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L134 Won't Idle Without Choke

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ggordon49 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ggordon49 Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep. 2018 at 7:18pm
This is a silly question I know, but have to ask.... Did you cap the wiper connection? Appears open in your pic.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote DonH Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep. 2018 at 7:36pm
You have to make your final adjustments to the carb with the air cleaner connected so the PCV system can meter the air properly. The fact that the engine can run properly with the PCV blocked indicates that the PCV system is the cause of the problem. The PCV valve could be faulty. The line from the valve to the valve cover could leak. The gasket at the cover could be leaking.  The crankcase must be properly sealed for the system to work properly and this includes the valve cover gasket and the gasket at the oil filler tube cover and the hose connecting the oil filler tube to the air cleaner.

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Mike F View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike F Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep. 2018 at 8:17pm
Larry 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep. 2018 at 9:33pm
Vacuum reading is dependent on elevation, and would be what you are getting at 4000' or so above sea level.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike F Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep. 2018 at 10:49pm
Larry,
 
Please feel free to elaborate or correct me if I'm wrong. 

PCV valves are pretty simple yet mysterious things.  Before PCV valves an engine had a draft tube to vent the engine  then some engineer came up with a PCV valve.  Their function it to allow blow by exhaust gasses to be drawn into the induction stream in a controlled manner and burnt off.  They are basically a plunger in a tube with seats at both ends and a couple springs that hold the valve partially open under low vacuum.  In operation an engine will have high vacuum / low crankcase pressure at idle the valve will be closed.  As the engine speed increases vacuum decreases (due to the opening of the throttle body) and crankcase pressure increases (due to more stuff blowing by the rings). As this happens at some point the vacuum and crankcase pressure come closer to an equilibrium and the spring pressure opens the valve.  This allows the crankcase gasses to be drawn into the intake stream.  when the engine slows the pressure / vacuum balance goes back to the vacuum and the valve closes.  This will happen even at idle anytime that crankcase pressure + increases to equal intake vacuum -.

So in operation you end up with hot corrosive gasses passing through a valve that is almost closed.  As this happens the gas stream, is corroding and depositing stuff on the seat faces of the valve.  eventually the valve is so corroded and or carboned up it can no longer do what its supposed to do and you have a vacuum leak at idle when the valve is supposed to be closed.  sometimes one can simply clean the valve and in doing so restore it to a functional state.  Other times if the seat or springs are damaged restoring function will require resolution of these issues.  Springs are just springs and seats can be lapped so, one should be able to effect a reasonable repair. 
The interval at which this will happen is dependent on the state of the seal of the rings in engine.  In a new engine when the rings have yet to create a seal, or in an older worn out engine there will be more blow by.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lhead Quote  Post ReplyReply Direct Link To This Post Posted: 22 Sep. 2018 at 4:38pm
Ggordon, yes the vacuum port is blocked. What you see in the picture is a barged fitting that I use to connect the vacuum guage to. In that picture it has a cap on it.

DonH, thanks for the tips. It doesn't seem like the air cleaner system would offer much resistance but I guess its enough to warrant tweaking. I saw on another thread that someones jeep wouldn't run with the air cleaner attached.

TERRY, I'm at about 1600' elevation near San Diego. I'm not sure what the vacuum should be in the engine but it is all new so I would expect more that 17-18 in.

Mike F, thanks for the good stuff on PCV valves. As I mentioned earlier, I disassembled the PCV valve, cleaned (sand blasted) all the parts and reassembled. There is very little to go wrong if clean. However, there is a hole through the middle of the "plunger" that would equate to a constant vacuum passage even with the valve "closed". 

I'm still working on the assumption that my total vacuum is too low and with the PCV valve connected there isn't enough vacuum to pull the mixture through the carb without some choke. I'm just at a loss as to why my vacuum is so low.

Thanks all!

Larry...


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lhead Quote  Post ReplyReply Direct Link To This Post Posted: 22 Sep. 2018 at 4:41pm
Here is one more thought on the vacuum issue. The engine is essentially new so isn't really broken in. Most of its running has been at idle or so. it might have a total of 3 miles driving.  I'm thinking of disconnecting the PCV valve for awhile and driving the jeep for awhile to break the engine in better. Maybe that would product more vacuum then I could reconnect the PCV valve.

Thoughts?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SteveBonny Quote  Post ReplyReply Direct Link To This Post Posted: 22 Sep. 2018 at 5:41pm
Originally posted by Lhead Lhead wrote:

Here is one more thought on the vacuum issue. The engine is essentially new so isn't really broken in. Most of its running has been at idle or so. it might have a total of 3 miles driving.  I'm thinking of disconnecting the PCV valve for awhile and driving the jeep for awhile to break the engine in better. Maybe that would product more vacuum then I could reconnect the PCV valve.

Thoughts?

Seems a bit of a stretch.  I doubt it will fix itself by adding hours but should do no harm to try and driving may help to find more symptoms.   The PCV test seems to indicate you still have a measurable leak somewhere.....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lhead Quote  Post ReplyReply Direct Link To This Post Posted: 22 Sep. 2018 at 6:00pm
Thanks Steve. I agree that it's a stretch but there isn't much downside to trying it. On the upside, even if it doesn't help the vacuum problem, at least I got a few miles having some fun!

Next step after that.....intake manifold comes off.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SteveBonny Quote  Post ReplyReply Direct Link To This Post Posted: 22 Sep. 2018 at 9:31pm
Haha, I agree, sounds like a good excuse for a road test!  A guys gotta have fun.......
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike F Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep. 2018 at 12:34am
If you sandblasted the seating surfaces in the PCV valve it is not likely to seat properly. They need to mate to make a seal. I have never been  able to get my original one apart to know what it looks like.   If you run the engine without the system it place you should provide some sort of vent for the crankcase. Otherwise pressure will build up and bad things will happen. If you have over 100 psi cranking compression your rings are doing their job. I would just pickup a PCV valve from your local auto parts store and plumb it in the system. It will work until you can find a proper replacement 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SteveBonny Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep. 2018 at 12:41am
The crankcase would still be vented at the filler tube, so it should be OK.   I'm not sure all PCV valves are created equal either so a valve picked at random may have different orifice / cracking pressure etc.
I think you make a fair point though the sand blasting could have damage the valve seat creating additional leakage at idle when it is supposed to be closed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike F Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep. 2018 at 1:12am
Filler tube is supposed to have a gasket on it. However, the tube to the intake is open maybe allowing pressure and gasses to escape in to the intake. And onward into the carburetor.  I’m pretty sure a PCV valve is PCV valve but Steve may be right. If there is an option get one for something with a small motor. Just need one with hose barbs on both sides. And the direction of flow is right when you put it in. If I’m wrong, well your out out $10.00, I’m now an expert, and we are all a little further advanced in our education.  In that we know what doesn’t work. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lhead Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep. 2018 at 4:26am
Good input guys. I'll try a couple of things. I have a PVC from and old CJ2 that I'll try. I'll also try an temp one. Re: the gasket on the filler tube, I do have one, but it seems to me that the big tube going from the crossover pipe (carb to air cleaner) into the filler tube pretty much makes the gasket irrelevant. I guess the whole thing has to work as a system so I'll put the air cleaner on and connect everything as it is supposed to be and see how that works.

Larry...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ol' Unreliable Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep. 2018 at 6:02am
Just a note about the distributor rotor being off 180 degrees: The part of the distributor that the rotor fits on can be installed 180 degrees off.  It's easy to install incorrectly (voice of bitter experience).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Unkamonkey Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep. 2018 at 6:25am
Originally posted by Ol' Unreliable Ol' Unreliable wrote:

Just a note about the distributor rotor being off 180 degrees: The part of the distributor that the rotor fits on can be installed 180 degrees off.  It's easy to install incorrectly (voice of bitter experience).


Just what do you do Ol'Unreliable? I seem to see you here a lot this time of night. My excuse is that I have Insomnia and I read too much. I have done Jeeps for 50 years. If you read some of my replys, I don't actually give them an answer, even if I know exactly what it is. I just tell them where to find it themselves. Why not, I figured it out? I must have a touch of teacher in me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SteveBonny Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep. 2018 at 2:58pm
On the side of the oil filler tube there is a line connected to the air filter crossover tube.  The crankcase is always open here whether the filler tube has a gasket or not.
This system is supposed to be sealed (except the air filter inlet).   The manifold vacuum sucks crankcase gas in through the PCV which is connected to the crankcase.  Clean air into the crankcase comes from the air filter through the line into the dipstick tube.   If  you plug off the PCV the gas will get pushed from the dipstick tube into the crossover tube from the air filter.   Only down side is you may get some oil film in the crossover tube.
I think originally this system was fitted to military vehicles to seal them off from water into the engine.   You can submerge the engine and not have water going in through an open crankcase vent.  Later on it was applied to many car engines as an improved method of venting crankcase gases and preventing contamination of the oil.  My 2 cents!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DonH Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep. 2018 at 6:17pm
Here is an explanation of how the PCV system works and the components involved complete with pictures and diagrams:


DonH




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