Carb/Distributor/Spark Plug Adjustments

Hornsgalore · Post by **Hornsgalore** » Sun Jun 08, 2014 12:05 am

I am new to the M38A1 Jeep. I just inquired a 1953 M38A1 Jeep and had a few questions.... The jeep runs a tad bit rough and really rich. What adjustments can I do on the carb or a combination of things to get rid of it running rich and rough? Any info would be great...... Thanks!

Post by **wesk** » Sun Jun 08, 2014 10:01 am

First, determine why it is running rough. The following assumes you are saying it is rich & rough at all RPMs and all temps and that you have the stock Carter YS950S carb with vacuum operated metering pin and accelerator pump.

Some simple checks before you start changing adjustments are:

1-Disconnect one plug wire at a time and if all removals cause it to run rougher ignition is probably ok. If one or more allow it to run the same remove those plugs and check their condition. If they check good then check the plug cable condition. If the plug looked good when removed then screw it on the end of the lead and crank the engine. If she sparks the cable is good. If not substitute a known good plug and recheck.

2-Once you are satisfied your ignition is good, move on to the cylinder condition. Do a compression check. Remove the four plugs and using an automotive compression gauge check each cylinder compression. Write them down!!!! If they are the same then even if all are low the engine should not be running rough.

3-Satisfied that a cylinder imbalance does not exist then move on to the fuel system. Rich running will be a lack of air (choke plate not full open) (air filter oil level too high). Too much gas, metering pin diaphragm bad or spring improperly installed or incorrect pin or accelerator pump diaphragm bad or float level set too high. Note that idle mixture adjustment will just affect idle and the transition from idle.

Often times a vacuum leak causes a not too mechanically inclined person to over richen the carb thinking that was the problem and this will initially confuse another person trying to troubleshoot the problem. So when you finish the steps above and still have a roughness the try a propane enrichment check around suspect vacuum leak sources.

All of this info is found in the manuals that are free for you to download here on this web site. Especially read and be sure you understand the operational characteristics of these YS series carbs in the exerpts from the carb manual on our downloads page.

skyjeep50 · Post by **skyjeep50** » Sun Jun 08, 2014 10:07 am

Sounds like the jeep needs to have what is commonly referred to as a "tune up". You will undoutedly have a bunch of how-to questions relating to each adjustment so the place to start is the "Downloads" section of this website (click on the link at the top of the page) - read through the parts, operations, maintenance manuals and related information there to get a good general knowledge of what's required to maintain your jeep. Then as you get stumped by something (we all do) the forum is a great place to ask for specific help.

Hornsgalore · Post by **Hornsgalore** » Thu Jun 12, 2014 10:30 pm

So I went through the whole process of checking all spark plug wires, pulled each spark plug out and cleaned them, I pulled the dist. Cap and cleaned everything in there and also gapped the points, I put the motor on TDC and aligned the dist. Correctly, I checked to make sure all plugs were getting sufficient spark and they are...... I'm still at question..... It still runs like it's missing and really really rich.... What should I check next??? Would rebuilding the carb take care of more of these issues? I am wanting to convert it to an electronic ignition and put new wires etc. To see if that helps.... If there is anyone out there who would like to call me or that I can call that would be really awesome.... I'd love to talk in person with someone about all this.... It is 805-503-0219 thanks for all the great info!

Post by **wesk** » Thu Jun 12, 2014 10:39 pm

You've done all I recommended in my first sentence. What about the last three sentences?

2-Once you are satisfied your ignition is good, move on to the cylinder condition. Do a compression check. Remove the four plugs and using an automotive compression gauge check each cylinder compression. Write them down!!!! If they are the same then even if all are low the engine should not be running rough.

3-Satisfied that a cylinder imbalance does not exist then move on to the fuel system. Rich running will be a lack of air (choke plate not full open) (air filter oil level too high). Too much gas, metering pin diaphragm bad or spring improperly installed or incorrect pin or accelerator pump diaphragm bad or float level set too high. Note that idle mixture adjustment will just affect idle and the transition from idle.

Often times a vacuum leak causes a not too mechanically inclined person to over richen the carb thinking that was the problem and this will initially confuse another person trying to troubleshoot the problem. So when you finish the steps above and still have a roughness the try a propane enrichment check around suspect vacuum leak sources.

Troubleshooting is time consuming and often boring but you must follow the list step by step until you are done.

QCIM38A1 · Post by **QCIM38A1** » Sat Jun 14, 2014 10:39 am

miss will be obvious, engine goes PUTT-PUTT-PUTT-PUTT at idle, rather than "PUURRRRRRR" like it should.

Post by **wesk** » Sun Sep 21, 2014 9:24 am

Hornsgalore,

Have you resolved your jeep's issues yet?

Hornsgalore · Post by **Hornsgalore** » Sun Sep 21, 2014 3:14 pm

Hey Wes thanks for checking in..... I am in the process of doing a restoration on this jeep and haven't messed with the motor in awhile... I am just going to buy a new carb when I get it all put back together to see if it will solve my issues. It's cheaper to buy a new one then to rebuild the one I have.

Post by **wesk** » Sun Sep 21, 2014 7:06 pm

Where did you locate brand new YS950S carbs at?

Hornsgalore · Post by **Hornsgalore** » Sun Sep 21, 2014 11:51 pm

Found them on eBay for the f134 motors