's fuel pump I replaced it with. Just ordered a new Redline fuel pump. Maybe there is a good reason it is twice the price . Hopefully that fixes it. I am really tired of feathering the gas pedal and losing half speed going up a hill.

 

Have you tried using the stock return style fuel filter without the fpr and the return line hooked up?

Dwayne

 

No, but the fpr is turned almost all the way in. The only way to get the pressure at the carb above 2.0psi is to squeeze the return? I'm thinking the difference is in the two pumps because the original redline had the regulator set in the middle and easily maintained 3.25psi

I am concerned with the failure of the first redline pump so I installed an inline filter before the pump as an add to protect the new pump. I did bypass it as a test but made no difference.

 

I'm still having the same issue without the FPR too. I'm using the mechanical fuel pump though (new pump).

 

Hopefully mcmud will find his way back here and give me some input on my carb settings.

 

i have the same engine/tranny set up as you and i run a weber carb also. when i got it the poor jeep wouldn't barely run and had trouble doing 50 on the highway. i installed a holley low pressure pump on the wheel well in the engine bay and a clear fuel filter up there also. i did not hook up the fuel return line and use an fpr and have none of the problems you guys are having. the owner prior to me had a mr gasket pump and fpr and tried to hoop up that return line and i think all that was the trouble. when i went to a good quality pump and fpr and removed that return line, everything was good.

if you put that return line in place after your fuel pump but without a pressure regulator on the return, its a free flowing return that puts no pressure on anything else. i would put your vent back on the return and let your fuel pressure regulator set the pressure to the carb, like it is designed to do. yes, out jeep came from the factory with a return line but since we have modifications done, you no longer need to use the same system. you can, but its not required. i choose not to and have no trouble with starting or losing speed/power on the top end. maybe you fellas should try it this way and see if it works for you?

 

actually, that is how the OEM fuel filter works, it is an fpr. So as long as you run the filter with the return line and stick with the mechanical pump, there is no need to run the holley fpr(the mr. gasket ones are notorious for failing).

 

SpikesHD,

Lets give this a fair trial. Once the engine is fully warmed shut it down to allow say five minutes, no more of heat soak.

Back the speed screw out until its tip loses contact with the stop. When you think you're there run it back in to the first indication that the sector gear budges. Kind of an in and out trial until you're sure that the slightest inward turn will cause effect to the (sector gears) throttles position.

Turn it in 1/2 turn, and leave it there.

Go to the mix screws turning them in until they are lightly seated and then back them both out 3/4 turn.

Start the engine.

If the idle is rough, evenly back each of the mixture screws out to a point that the idle smooths. At this time you should not be looking for any particular engine curb idle rpm but just a smooth steady idle, irregardless of engine speed.

If you find that a satisfactory smooth (not speed related) idle cannot be had with these settings go to the speed screw with a 1/4 turn in and then work the mix screws.

Once it has a smooth idle quality give it a thorough test drive.

If you should need to exceed these base settings suspect debris clog in the idle jets, possibly in the mains.

The screws on the body at the linkage side are not tune adjustments. Those hold the venturi and aux. venturi in place. All should be set tight.

 

SpikesHD,

Lets give this a fair trial.

I did this, the screws on he side came out several turns each before the idle
smoothed out nicely. Is that normal?

I haven't road tested the Jeep yet (I had a couple of beverages after work) but a few full throttle runs down the driveway (~300 ft) are very promising!

I'll report back next time we have rain in the forecast... I'm a Jeep fan, but a bigger Harley fan!

Thanks!:cheers: