Weber carb help - JeepForum.com
 
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post #1 of 10 Old 08-12-2017, 07:24 AM Thread Starter
moparmagic
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1985 CJ7 
 
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Weber carb help

Many of you have probably seen some of my earlier post, but just a little back ground. I have a 85 jeep cj7 4.2, auto trans, headers and a weber 38dges on it. Not real sure what the PO has done and not done. It has the nutter bypass on it and the rush upgrade. I have been struggling to get it to idle without turning the idle screw in so far that it exposes ports causing the carb to drain when the engine is off. I have read all the info I can find on tuning and nothing seems to help. I have even drilled the throttle plates( not sure if I did something wrong but seems to have made matters worse). I'm either thinking of replacing the throttle plates and trying a rebuild or replacing with a motorcraft 2100? Can you replace the throttle plates? If so where can I buy them? Any suggestions? I don't have a lot of money available at this time to put in it. Looking for a cheap fix if that's possible. I have seen the carb kits on ebay but I don't have 300.00 to put in it right now!

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post #2 of 10 Old 08-12-2017, 07:43 AM
swatson454
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Are you at least at 12* initial timing and manifold vacuum to the distributor?


Shawn

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post #3 of 10 Old 08-12-2017, 09:07 AM
stripperguy
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What intake manifold do you have?
What size hole(s) did you drill?
Do you have manifold vacuum for your distributor? If so, does the rpm rise when you disconnect the vacuum line?
Do you know the idle jet size? (they're clearly marked, only takes a minute to pop them out)

1977 CJ5 is a CJ build ever really done?
2002 TJ gone
2005 TJ also gone
2005 LJ insurance wreck
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post #4 of 10 Old 08-13-2017, 04:13 PM
NittanyGen
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Quote:
Originally Posted by swatson454 View Post
Are you at least at 12* initial timing and manifold vacuum to the distributor?


Shawn
At least 12*? I thought it was supposed to be 8 or 9? I only ask because I have same carb and have issues as you know. Why should it be 12 degrees?

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post #5 of 10 Old 08-13-2017, 06:24 PM
swatson454
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He needs all the help he can get to keep the rpm from dropping too low when he puts it in Drive.


Shawn

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post #6 of 10 Old 08-13-2017, 11:07 PM
whollsee
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10* +/- 2* for auto on my engine bay decal and that is without mods remember. 12* works very well for me with mods.

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post #7 of 10 Old 08-14-2017, 01:03 AM
BagusJeep
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Quote:
Originally Posted by moparmagic View Post
85 jeep cj7 4.2, auto trans, headers and a weber 38dges o - nutter bypass on it and the rush upgrade. - I have even drilled the throttle plates
Sounds like a good setup, no need to replace anything on there. The hole in the throttle plate can be soldered back up if you need to, no big deal or cost. However, unless it was a gigantic hole, it is unlikely to be your problem.

You need to start with the basics of an idling engine first and check the real ignition timing (the timing marks have to be verified by measuring piston movement, do not ASSUME they are right as they can shift). Then check for vacuum leaks, they can cause all sorts of issues. As it is a 1985 it came with yards of leak prone hoses, sort out what you have and then DISCONNECT IT, except for the connection to the distributor vacuum advance you may want to try with all vacuum ports plugged, also check around any adapter under the carb. I have had these leak as they are sometimes not totally flat.

Now check your idle jets for size, something around a 50 or 55, if they are in the ball park it should idle without any opening of the throttle butterfly.

One good tool for setting up the idle is a vacuum gauge, it may give you some idea what is happening inside the manifold. You can also connect it to the port just above the throttle to verify it is shut, you will have a little vacuum as you have a hole in the butterfly but it is really important to make sure the butterfly is below the progression hole i.e. shut or almost shut.

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post #8 of 10 Old 08-14-2017, 05:25 AM
whollsee
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Quote:
Originally Posted by BagusJeep View Post
One good tool for setting up the idle is a vacuum gauge, it may give you some idea what is happening inside the manifold. You can also connect it to the port just above the throttle to verify it is shut, you will have a little vacuum as you have a hole in the butterfly but it is really important to make sure the butterfly is below the progression hole i.e. shut or almost shut.
A little vac may not hurt at all. I did worry that holes in the butterflies would still see vacuum at idle even if progression holes are covered. Not so. Getting a 0" reading at idle when I finally got to checking last weekend- with 1/8" holes. Blip up to 6" on revs then straight back to flat. I think Stripperguy on his tuning thread reported the same. Perhaps... if the prog orifi are covered by the edge of the plates then the S-port is sealed off regardless.

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post #9 of 10 Old 08-14-2017, 06:04 AM
swatson454
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I agree: holes in the throttle plates won't pull a vacuum on the s-port.


Shawn

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post #10 of 10 Old 08-14-2017, 06:17 AM
stripperguy
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Where did you go Mr mopar (or is it Mr maggic)??
I can't speak for everyone, but I'm anxiously awaiting your tuning results...

1977 CJ5 is a CJ build ever really done?
2002 TJ gone
2005 TJ also gone
2005 LJ insurance wreck
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