M38A1 carburetor question

[oilleaker1]

Assuming the fuel pressure is right now, You may have too high a float level, or a vacuum leak with the idle mixture set high to make it idle. The # 1 leak point is the carb base gasket. I had to make paper gaskets for either side of the heat insulating block under the carb and put star washers under the nuts to keep it from coming loose. The PCV valve is located where the side ( valve) cover pipe vents and is a larger hexed body about 1 1/2 inches long. It has a sealing disc inside it like a check valve. Dirt interfering with the needle and seat assembly will also stop the float from regulating the fuel height in the bowl. Double check these first. Don't even think of useing silicone sealer. Gasoline and it don't match. It grows and thin thread of it to pencil size. Choke is open of course? Vent to fuel float bowl is open? Do you see gas leaking over anywhere? Idle circuit( where the needle adjusts the air mixture) in carb open and not blocked? I think you are close to finding the problem. Easy check for worn throttle shaft is to open the linkage a little and feel if it slops around in the throttle body. Air leaking here makes it rich too. It's got to be clean! More fun for you! John

[BigJim]

I think I am getting closer.I did not understand everything in your last post but I know it is not leaking gas anywhere and the choke is opening and closing as it should.I am gonna replace the pcv valve because I know it has not been replaced in at least the last 25 years that I have had it.I think the throttle body is ok.I will try and tighten the nuts where the carb mounts but I think it has a good seal there.It runs so good under power I just need to get it to idle then I will have it.Then I can move on to the job of painting it.Thanks for the help.Jim

[wesk]

# 5 is the PCV valve.

To the right is one of the two fording valves. Make sure this valve is open. If they are not you will have the type problems you are having.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[BigJim]

Thanks Wes.It boggles my mind the amount of info you guys have at your fingertips.I think that must be a part of the problem.I pulled off a line that went to the valve and left it open and cranked it up.I did not run it long enought to really get the engine warm but I did not smell those strong exhaust fumes like I normally do.I am going to replace the pcv valve I know it has not been done in at least 23 years.I am sure I will be reporting back in soon.Thanks again.Jim

[BigJim]

Couple more pieces to the puzzle.It appears that the previous owner made some modifications on that area.Section L on the diagram you sent has been completely removed and there is just a short piece of rubber hose that connects the pcv vallve to the elbow that comes out of the crankcase.That does not bother me particularly and it has run a long time like that so I assume that is ok.I will replace the pcv valve next.For now however I have it taken loose but in playing around with it I have noticed that if I keep the choke cracked open slightly it will idle way back and continue to run.It still idles rough and is still running rich when I do that but it sat and idled about 20 minutes without cutting off.I tried to tighten the nuts at the bottom of the carburetor and was able to turn them about 1/2 turn each.Then while it was running I sprayed carburetor cleaner all around the throttle body and all over the carb and did not notice any change in the engine speed.I have probably gotten it back to as good as it ever was but I know it will do better.I think I am getting closer.In the words of the great philosopher Chevy Chase"This is no longer a vacation this is a quest".I am gonna get this thing running right.Let me know your thoughts.Thanks again for all the good advise.Jim

[oilleaker1]

If you have to apply choke some to get it to idle, you are still not sending enough fuel through the idle circuit. This means your throttle plate must be open some with the stop screw and you are trying to run it off the main circuit. If you screw the idle screw ( needle) all the way out of the carb, does it run the same? If it does, it's blocked or plugged up. ( my next guess ) Carry on on your quest! Permission granted!

[oilleaker1]

If you find no change removing the idle screw, clean it's passage way of all blockages. Then screw it all the way in, and back out one full turn. Start the engine, slow it down with the stop screw to the slowest idle, adjust the idle screw for fastest idle, and then repeat until you get the slowest smoothest idle. Around 6-650 RPM's is where I like them. Strobe check your advance if you have the 24 volt plug wire adaptor, and run the timing light off a 12 volt seperate battery. Timing will throw off all the above. At 5 degrees BTDC your points should be just starting to break on # 1 cylinder when you are turning the engine over by hand to check things. This static timing check should put you within 2 degrees of spot on. If you have long hair, wear a stocking cap so it doesn't get caught in the fan belt! John

[wesk]

[BigJim]

One step closer.I think you were right about it running off the main circuit.I had the set screw screwed it in to keep the engine running at a high enough rpm so it would not cut off.That is why(I guess) adjusting the idle screw did not make any difference.When I screwed the idle screw out it did make a difference.It would have cut off if I had not put it back in.Then I determined if I screwed the idle screw way out(about 3 1/2 turns) it would idle on its own without the choke being cracked.I don't think that is the appropriate setting and it still runs very rough and very rich but it is running now.I am gonna put the pcv valve back in when I get a new one and get that buttoned back up and see what it does then.Also,many years ago I had a mechanic trying to correct this same problem and he took the little plug out of the very top of the carburetor and it seemed to run better so he put a fitting in there with a piece of hose and a small filter that is under the dash.I pulled it out and put my finger over the hole and it did not make any difference but I am gonna put the plug back in there and put the pcv valve back together and then try when everything is hooked up as it should be and adjust it again.I think I am closer than I ever have been but still not there.Why do you suppose it is running so rich.My wife just about kicked me out of the house when I came in and she said I should burn my clothes .I would but it might blow the house up the gas fume are so strong.I think if that were corrected it might smooth on out.Thanks Jim

[wesk]

That was the bowl vent he opened up and connected the hose to. When you plug that vent the carb will feed ok for several minutes but as a vacuum builds up in the bowl it will stumble and start running lean. Not the same issue you have now.

Try to keep the two adjusting screws sorted out in your head,. The idle speed screw and idle mixture screw are often mixed up. I find it helps to keep them seperate if you call the idle speed screw just the "speed screw" and the call the idle mixture screw just "Mixture" screw.

Now with both screws properly ID'd turn the idle mixture screw all the way in lightly till it stops. Now back it out 1 1/2 turns. Now turn the speed screw out until it no longer touches the throttle cam. Now have a helper start the engine while you operate the throttle under the hood. Once she starts make sure the choke is left wide open. Now try to find the lowest speed the engine will idle smoothly at without quitting. Hold the throttle very still at that point and now turn the speed screw back into contact with the throttle cam. At this point the engine should idle smoothly at around 500 to 650 RPM. This is the correct way to establish an initial idle speed and mixture.

Now let the engine warm to normal operating temp. Now blurp the throttle to it's mid travel point. Did the engine quickly respond and accelerate? If it stumbled significantly then enrichen the mixture a half turn and try again. If no change try one more half turn. If no change there is a problem with the accelerator pump. Return the mixture screw to it's original setting 1 1/2 turns out.

Now open the vacuum chamber for the accelerator pump and see if the diaphragm is in good shape and make sure the spring is between the diaphragm and the cover.

Let us know how things are going.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[BigJim]

Thanks Wes.I had posted some more info before I read your reply so check it out when you can.I did mean that I had to add a little choke to get it to idle but I have since gotten it to idle without having to add choke( see previous post).The vacuum leak is where I will go next.Since I am not using the old mechanical fuel pump I should be able to eliminate that.Other than just taking it all apart what is a good way to test for vacuum leak.Thanks again for all your help.I have learned more about that jeep in the last 3 weeks than I have in the 20 plus years I have owned it.

[BigJim]

Not familiar with what you are calling vacuum chamber and accelerator pump.I assume that is one of the side chambers on the carburetor is that correct.I thought I had read where the proper setting of the mixture screw(notice the correct terminology) was 1 1/2 turns out and when I had it set there the throttle response was excellent.It did not hesitate at all but would not stay running at idle.When I turned the mixture screw on out to about 3 1/2 turns it idles but still runs rough and rich throttle responce is still excellent.Would the vacuum leak cause that?Also since I now have the fuel pressure regulator installed what is the correct setting.I have it on about 3 1/2 lbs right now.

[wesk]

Propane enrichment is the simplest. You use a standard propane bottle and turn it on low but do not lite it. As you point the nozzle at suspect areas if there is a leak there will be an increase in engine speed. It is easiest to handle if you turn it on at each individual location you wish to test rather than leave it on all the time or while relocating to a different suspect area.

It not as hazardous as it seems. If by some freak chance the propane ignited you would then have a lit propane torch in your hand. No explosion. Just a lit torch that you will need to be careful where you point it until you turn the valve off.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[oilleaker1]

Another thing while you are wearing out the screws on the carburator, is check the condition of the side chamber diaphrams. If they are the old style, alcohol gasoline will destroy them. The new kits with the upgraded rubber are more resistant to the new crappy gas. I always run premium non-alcohol gas, but always wonder if the station is telling you the truth about whether they have what they say in the pump. Those vacuum supply tubes Wes talked about run around the front of the engine from the intake below the carb. I had to plug those off on mine when mine didn't run. Eliminate that with a test by plugging also. Blow up the house with your clothes!!!!! My wife hates exhaust smell also. Since your carb changed when you pulled the mixture screw, I'm leaning toward a vacuum leak or bad , cracked or holed diaphram. I enjoy working on your Jeep without doing it. John

[BigJim]

I am just glad I found someone who knows what they are talking about.I have gone down so many rabbit trails over the years from people who said they knew what they were talking about and did not.My guy at the local parts house was certain the pressure regulator would not help.He was wrong.Couple more questions(big surprise right).Can you take off those side chambers without taking the carburetor off the engine,and when you plugged the vacuum lines off did you leave them like that or was that just for a test.Thanks Jim