Rough Idle/Bad Timing? - JeepForum.com
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post #1 of 29 Old 11-12-2019, 04:32 PM Thread Starter
cpadget
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Rough Idle/Bad Timing?

Jeep runs a bit rugged at idle, which is between 650-800 depending on the day. It pops a bit from the exhaust. The second I run the RPM's up, it cleans up nicely. It runs strong at anything above about 900. MC2150, nuttered, and recent Team Rush. When I replaced the plugs during the TR, I took pictures of them, they all looked pretty similar. Pictures attached

Could this be timing or 2150 adjust that is needed? Again, I will stress that it runs pretty well, but it would be nice to have it purr at idle as well.

Thanks for any thoughts

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plug1.jpg   plug2.jpg  
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post #2 of 29 Old 11-12-2019, 06:10 PM
uptillnow
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What is your jetting on this MC2150? It is rich, or weak spark not burning efficiently.

Timing? 10-14 BTDC at 600 RPM idle?
It does look like late timing, although these Motocraft distributors have what I call "emissions timing". This means that you may have good initial timing, but the distributor total advance is no more than 18 degrees and most of the time less than that.

A way to check your total advance is with a dial timing light.
Or
You can check your advance slots for the 13R-18R slots, wanting the advance arm in the 18R slot. see pictures
UTN

EDIT: These are Matt's pictures that I use a lot. Thank you Matt.
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post #3 of 29 Old 11-12-2019, 06:32 PM Thread Starter
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So is it likely that mine is in the 13R slot? I don't have any reason to believe that was ever changed. I am not sure on the jetting on the carb. In Phoenix, at 1000 ft elevation, what jetting am I looking for?
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post #4 of 29 Old 11-13-2019, 05:57 AM
TerryHowe
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Do you still have the stock Carter BBD carb? Drippy carb maybe, clogged idle tubes? https://www.jeeptech.com/engine/carter.html

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post #5 of 29 Old 11-13-2019, 06:48 AM
pedal2themetai
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hi, the black looks like oil fouling. white is lean .. normal is lite brown. might try enriching up the mixture a little 1/4 to 1/2 out a turn and see what that does. My ranger was doing the popping thru the exhaust and I enriched it hole turn and it runs great now with no popping.
good luck
tim
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post #6 of 29 Old 11-13-2019, 08:43 AM Thread Starter
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Quote:
Originally Posted by TerryHowe View Post
Do you still have the stock Carter BBD carb? Drippy carb maybe, clogged idle tubes? https://www.jeeptech.com/engine/carter.html
Terry, MC2150, no computer
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post #7 of 29 Old 11-13-2019, 08:44 AM Thread Starter
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Quote:
Originally Posted by pedal2themetai View Post
hi, the black looks like oil fouling. white is lean .. normal is lite brown. might try enriching up the mixture a little 1/4 to 1/2 out a turn and see what that does. My ranger was doing the popping thru the exhaust and I enriched it hole turn and it runs great now with no popping.
good luck
tim
Not being a motor guy at all, I have never seen a plug that was dark brown on one side and white on the other. I will play with the mix and see what happens
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post #8 of 29 Old 11-13-2019, 09:11 AM
Matt1981CJ7
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cpadget,

It's normal for the plugs to color on one side but not the other. That's the side of the plug the fuel is burning on.

Your plug definitely looks rich. Have you adjusted the carb for the lean/best idle mixture?

The exhaust popping could be from loose manifold bolts. The 258 is notorious for that.

Matt
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post #9 of 29 Old 11-13-2019, 09:52 AM Thread Starter
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Matt, thank for the reply. I have not done any adjusts on it since install. I do have a small exhaust leak, down near the cat or muffler. I will check the manifold bolts and torque them appropriately. I assume playing with the mixture screws will be obvious in how it changes the idle?
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post #10 of 29 Old 11-13-2019, 01:10 PM
Matt1981CJ7
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A vacuum gauge comes in handy for adjusting the idle mixture. Connect it to a manifold vacuum source. Start with both mixture screws adjusted to 1 1/2 turns from lightly seated. Then adjust each screw equally until you get the highest steady vacuum reading.

Matt


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post #11 of 29 Old 11-13-2019, 01:50 PM Thread Starter
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Matt, I have read a bunch on here about hooking distributor up to Ported vs. Manifold. I believe I have mine hooked up to the ported on my 2150. Is this correct. Where else would it get hooked to, and why would you want it different?
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post #12 of 29 Old 11-13-2019, 02:09 PM
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I believe that's ported vacuum. The easy way to tell is if there is vacuum at the port at idle, then it's manifold vacuum. If not, it's ported.

I recommend running manifold vacuum advance. It will give you a cooler more efficient idle.

Matt


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post #13 of 29 Old 11-13-2019, 02:38 PM Thread Starter
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Thats what I read. So if I was to run that vacuum line from the distributor to manifold vacuum, would I run it to the 5 port CTO block coming off the manifold? Or where would I run it to?
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post #14 of 29 Old 11-13-2019, 03:01 PM
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No, don't connect it to the CTO. Here's is where I'd connect it.
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post #15 of 29 Old 11-13-2019, 03:43 PM Thread Starter
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Got it. I will experiment with that
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