Posted: Tue Jan 15, 2008 6:41 pm Post subject: Fuel? Start Problems?
Maybe someone else has had this problem. My 38A1, if left a day or two without starting, won't kick off unless it has a squirt of start fluid. Then it will kick off with no problems the rest of the day. I had some water in the gas tank when I got it, so put a sediment bowl before the carb to catch water/trash. I can empty the glass bowl and cranking it over, the fuel pump will fill the bowl very quickly, but still doesn't want to kick off. I have set the needle adjustment with a vac gauge and when it runs, it runs great, so any guesses or knowledge on my problem? It isn't like this is my first M, as I have a 38, two 37s, WC53 and a GPW and none of these act like this. The carb is a new one, so any hints would be appreciated.
Thanks, guys.
Eric
When you say your carb is new are you saying you have a new NOS YS950S Carter on your jeep? Or do you have a rebuilt unit? Have you confirmed that the accelerator pump functions correctly? Have you confirmed your choke plate closes completely? Is your A1's vent and vacuum system stock? _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Wes, thanks for the reply. No, the carb is not a YS. I suspect it is for a CJ. Choke works properly, accelerator pump seems to be working okay. The whole jeep is stock except for the carb. All lines are proper in their respective places. What gets me is that all works properly after the initial kick off. Let that sucker sit overnight and you can crank the battteries down. I have the original YS, the guy I bought it from couldn't get it started and put the new carb on. (of course the fuel filter was stopped up and he didn't check that) so I will probably try putting the YS back on and see what happens. Thanks for the info...Eric
I'd look for a bowl leak on that carb. Or get her running and let her sit awhile then pull the top off the carb and see what is left in the bowl. I wouldn't run the sediment bowl downstream from the pump. It should be between the pump and the tank.
Is the engine otherwise healthy? Fat blue spark, good compressions and correct timing? _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Once it is running, it runs great. Compression check is in the ranges, had the timing light on it and all does as it should. Really pretty spark and will reach out there when you pull it back. Vacuum is good and steady. Will try pulling the top of the carb next time I am up where I have my farm.
Thanks..Eric
I've just joined today, so I'm excited to see that there are folks with some of the same 'A1 problems I've got!! I, too, have hard-start problems; I've rebuilt the YS carb, but I suspect vacuum- line problems. This jeep had had the various lines (vacuum, fuel, oil) replaced, and I'm not too sure all the vacuum lines are where they're s'posed to be!! Is there a vacuum- line routing diagram? My manual doesn't show much. I'm familiar with the CJ's, but this is a whole 'nother animal!!
JimMiller
'53 M38A1
Hello Jim,
If your A1 is early and retained it's original fording system vent plumbing then it is quite complicated but the TM's show all you need. The later A1's deleted the fording vent system.
This is the early complicated vent system up to serial MD23359.
This is the same system from serial MD23359 thru MD9295 about Nov/Dec 52.
From then on no underwater venting system. Just PCV, distributor and fuel carb bowl vent. The tank vent line is omitted and a bell shaped small vent valve is threaded directly to the tank's vent port. The distributor and carb bowl vent lines connect to the induction crossover pipe. The fording valves are also omitted. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Nov 02, 2007 Posts: 437 Location: Seguin, Texas
Posted: Mon Jan 21, 2008 12:19 pm Post subject: A little confused
So is the ventilation system the same as or different then the vacuum system? I thought the vacuum system was for running the wibers and providing pre-start vacuum to the intake manifold to start the mainjet metering fuel flow where the ventilation system was primarily to provide ventilation to the crankcase to prevent the accummulation of sludge? I also have a similiar problem with my M-38A1 in that the vacuum system appears to have been totally disabled which means I have to rely on piston and valve action to obtain any intake manifold vacuum. The engine eventually starts but it takes a little cranking to get it to fire.
Thanks for the information, Wes! Mine is certainly not like the diagrams; I'll check that next, to be sure everything is providing vacuum to what it's s'posed to, then I can check further. The primer system is interesting; it tells me that this is indeed a common problem!! Thanks again...
JimMiller
Vicksburg, MS.
'53 A1, '48 '2A
On the early M38A1 and all the M38's the vent, vacuum, wiper and PCV systems are very intertwined. This is because when using the fording system we use two manually operated valves to control venting and vacuum flow directions. When you view the individual systems on these Fording capable jeeps the intertwining is very evident. For example when selecting the "Fording" mode the PCV (Positive Crankcase Ventilating) system and the vacuum system can must be disabled in such a way that the crankcase pressures are directed through the vent system to pressurize the engine, tranny, and transfer to keep water out and the yet the vent system must still vent the fuel tank, master cylinder and fuel bowl and distributor to a sealed induction source for air. In normal ops the PCV valve will control crank case ventilation (more for emissions reasons then for keeping sludge levels down), the vent system will provide ambient air to the master cylinder, fuel tank and carb bowl and the fuel vac pump / manifold vacuum will operate the wipers and provide positive ventilation to the distributor.
On the later M38A1's the fording capability is dropped. The PCV system is an independent system operated by manifold pressure. The vacuum pump / manifold vacuum provides wiper drive and distributor venting. The remaining vent system consists of the carb bowl vent to the induction crossover pipe _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Nov 02, 2007 Posts: 437 Location: Seguin, Texas
Posted: Tue Jan 22, 2008 2:26 pm Post subject: Makes a lot of sense
thanks for clearing all that up, Mr. K. I would have liked to have been around when they were developing the fording system.......I can imagine just the testing alone woulda been a hoot.
So, in the non-fording later versions the pipe HH or 12 connects the PCV device to the intake manifold just below the carb. Was the pipe X or 9 still used and was item Y a "T" or just an "L" connector? Then this leads me ask.....which side of the vacuum pump was the vacuum and which side was the discharge? Can the vacuum pump work with on side plugged....or should it be open ended? I'm guessing originally the discharge of the vacuum pump was connected to Y through X.....but then this would tend to counteract the vacuum needed for carb operation...but surely you wouldn't have the suction side of the vaccum pump facing the pressure side of the PCV......good grief......
The center vent line on the fuel pump was deleted and a vented cap was used on that port. That center port on the fuel pump is not connected to the vacuum half of the fuel pump and it is not connected to the fuel pump half either. It is the body vent and is open to the crankcase pressure. If the PCV valve is closed on a late or early model or the fording valve is closed on an early model this port allows crankcase pressure to reach the bell, tranny & transfer on the early model and on the late model it is only vented overboard by the vented cap. The vacuum pump has an outlet line connected to the intake manifold and an inlet line connected to the wiper system "T" fitting.
Late M38A1 vented cap on center fuel pump vent port.
Here's another shot of the late M38A1 without Fording vent system.
In this early vented M38A1 line X delivers vacuum from the manifold to the vacuum pump where it is boosted and the added suction is then applied to the wiper "T" thru line V. Line S connects the bell housing/tranny/tranfer to the center fuel pump vent fitting which is connected to the pump lever cavity which is exposed to raw crankcase presures (both positive and negative). If your fuel pump diaphram ruptures you'll get fuel in this cavity which can enter both the crankcase and the vent line S. If the vacuum pump diaphram ruptures you'll have suction applied to this cavity all the time and you'll pull oil into the wiper lines and the vent fitting or line S will allow a higher then normal manifold vacuum leak that will be seen in a higher and leaner idle and stumble off idle. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Nov 02, 2007 Posts: 437 Location: Seguin, Texas
Posted: Wed Jan 23, 2008 10:37 am Post subject: Extremely helpful info
Thanks very much for the pictures, the drawings, and all the explaining. The whole vacuum/ventilating system is starting to make a lot more sense to me now.....although its also sorta starting to worry me. My wipers are gone....as is all the plumbing and control. Where the tube from the wipers would have been attached to the vacuum pump I have a plugged rubber line about 3 inches long. This is ok....sorta like simulates a closed valve or off condition at the wipers. I have no center chamber breather fitting or connector or anything else on the fuel/vacuum pump.....in fact it looks to me like the central chamber is open to the outside. I'll have to check this out more closely. The other side of the vacuum pump is still plumbed with X to the "T" at the end of the PCV and pipe HH is still installed between the "T" and the intake manifold. Where I start to have a concern is with the tube that's supposed to be installed between the oil filler neck and the air cleaner induction pipe. As i purchased this jeep this tube was gone.....missing......not installed. It concerned me...being an open port straight to the heart of the crankcase.....so I simply capped it off. Now it looks to me like this is the fresh air intake to the entire crankcase ventilation system whenever the wipers are off....and really NEEDS to be installed.
Anyway.....thanks again for all the great, useful information......now its just a matter of being able to apply what I've learned.
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