I doubt the financial calculation will pencil out for me to fix this one but I thought I would run it past you guys. This is an air cooled Yanmar single cylinder Chinese copy generator engine running at 3600 RPM. Simple cam driven injection pump to an old-fashioned looking injector. This unit came to me a couple weeks ago with water in fuel. Cleaned it out, put good fuel in it, tested it with no problem for an hour or more. Customer took it, ran good for 1 day, then it started giving trouble again. Symptom is that it starts right up, runs clean for a few seconds to a minute and then it begins to partially/intermittently misfire and lose a little speed and surge up and down between this and full speed. Blowing light white fuel looking smoke with every miss. The fuel looks clean, the filter is clean, and the last thing I did was check valve clearance. It acts a bit like a diesel injection problem but the clean starting and initial running had me going to valves but nothing to see there.
Sounds like a fuel supply problem to me.. air= white smoke.
Fuel line partially clogged ?
Maybe check the fuel return line to the tank to be sure it is open, ran into an 8.2 detroit in a boat that kind of did the same thing, long story but fuel return line had a valve that had been turned off by someone, had me scratching my head for a while! The other thing is run it out of a jug and bypass the rest of the fuel system because it kind of does sound like air, maybe bad lift pump?
Yes, it is evidently a supply problem but it is so bone simple none of the usual suspects apply. Gravity feed so no lift pump or air suction problems. I took the rubber line off the IP inlet and let it drain, good flow. So I put it back and lo and behold it runs good again. So for good measure I took the tank completely out and washed it out, no flakes or bugs or plastic to report. I have replaced all the fuel lines and the filter and again it runs good but that is what happened the last 2 times also and then it started messing up later. We shall see....
blocked tank cap? blocked exhaust muffler? maybe loosen flange bolts or nuts and try again mark
What about the injector return lines?? some go back to the inlet filter & some back to the fuel tank.. If they're cracked & go back to the pump inlet or filter head, they might be picking up air..
Does it have a banjo fitting on the inlet at the injection pump with a strainer in the bolt that is clogged? That would cause said problems if so, Isuzu and Mitsubishi have them.
Not a banjo fitting but just a hose inlet that is somehow pressed into the body. Not really any place to take it apart or any place you would expect to find a rock screen. I did notice the shutdown solenoid, which drops a plunger to close off the fuel inlet passage and deprive it of fuel, is leaking while running. I got one of those coming in case somehow air was getting in there too, but I doubt that.
Well, I got it fixed again...I hope.... I tried to get the shutdown solenoid out with a crow foot but the silly fuel tree thing spun off the injection pump body instead so I had to remove the whole pump assy from the machine and it was tucked in there pretty good. Once it came apart it became obvious what the problem was, wrong o-ring or something, why do people do this kind of nonsense? Being Chinese maybe it was always like that. Back together and it was dry as a bone and ran great for hours. I'm not 100% convinced the leak was the cause of the problem because it is below the level of the tank but there is a fair bit of pumping back and forth action in this area because the of injection pump spilling so it could also be sucking a little air. I also replaced the filters and all rubber fuel tubing, washed out the tank again and poked out any fittings, etc. etc.
Lol.. whoda thunk it.. btw> that oring is to big..{fat} but if its not leaking & the engine stay running, nobody but us has to know.. wink, wink. Good job.. I've NEVER seen a "tree" like that on a fuel system.. weird..
When it is installed the "log" of that tree is slightly inclined upward mostly horizontal to the left of the pump. So the fuel comes straight down into the larger fitting, then the smaller fitting is teed into the injector leak-off return line. It must be there to help purge air. I also have never seen one like it. All the rest have just an L-shaped piece with one fitting for fuel inlet only and can be kind of a pain to prime.
Post #7.. "a lot of people" don't know that the inj. return line on some engines, goes back into the pump or filter head.. & when they're fighting an air in the fuel problem, it gets over-looked.. & it was actually just a guess on my part.. cuz I'v never seen your engine before.. BUT I've run into it before on diesel engines. & it its bad enough, it'll keep the engine from starting.. The Ford p/u trucks were REAL BAD about it.. 6.9 & 7.3's Those guys would spend hundreds, if not thousands of $ trying to fix that problem.. only to fix it w/ a 15.00-20.00 injector hose & clamp kit.. AFTER they got the pump rebuilt, replaced all the injectors.. bought a new lift pump.. not to mention all the labor..
Yes, I know what you mean, in this case it was teed into the injector return and back to the tank. That way too when the tank is full it can get a nice dose of unfiltered fuel without having to go through that pesky filter, don't ask me, it's Chinese....