OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions on Other Engines Mitsubishi Hunts and dies

Hi.
The neighbour has just had me take a look at his Scorpion Sine Wave Genset that has been sitting for a bit over a year. It starts first pull and then just hunts on the governor for a little while and stops. If you put it on half choke you can get it to stay running and if you override the governor it will rev quite freely. So, I have taken the fuel bowl off, checked for crud, pretty well spotless, blew through the lines and checked the float operation and fuel flow rate, all good. Took the fuel tap out of the tank and cleared some crud from its filter, reassembled everything, exactly the same. The engine is a Mitsubishi OHV 4 stroke. Any ideas?

I'm not clear on what you mean by "override the governor". Do you mean it will answer the throttle properly if you open it manually? Can you hold it on its governed speed (which is exactly 3,000 rpm) and have it run smoothly? Or does it stumble and stall if you do that?

Hi Grumpy. Yes, if you manually operate the throttle butterfly it will rev up and run smoothly, I don't have a tach to check the exact revs but the voltage holds steady at 240. On about half choke it will run smoothly as well but a little either way of the sweet spot it dies.

I'm not really understanding the symptoms yet. You seem to be saying that it runs perfectly if you just hold the throttle steady in any position, but if you allow the governor to control the throttle, it leans off and stalls. On the face of it that doesn't make sense. Can you clarify what is happening?

That's exactly what's happening except it hunts up and down and then just stops, and like you, I just don't understand it either! It will restart instantly after it stops and then does exactly the same thing again. It really has me scratching the head, and the skin was getting worn pretty thin there already.

Let's go back a step. You said it is completely OK with the choke partly closed. Can you confirm that? If that was just a random event (it happened to keep running a bit longer that time, when you tried the choke) I'd be suspecting an ignition problem, but not if the choke actually affects it - that could only be mixture.

is it possible it has some sort of vacuum line on inlet side of carb might have perished maybe ? some weird n wonderful things coming up now and then .
sorry to interrupt you grumpy

Feel free to interrupt vccomm, you are at least as likely to be right as I am. Right now we are in the "That's weird, I wonder what could cause it?" mode. My experience says when that happens, usually something is wrong in what I think is the input data: either it's wrong as reported, or I've misinterpreted it.

I had thought of a loose carburetor and therefore leaky gasket at the flange, but if so, why would it work properly when he grabs the throttle linkage? There is one possible answer that occurs to me: maybe when he grabs the throttle linkage, he does it in a way that presses the carburetor flange against the intake port, and stops the leak? I think checking that the carburetor isn't loose would be a smart move at this stage.

just thinking out loud...

It could it be that the main jet is partially coated? I have a few carburetors where the main jet would have a wax like substance in them, coating the walls of the jet. This would cause the engine to hunt until thoroughly warmed. A thorough cleaning of the jet usually fixes the problem. At least that what happening some the EPA compliant engines here. Even had to resize main jet to the next size on a couple.

Thanks for the feedback guys. Yes, if you hold the choke on about half choke it will keep running for as long as you hold it in just the right spot. Also if you operate the throttle butterfly by hand, at top of the carby, it will keep running. I have actually checked the gasket and ensured the carby is tight Grumpy. I think the next thing will have to be remove the carby and give it a thorough clean. There may be some gunk in an air bleed or jet. Will let you know what if anything I find.

Why did you clean the fuel filter and not replace it, is not the right thing to do. The first step would be is to replace a dirty fuel filter (in order to eliminate that issue) and then clean the carby.

Until you follow correct procedures you will run around in circles wasting your time.

Note that what you are explaining appears to be a fuel problem.

Thanks aussietrev, I'm not familiar with the carburetor that Mitsubishi is using, and at the moment I'm a bit mystified about what could cause it to be lean when you aren't touching it, but OK when you hold the throttle open. I agree with both AVB and you that one of the standard things to do with a strange engine that misbehaves is to give it a proper tune-up, including cleaning the carburetor and inspecting the gaskets and controls. Even if the problem is not in the carburetor, that process will lead you to work through the external linkages etc, and that could lead to finding the problem.

I'm conscious of the experiences Mark Electric has had with the notoriously finicky Suzuki M120X 2 strokes, which seem to have to be set up by a combination of black art and sheer perseverance. Perhaps you've found another engine like that, with a linkage system that is both so arcane and so unstable, that only long experience (or advice from someone with long experience) with that particular engine is likely to solve the difficulty.