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JD 420 RPMs wide open

1038 Views 8 Replies 6 Participants Last post by  DTapley0417
Hi all

I picked up a 420 with a P220 in it a few months back to snowblow with. I mowed with it one time and during the mow the RPMs went through the roof. I had to turn the unit off in fear it would blow up. Since then It would idle and it would begin to hunt or surge. Once any throttle is added it runs 100% wide open and will not come down. I checked the linkage but everything seems to be in the correct spot.

Things I did to resolve:
Cleaned carb
New gaskets
Reseal intake
New gas lines

I came to the conclusion it was the flyball spacer. I removed the engine and got to the spacer but it’s in tact and the spacer will barely even budge. Could the spacer still be the issue? What else should I look for to cure this issue? Any help would be greatly appreciated
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Mrbeef has a video on the fly all’s,just search for his stuff

I have been checking them as well. My spacer seems to be good. I’m wondering about the cup? Do you know what I should be looking for if it’s worn?
if the governor plate on the crank barely moves, thats most likely your issue... it needs to be able to move freely to push on the governor arm to regulate speed. if its stuck, it wont move out with the balls and close the throttle at the desired rpm.
Thank you! I’m going to check that out this evening. Do you know on the governor cup, how to tell if its needs replacing? I was searching and I’ve seen a lot of guys say check or wear on the governor cup but I’m not sure what I should be looking for. Thanks for the info!
Now this isn't too much help as I cannot remember the details as it was a few years ago, but I had a 318 with B43G engine. I thought the flyball was bad too. I bought a gasket kit and carb jet from boomers_influence. I will still having trouble and he told me how to test to see if it was the flyballs without taking anything apart. For the life of me I can't remember how I did it. In the end my RPM surging was the main carb jet. Looked clean but a microscopic buildup of varnish made the jet ever so slightly smaller.
I appreciate it. I actually bought a new carb from boomer. I’m stumped on what to do. I believe it has to be the governor but now that the spacer was intact I am not sure which way to go from here.
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