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Just got my 1952 M38A1 running. F head. Debella kit in YS carb. Good fuel supply, no vacuum leaks, good mid range and full throttle. Idle surges because it runs out of gas. Almost dies, then idles, over and over. If you spray carb clean into carb inlet, idle smooths out or increases with volume. No carb clean, back to surging. I got 3 springs in the kit to replace my 2 over the two side diaphrams. The question is: 2 long springs one coarse, one fine, 1 short coarse spring, where and which goes where? I thought I did right by copying what was there, but since it has never run for me, I'm at a huge loss. I do know I don't have enough fuel on and off at idle. I've checked very close for vacuum leaks twice and disconnected the vacuum part of the fuel pump from the intake and plugged it. No change. Excellent fuel delivery and float level. Starts well. Just won't stop the surging at idle and does miss a little at 1/4 throttle. Timing rock on and steady on light, even swaped out condensors, no change. Cuz old buddy, help!!!!!!! John

If you used the new (all new modern rubber parts) kit that Midwest and AJP are selling for $55 that kit comes with both YS637S (M38) parts and YS950S (M38A1/M170) parts. The difference in gaskets is obvious. The metering rods look very close so you must go by the part number on the rod (75-595S for the M38). The two large diameter springs go between the diaphragms and the side covers. Be careful which parts list you use when assembling the carbs.



Heavy spring X accelerator pump and light spring BB metering rod. Small diameter spring N goes on idle mixture screw. Very tiny spring MM goes inside intake needle. Spring WW with the ears goes on the choke valve shaft.The above drawing is the one from TM 9-1826A which has been corrected by me for spring BB's location.

Great help! The heavy spring X is the one I think I incorrectly replaced with a lighter spring. I had a gut feeling since it was in the package with that diaphram that something was not right. Mine had a different longer, lighter spring there when I took it apart. I'll let you know if that fixes the surging. Thanks much Wes! John

Results! Changed the rear spring----no change, change to the lighter front spring----no change, deduced that it runs fine except on idle circuit----Took off the top and emptied the bowl. Gas needs to go up the tube and feed the idle circuit. Took the BRAND NEW tubes off-----Found brass shavings in one of the two outer tube holes. Cleaned it out------- Started after filling the bowl and adjusted to a perfect idle. Now that's picky. Sure is a pleasure now! John