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Unread 04-29-2015, 09:19 PM   #1
boduke5051
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1990 YJ Wrangler 
 
Join Date: Oct 2014
Location: Jenks, Ok
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small hiccup type backfire on decel after nutter

Nuttered the Heep tonight after work. Overall, quite an improvement! Starts great, smoother idle, definitely seems to have more acceleration.

Couple small concerns though. The Nutter threads i followed showed to set the timing at 8 degrees, plus our minus 2. Mine seems happiest at about 12 degrees which is outside that range.

It seems to now have a small rumbling backfire on decel like when i let off the throttle to shift. Most noticeable when shifting from first to second. Or when downshifting to drop some speed.

Also, it used to have a pretty bad flat spot when i really got in the throttle to accelerate while already moving. It had gotten better, but it's still there just a little bit.

Anyone have any suggestions?

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Unread 04-30-2015, 02:47 AM   #2
dancytron
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Do you have manifold vacuum or ported vacuum hooked up to the vacuum advance? If you have it on ported, try changing it to manifold. Might end up putting main adjustment back closer to 8 degrees.

Then adjust the vacuum advance on the distributor. (Search for a thread on how to do it. You just put an allen wrench through where the vacuum advance tube hooks up).
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Unread 04-30-2015, 05:06 AM   #3
Mike Romain
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I have mine set at 9 or so on ported advance and when I decelerate down a hill it will burble and pop a little, something like the old muscle cars use to sound like. I have seen some engines that liked over 10, but I am/was close to sea level. Higher altitudes like a bit more.
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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
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Unread 04-30-2015, 07:16 AM   #4
boduke5051
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@ Dancytron: It's on ported right now, I'll play with it at lunch and see if the manifold vac port makes any difference. I'll also look into adjusting the vac advance when I get home tonight, forgot to grab my allen set before I left the house this morning.

@ Mike Romain: your description of the sound is a better one than my hiccup. It is a little bit of burble/pop. My wife was saying last night when I came home from my test run that it almost sounded like a motorcycle when I'd let off the throttle, lol. I checked my elevation, according to Google Tulsa is only 722 feet so I'm thinking 12 degrees might be a bit much.

Couple of other bits of information: Coming in to work this morning, I didn't notice the burble/pop at all. Only thing different from last night that I can think of is that it was probably in the low 70's when I was making my test runs last night, and this morning it is currently low 60's.

Also I noticed something strange when I was doing the nutter last night. The orange/purple wires were right where I expected to find them on the firewall from the distributor, but on the harness side of the plug that goes from the firewall to the ICM there was no wire that was connected to the purple wire on the ICM side of the plug. I happened to have a small crimp on style socket connector from an old job, so I crimped it on, and soldered it, then put it in that empty 4th hole on the harness side of the plug.

Sorry for the cruddy pic, it didn't look as flash blinded on my phone.

icm-plug.jpg
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Unread 04-30-2015, 08:21 AM   #5
Mike Romain
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You are correct on the purple wire, it only goes to the ICM plug and stops. The ECM was controlling the advance before, now it is direct.
Did you get your stepper motor pins centred? The should show 1/8" of shaft before the taper starts. This affects the final mix and gas mileage. Full in is full rich, full out is full lean. The ECM tried to keep them centered.
Edit: your photo finally showed up on my phone app, I see you have no stepper motor on that Weber. :-)
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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 04-30-2015, 08:55 AM   #6
boduke5051
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Ok, good deal. I must have missed that when reading the threads. I was concerned that I might have screwed something up by adding that connection. Thank you for the info!
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Unread 04-30-2015, 09:06 AM   #7
Mike Romain
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Quote:
Originally Posted by boduke5051 View Post
Ok, good deal. I must have missed that when reading the threads. I was concerned that I might have screwed something up by adding that connection. Thank you for the info!
Also to prevent misfires, the orange and purple wires should be twisted together all the way along to prevent RF interference.
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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 04-30-2015, 09:16 AM   #8
boduke5051
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That part I caught, and did twist them. Had my boy hold one end while I spun the other end with my drill.
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Unread 04-30-2015, 09:34 AM   #9
boduke5051
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Something else that I just thought of. I wonder if the carb may need some readjusting now. The P.O. had just put it on there when I got the Jeep, and said he had a really hard time getting it adjusted right. One of the first things I did to it was replace the ICM because it was having a really hard time starting in the mornings.

So I wonder if the combination of a weak ICM and Nutter not being done was the cause of him having a hard time setting the carb, and might mean that the carb is not set correctly now that everything else has been fixed?
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Unread 04-30-2015, 10:50 AM   #10
boduke5051
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Ok, went out and played with it some more at lunch. I've decided the problem was the nut behind the distributor wrench (namely ME)!

Was in the middle of doing the Nutter when I got a phone call about some family business that wound up putting me in a fairly foul mood, and apparently I wasn't thinking clearly.

When I set the timing, I forgot to pull the vac line off the distributor and cap it. So it was still running the vac advance while I was setting the timing. No WONDER it didn't want to set right!

Disconnected and plugged off that line this time, set the timing right at 8 degrees, purring like a kitten now. The burbling is still there, but just barely. I only heard it once about a half mile into 10 mile test run. Thought I might have heard it faintly on a downshift after that, but it was almost unnoticeable. Ran it for about 3 miles worth of ground streets, and about 7 worth of highway to get back to work, runs great!

Thank you guys for all the help!
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