Posted: Thu Dec 22, 2016 12:19 pm Post subject: Is this Carter YS correct for my M38?
Hi and Merry Christmas to all!
My M38 had a Delorto carb, but for originality I got from ebay a Carter YS stamped 0-548. From day one I had a starting problem, especially when the engine is warm. Even with the engine cold, sometimes I have to choke it, even in the summer. Once started all seem working OK, idle acceleration etc.
After many rebuilds, checking the float level etc, I'm now wondering if my YS 0-548 is for another military application, in which case I will have to find out if it has the correct parts inside.
No such Carter YS with number 0-548. Some have the O-548 casting # on their bowl. You should have posted a photo of the carb so we can be sure what you are describing.
This is a proper M38 YS637S
This is how it is installed
This is the proper mounting gasket
Below are descriptions of it's operating circuits:
Float circuit
Low speed circuit
High speed circuit. Note the metering rod is operated by engine vacuum!
Accelerator pump circuit. Note that the pump is operated by engine Vacuum)
You cannot start an engine with this carb using the accelerator pump for starting fuel. First the engine must be operating before the accelerator pump will receive engine vacuum to operate. Therefore the common start procedure is to use full choke as explained in the operator's handbook. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Aug 31, 2015 Posts: 29 Location: Asheboro, NC
Posted: Fri Dec 23, 2016 5:14 am Post subject:
Your pictures indicate a correct YS637S for the M38. L-head - 637S. F-head - 950S. 950S won’t mount on standard L-head intake. _________________ Old fashioned service never goes out of style.
Yes, that is a YS637S. The O (548) is the bowl casting #. The Carters came with the base prefix part of their number cast into the bowl, thus the YS by itself. Then an assembly tag attached to one of the air horn screws ID'd the specific model number.
You can see this triangle shaped tag on the YS950S top left of left carb.
Note that the parts illustration in the original Carb overhaul manual had an error that I have corrected.
Item BB had been shown on the wrong side of the diaphragm.
The parts blowup in the M38 ORD 9 SNL G-740 is correct. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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Joined: May 14, 2009 Posts: 972 Location: South Dakota
Posted: Sat Dec 24, 2016 6:23 am Post subject:
ArisL, I have 3 M38's, one is a A1. Your description on hard starting is quite normal. I always have to choke all three when cold. Normal. Once in a while when hot also. I've never understood why. Seems there is no fuel after sitting hot, and the vacuum operated accelerator pump doesn't supply enough fuel for re-start. I usually just step down on the gas petal and crank longer and it eventually will start. I do have to choke them if that fails. Possibly when sitting hot it may have flooded also. Hence the step down and crank for a while. The mechanical WO Cater carbs are superior to these waterproof carbs. I see why they made them, but they were not a improvement. I don't drive under water-------LOL. When you open the hood on a nice correct looking m38, I just can't bring myself to change to a WO. Doesn't look quite right to me. So, I just live with them. John
Because the accelerator pump is vacuum operated. To improve the engine's vacuum production at the carb during cranking you must apply full choke. This will increase the sucking (Vacuum production) efforts of the engine. This will in turn charge the two vacuum diaphragm pots on the carb. After a few seconds of cranking under full choke the accelerator pump will squirt just like the WO Carb's mechanical accelerator pump when you pump the gas pedal. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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