Ms500i lean issues

[Bigmac]

I have been gifted a troubles saw, an MS 500 that the dealer doesn’t want to touch. It would start an idle and sound OK and lean out if you put under any load, then I did the simple things and pulled the fuel filter to check to see if it was clogged and it was fine and pulled the throttlebody cover off and blew out all the chips and now it doesn’t want to restart on its own. It will start and run with a prime.

The primer bulb would not pump fuel well, unless the fuel cap was released, but it still wouldn’t run well with the fuel cap off.


Any help or ideas are welcome

 

[Bigmac]

I am a 500 I virgin….

 

[Woodslasher]

Tank vent ok? The whole no pump without a cracked cap thing sounds very suspect. My 500's primer will push fuel forever so the fact that yours doesn't seems indicative of a fuel line or fuel vent issue that may be at least partially responsible for your issue.

 

[Bigmac]

Thank you! And that’s what I feel as well, but it will not run with the fuel cap completely off either

 

[Bigmac]

Tank vent ok? The whole no pump without a cracked cap thing sounds very suspect. My 500's primer will push fuel forever so the fact that yours doesn't seems indicative of a fuel line or fuel vent issue that may be at least partially responsible for your issue.

I think the tank vent could be an issue, just don’t know how the system works

 

[Woodwackr]

Thank you! And that’s what I feel as well, but it will not run with the fuel cap completely off either

It shouldn’t even start with the cap of

 

[Bigmac]

It shouldn’t even start with the cap of

So it likes a certain controlled amount of air in too much air is bad for the vent? Seems odd logicaly. But I’m learning

 

[Woodwackr]

So it likes a certain controlled amount of air in too much air is bad for the vent? Seems odd logicaly. But I’m learning

It ain’t a normal saw

 

[bogieboy]

Check the chain side av limiter at the back corner of the cylinder, if its broken out, odds are good that it got pinched and pulled on way too hard, which may have torn intake or the pulse lines/fuel lines. These saws need a goood strong pulse to build the pressure for the injector... could also be a harness issue, if theres a partially broken wire, (similar to how a 201t runs like crap when a wire breaks in the harness)

 

[emanuel]

It ain’t a normal saw

Its not that complicated of a saw as you make it sound either. To me it looks like the machine is starving for fuel; I’d carefully check for cracked fuel lines first, cracked intake boot, the fuel pump diaphragm condition (its in the primer bulb assembly), tank vent. I think this should find the problem, I doubt its the main seals leaking seeing how the bulb has troubles pumping fuel.

 

[Coupe]

Primer bulb is not going to pump well if intake vent is blocked.Think one of the things I would do if it was me would fish out the tank filter take it off and put a mytivac or small pump on it and test for leaks. Doing it that way will test you carby for leaks as well. There is a lot of things that can make them lean off like that is worn crankcase seals. Hope you get on top of it as there is a lot of trial and error sometimes to find it.

 

[Bigmac]

Put a new tank vent in no change in running, the primer bulb did work better though. So far all of the lines hold pressure.

 

[Bigmac]

And when I pulled the prime line, fuel came out.

Dose this have a fuel return line or a prime and fuel line

 

[huskihl]

500 doesn’t care if it has a gas cap on it or not. It needs fuel pressure to the injector. I would look at the diaphragm fuel pump behind the on/ off switch/primer bubble

 

[huskihl]

And sometimes the fuel values get outside of the factory parameters and the brain can’t figure out how to get them back. And the only way to reset that is by hooking it up to the MDG software. I know of one saw in particular that a builder received for porting and it had a slightly scored piston. The builder replaced the piston, ported it, and sent it back. A few weeks later he got the saw back again with another scored piston. Hooked it up to his MDG to do a reset, replaced the piston again, and to my knowledge it runs fine now

 

[Bigmac]

Well, after loss of troubleshoot, shooting all the lines, the primer bulb and everything and decided to do a pressure VAC test…. PTO crank seal!! Also found that the clutch had three broken chunks off of it rattling around in there not sure if it’s common for that to happen on these or what?

I

 

[Ketchup]

Well, after loss of troubleshoot, shooting all the lines, the primer bulb and everything and decided to do a pressure VAC test…. PTO crank seal!! Also found that the clutch had three broken chunks off of it rattling around in there not sure if it’s common for that to happen on these or what?

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I’ve busted off clutch shoe ears when the clutch wouldn’t release with an impact. So I kept impacting. Eventually it came off and very similar bits fell out. Different saw though and the clutch still works.

 

[Bigmac]

I’ve busted off clutch shoe ears when the clutch wouldn’t release with an impact. So I kept impacting. Eventually it came off and very similar bits fell out. Different saw though and the clutch still works.

This came off very easy, it’s just an 1128 clutch, so nothing new there, saw is just new to me. Learning a lot, definitely have a better understanding of the fuel system now

 

[EFSM]

I think those pieces broke off here. I'd expect it would still work.

 

[Bigmac]

Got the new pto seal, and that didn’t fix it! So I reluctantly pulled apart the primer/pump and wow! The pump is like a carb, so weird! And…. The inlet screen was completely clogged, like I’ve never seen an inlet filter clogged! Lol.

So after that, the primer bulb started to function correctly, and the saw runs correctly, I believe! Lol