Joined: May 14, 2009 Posts: 972 Location: South Dakota
Posted: Tue Sep 08, 2015 7:21 am Post subject: 637S problems and Question
I have a 637s YS carb on my M38's. I've got problems and am trying to figure it out. Firstly, I see 3 different kits. Black diaphrams, red, and grey. Currently I have grey. Rick G has red, my M38 A1 has black. Omix ada, Crown, seem to be all over ebay. Both diaphrams leak all the time. I've block wet sanded the covers, and touched the body lightly with a flat file. All in trying to stop leaks. Even some gas/oil resistant sealant. I have fuel problems at low RPM's and poor starting. All gas related. Sometimes I have to prime it to start it. No gas there. Fuel pressure running is 4 lbs. Vacuum reading at idle with the assited pump = 20-23. There is always a dead spot off idle. If 4 wheeling, up a hill, it will run out of gas at low RPM's and you are done. Pull the choke, it fires and dies. Then you manually push the Jeep sideways, and roll start it in 2nd gear going down hill. It still takes a bit before the gas is there and then off you go. I checked the fuel line for air leaks, pressure tested the fuel pickup in the tank, opened the cap to make sure it's venting, blown the line out from the tank to the fuel pump inlet, tried everything. I have to pump a long time with the starter to get it to start after a overnight rest. Bowl is empty again due to the darn leaks. It acts like either the metering rod is sticking or the accelerator pump isn't working. The pin that holds the rod can fall out of the diaphram tube when removed that goes through the metering rod. So who has the best diaphrams in their kit, and who has them? I do not know if the dead spot is from either diaphram operation. Any experience or help with this from you guys? Thanks, John ( forgot to mention, it idles like a swiss watch when you get it running, and always a a dead spot just off idle)
Joined: Aug 31, 2010 Posts: 1741 Location: SO IDAHO
Posted: Tue Sep 08, 2015 9:06 am Post subject:
John, I checked and the my spare diaphragms we were talking about this weekend are black.. _________________ keep 'em rollin'
RICKG MC 51986 DOD 01-52, '50 CJ3a
Joined: May 14, 2009 Posts: 972 Location: South Dakota
Posted: Tue Sep 08, 2015 12:12 pm Post subject:
I'm trying my eXtra carburator. All the gas is non alcohol that I've been running. All springs and Check balls are correct. Wes's comment on a Crack is what I'm checking out first. Ordered a kit from Midwest Military also. I'll keep you guys informed on the diagnosis. John
Joined: May 14, 2009 Posts: 972 Location: South Dakota
Posted: Tue Sep 08, 2015 5:39 pm Post subject:
Well boys and girls, I have a update. Not without pain and suffering I might add. I swapped carbs and the gas leak is now gone. The old one was empty again. Looking closely at the bottom, I'm pretty sure I see a hairline. Wes wins again. But----------- the starter quit making foot connection. I have the early M38 starter that I bought as being NOS off the shelf. The two post switch assembly was burned up inside, so I bought a nos kit that replaces it all. Worked well for about a year. Until today. Throwing more at me as usual. So, I removed the starter, disassembled, and found that it was beginning to carbon up and lose contact. I cleaned it, looked fine, but sure didn't look like it was extending the round disc very high. It barely made contact. Then I noticed the plunger the cam lifts was threaded. If I put a washer in there-------no wait--------I'll be damned. There is a threaded stop screw already there to adjust it. Cool. It worked. The starter now is the best it's ever been and easier to engauge. Now, back to the carb. Starts excellent. Idles excellent, but there still is a dead spot off idle. I made sure the right springs were on the two diaphrams correctly. No joy. So, Check timing? Or do I need to go back into the carb where the ball and weight are and tap the ball to make sure it seats? What else would cause fuel starvation just off idle. The diaphram and spring are not it. I'm all ears. John
Nice thing about carbs are they really are simple machines.
Stumble off Idle is usually the accelerator pump but it can also be an overly lean idle mixture that the accelerator pump just can't overcome.
Perhaps the lean issue is further downstream in the form of excess air finding it's way in through induction leaks
And then there is the ignition side where a stuck set of advance weights can leave a stumble on acceleration. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: May 14, 2009 Posts: 972 Location: South Dakota
Posted: Tue Sep 08, 2015 6:03 pm Post subject:
Ok, I'll check the weights, but I disassembled and cleaned and greased it all. I'll also check timing with a strobe. Do you think the ball and weight could cause it by the ball not seating? JJ and HH? Throttle Shaft is nice, intake and exhaust gasket new and nuts checked for tightness. Base insulator is nice. Grasping a little here for ideas. Definately gaining though. John
A quick check of idle mixture would be to deliberately enrichen it a turn and a half and see if she still stumbles. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Nov 24, 2010 Posts: 1390 Location: Orem, UT
Posted: Tue Sep 08, 2015 8:18 pm Post subject:
Are you trying to get this going for the CFFC run? I hope so, we will have a good count of M38s there, one of them being the leader of the band. _________________ Brett
'51 M38
PHOTO DIARY OF MY BUILD
Joined: May 14, 2009 Posts: 972 Location: South Dakota
Posted: Wed Sep 09, 2015 5:13 am Post subject:
Brett, it depends on how it cooperates. It would be cool to have a picture of them together. A weather forcast will also help decide since I have only a summer top for it. No heater either. My wife loves the open views the best, but not 28 degrees in her face. . Look forward to meeting you and a few others for a first time there. John
Joined: May 14, 2009 Posts: 972 Location: South Dakota
Posted: Wed Sep 09, 2015 3:10 pm Post subject:
More update. Checked the mixture screw by opening, no joy. Checked the flyweights oiled them, made sure springs were not loose and good, no joy. Changed the timing up and down listening to the idle by rotating the distributor, it runs better, but still no joy on the dead spot. Re-grouped and called Scout Pilot. Here is the recommendation: The main jet and metering rod are most likely worn since they are originals. So, definately install a kit. Next: start the engine and get it idling at around 6-700 RPM's. Loosen the distributor and advance it for the best vacuum reading at the manifold without the fuel pump assist. Then retard the timing by 100 RPM's Lock it down. Next open the throttle stop screw, or close it, for the highest vacuum reading. Last, set the idle mixture screw for 700 RPM's. This should fix it. Currently waiting on the kit. If the idle is too high for your liking, you can close the throttle stop screw a little as long as it doesn't begin stumbling or picking up a dead spot again. Hope it works. John
I hope you get lucky with it. What ever happened to basic tuneup? Set the timing to 5 BTC, and check operation of centrifugal advance to 11 BTC. Then leave the timing alone. Back the idle mixture screw out 3 turns from closed. Tweak for smoothest idle at 650 RPM. If it doesn't run right at this point then you need to fix something that is not right or broke but this is the normal adjustment range and if you can't find happiness at this point then she is broke and needs repair, not modification of the adjusting parameters to hide the real problem. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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the starter quit making foot connection. I have the early M38 starter that I bought as being NOS off the shelf. The two post switch assembly was burned up inside, so I bought a nos kit that replaces it all. Worked well for about a year. Until today. Throwing more at me as usual. So, I removed the starter, disassembled, and found that it was beginning to carbon up and lose contact. I cleaned it, looked fine, but sure didn't look like it was extending the round disc very high. It barely made contact. Then I noticed the plunger the cam lifts was threaded. If I put a washer in there-------no wait--------I'll be damned. There is a threaded stop screw already there to adjust it. Cool. It worked. The starter now is the best it's ever been and easier to engauge. Now, back to the carb. Starts excellent. Idles excellent, but there still is a dead spot off idle. I made sure the right springs were on the two diaphrams correctly. No joy. So, Check timing? Or do I need to go back into the carb where the ball and weight are and tap the ball to make sure it seats? What else would cause fuel starvation just off idle. The diaphram and spring are not it. I'm all ears. John
. Look forward to meeting you and a few others for a first time there. John
