Vacuum, RPM, and Carb Tuning - JeepForum.com
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post #1 of 47 Old 11-18-2015, 02:54 PM Thread Starter
bluwavguy
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Cj Vacuum, RPM, and Carb Tuning

On a recent post I had a lot of good feedback and hoping to hear more.

Following JeepHammers post I upgraded the larger distributor and rotor. The Accel 8mm wires were brand new so I kept them on (I can buy the MSDs if required). Installed a new Borg Warner Coil as well. Installed a vacuum gage and tach.
I've rot re-routed the ground wire as suggested but going through my wiring this week.
Installed a new vacuum line from the distributer vacuum advance port to the carb.

Carb Tuning the New Holley 2bbl.
I set the float level (as per JeepHammer) just below the sight. Closed off the two fuel/air idle screws and slowly opened the engine side then matched the opposite side. Not more than 1/2 turn each. a minor turn is a major change in rpm/vacuum.

So my vacuum is about -12 to -13in.hg. and rpms are about 1100. That's the lowest setting I can achieve.

Ok, what bothers me is that I cannot get a lower RPM setting, I don't think my timing is off (I don't have a timing light but parked the engine sounds great when rev'd up). But at lower RPMs the engine seems to run a little rough.

I'm considering replacing the electronic ignition module (it looks as it may be the original unit).

Any help would be great.
Thanks in advance. Brian

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post #2 of 47 Old 11-18-2015, 03:24 PM
Matt1981CJ7
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Brian,

I suggest you buy, or rent, a timing light. Carb tuning without the proper timing is a waste of time.

Also, your vacuum is very low, assuming your cam is stock. If 12-13" is the best it'll do, I'd start hunting for a leak.

Matt
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post #3 of 47 Old 11-18-2015, 03:33 PM
orange150
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FWIW, I'm sitting between 20" & 21" of vacuum.

I'm curious how that 2bbl Holley works out for you.

'82 CJ-8
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post #4 of 47 Old 11-18-2015, 06:21 PM
Mike Romain
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Low vacuum and high idle imply a vacuum leak.

Mike
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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post #5 of 47 Old 11-18-2015, 06:48 PM Thread Starter
bluwavguy
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Matt will do so or take it to my friend's commercial mechanics shop.

Orange150. In 2x2 she runs great in 1&2nd gears...depending on the grade 3rd and 4th are sluggish. In 4x4L the carb performs great in all gears...I'll be posting more as I get this sorted out. If I had a clue what I was getting into I may not have gone from the PO's older 500cfm holley to the new 350cfm street avenger.

Mike...OK, as far as the vacuum and possible leak.
Here is a listing of the lines to carb
1) Distributor (new line and clamps)
2) Valve Cover (original line and no clamps which I'll rectify tomorrow.)
3) New Vacuum Gage (sealed all threads with yellow teflon tape on the vice)
where else should I look for vacuum leaks?
So, just to understand...I should have an idle rpm of around 1000+/- and vacuum of around 20".
Of course when I throttle the carb the vacuum jumps towards 0 then to +20 easily...

Lastly, I'm going through all of the ignition,alternator, solenoid, electronic module wiring....the electronic module is ancient with the insulation (its turned to gel) dripping down the fender...I cannot help but change this out once I find one...

Thanks guys...Brian
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post #6 of 47 Old 11-19-2015, 05:12 AM
Mike Romain
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Goo leaking out of the ICM is never a good thing, it implies overheating and upcoming failure. This can be caused by just leaving the key in run with the engine not running.
You can use something like carb cleaner or even WD40 and spray around the base of the carb and along the intake runner to see if the idle changes. You should be able to idle down to 700 or lower.

Mike
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.
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post #7 of 47 Old 11-19-2015, 09:49 AM Thread Starter
bluwavguy
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Mike and others.
I plugged the valve cover inlet to the carb, re-adjusted the idle mixture, and added a heavy duty throttle return spring (this is why my idle was so high).
Vacuum is around 17" and RPMs around 900. At one point the RPMs were down to 600.
Have yet to connect a timing light.
Ordered a new ICM and pickup coil. So at least my ignition will be fully refurbished with new parts for the exception of replacing the distributor.
Test run was decent going up the hill and no backfire on the downgrade.
Question is now what to do with the valve cover vent line?
Thanks Guys...
Brian
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post #8 of 47 Old 11-19-2015, 10:25 AM
Matt1981CJ7
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Wait, what "valve cover inlet to the carb"? Are you talking about the PCV valve? That should remain connected.

Matt


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post #9 of 47 Old 11-19-2015, 06:24 PM Thread Starter
bluwavguy
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Matt, its the 3/8" vent line from the valve cover (which has two ports of which I've capped one), and the 2nd is connected to the carb port (closest to the firewall).

Actually, I've reconnected the line but need to clamp it on both sides.

I don't think I have a PCV valve anywhere....the PO was in progress of rebuilding the CJ when I bought it so I'm not sure what is required.
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post #10 of 47 Old 11-20-2015, 05:06 AM
Mike Romain
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The front hole in the cover needs a PCV valve on the hose or the carb won't work. The back hole is an air intake that needs an air filter on it or to be hooked to the stock air filter.
This is your crankcase venting system.

Mike
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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post #11 of 47 Old 11-20-2015, 07:23 AM Thread Starter
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Mike, thank you. I'll locate the appropriate parts to set this up.
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post #12 of 47 Old 11-20-2015, 09:15 AM
John Strenk
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A vacuum line from the valve cover to the carb without the PCV would of been a much bigger vacuum leak than just 12".

But there is nothing to clamp it to on the valve cover so I'm thinking the PCV is there but you just don't recognize it...
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post #13 of 47 Old 11-20-2015, 11:28 AM Thread Starter
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John, for simplicity I'm attaching images of the system as is from a few min ago.

As shown the rear vent goes to the carb and the fwd vent is capped. The PO left it open to the air.
The second image shows the bottom of the air filter with no port.
1) Assume I need a PCV on the front vent line port to the bottom of the air cleaner
2) Assume the rear vent line stays connected to the carb port.
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2015-11-20 12.58.58.jpg   2015-11-20 12.58.06.jpg  
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post #14 of 47 Old 11-20-2015, 12:05 PM
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Maybe this will help. Heres the factory setup and some reading for you:

http://home.sprynet.com/~dale02/vac-pcv.htm

Matt
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post #15 of 47 Old 11-20-2015, 12:10 PM
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To clarify. You need a PCV valve, connected to manifold vacuum at the carb, in the front hole.

The rear hole is just a open fresh air intake to the PCV system. It either connects to the air cleaner or you can use a stand-alone filter.

Matt
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