John Deere 950 (YM336D) engine speed problem

Post your questions or problems you are haviing with your Yanmar tractor here.

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diysteve
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John Deere 950 (YM336D) engine speed problem

Postby diysteve » Fri Jul 24, 2015 2:18 am

I have recently purchased a John Deere 950. It has a Yanmar 3T90J engine.

I am having trouble with setting the engine speed and keeping it constant especially below about 1200 rpm. Getting it to idle at the suggested low idle speed (850rpm) is all but impossible. I have driven many different tractors and have never struck this before.

Here are my symptoms:
1) As per instructions when I start the tractor I put the throttle all the way forward. As soon as it is started I throttle it back to about 1500 rpm. As it warms up the engine speeds up almost to full speed. I reduce the throttle some and it tries to die so I increase the throttle till it is running about 1500rpm again. It does this about 3-4 times before it will run at a constant speed. The throttle ends up in the same position each time I do this.

2) Once the engine is warm it runs at an even speed above about 1200rpm. If I try to reduce the throttle back to an idle it tries to die but increasing the throttle just a little to stop it dying revs it up a lot. It is quite an art to balance the throttle so it is not revving its head off or dying.

3) It also seems that if I put load on the engine (just going for a drive, as I don't have any other way at the moment) the governor doesn't adjust and I have to give it more throttle.

I am thinking something is wrong with the governor but I don't know what. I would really appreciate some help solving this problem.

The tractor has done just under 6200 hours and is in excellent condition otherwise.

Cheers.
John Deere 950 (Ym336D)

Aaron
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Re: John Deere 950 (YM336D) engine speed problem

Postby Aaron » Fri Jul 24, 2015 9:04 am

The most common problem is the fuel rack on the pump gets sticky. It should slide just by tipping the pump side to side. You will need to unhook the governor linkage through the inspection plate and then pull the pump off to really check it out and see if that is the problem.

Norm
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Re: John Deere 950 (YM336D) engine speed problem

Postby Norm » Fri Jul 24, 2015 9:51 am

To begin with, just remove the inspection plate , move the throttle lever back and forth and see if the rack moves accordingly. If not why not? If you have a foot throttle make sure it restores properly by spring tension. It can interfere with hand throttle.

diysteve
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Re: John Deere 950 (YM336D) engine speed problem

Postby diysteve » Sat Aug 08, 2015 2:02 am

Thanks for the help. I finally got time to look at it again today. The rack is a little slow to move when there is no spring pressure on it but with spring pressure I think it is fine. It may be just a little sticky at the low end of the rev range. How do I fix the stickiness and is there anything to watch for when removing and re-installing the injection pump?

I did notice that the rack was not quite adjusted correctly. The punch mark on the rack was about 1.5mm away from the edge of the housing. I followed the process for adjusting the governor in the service manual and the problem seems to have improved a lot. It is still not behaving perfectly at rpm below 1200 but is greatly improved. Also the tractor started easier from cold.

The manual says torque spring adjustment should not be attempted but the gap looks about 2mm larger than the 12mm the manual suggests. Should I try adjusting it and what would that achieve?

Thanks for your help.
John Deere 950 (Ym336D)

winston
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Re: John Deere 950 (YM336D) engine speed problem

Postby winston » Sat Aug 08, 2015 4:41 am

Would the shortening of the torque spring make for stiffer operation? I can't see where you could go wrong with changing it. You can always go back to where it was if it doesn't help.

sutto55
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Re: John Deere 950 (YM336D) engine speed problem

Postby sutto55 » Mon Aug 31, 2015 9:50 pm

I had the same issue with my engine. After changing pump and adjusting eventually got it running with help from this site.
All was good except for the hunting at low throttle. Ended up the throttle shaft that goes from outside connected to the throttle lever through the block and connects inside to the governor spring was worn. There was about 1mm of play on the outside. Made a new bush and shaft with tighter tolerance and it now doesn't hunt.

There is an O ring on the shaft inside the bush and that is where most of the movement was from. It would rock back and forth and used the O ring as the pivot point. The new shaft I made I put 2 O rings on it, one near each end of the bush. Hopefully when wear is present again in about 40 years the same thing wont happen. :)

diysteve
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Re: John Deere 950 (YM336D) engine speed problem

Postby diysteve » Tue Sep 01, 2015 3:55 pm

Thanks sutto55. Mine was worn too. I made new parts which improved the problem some. I like your idea of two o-rings. Next time :D

What adjustments did you do?

It seems that the governor doesn't adjust the fuel pump or as Aaron said the fuel rack is sticky. I have checked the rack as Norm suggested but haven't been brave enough to remove the fuel pump completely yet. I have followed the governor adjustment procedure in the manual and again it helped a little.

I am using the tractor to run a small boom sprayer to grow a red onion seed crop for the company I work for. The sprayer requires an even speed to be maintained so the engine not responding to extra load is quite a problem for getting chemical rates correct.
John Deere 950 (Ym336D)

sutto55
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Re: John Deere 950 (YM336D) engine speed problem

Postby sutto55 » Sun Sep 13, 2015 6:42 pm

One thing to be aware of if you remove the pump is to set the fuel rack into the centre. The travel allows the rack out far enough to jam on the housing. The other problem I had was installing the new pump. The spring clips on the back required some persuasion to get them into the block to allow the pump to seat properly.

Adjustments I made have it running well now, but I was concerned that I had to change the adjustments so much from what they were. I can only hope the previous owner made the adjustments trying to get the engine to run.

sutto55

diysteve
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Re: John Deere 950 (YM336D) engine speed problem

Postby diysteve » Wed May 29, 2019 2:26 am

Hi.
It's been quite a while since I last looked at this problem. Family and work commitments plus I wasn't using the tractor.

The other day I removed the injector pump and took it to a diesel pump specialist. He was happy all was working correctly.

It must be the governor adjustment. I have set it like the manual says but I am getting the same symptoms plus it is harder to start as the rack does not move far enough to give it full fuel.In the next few days I am planning to turn the whole torque spring assembly in a turn or two and seeing if it improves anything.

Could the main spring that connects the governor arm and the throttle leaver have stretched over time? The tractor is a 1980 model and has done 6300 hours.

If anyone has experience with adjusting these governors the help would be much appreciated.

Cheers
Steve
John Deere 950 (Ym336D)

Aaron
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Re: John Deere 950 (YM336D) engine speed problem

Postby Aaron » Wed May 29, 2019 9:53 am

Could the main spring that connects the governor arm and the throttle leaver have stretched over time?


Usually what happens is someone tries to remove the pump for whatever reason and they don't unhook the governor linkage from inside. They end up stretching and bending the linkages while trying to pry the pump out.

diysteve
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Re: John Deere 950 (YM336D) engine speed problem

Postby diysteve » Wed May 29, 2019 7:07 pm

Hi

Problem sorted and the tractor runs perfectly.

After mucking around with the settings on the governor and getting to understand how it works I once again followed the instructions in the service manual for setting the governor then turned the governor torque spring away from the governor arm one turn. It holds its rpm perfectly and quickly recovers when load is added.

Thanks for the help from everyone.

Cheers
Steve
John Deere 950 (Ym336D)


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