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Unread 12-23-2013, 07:01 PM   #1
capt205
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1983 CJ7 
 
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Got the MC2150 dialed in real good about a month ago... great idle, great response, no surging or stutter.

Last night while out driving with the wife, I notice a stutter that starts getting worse. Shut it off at a store, 15 mins later, come out and starts fine, however, it falls flat on its face when trying to accelerate. Carb has new power valve, new jets, getting, good pump shot, no new changes, since last month, and has been running perfect.

Double checked pump shot (good) checked timing (good), checked mixture (good). No backfire since new PV, and no fuel in PV cover. Really, as far as I can tell carb is un-changed. This happened while driving, then sitting for about 15 mins.

Pulled filter, dumped out gas, through cheese cloth, its clean. Blew compressed air from where fuel line connects to pump, back to tank, fuel blew out open tank fill.

I'm thinking bad fuel pump, (replaced about 6 months ago with NAPA pump) or bad gas, or obstructed pickup.

Idles perfect, revs perfect sitting in driveway, try to drive...bog.

Any suggestions?

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Unread 12-23-2013, 07:53 PM   #2
waterdowg
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Check to make sure all bolts on the carb are tight. Also check all your vac lines. You may have a vac leak.
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Unread 12-24-2013, 12:40 PM   #3
capt205
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All bolts tight, no vac leaks. Had carb off yesterday, replaced the thick gasket when I reinstalled.

Tomorrow, I'm going to try to run it from a gas can with clean fresh gas plumbed to the fuel pump, taking the tank and lines out of the equation.
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Unread 12-25-2013, 01:43 PM   #4
capt205
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OK...Ran with fuel pump plumbed to gas can with fresh clean gas...does the same thing.

Installed new fuel pump, does the same thing.

Tomorrow, going to try new power valve.

Question though...when reving the motor, should the power valve nozzles squirt, spray, drip or drizzle fuel in.

Right now, in the driveway, reving the motor produces a very short fine misty spray from the nozzles.
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Unread 12-25-2013, 07:09 PM   #5
John Strenk
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Power valve nozzles? Do you mean the accelerator nozzles??
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Unread 12-26-2013, 08:15 AM   #6
capt205
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Quote:
Originally Posted by John Strenk View Post
Power valve nozzles? Do you mean the accelerator nozzles??
Edit... they are the Pullover discharge nozzles.

Maybe I'm wrong on what they are...above the accelerator nozzles, are 2 nozzle looking things. I assumed they had something to do with the PV. When I rev the motor by hand, I see the acc pump squirt a good shot from the pump nozzles, then a momentary misty spray out of these other nozzles.
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Unread 12-26-2013, 08:49 AM   #7
Matt1981CJ7
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I think an accelerator pump shot should produce a nice long squirt.

Matt
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Unread 12-26-2013, 09:15 AM   #8
capt205
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Getting good shots from acc pump. With motor off...I get 3-4 good shots as well, when working the carb by hand.

Checked the vac advance on DUI dizzy, unplug the line, rpm drops, plug back in, rpm rises, hit the throttle, watching timing mark with a timing light, the mark moves to where it has always moved to before this all started. Let off the gas, mark returns to set point.

Like stated this happened to a well running motor and carb, in a matter of minutes without any previous changes or tinkering that I can tie back to it. one minute its running perfectly, and the next, its a bogger. Idle and revs fine in the driveway.

I'm off today, so I'm hoping to solve this...
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Unread 12-26-2013, 09:30 AM   #9
Matt1981CJ7
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Do your plugs show symptoms of a lean mixture? That would point to a bad power valve, or other carb issue.

If not, it could be ignition related.

Matt
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Unread 12-26-2013, 10:25 AM   #10
capt205
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Plugs are a nice even tan color, not wet or oily. No black sooty or carbon build up.

DUI is triggered through a relay, and feed by 8g wire. Cap and rotor contacts look good. How do I check the built in coil?
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Unread 12-26-2013, 11:14 AM   #11
Matt1981CJ7
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Check out Post #3 on this thread.

Matt
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Unread 12-26-2013, 11:37 AM   #12
Matt1981CJ7
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capt205,

This is a long shot, but have you checked for a collapsing fuel line?

Hmm....a flat stumble under load only...I'm running out of ideas that you haven't already tried.

Matt
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Unread 12-26-2013, 12:27 PM   #13
John Strenk
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Have you recently fill up with gas?
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Unread 12-26-2013, 12:31 PM   #14
capt205
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So today, I put in a new power valve, still bogs, new acc pump, still bogs, re-check timing, spot on. Electric choke is working correctly. Re-check for vacuum leaks, can't find any, vacuum gauge is nice and smooth, no erratic movements. No audible misses or sputters while at idle, or when reving in the driveway. Have good voltage on volts gauge. DUI is getting voltage direct from battery through a relay. Re-checked all plugs for fouling, they are nice and tan, and clean. Re-check gap @ .50

Only rubber fuel lines are the one's right at the tank, a short 4" piece up front, from the steel line end, to the pump, and from the pump to the filter. I don't see any leaks or moist spots on any fuel lines, and other than the rubber lines at the tank, which I can't see by myself while trying the re-create the symptom, no signs of collapsed hoses. Filter is a brand new WIX, correct position with return nipple at 12 o'clock. Fuel pump is brand new, and working.

I did recently fill up with about 12 gallons of gas from a high volume station. Yesterday, I plumbed a 5 gallon gas can with fresh gas from a different station, into the newly installed pump, with clear hose, and tried to run it. It started, idled, and reved fine, bogged under load.

This carb was a new MC2150 from the eBay guy, and after getting it dialed in, has run very well. It is not dirty and worn out, no junk in the bowl. It's less than a year old.

I'm going back out to re-check float level, if that does not help, I am at the end of my abilities to diagnose this.
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Unread 12-26-2013, 01:52 PM   #15
capt205
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Float set at 7/16

I am now officially frustrated. Beautiful Jeep weather here, and I'm at the end of my skills.
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