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Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

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post #1 of (permalink) Old 02-28-2008, 05:58 PM Thread Starter
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MC2100 is great! Still need help though...

Hi everybody

Just got done swapping my carter for a motorcraft 2100. Very easy... It took less than 1 hour to get her running. Check out my throttle bracket in my gallery...that took a few hours of trial and error.

Here's the problem I'm having:
There is a spot during the acceleration curve, where if you hold the throttle just right, it seems to choke out the carb. This happens going from idle(650-700rpm) and ends just over 1000rpm. In 3rd gear around 1000rpm there is a slight surging.There is usually a lope in the idle when this happens as well.

Furl pump is pretty new I replaced fuel filter, the cap/rotor are also pretty new. Don't think there are any vacuum leaks at the base... Timing set around 8* or 9*...

I replaced the plugs with some cleaner, but still used, plugs(my carter had the old plugs fouled pretty good). The rig ran really well for a couple of hours today, but for some reason is now back to having a lope in the idle, and pushing the throttle just right will stall it out.

Accelerator pump? When the engine is off, I pump the throttle, gas sprays out of both jets.
I didn't rebuild the carb...It came off a 74 bronco that was running well...It looks to have been rebuilt recently.

Any ideas?

Tim
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post #2 of (permalink) Old 02-28-2008, 06:29 PM
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Best to rebuild the carb... cheap, easy and effective. Then you know what you've got.
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post #3 of (permalink) Old 02-28-2008, 08:28 PM
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Based on the symptoms, you might try adjusting idle screws or the accel. pump linkage inboard (for a quicker squirt)...

*IF* you don't have a tach and are just guessing about the RPMs... I'd say it's a bit higher in the band where it transitions from idle... while a "rebuild" may be needed in the long run, pull it down, blow it out, and see where that gets you. Mine (304) will run like total @$$ if the bowl gets too much crap in it or a jet gets clogged...

Can you confirm a 1.08 venturi... if not, your 258 won't run well on a carb designed for a 50% larger displacement mill...

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post #4 of (permalink) Old 02-29-2008, 12:21 AM
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Both places it stumbles is part throttle at nearly the same opening. Could be several things.

I suspect you may have too much advance too soon. Start by disconnecting the vacuum advance line. The Ford carb has a different advance curve than the old one.
Try it.

1. If the stumble is still there try the "propane trick" to see if it's going lean at that point.
If yes, it is going lean, then rebuild the carb, making sure the tiny passages under the clusters and next to the throttle plates are open and free of dirt.

2. If the stumble goes away with the vacuum advance disabled, make absolutely sure the vacuum you are using for the distributor is PORTED vacuum, NOT manifold.
Ported is above or at the throttle plates - near 0 at idle, gets stronger as the R's increase.
Manifold vacuum - wrong one - is strong most all the time.
Try it again, then let us know.

Last edited by RRich; 02-29-2008 at 06:20 AM.
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post #5 of (permalink) Old 02-29-2008, 02:27 PM Thread Starter
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It is a 1.08 venturi...it's stamped on the driver side of the unit
I've got a tach in there, she's idling 650-700, and the "flat spot" occurs just past there. Touching the throttle slightly will stall it out. Pulling it hard will get it past that flat spot...

I was able to get her running nice last night by playing w/ the air/idle screws, even though I had them set to what seemed "proper" earlier, when she was running smooth and strong. Re-adjusting helped. I had to adjust them again today a bit to get her running smooth...Maybe this is the right setting. We'll see how long it lasts. I just want to get it to a point of consistency, for the past 3 days, it's running a little different everyday.

...and I'm using the ported vac(off the right side of the carb) for my advance. The Vac is 0 at idle, and increases with the throttle
I pulled the top off the carb, plenty of fuel in the bowl, float moves freely.

I'm going for a drive now. Hopefully the air/idle screws won't need adjusted any more.

A rebuild may be just the thing to get that consistency...leve's common sense approach to problem solving strikes again!
Tim
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post #6 of (permalink) Old 02-29-2008, 03:01 PM
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Quote:
Originally Posted by Tim-E View Post
A rebuild may be just the thing to get that consistency
Just keep in mind that a "rebuild kit" *ONLY* gets you new gaskets, check ball(s), accel. pump diaphragm, needle & seat. Unless those parts are bad (accel pump dia. hard, gaskets leaking, leaking needle/seat, etc)... a "rebuild" will gain you absolutely nothing a good cleaning won't cure...

While most will say the 258/2100 swap is simple, I've seen folks fight them for months before finally giving up... usually power valve issues or the inability to tune them correctly. Since yours is running good, that's probably not the case...


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post #7 of (permalink) Old 02-29-2008, 04:28 PM
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1. So how did it run WITH THE ADVANCE TOTALLY DISCONNECTED?

2. How did the propane affect it?

We can only help you by suggesting ways to tell what's wrong. YOU have to do it and tell us what happened - IF you really want help.

If you'd rather just throw parts at it, AutoChina will love you.
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post #8 of (permalink) Old 02-29-2008, 06:19 PM Thread Starter
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Thanks stickin with me here!
I noticed little to no difference while driving with the advance disconnected. Adjusting the air/idle mixture has it idling consistently now, and the acceleration curve is smoother.(but not perfect...)
However, the lurching/surging feel that I'm getting around 1000-1100rpm is remains. Just holding the gas pedal at a constant 1000-1100rpm, in any gear, there is still a noticeable surging. Does this tell us anything?

I'm reading up on the propane trick right now. I'll try that out tomorrow. Seems like a great trick for an issue that has plagued me for years! Seems like a fun way to spend my Saturday... (wow Rich, was posting in this thread your 10000th post? I'm honored!) Thanks again.
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post #9 of (permalink) Old 02-29-2008, 08:00 PM
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You have to eliminate things as you go.

With the advance disconnected it shows that isn't the problem -- as long as you have the initial timing at about 8 degrees.

Make sure you are using the FACTORY ORIGINAL PLUGS the engine was designed to use. Aftermarket junk will cause lots of troubles, no matter what the ex-burger flipper kid at AutoChina says, or ad lies say.

The propane trick will verify it's a lack of fuel - too much won't do that unless it's a flood - unlikely. You'd be complaining of clouds of black smoke.

At idle it's running on the idle circuit - 400-1100 or so.
As the throttle opens, the idle circuit stops having as much influence as the transfer circuit starts working 900-1500.
Then above the transfer circuit the main run circuit kicks in 1300+.
They do overlap.

When you richen the idle mix, it helps cover up where the transfer circuit takes over. The problem is still there, but not so obvious.

The propane trick will verify it's lean and not something else.

If it is lean, try a couple of tricks before stripping down the carb.

1. Mexican tune up - rev it up to 2500 or so, with your hand or a CLEAN RAG completely choke off the carb until it dies. Often the sucktion will pull out the tiny dirt clogging it.

2. Still No? Engine off - spray carb cleaner down the tiny bleed holes and let it soak for awhile. The bleed holes are the tiny holes in the venturis near the clusters.
Wait, then do the Mexican tune up again after soaking.
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post #10 of (permalink) Old 02-29-2008, 08:32 PM
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When you are getting the surging are you driving or just sitting at 1000-1100 RPM with the clutch in? If it does it when driving does the jeep seem to surge with the surges in the engine?

Wilhelm

I will start using Metric only when the duodecimal system is adopted!!
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