YM240 smokes heavily, lacks power

As mentioned in another thread, my recently purchased YM240 runs weakly and blows a lot of dark gray smoke. It will rev up to around 2200 rpm or so, but profusely pours smoke from the exhaust and lacks power. The motor was disassembled when I bought it last week, and I got it together and it ran strong, but not quite right. Is there a logical sequence or symptomatic troubleshooting method to follow in analyzing this problem? I have attached photos of the smoke under full throttle, at 2200 rpm, and a photo of the smoke when the throttle is quickly reduced, when it turns a gray-blue color. Overall it lacks power and doesn't seem to run cleanly. I am draining the tank and will try it with other fuel, but I filled it yesterday with fresh fuel from the local station. It worked fine in my pickup. Thanks in advance.


Under full throttle conditions:



Under quickly closed throttle:

Looks like it's fighting to breathe, air cleaner all clear ?

Yes, the air cleaner is clear. In fact, the photos are actually taken with no filter on at all! I should have pointed that out, sorry.

Air cleaner is clean, got good fuel. I would think injectors might be possible, also symptomatic of a plugged muffler. Not hard to pull the muffler and see.

Removing the muffler didn't change anything except how high the smoke pours out. I've heard California talk about how much of the noise on these 2 cylinder tractors aren't actually from the muffler. The tractor was loud-REALLY loud-but not as much louder as I had expected. I drained and replaced the fuel with fresh diesel from another station, all with no change.

What is the next step? Will these engines run on one cylinder only? Will pulling an injector line to see if one is stuck or not reveal if I have a stuck or malfunctioning injector, or merely keep the engine from running at all?

I discovered what may be another part of the puzzle, and not a happy one: The air filter was off to ensure no restrictions were affecting the engine's air intake. After shutting down, and while the decompression was activated, I heard a hissing or sizzling sound from in the intake. If my understanding is correct, that cannot have been compression leaking through the valves. I can't think of any other source of the sound except water on hot metal.

So, the only logical thing that might make that sound is leaking coolant. The coolant level is fine, and there are no bubbles at either startup or while running the tractor. However, the tractor was apart when I got it, for a head gasket replacement. Supposedly the head was fine when checked by a machinist, and he had a receipt from Hoye for the new gasket and hoses. I don't see how coolant could be getting into the cylinder while the engine runs, though, to make it smoke so heavily. The smoke smells like burning diesel, not like burnt antifreeze.

Coolant normally comes out the exhaust as white smoke. Some folks slowly loosen the injector lines one cylinder at a time while running in trying to find if one cylinder is causing the problem. Still sounds like possible injector problem. I wonder if the former owner had the injector pump off for any reason?

As you can see by the picture, the smoke is definitely NOT white. I don't think it's burning coolant. I'm certain that the profuse smoke isn't from coolant.

Is it as dangerous as it sounds to loosen the fuel lines to an individual injector's fuel lines while the motor is running? I'm assuming the bleed screw is used for this? I'm not trying to second guess, I just don't want to get a hydraulic injection of diesel, or light myself on fire. I know diesel motors don't have the hazard of a gasoline engine, I just want to minimize the number of scenarios that involve me burning...

It sounds like removing fuel to one cylinder at a time is a viable method to check if there is a stuck injector. If they both do it, does that probably mean it is in the pump, or that both injectors are bad?
Thanks again for the tips.

I didn't think there were any bleed screws at the injectors. I'm thinking loosen the tubing line coming from the pump at the injector. You didn't respond to the question about the former owner having the injector pump off. Do you know if he might have had it off? If you would feel safer here is an article on testing your injectors. Testing Injection Pump and Injectors

Winston1, I didn't mean to leave out a response about the injector pump. The previous owner said the only things he had done were pull the head and associated parts and get the head inspected and reinstalled with a new head gasket. He didn't say anything about the pump coming off or being adjusted or tinkered with.

I don't know what to believe, though, because he told me the tractor always ran great, but would overheat after an hour or so of use, and sometimes use a little coolant, so he replaced the head gasket. He said he found an area where the gasket was passing compression into the cooling system. I put the injectors, fuel lines, and valve cover on, bled the system according the the instructions on Hoye's website, and after some fiddling it fired up and ran fine. After a bit of running and sitting overnight, and topping off the fuel, it now smokes like a tire fire when it's run.

I didn't articulate what parts are on the tractor, I loosened the banjo bolt on the fuel line into the injectors. This tractor doesn't have a separate air bleed. Sorry.

I think I also gave off the wrong tone when talking about the color of the smoke, I didn't mean to sound snippy, insulting, or rude. If anyone took it that way I'm really sorry, and it wasn't intentional. I didn't intend to sound like a know-it-all or be dismissive. I hope it didn't come across in that fashion. I really appreciate the guidance and time spent helping a stranger. I hope I'm able to figure out this issue so that I can begin using the tractor.

Nothing sounded insulting or out of the way to me at all. If this tractor cranked up and ran good at first with no smoke I would doubt you have an injector problem. You stated you topped off the fuel and it set overnight and now it smokes like a burning tire. Almost sounds like the fuel top off had something to do with the problem but I can tell you don't really think so.