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Discussion Starter · #1 ·
I have a late 90's m-gator with the 3 cyl Yanmar diesel engine. My issue is that the top out speed of this machine is currently 7-10 mph. I cannot figure out where my issue is. I also have a newer mid 2000's M-Gator A1 and its top out speed is 25-30 so I know that i have an issue with the older one. Thanks in advance for any help!!!
 

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I have a late 90's m-gator with the 3 cyl Yanmar diesel engine. My issue is that the top out speed of this machine is currently 7-10 mph. I cannot figure out where my issue is. I also have a newer mid 2000's M-Gator A1 and its top out speed is 25-30 so I know that i have an issue with the older one. Thanks in advance for any help!!!
Does the engine seem to be revving up the same as it did before the problem? If so, I would guess that you have a clutch issue, such as a stuck sheave that isn't up-shifting. Look at the clutches and see if one is not closing all the way, you can do this in neutral by revving the engine. Your clutch is not protected from the elements and it could simply be stuck or, it could need replacing.
 

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Discussion Starter · #3 ·
I have put the gator in neutral and revved the engine. Both of the clutches seem to be contracting and retracting correctly. I also removed the cover of the clutch mounted to the crankshaft and the internals were surprisingly clean. I would like to agree with the fact that it doesnt seem to be up-shifting, but at the same time it almost seems like the engine itself isn't revving high enough. The engine seems to be running nearly perfect, ie, idle, start condition, revving, it just seems that it doesnt rev as high as my other gator. I received these M-Gators from Ft. Bragg and they were completely cannibalized so it has been quite a task reassembling these machines.
 

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First I would determine if the engine can rev to it's full rpm. Inexpensive optical and contact tachs can be bought from RC hobby suppliers. If it doesn't turn as fast you'll know to look for a rev limiter of some sort. If it can get up to 3'000 to 3'600 then it could be the gearing in the transmission or the clutches not going to the end of their travel either because of malfunction or something in the clutch to intentionally prevent it from fully opening/closing.
 

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To continue with Danes troubleshooting, if it does not reach full rpm, check your fuel supply tract. Could be a plugged filter or fungus in the system somewhere. There is a fungus that grows in diesel fuel. If there it looks like grey BB's and can be mashed with your fingernail. If the machine has set up for a while the fungus could be the issue. There is a product called Biogard that will dissolve it.

Hope this helps
 

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Discussion Starter · #6 ·
I will pick up a contact tach when I go to town. As far as a fungus in the fuel system, like I said above, This machine was cannibalized by the Military before I received it. I had to completely reassemble the fuel system other than the injector pump and no signs of fungus. Good info to know for future reference though. I will post the RPM's after I test it. Thanks for everyones help so far!!
 

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Discussion Starter · #7 ·
Sorry it took so long to update this thread. I still haven't been able to pick up a tach to check the rpms. I did however determine that the engine is capable of reaching higher rpms. I jacked the rear tires off the ground and put the machine in forward gear and held the throttle to the floor and the engine was more than capable of reaching high rpms.
A few things I have noticed while driving this machine is: I get a single small puff of white smoke when I start it (typical and not a concern to me), also on take off the machine is quick and snappy, accelerates rapidly until it gets to 7-10 MPH range and then tapers off to a steady speed. I cannot feather the throttle to gain any speed nor does it slowly gain speed while driving.
I am wondering if there is some type of govener or some other speed restriction device that may be causing this issue.
 

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1. When going as fast as you can on level ground does the engine sound like it's reving as high as it did when you had the back end off the ground?

2. If you drive the Gator up a hill when going full speed can it maintain that speed or does it bog down?

I'm trying to narrow down if the speed is intentionally limited or if engine can't make enough power to make the Gator go any faster. Have you played with the adjustment screw on the injector pump that limits the throttle arm travel?
 

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Discussion Starter · #9 ·
While driving the engine does not seem to rev as high (not a drastic difference but noticeable)as with the rear wheels off the ground and it bogs down considerably when trying to pull a hill.
As far as the adjustment screws on the injector pump... I am not exactly clear on whats what with this particular injector pump. Any insight on the pump adjustments would be greatly appreciated!! I just have the feeling that this problem is something simple.
 

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What engine does the A1 have? I assume it's some variation of the Yanmar 3TN.



It's a long shot but it's something that can be adjusted and since yours has been around the block a few times it's possible someone has tampered with the throttle stop. It's the screw where the yellow arrow is pointing and it limits the travel of the throttle arm. Mine in the photo still has the anti tamper cap in place.
 

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Discussion Starter · #11 ·
Thanks Dane, I'll check into that after lunch. Are there any other adjustments for the injector pump that could cause this issue. Also would you know where the cheapest place to purchase a lift cylinder for the dump bed. JD quoted me one for $840.00 and that's not going to happen anytime soon...lol
 

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There are two other adjustments that I know of but I don't know enough to advise you any better than the Internet. Here is a link to the injection pump service manual. I don't know what engine specifically is in your Gator but the manual should give you a good idea of what's involved.
 

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Discussion Starter · #13 ·
Ok, thanks a ton dane for the yanmar service manual link. Helped me considerably with adjusting the pump. I was mildly successful with gaining additional top speed. I can now cruise more around the 15 mph range, which is good enough for the tasks this machine will be assigned to.
What I ended up doing was adjusting the low idle speed to stop it from jerking when putting into gear. I also set the high idle speed to a more appropriate setting. Because it wouldn't pull hills very well at all, I adjusted the "fuel regulation screw" giving it additional fuel creating more torque for the hills.
Now when going up hills it chuggs some black smoke and takes the hill as if it wasn't even there. Thanks to everyone that helped me with this issue.
 

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Did you pull the injectors and look at or test them? Maybe a good cleaning would help. At the minimum I'd try some injector cleaner in the fuel to see if that helps.
 
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