MS362cm seems to be running out of fuel

[Jaws]

I have a 362 that I rebuild, started right up and ran fine. Next day I come to use it and starts fine , revs to full rpm for 20 seconds then dies out like its running out of gas. When you let of the throttle it idles fine. but she will not rev fully unless you open and close the fuel cap. then she will repeat the process.
So here is what was done so far.
-New piston and cylinder ( Dukes Nikasil )
-Pressure and vac checked crankcase / no leaks
-New fuel solenoid and filter
-Pressure tested fuel line
-New tank vent
-Connected MDG1 and every thing checks out 100%
-Swapped carb with another 362 and still the same problem

What has me floored is she always starts first pull and idles for hours.

 

[J D]

Tank vent is blocked

 

[pioneerguy600]

Even with a blocked tank vent the engine should run for more than 20 seconds before shutting down. It does seem plausible though as the OP claims it will run fine again after venting the tank. Maybe the 20 seconds is a bit off timing wise.

 

[Jaws]

The tank vent was replaced and it runs about the same amount of time with the tank almost empty vs. full.

 

[cookies]

coil gap? flywheel magnets weak?
test tank vent by draining fuel then through the fuel hose on carb side pull a vac and see if it falls to atmosphere. fuel hose internally collapsed or pinched? spark plug replaced?

 

[Old2stroke]

For what it's worth, here's a theory that's a total reach. How about a weak impulse signal from the crankcase? It takes a fair bit of vacuum in the tank to open the tank vent valve and this might make it harder for the fuel pump to suck fuel out of the tank, so at idle where not much fuel is required, it runs well, but at high rpm where maximum fuel delivery is required, the combination of a weak pump working against tank vacuum might not be allowing enough fuel delivery. Be interesting to follow the suggestion of putting a vacuum pump on the tank and seeing how much it takes to open the tank vent.

 

[Lightning Performance]

For what it's worth, here's a theory that's a total reach. How about a weak impulse signal from the crankcase? It takes a fair bit of vacuum in the tank to open the tank vent valve and this might make it harder for the fuel pump to suck fuel out of the tank, so at idle where not much fuel is required, it runs well, but at high rpm where maximum fuel delivery is required, the combination of a weak pump working against tank vacuum might not be allowing enough fuel delivery. Be interesting to follow the suggestion of putting a vacuum pump on the tank and seeing how much it takes to open the tank vent.

It's not a far reach. It was my first thought.
Weak impulse or a cracked impulse line.

A stiff diaphragm or pin hole adds to the pia running.

Could have a clogged carb screen or partially plugged inlet before the needle and seat.

Loose welch plugs can also cause an air leak internally and kills your throttle transition from idol to midrange.

 

[sand sock]

Fuel line is collapsing

 

[oldbuzzard]

Got a 362 sitting in my garage with the same problem. I bought another carb for it but I haven’t had a chance to put it on. When I bought the saw I was told it had been straight gassed but the top in was fine when I pulled the cylinder.

 

[Old2stroke]

The OP changed the carb and the tank vent, so it's hard to explain what appears to be a fuel pump delivery issue that is still affected by tank pressure.

 

[Jaws]

Got a 362 sitting in my garage with the same problem. I bought another carb for it but I haven’t had a chance to put it on. When I bought the saw I was told it had been straight gassed but the top in was fine when I pulled the cylinder.

That is interesting because this saw was straight gassed too However they ran it for a couple of months after that until it totally quit running.

 

[Jaws]

Fuel line is collapsing

Ruled that out by attaching vac pump at the carb end of fuel line

 

[ZeroJunk]

It's a little frustrating, but I had two pieces of equipment this week where the replacement carb was bad out of the box.
One was BR600, the other an HL94. But, that is a possibility.
Subsequently you change everything else on it just to get back to the carb.

 

[cscltd]

Take fuel filter off and rested with full tank.
was it oem fuel filter or aftermarket junk ?

 

[Jaws]

Take fuel filter off and rested with full tank.
was it oem fuel filter or aftermarket junk ?

OEM orange filter and I assume you meant reset?

 

[cscltd]

I meant retest but iPad thought something different-lol
i would still try another or no filter for short test.
but I have found the wiring harnesses on cm saws can be a source of a lot of issues and giving false running issues and end up replacing them.

 

[Wood Doctor]

Since you have checked everything else, I would replace the ignition module if you have not already done that. I ran into this problem with an MS 661c M-tronic several years ago. New ignition module (not cheap of course) fixed it.

 

[Captain Bruce]

Got a 362 sitting in my garage with the same problem. I bought another carb for it but I haven’t had a chance to put it on. When I bought the saw I was told it had been straight gassed but the top in was fine when I pulled the cylinder.

So, is it finished, or was that just your 2 cents?

 

[Captain Bruce]

I have a 362 that I rebuild, started right up and ran fine. Next day I come to use it and starts fine , revs to full rpm for 20 seconds then dies out like its running out of gas. When you let of the throttle it idles fine. but she will not rev fully unless you open and close the fuel cap. then she will repeat the process.
So here is what was done so far.
-New piston and cylinder ( Dukes Nikasil )
-Pressure and vac checked crankcase / no leaks
-New fuel solenoid and filter
-Pressure tested fuel line
-New tank vent
-Connected MDG1 and every thing checks out 100%
-Swapped carb with another 362 and still the same problem

What has me floored is she always starts first pull and idles for hours.

Read about this years back, when it happened in my Shop. Its somewhat routine with the large number of YT professionals, in their '20's.
Someone replaces carb components; either the entire fuel system, or just a leaky hose. The hose is pinched at the tank, because, the in-tank hose is too long, and the filter is like an anchor.

Give the fuel lines, which deliver without obstacle, to the carb. Good Luck.

 

[oldbuzzard]

So, is it finished, or was that just your 2 cents?

Guess I need to post an update. Swapped carb and no change in problem. Bought a replacement coil but have not had chance to install it yet. Also Im going to make a test harness for checking the wiring. I have already checked out the fuel system.