637S problems and Question

oilleaker1 · Post by **oilleaker1** » Thu Sep 10, 2015 4:02 am

That's why I,m starting with a re-build kit. Again. The ebay carb and omix ada kit which wasn't marked as such may have thrown me to the wolves from the get go. We'll see what happens on carburator # 2. I'll let you know what works to fix this. I doubt this is a distributor issue , it's all like new and nice. The engine is a total rebuild, valves, springs, guides, pistons rings bearings, bored, completely new. To my ears it just isn't getting fuel off idle. The old rule of thumb of fastest idle and backing off 100 RPM's on the distributor is fine. I also know why they moved the timing up front from the rear motor plate now. When I static timed the engine I didn't have all the crap in the way to view the timing marks. Now when running you might just get a glimpse and it's at too high a angle to see with the timing light. We'll soon find out. It has to get fixed anyway or driving it on Jeep trails is out. Just when you need it, which is most of the time, it stumbles and dies. Very frustrating and embarrising. I've had this before on my civilian Jeeps with the WO carburators and it was always the metering rod adjustment. The accelerator pumps were new. Kit should be here today and the carb is dissassembled and waiting. John

oilleaker1 · Post by **oilleaker1** » Fri Sep 11, 2015 6:24 pm

OK, here we go: Kitted the carb. Adjusted the timing, and set the mixture and throttle stop. With a dry carb, I have to spin the engine over a long time. Had a nice idle, no leaks, and the dead spot was less. Went for a drive. The timing seemed retarded and the Jeep was down on power. I stopped and advanced the distributor a bit and got much better results. Took off, uphill, the Jeep died in a stumble and would not restart. Same as before. Seems whenever I go up a hill and put a load on it, it stumbles and if you let it die, it won't restart. Now here is where it gets interesting. Remember I had 4 pounds on a snap on gauge at the carb in fuel pressure running. If I prime it with carb clean it starts. If I choke it it starts and dies. When I keep it running, out on the flats, I have full throttle with no stumble. Strange set of circumstances. What on earth could it be? I decided to change to a WO carter carb I have. Guess what, very little gas at the fuel line outlet going into the carb. Not enough fuel? With 4 pounds tested? I grabbed the disconnected fuel line at the fuel pump inlet and sucked on it. Immediately got a mouth full of premium. Ummm Good!

Ah ha! I have pressure, but not much flow. My pump is a early AC M38 military pump with no lever. I put a kit in it from Then and Now. So, I took it off and apart. Before I took it apart I hand pumped it. Very little arm movement and it stopped. Not much pumping action. The check valves, all six of them, looked beautiful. No crud, no nothing. Then I noticed that the center metal disc that sandwiches the diaphram was making a mark on the metal valve body. Hummmmm. I actually still had the old stuff I took out of the pump. Not only was the metal disc too wide, the shaft with slot for the lever was 1/4 inch longer than the old one. wrong diaphram! I overlooked that since it lined up with all the covers and screws. My bad. The old diaphram looked pretty good, so I cleaned it and installed it. It now has great pumping action. So, cracked carburator and a improper diaphram are what the battle has been about. I hope this may help one of you guys in the future. It's been 4 long days of trouble shooting. Even the trouble shooting can fool you. I'm feeling much better knowing what the heck was going on. So in retrospect : compare old parts with new when re building. After all, it's just a little Jeep. John

Post by **wesk** » Fri Sep 11, 2015 7:56 pm

It would be nice if everyone did what you did John and brought their findings back to the board when they finished up.

Some lessons I see from all of this:

New does not guarantee good.

Rebuilt does not guarantee good.

Organize troubleshooting.

Don't adjust things outside normal adjustment parameters to mask a malfunction's symptoms. If that is the only way to make her run right then something is wrong!

Keep an open mind.

Back to the fuel pump. I will point out that 3 1/2 to 4 PSI does not always mean enough volume is getting through. This is why for almost a century now we old farts have been taking timed flow samples in a jar whenever fuel delivery becomes suspect in a mis-behaving engine. I know most manuals do not suggest this test because it can be dangerous if one gets careless. I suggest each owner take advantage of the days his jeep is running well and inserts a "T" in the fuel line between the pump and car and have a shutoff at the "T" for the line you fill your jar with. Then on a good running day with the engine fresh from a short drive take a 60 second flow sample at idle and at 2000 RPM. Make a note of the results in your service manual.

Bretto · Post by **Bretto** » Sat Sep 12, 2015 4:43 am

Great news, excellent troubleshooting right there. I like when a guy can tackle their own business and not toss in the towel. But I wouldn't of expected any less of you.
I bet your smile dial got turned all the way up to 11. The big question now is, am I going to see this fine green machine in Colorado?

scoutpilot · Post by **scoutpilot** » Sat Sep 12, 2015 5:16 am

Lessons learned by experience. Some problems appear to lead in one direction only. John, you've done well. You didn't panic, you looked at the situation objectively with an understanding of how everything works together and if one thing isn't right, it will affect everything else down the line. I am so glad you were able to correctly diagnose the issue. Now then. Get out there and drive![/b]

oilleaker1 · Post by **oilleaker1** » Sat Sep 12, 2015 6:45 am

Thanks for all the upbeat comments. I know Jeeps will all work well when properly assembled in all catagories. They are a pleasure when they are in their niche of trail driving off road or slow highway cruising. I want to thank all my mentors and friends who have helped me over the years. You guys are a great bunch to hang out with. Bretto, I'm feeling like it will be green this year! If it isn't going to snow, I'll bring him. If I can be of help with others in their problems, I'm always glad to jump in. The more you learn from manuals and experience, the more you can help. I love it when they say " How in the heck did you know that?"

John

RICKG · Post by **RICKG** » Sun Sep 13, 2015 10:38 am

Nice work Oilly! See ya next week!

oilleaker1 · Post by **oilleaker1** » Sun Sep 13, 2015 10:41 am

Thanks Rick. Test drive in low 4 wheel was a success. Ready for the trail.

Bretto · Post by **Bretto** » Sun Sep 13, 2015 7:57 pm

Wow 1 week..