40C motor pulsing

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BradE
40C crawler
40C crawler
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Location: Northeast Kingdom of Vermont

40C motor pulsing

Post by BradE » Mon Jun 06, 2016 4:50 pm

At medium to lower rpms and at idle, the engine seemed starved for fuel; it would slow down, the gov would kick in, and the revs would increase. This happened only after the engine warmed up.
While servicing the transmission, air cleaner, oil change, etc., I decided to replace the coil, plug wires and plugs.
The pulsing all but disappeared, but now shows up at idle speeds lower than before, so I suspect the coil was part of the problem. At least this is progress!
While pulsing, I would hold the governor arm still until the engine came close to quitting(I didn't let it die), let go and it would get enough gas to keep running.
My conclusion is at low idle, the engine isn't getting enough gas, slows down, forcing the governor to open the throttle a little, and then it's fine for a few seconds before it does it again.
Question
Should I overhaul the carb again? (It was done by someone else two years ago, and I have had this issue almost ever since.) I suspect something plugging the low idle circuit. Is there something else I should look at like points/condenser or timing?
I was thinking it could be the float adjustment, but wouldn't a misadjusted float affect ALL engine speeds, not just idle and not just after running for 5 minutes?
JD 40C 4 roll 1955, snow tracks and sprockets from a 350

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Stan Disbrow
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Post by Stan Disbrow » Mon Jun 06, 2016 4:55 pm

Hi,

I am thinking air leakage at the butterfly shaft. Something usually not addressed most of time during a rebuild.

Stan
There's No Such Thing As A Cheap Crawler!

Useta Have: '58 JD 420c 5-roller w/62 inside blade
Useta Have: '78 JD350C w/6310 outside blade
Useta Have: '68 JD350, '51 Terratrac GT-25
Have: 1950 M, 2005 x495, 2008 5103 (now known as 5045D)

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BradE
40C crawler
40C crawler
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Joined: Tue Apr 03, 2012 11:00 am
Location: Northeast Kingdom of Vermont

Post by BradE » Mon Jun 06, 2016 5:06 pm

Thanks for the speedy reply. But do you think this would be the case when the symptoms appear only after warming up for 5 minutes or so?
JD 40C 4 roll 1955, snow tracks and sprockets from a 350

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Paul Buhler
350 crawler
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Location: Killington, VT

Post by Paul Buhler » Mon Jun 06, 2016 7:33 pm

Brad:
I reworked my carb a few times before getting it straightened out well enough. Stan's comment about air leaks is on the mark. The TSX carb was counterintuitive to me since the idle screw adjusts air rather than fuel. On small engines, surging is usually an indication of a plugged port somewhere. I used this same logic when cleaning my carb. There are available drill bits and small wires that can be used to clean jets, tubes and ports if used carefully. I found carb clean, long stiff single brush bristles, thin soft wires and compressed air my best friends for this project. I also wrapped my throttle shaft with cotton yarn soaked in oil to help seal from air infiltration at this point. BTW, I still can't get my idle screw to work as designed, but my dozer starts easily and runs well;it just idles a bit rough.
Send me an email, and I can send you a .pdf of a carb manual that I've found helpful.
Good luck. Paul
Last edited by Paul Buhler on Tue Jun 07, 2016 3:27 pm, edited 1 time in total.
Paul Buhler
Killington, VT
420c 5 roll with 62 blade, FOPS, and Gearmatic 8a winch

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gregjo1948
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Location: Newark Valley,NY,USA

Post by gregjo1948 » Tue Jun 07, 2016 3:44 am

I don't remember if there's a spring on the governor but if there is, it may be a little weakened over time allowing then rpms to drop lower than they should before opening the throttle and holding at a steady speed.
JD 350B diesel 6way blade, Case 580B Loader/backhoe, Farmall 504 high crop w/ flail boom mower, International 404 , International 284 diesel w/belly mower, 1972 Ford F600 dump truck, Galion 3-5 roller, Allis Chalmers D17, 1620 Ford

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Stan Disbrow
350 crawler
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Post by Stan Disbrow » Tue Jun 07, 2016 4:53 am

Hi,

It may also be time to take a look at the oil inside the governor as well.

Stan
There's No Such Thing As A Cheap Crawler!

Useta Have: '58 JD 420c 5-roller w/62 inside blade
Useta Have: '78 JD350C w/6310 outside blade
Useta Have: '68 JD350, '51 Terratrac GT-25
Have: 1950 M, 2005 x495, 2008 5103 (now known as 5045D)

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traber1
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Location: Albany, NY

Re: 40C motor pulsing

Post by traber1 » Tue Aug 15, 2017 4:58 pm

Oil in the govenor? Isn't this lubed by engine oil?

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Lavoy
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Re: 40C motor pulsing

Post by Lavoy » Wed Aug 16, 2017 9:19 am

Normally a carb idle circuit problem. Guessing the person that worked on the carb did not pull the jets and check all the passages.
Lavoy
Parts and restoration for antique and late model John Deere crawlers.
Owner and moderator www.jdcrawlers.com

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