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Unread 10-21-2011, 05:10 PM   #16
mcmud
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1983 CJ8 
 
Join Date: May 2008
Location: N.E. Alabama
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Quote:
The reason I know it is leaking where the throttle linkage comes out of the carb, is that when I spray carb cleaner directly in that spot with the red spray tube the motor will attempt to stall. This explains why my air/fuel screws can be turned all the way in and not greatly affect how it runs (which it normally would in the past).
The only explanation here is that the throttle rod/shaft bore leaks. All carbs, new or old, will have reaction if you apply carb cleaner directly to the bore at the throttle shafts. Had you sprayed an adequate amount of carb cleaner into the throat onto the throttle plates fluid would have spilled from the bore.
The air leak at the shafts will not cause added fuel to enter the throat, to the contrary, it will cause a weakening to the mixture and a rather uncontrolled increase in the engine speed. While your mixture screws had little to no effect it is because ample fuel was being pulled by the plates from the wrong location.

Quote:
The question is, is why when I hit the bump in the road did this happen?? I can't answer that at this time, but I do not believe in coincidences....
The bump may have caused the float to become unsettled, causing a temporary rich bog or the throttle/accelerator linkage to bind, possibly the throttle rod rested in the wrong side of an oblong wear at the bore. While the throttle plate was/is bound open or possibly an aftershock adjustment caused you to set the speed screw to far in. This setting allows fuel to be drawn from the enrichment circuit... so much that the engine will idle and run albeit rather uncontrolled without having the flow of the curb idle mixture via the mixture adjustment screws, at the proper holes... located beneath the plates.

In afterthought it might be possible that a missing throttle return spring may cause the throttle to not return as it should but unless there is some hindrance to the free movement to the accelerator linkage this is unlikely since the throttle shaft return spring would be be sufficient otherwise.

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Unread 10-21-2011, 07:58 PM   #17
4.7stroker
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If you have a carb shop local they are quite capable of re-bushing the throttle shaft and it isn't that expensive either.

Dwayne
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Unread 10-22-2011, 06:56 AM   #18
paintguy
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ok mcmud, thank you for the reply and info -- I only have one spring on the throttle linkage? I believe I am missing the return spring -- does anyone have a pic of their throttle linkage set up that I could reference?
So mcmud, if there was an air leak where the throttle shaft exits the carb, it would make it run lean not rich? would'nt that leak cause excess air in the intake therefor increasing fuel intake making it run rich and therefor making the engine run with the air/fuel screws turned all the way in?
Thank you!!

the one spring i have is the return spring -- I don't think that is my problem. I am running wicked rich -- I checked the float and needle and cleaned the bowl. i am not understanding mcmud about your description of fuel entering from some other location inside the carb therefor making the air/fuel screws to have very very little effect when turned in or out...??? What would make the carb run rich if the float/needle is not hung-up or out of adjustment?
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Unread 10-23-2011, 09:14 AM   #19
paintguy
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Where is the powervalve located? Is it on the front of carb bottom?
Also, I left it in the garage for a few days to clear my mind on it, and this morning i started it up and it ran and idled fine until it got up to normal running temp and then the idle lopes -- hi then low then hi..etc. and I can turn the air/fuel screws all the way in with no affect? I am not idling it high when experimenting with the air/fuel screws either -- this would make me believe it is running rich somehow?
Thank you for all your input so far -- I am going to go pull a few plugs (new autolites) and bet they are black?? She runs great on the road though?? good acceleration exept maybe a slight hesitation when up to normal op. temp. when I pick back up the throttle.
Thanks!!
Yup -- pulled a few plugs and they are black (not wet but dry black) -- also, after driving, exhaust smells awful -- like too much fuel in cat and makes that sulfur smell??? What would have failed in the carb for it to run rich?
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Unread 10-23-2011, 09:43 AM   #20
johnny27030
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The best thing to do imo is go to the autoparts store and buy a carb kit. It sounds like you are constantly pulling fuel through your main jets hence the air and fuel mixture screws make no diffrence. This is prob caused by float adjustment or needle and seat having trash in it. I cant remember.....is this a powervalve carb? If so that could also be a problem. If it were mine I dont like to put bandaids on carbs. Once you pull the carb and disassemble you may be surprised at how simple the answer is. Oh and btw all the carb kits ive seen have a nice parts diagram and installation and setup instructions for that particular carb
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Unread 10-23-2011, 12:10 PM   #21
mcmud
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Quote:
Originally Posted by paintguy View Post
So mcmud, if there was an air leak where the throttle shaft exits the carb, it would make it run lean not rich?
True.

Quote:
would'nt that leak cause excess air in the intake therefor increasing fuel intake making it run rich and therefor making the engine run with the air/fuel screws turned all the way in?
No.
While the mixture screws are set closed (in), at idle, the only way the engine can receive fuel is by drawing from the transition slot.... a throttle plate that is opened too far is allowing/causing that flow.

Quote:
the one spring i have is the return spring -- I don't think that is my problem. I am running wicked rich -- I checked the float and needle and cleaned the bowl. i am not understanding mcmud about your description of fuel entering from some other location inside the carb therefor making the air/fuel screws to have very very little effect when turned in or out...???
Perhaps this photo will help. On it you will see the hole in the bore that is below the plate, this is the idle mixture hole, typically you would see the tip of the mixture screw extending through it.

The slot is the enrichment/slot.
As the throttle plate sweeps past, fuel in the channel which feeds the enrichment/transition circuit is drawn to the depression in the intake.
If the throttle plate is set where any portion of this slot is exposed... it flows.

The dashed red line indicates how the plate should rest... below the slot.

Quote:
What would make the carb run rich if the float/needle is not hung-up or out of adjustment?
The allowance of fuel is much greater at the enrichment slot than at the idle mixture hole while the mixture screw is trimmed to spec.

On the subject of the Power valve, this jet feeds a supplemental channel to the main circuit (boost venturis) and there is flow at that nozzle only while there is sufficient air velocity at the boosters. In order for this flow to occur you would have had to open the plates well beyond the transition slots.

If the float is stuck this would cause a taller fuel level (head) in the bowl, which would allow the boost venturis to tip in at a much lower rpm than is designed.
Still the throttle plates would need to be opened to allow enough air to pass in order to cause it.

Check on the position of the throttle plates, maybe disconnect the accelerator cable to see if it is causing the throttle lever to rest unclosed.

Possibly the idle speed screw is set too deep, back it out so that it's tip looses contact with the stop and verify that the throttle lever(that part which the accel cable/rod is attached to the throttle shaft) doesn't move more toward the closed position when rotational pressure is applied to it.

I thought that I read where you've pulled this carb in favor of another, is the carb with the issue mounted to the vehicle?
barry-grantt-27slotpositionbs.jpg  
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Unread 10-23-2011, 07:52 PM   #22
paintguy
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Yes, mcmud, my mc carb is still bolted to the vehicle. Thank you for the answers to my questions and the great pic -- i will check and make sure the throttle plate is seating properly.
Thank you!
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Unread 10-24-2011, 10:03 AM   #23
paintguy
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mcmud, my throttle plate seems to be closing properly -- though, how do I really know this other than I can hear the metal on metal sound when it closes as long as the choke is not engaged? I did disco the throttle shaft from the linkage to make sure it wasn't hanging up.
I definitely have a leak at my throttle shaft on the throttle linkage side (driver's side) -- I saw fuel leaking from it this morning. Would this cause any of my symptoms: loping idle, running too rich, very little response from air/fuel idle screws? I believe it would explain a loping idle and the ineffectiveness of my air/fuel screws but not the running rich right?!! Arghhhh!!
Thank you!
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Unread 10-25-2011, 07:52 PM   #24
mcmud
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Quote:
Originally Posted by paintguy View Post
mcmud, my throttle plate seems to be closing properly -- though, how do I really know this other than I can hear the metal on metal sound when it closes as long as the choke is not engaged? I did disco the throttle shaft from the linkage to make sure it wasn't hanging up.
One sure way is to pull the carb... the other way is to be sure that the idle speed screw is backed out away from the stop and be certain that the fast idle screw is not in contact with the fast idle cam, then apply rotational pressure to the throttle lever toward closed.

Quote:
I definitely have a leak at my throttle shaft on the throttle linkage side (driver's side) -- I saw fuel leaking from it this morning. Would this cause any of my symptoms: loping idle,
Yes
Quote:
running too rich,
NO!
Quote:
very little response from air/fuel idle screws?
Maybe a tad.

Quote:
I believe it would explain a loping idle and the ineffectiveness of my air/fuel screws but not the running rich right?!! Arghhhh!!
Thank you!
The air leak weakens the mixture.
Running rich is due to an over abundance of or uncontrolled flow of gasoline.
This may be the result of a float set too high, an open throttle plate and thus a premature flow from the transition circuit or possibly a flow at the nozzle. A busted diaphragm at the PV could cause this... at any time the throttle plates are open.
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Unread 10-25-2011, 10:18 PM   #25
Alabamaranger
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You have to remove the carb to get the power valve, but under a small 4 screw cover on the bottom front of the carb is a valve that screws into the carb. It is meant to be activated by vacuum and closed by vacuum at idle and cruise. It enriches the fuel mixture once vacuum drops to a preset value. That's for higher load conditions needing more power and a richer mixture. If you remove the cover and gas comes out, the valve needs replacing. As well, you can unscrew the power valve and make sure the diaphragm holds vacuum and the needle moves with suction from your lips. Replace if it leaks vacuum. If it leaks it will add way too much gas to your engine when it doesn't need it and your idle mixtures screws will be useless.


at 1:32

Here is some info I wrote years ago (pdf)

http://www.google.com/url?sa=t&rct=j...8pKXPA&cad=rja
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Unread 10-25-2011, 10:20 PM   #26
Alabamaranger
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Float Set

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Unread 10-26-2011, 04:32 PM   #27
paintguy
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Thanks Alabamaranger and mcmud -- I will be taking the carb off soon, and will inspect the throttle plates to ensure they are closing fully and the pv diaphram for leakage -- I do have a spare rebuilt mc2100 with a leaking throttle shaft bushing and the pv is new -- do the 2100 and the 2150 use the same pv?
Also mcmud, at idle the throttle plates should be fully closed right? or, are they always open a hair (depending on how high or low the idle is set)?
Thank you!!
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Unread 10-26-2011, 05:58 PM   #28
mcmud
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Quote:
Originally Posted by paintguy View Post
......Also mcmud, at idle the throttle plates should be fully closed right? or, are they always open a hair (depending on how high or low the idle is set)?
Thank you!!
Yes they must be set so that idle quality air will pass between the edge and wall of the bore.

Position the plates so that zero portion of the transition slot is visible, record that screw setting so to strive not to exceed it once it is mounted. This may require a bit of trimming (outward with the screw) so that a reasonable idle speed can be had with the mixture screws allowance added to the air passing the plates.
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Unread 11-04-2011, 02:14 PM   #29
paintguy
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I finally got time to replace the power valve and it took care of my rich condition -- now I have to decide weather or not to find someone to rebush the throttle shaft, or by a NEW carb -- meaning a Redline Weber....any thoughts anyone?
Thank you All for helping me solve this issue!
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Unread 11-04-2011, 02:29 PM   #30
Jax89Jeeper
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Quote:
Originally Posted by paintguy
I finally got time to replace the power valve and it took care of my rich condition -- now I have to decide weather or not to find someone to rebush the throttle shaft, or by a NEW carb -- meaning a Redline Weber....any thoughts anyone?
Thank you All for helping me solve this issue!
The weber carbs are more of a PITA to get tuned properly, the MC is the better of the two.
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