Saabman

The next step will be to dissemble the pump and see what is causing it to operate at a reduced rate. once the replacement pump turns up ill crack into the dodgey one. Unfortunately it appears to be ultrasonically welded so disassembly will be a one way street..

Looks like we are getting somewhere now. checked the Fuel (Gas) cap. No vent there - the tank is vented via a carbon filter to the air intake. Air flow is fine. Disconnected the fuel pump from the carby and stuck the end in a jar and ran the engine up (the carby holds a fair bit pf fuel and the engine will run for a while with no fuel supply. At idle and low RPM the flow seemed ok but as the RPM increased the flow decreased and eventually stopped. I wasnt able to get another pump here at a reasonable price so pinched the pump from my lawn mower which has a 450 - 500 cc motor so should be close enough to work and tried the test again. The first thing I noticed was the fuel flow was much higher at low RPM and at high RPM while the flow did decrease it still kept pumping. The second test only ran for about 20 secs and I collected substantially more fuel than I did in the first test which was about 40secs. So I have left my lawnmowers pump in the Mule and took it back out to the farm and took it for a good run up some hills loaded up a trailer and dragged that up through a boggy paddock and she didn't skip a beat. So it looks like the fuel pump was the culprit (after the gummed up choke was sorted). Interestingly though I put the Mules Fuel pump in my mower and cut the front yard at home and it seemed to work fine. Though the mower doesnt tend to run at as high an RPM as the mule and any heavy loads are generally short lived so the issue would not be so evident - Ive got a new pump on order at any rate. Thanks for all the input and suggestions - I hope the discussion helps someone else in the future.

Hadn't thought of gas cap vent been an issue- I will look into that. The fuel filter was original I replaced it with just a generic clear type Ryco inline filter which was quite a bit larger than the original. Ill get a new pump in and give it a shot as well.

Being haveing a play around with it again this week. I replaced the fuel filter and also put a clear filter between the fuel pump and the carby so I could see what was going on with the fuel delivery. I drove aorund with the seat up so I could see what was happening to the fuel flow and low and behold it beacame quiet evident that the fuel pump was not supply sufficient fuel flow. Just increasing the throttle opening while in neutral was enough to see the fuel level drop in the second fuel filter. is it the pump or an issue with the crank case venitlation - the pump delivers a heap of fule if i suck on the vacum tube so that seems to indicate the pump is OK so maybe the check valve or ive got a big crank case leak.... more to come

OK Ive had a chance to get the Mule out to the farm and its had a good run. And the results so far is it runs MUCH better than it has for a long time. Starts first go and idles smooth and generally drives around well. All good so far. But my wife and sister inlaw who have been using it the most over the last week still report that it dies on inclines and noted during a bit of an emergency (long story with a sad ending to one our dogs) it would also die traveling at sustained high speed. Which seems to point to maybe a blocked fuel filter - I never really thought about that one - you know the simplest things are often the problem 😐 As the fuel pump is run by crankcase pressure/vacuum that would explain the comment made by @kenfain earlier in the thread regarding the crank case ventilation being critical. It will be a few days before I get back out to the farm and have another look at it. I think I will start with a new fuel filter - ill fit a clear one so I can see the fuel flow and hopefull get an idea if that is the issue.

Yes Im thinking the issue is a result of the choke been stuck and the presence of the yellow gunk which im guessing is some condensed vapours from the oil. Interestingly while ive been working on the Mule Ive also been trying to get my KLE500 motor bike back on the road which also has the carbies glued up with a similar residue. The bike has been sitting in a shed untouched for nearly 10years. Must be Kawasaki special oil.🤣

that makes my theory rather unlikely, I Was going to stick a scope down the filler neck and have a look inside the tank to see what was going on in there but dont think I will bother now. I did had a good look at it today and found the choke totally gummed up with a yellow residue which was stopping the choke from moving at all - so stripped the carby down and cleaned it all up. and will see if that has help the situation. I dont think it is the cause of the dying on inclines though as it was playing up before the choke seized up and often found pulling the choke on help alleviate the symptoms - it was as if it was leaning out - A possibility is that what ever this gunk was may have been building up over time in the carby restricting the main jet and causing he lean running and going up hills required a bit of extra throttle but the restriction casing it to lean out and die. But a carby problem doesnt fit with the OPs description as he replaced the carby etc and the problem returned after a short while. the distribution of the residue was primarily on the choke butterfly and the ower part of the carby throat at the choke butter fly and appeared to taper out as it progressed through the the carby, which almost looked like it came in from the crank breather . I tired putting the front wheel up on ramps to simulate a hill but at least for my static test it ran fine - ill take it back to the farm next week and see if I have made any headway.

I realise this is an old thread but as there is no solutio yet Ill take up the challenge. I have a 610 not sure of the year ATM but prob around 2015 or there abouts with only 500hrs on it. It was my wifes uncles run about on the farm in his later years and we have just inherited it but it also dies going uphill. This is so bad it makes the unit almost undrivable. I hadn't considered fuel pick up as an issue as it runs fine on the flat even with a low fuel level. But if the pick up has a crack and seals up when level and flexes when on an angle its a possibility. Im just about to start looking into it this week need and will report back what I find as I progress.