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Unread 05-17-2013, 07:18 PM   #1
echobaker
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Join Date: Mar 2012
Posts: 6
AMC 258 Diagnostic Help

I'm having a bit of trouble with my engine. It's an AMC-258 with a Carter BBD, and it lives in my 1978 Jeep CJ-7. Here's my situation:

---HISTORY---
I recently rebuilt my carb. This went well, and it ran quite nicely.

Reckoning this particular challenge to be solved, I moved onto the next one - the ticking noise coming from the engine, particularly at low RPM. Believing this to be the result of deposits built up around a valve, I bought a bottle of Sea Foam Engine Treatment and a can of Sea Foam Spray. I put half the bottle of Engine Treatment in the gas tank, and the other half into the oil fill cap at the top of the valve cover. The engine went from smooth operation into a kind of subdued rumble. I drove the Jeep around for the day, then filled it back up to dilute out the Sea Foam in the gas tank.

This achieved the intended purpose of ending the ticking noise from the engine, but seemed to have caused other issues (more on these in a moment).

After refilling the tank, I ran about half the can of Sea Foam Spray into the intake. Again, the engine seemed to struggle but likewise seemed to come back to life a bit after the spray was stopped.


---SYMPTOMS---
-When the engine is cold, it runs a little bit rough.

-Engine-braking while the engine is cold causes backfires. I adjusted the carb from RICH-2 (the setting recommended by the carb rebuild kit) to RICH-1. This reduced the frequency and severity of the backfires, but did not stop them completely.

-Occasionally while in the range between cold and warmed-up, the engine stutters in kind of a syncopated rhythm and loses most of it's power. Holding down the gas pedal partially compensates for the loss of power and allows for driving to continue, but it produces a strong smell of rich exhaust.

-Avoiding engine braking almost completely prevents the stuttering, but it still happens from time to time.


---MY THOUGHTS---
It seems that under circumstances related to engine temperature, a certain amount of fuel passes through the engine unburnt. The temperature-dependence suggests to my untrained mind something to do with the choke (and therefore carburation in general), but the only thing I can think of to explain the symptoms in terms of the carb would be the notion of it being adjusted too rich. However, when the carb was rebuilt and running at the recommended setting (RICH-2) it was fine until the Sea Foaming.

The other thought that occurred to me was a problem with the spark plugs. If the question of temperature was left out, I could almost convince myself that it made sense. But I'm not seeing how the effectiveness of the spark plugs would be affected by the engine temperature, and certainly not only while it was between cold and warmed-up.

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Unread 05-17-2013, 07:49 PM   #2
Fradyak
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1986 CJ7 
 
Join Date: Aug 2010
Location: Jackson, NJ, New Jersey
Posts: 9
My 86 never runs right when the engine is cold. I have disabled the computer for the carb, and installed an HEI distributor. It seems to be normal. Though check to make sure your choke is working right. Once I got mine working, it starts right up, and I just got to let it warm up until it idles down. Then I'm ready to go. In winter it sometimes take 10 minutes before I can drive it.
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Unread 05-18-2013, 04:53 PM   #3
UtahCJGirl
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1977 CJ7 
 
Join Date: May 2013
Location: West Valley City, UT
Posts: 25
I would check the float to make sure it is adjusted and there is also a possibility that the accelerator pump needs to be adjusted. There should also be a check valve ball under the pump plunger.
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Unread 05-18-2013, 08:26 PM   #4
gosupes
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1986 CJ7 
 
Join Date: Jun 2004
Location: Monroe, WA
Posts: 1,527
Quote:
Originally Posted by Fradyak View Post
My 86 never runs right when the engine is cold. I have disabled the computer for the carb, and installed an HEI distributor. It seems to be normal. Though check to make sure your choke is working right. Once I got mine working, it starts right up, and I just got to let it warm up until it idles down. Then I'm ready to go. In winter it sometimes take 10 minutes before I can drive it.
No, it's not normal. I let mine idle for a minute or so and I am good to go, even in the dead of winter.
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1986 CJ7, 4.2 w/4.0 head, TFI-HEI hybrid ignition, Clifford manifold w/Holley 390 w/cold air intake, OBA, 4.5" lift, Woody CV shaft and Tattons in front, 4.10 gears - lunchbox in front, Truetrac in the back, twin-sticked, blower upgrade for running topless, trying to keep it simple.

It's just a Jeep, and if you don't wheel it once in a while, it's not even that.
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Unread 05-19-2013, 05:37 AM   #5
86cj74.2L
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2004 WJ 
 
Join Date: Jul 2006
Location: Stouchsburg, PA
Posts: 6,337
Quote:
Originally Posted by gosupes

no, it's not normal. I let mine idle for a minute or so and i am good to go, even in the dead of winter.
+1
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