1986 CJ-7- 258 with 2150 Motorcraft Carb idle problems - JeepForum.com
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Unread 03-24-2010, 05:45 PM   #1
ET48
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1986 CJ7 
 
Join Date: Jun 2008
Location: Wooster, Ohio
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1986 CJ-7- 258 with 2150 Motorcraft Carb idle problems

Alright just need some opinions here.

Got a 1986 CJ-7 with inline 258 with motorcraft 2150 conversion and Nutter bypass.

Fuel supply: Newer replacement mechanical pump and supply line with inline plastic filter.

No return fuel line.

No vaccum leaks.

Problem:

Jeep runs fine going down road. Will cough when floored. Loads up with fuel during idle. Idle adjustment screw completely backed off. Butterflys are sealing against throat of carb. After driving, will idle at around 1,000 rpms. Bump throttle and carb will idle down lower to around 750 rpm.

Fuel filter seems to be "expanded" from extra fuel pressure.

Question:

Is my mechanical fuel pump supplying to much fuel pressure to the carb (without a return line or pressure regulator), expanding the fuel filter, and forcing the needle valve in the carb open forcing high idle?

Seems that the butterflys have to be completely shut against the carb throat for lower idle. (will still run rich with butterflys basically shut).

Will adding a simple fuel pressure regulator fix my problem?

How many lbs of fuel pressure should the 2150 carb see?

Is the Mr. Gasket adjustable pressure regulator any good?

Thanks for your guys help,
Ethan

Here two pics of my set up:





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ET48
1986 CJ-7 LAREDO, 4.2L, 5 speed, 3.31 Gears, D30, D44, 2.5" ProComp lift, 3" BL, 33" TSLs.
1998 TJ SAHARA, 4.0L, 5 speed, 4.11 Gears, D30 (Aussie Locked), Ford 8.8, 4.5" Custom LA, XRC8, AA SYE, TW DS, ZJ tie-rod, Full-Traction front adj. track bar, 35" KM1s.
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Unread 03-25-2010, 03:52 PM   #2
ET48
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Bump???

10 char
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ET48
1986 CJ-7 LAREDO, 4.2L, 5 speed, 3.31 Gears, D30, D44, 2.5" ProComp lift, 3" BL, 33" TSLs.
1998 TJ SAHARA, 4.0L, 5 speed, 4.11 Gears, D30 (Aussie Locked), Ford 8.8, 4.5" Custom LA, XRC8, AA SYE, TW DS, ZJ tie-rod, Full-Traction front adj. track bar, 35" KM1s.
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Unread 03-26-2010, 06:10 AM   #3
Mike Romain
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There is evidence showing that your float adjustment is either off or the needle has junk in it so it isn't shutting off. There is gas leaking out the top gasket, gas shouldn't be up that far.

The gas pump is an on demand style that puts out more psi with rpm, but it should not put out enough to overpower a working float needle.

The return line normally comes off the top of the gas filter so on a hot shutdown any vapors produced get blown back to the tank rather than vaporlocking the gas line.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 03-26-2010, 08:29 AM   #4
mcmud
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In addition.. you might consider either another throttle return spring or relocate the ones you have. Neither of them show any sign of tension using that location.

As to the Mr Gasket FPR...I've seen it written here on JF quite a few times that it is less than desirable but that seems odd when I pickup an auto mag to look thru, I see them in use on all types of applications.
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Unread 03-26-2010, 10:36 AM   #5
ET48
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I rebuilt the carb back when I installed it and reset the float at the same time, so maybe like you said, the float needle has junk in it. I'll re-check the float since I'll have the top off anyways.

I did notice the fuel seeping out of the carb but forgot to mention it. Must be that the fuel level is a little high (due to the float adjustment/or dirt) and I might need to get it sealed better.

Should not running a return line be a concern then? I understand about the pump and it makes sense, but is vapor locking the gas line a real concern. I haven't had that happen yet.


The throttle return springs:
I tried relocating them (not a problem) but when I put more tension on the throttle, the butterflys seat harder against the throat walls. Then when coming off idle, you can feel the butterflys unseat. (Makes for a rough start off idle).

All ^ that is probably due to the idle adjustment screw being completely backed off allowing the butterflys to seat hard against the throat walls. If I get the float or needle fixed, I might get the idle set better with the screw and eliminate this problem.

I've been seeing the same thing on the FPR. (Looks like I'll wait on getting one).

Thanks for the replies. Unless more guys have some ideas, I'll try all this tonight and get back to you.
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ET48
1986 CJ-7 LAREDO, 4.2L, 5 speed, 3.31 Gears, D30, D44, 2.5" ProComp lift, 3" BL, 33" TSLs.
1998 TJ SAHARA, 4.0L, 5 speed, 4.11 Gears, D30 (Aussie Locked), Ford 8.8, 4.5" Custom LA, XRC8, AA SYE, TW DS, ZJ tie-rod, Full-Traction front adj. track bar, 35" KM1s.
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Unread 03-26-2010, 10:41 AM   #6
Mike Romain
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Posts: 13,105
Running a return line isn't a bad idea, Jeep figured it was needed so...
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Mike
86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 03-26-2010, 07:09 PM   #7
ET48
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So, I pulled the carb of the jeep and started taking it apart.

Needle valve was spotless and clean. Haven't checked the float level yet.

I did notice that I did not have one of the holes pluged on the carb. The hole goes to the top of the float bowl. Does this matter or would this cause the idle to be high?

Jets:
Currently have 53F jets in it and I have 63F jets I could swap in, but I believe the correct size is 47 that I should have in there? Would the 53F jets be so big as too affect the carb and cause it to give me the problems I have?

Everything else seemed fine. Like I said, I'll get the float level results tomorrow, gotta find the little measuring carboard piece...
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ET48
1986 CJ-7 LAREDO, 4.2L, 5 speed, 3.31 Gears, D30, D44, 2.5" ProComp lift, 3" BL, 33" TSLs.
1998 TJ SAHARA, 4.0L, 5 speed, 4.11 Gears, D30 (Aussie Locked), Ford 8.8, 4.5" Custom LA, XRC8, AA SYE, TW DS, ZJ tie-rod, Full-Traction front adj. track bar, 35" KM1s.
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Unread 03-27-2010, 09:29 PM   #8
ET48
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Found some 47F jets and swapped those in before I put the carb back together.

Measured the float level, it was about an 1/16" too high. Readjusted to 7/16" from the top of the float bowl.

Checked everything else out and it looked good so I reinstalled the carb.

Got her running and adjusted timing to 8 degrees BTDC. Adjusted the mixture screws.

Results:
Way too lean. Plugs are white and the exhaust backfires while downshifting. Had the mixture screws 10 full turns out but still lean.

Couldn't stand it so I put the old 53F size jets back in. Runs like normal, idles too high~800 rpms.


Started looking at the carb more closely and discovered that this Motorcraft has a venturi size of 1.21! Desired is 1.08. I must have not known what I was doing back when I installed this carb. (Just had it lying around).

This carb is forcing too much air with the 47F size jets creating a lean situtation.

I'm going to try and find another carb in the junkyard that has the 1.08 venturi's, rebuild it fully and try that.

I'll keep you guys up to date.
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ET48
1986 CJ-7 LAREDO, 4.2L, 5 speed, 3.31 Gears, D30, D44, 2.5" ProComp lift, 3" BL, 33" TSLs.
1998 TJ SAHARA, 4.0L, 5 speed, 4.11 Gears, D30 (Aussie Locked), Ford 8.8, 4.5" Custom LA, XRC8, AA SYE, TW DS, ZJ tie-rod, Full-Traction front adj. track bar, 35" KM1s.
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Unread 04-03-2010, 07:22 PM   #9
ET48
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Called a few junkyards around here and had no luck finding a 1.08 venturi carb. There is still a few I can try but I came up with an idea:

Yesterday I bought a two line exit fuel filter and hooked it up to the jeep. Hooked up a return line that just ran into a gas can. Started the jeep and looked to see how big the stream was coming out of the return line. The 3/8" rubber hose was completely full coming out of the filter!

When I completed this test, the engine rpms came down by 100 just by adding the extra line. It starts easier and everything.

So today I ran a actual return line back to the tank and hooked it all up. Runs like a champ. Spark plugs are a nice brown color.

Jeep has plenty of pickup, doesn't smell gasy anymore, starts easier, and it got rid of the stumble right off idle.

Just about fixed everything. The rpms are still a little high, ~750 rpms at idle, but if I bump the throttle real quick, the rpms will come down to 650. Anyone have any clues to whats causing that?

Should have added the return line a long time ago. Almost got rid of all the problems.
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ET48
1986 CJ-7 LAREDO, 4.2L, 5 speed, 3.31 Gears, D30, D44, 2.5" ProComp lift, 3" BL, 33" TSLs.
1998 TJ SAHARA, 4.0L, 5 speed, 4.11 Gears, D30 (Aussie Locked), Ford 8.8, 4.5" Custom LA, XRC8, AA SYE, TW DS, ZJ tie-rod, Full-Traction front adj. track bar, 35" KM1s.
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Unread 04-08-2010, 07:33 AM   #10
Mike Romain
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Quote:
Originally Posted by ET48 View Post
Just about fixed everything. The rpms are still a little high, ~750 rpms at idle, but if I bump the throttle real quick, the rpms will come down to 650. Anyone have any clues to whats causing that?
Could the choke's fast idle cam be a little sticky?
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 04-09-2010, 10:33 AM   #11
ET48
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Right now I have the high idle for the choke completely backed off. I'll check it again though.
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ET48
1986 CJ-7 LAREDO, 4.2L, 5 speed, 3.31 Gears, D30, D44, 2.5" ProComp lift, 3" BL, 33" TSLs.
1998 TJ SAHARA, 4.0L, 5 speed, 4.11 Gears, D30 (Aussie Locked), Ford 8.8, 4.5" Custom LA, XRC8, AA SYE, TW DS, ZJ tie-rod, Full-Traction front adj. track bar, 35" KM1s.
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