poor idle

[woo003]

hi, I have a David Brown 780 with poor idle. the engine starts nicely and has good throttle response, however the engine idles quite poorly and puffs out some white smoke. i have only just acquired it and I am fairly sure the diesel in the tank is quite old. and there is a wet spot around the number 3 cylinder. I think this could be the problem. combined with the old fuel. I am going to flush the fuel system and will change the oil. however before I go replacing the injector. I am wondering if anyone has any other suggestions of a lovely cause. I have already adjusted the valves.
thanks.
 

[r.w.b.]

a heavy load on it.fesh fuel might add a quart automatic transmission oil to fuel
best fuel additive you can use
 

[used red MN]

How does it sound when the starter is cranking the engine? I am not sure if I can train an untrained ear over the web. While cranking an engine that all the cylinders are fairly close on compression the starter will make a fairly consistent sound. If a cylinder has low compression the starter speeds up on that cylinder when there is less resistance from the lower or minimal compression in that cylinder. A cylinder with low compression could have symptoms like you are reporting. In this video at 9:45 you can hear an engine cranking with one bad cylinder. The tractor is a newer larger Deere, so maybe you will not be able to convince yourself that the sound can be applied to your tractor. Leave the fuel shut off when you try this. What or where is it wet around cylinder 3?
Deere with a dead cylinder uneven crank

 

[woo003]

hi, thanks for both suggestions. I have added some injector cleaner and have flushed the fuel tank out. it seems to be running much better now. I will give it a bit more time to work to see if it fully resolves the problem. some online research has winded up with the suggestion of a cetane fuel booster. is this something anyone has experience with and weather it is safe to use in older engine. the engine did seem to have consistent compression because It cranked over smoothly and consistently.

however it seems like the tractor may need a new throwout bearing in the clutch. when the clutch is depressed. there is a whirring sound. I am fairly confident of this so I may split the tractor and replace it next time I have a free day. any tips would be appreciated about this. because it will be the first time I have split a tractor.

thanks.