MS200t with a vacuum leak I'm having a hard time tracking down.

[mp5n]

This 200T is baffling me. It’s acting like it has an air leak, but passed a vacuum and pressure test with flying colors even when turning the crank or flexing the top handle. Starts with the choke fine then dies. I checked the breather, fuel filter and fuel line for obstructions. All check out normal. Compression is at 160. I put on a known good carb from a good running saw and get the same thing. I then put the carb I had on the saw onto another saw and it runs great. I can turn the saws so that the bar is horizontal, both ways, and it runs good. As soon as I hold the saw in its normal bucking position it dies out. I thought it might be a main seal leak when the saw is running, so I replaced both and get the same results. No matter where I tune the carb it’s acting up. The fuel I have runs fine in everything else. Any thoughts would be appreciated.

Thanks in advance,
MP5N

 

[HuskStihl]

Fish tank

 

[struggle]

DO you have a carb that has the exccellerator pump built into it? They havae been known to drive people crazy trying to get a saw into tune.

 

[stihl for life]

Ive seen saws not get enough air into the gas tank check the vent hole or the fuel cap and see if they are letting air in. the best way to check that is to pressure test the tank buy blowing air into the gas tank through the fuel line . with no fuel in to thank of course and fuel cape on . if the gauge is gaining in pressure then the gas tank is not letting enough air in .

 

[Ozhoo]

You mentioned checking the fuel line for obstructions. Have you checked it for holes/cracks? Sounds like it's sucking air when sitting upright.

O

 

[Brian13]

Check the fuel line for any cracks or holes. And I would check the impulse line.

 

[mp5n]

Check the fuel line for any cracks or holes. And I would check the impulse line.

I pressure / vacuum tested the fuel line and vent. I've run it with the fuel cap loose also. I even ran a separate fuel line into a gas can and got the same results. I've ruled the carb out by installing a carb from a good running saw. Same results. I then put the carb off of the problem saw onto the other saw and it ran fine. When I leak test the saw I spin the crank to check the seals and flex the handle up and down and side to side to verify the intake boot is sealing. The impulse line is clear and flows fine through the handle to the port in the intake boot and back into the motor. Everything appears proper in the static condition.

I'm leaning towards a crank bearing problem that's causing an air leak when the saw is running. Any other thoughts?

 

[stihl for life]

is it possible of taking a vid and posting on here to show us what is going on ?

 

[trophyhunter]

I know you checked it already, but I would replace that impulse and fuel line. If it doesn't run then give it scuba lessons to find a leak, if nothing else that will rule out where the problem isn't at and you can concentrate on the intake back to tank.

 

[mp5n]

I know you checked it already, but I would replace that impulse and fuel line. If it doesn't run then give it scuba lessons to find a leak, if nothing else that will rule out where the problem isn't at and you can concentrate on the intake back to tank.

I always replace the impulse lines with factory Stihl lines when I go over these saws. I bypassed the fuel line by running a separate line into a gas can. This would eliminate the original fuel line and breather from causing the problem. The saw is exhibiting the normal symptoms of an air leak. It dies when you hit the throttle and will shut off when at idle. Like I said it will run fine when on its side but will die when you hold the saw normal.

I keep coming back to crank bearings allowing the crank to run out in excess of what the seals will compensate for. If the crank has grooves worn into the journals then when you turn the saw on its side the crank will shift slightly allowing it to get into the unworn section of the crank journal and reducing the run out. These saws run roller bearings on the crank and it's possible for a groove to be worn into the journals. I'll tear her apart this afternoon and take a look.

If anyone has any other suggestions please let me know.

Thanks to all,
MP5N

 

[struggle]

Did you spray the seals with soapy water when pressure testing and turning the crank at the same time?

Only thing I can come up with is like mentioned above is a tank test under pressure. That would instantly expose an issue.

 

[trophyhunter]

Did you spray the seals with soapy water when pressure testing and turning the crank at the same time?

Only thing I can come up with is like mentioned above is a tank test under pressure. That would instantly expose an issue.

Or, maybe slather the outside of those seals with heavy grease and see if the saw will at least idle in all positions? Found a crank seal issue on an earth auger motor like that once that passed vac tests like a champ but wouldn't idle for anything.

 

[Saw Dr.]

I have seen a handful of instances where the carburetor end of the intake pipe is the culprit. It gets compressed and hard. Pull the carb. If you can see clear imprints where the lettering on the carb is, you found it. Also make sure both inner and outer washers are on the intake right there, and not bent. Any nick/scratch in the carb at that point also could be your issue.

 

[blueberrymuzik]

When all other diagnostic options have been exhausted, here's a trick from the automotive side of troubleshooting- but use it with caution! If you suspect that you may have excessive crank runout, with the engine running, try directing a short blast of carb cleaner at the end of the crankshaft you suspect. If in fact you have a seal leak, your rpm's will jump up as the carb cleaner is "inhaled". Normally in automotive work I use ether to find vacuum leaks, but it is a bit extreme for chainsaws.

 

[trophyhunter]

When all other diagnostic options have been exhausted, here's a trick from the automotive side of troubleshooting- but use it with caution! If you suspect that you may have excessive crank runout, with the engine running, try directing a short blast of carb cleaner at the end of the crankshaft you suspect. If in fact you have a seal leak, your rpm's will jump up as the carb cleaner is "inhaled". Normally in automotive work I use ether to find vacuum leaks, but it is a bit extreme for chainsaws.

How on earth do you manage to get some 2 stroke oil into that carb cleaner spray so it doesn't strip the bearings dry and skid mark the piston if it get's "inhaled"?

 

[struggle]

When all other diagnostic options have been exhausted, here's a trick from the automotive side of troubleshooting- but use it with caution! If you suspect that you may have excessive crank runout, with the engine running, try directing a short blast of carb cleaner at the end of the crankshaft you suspect. If in fact you have a seal leak, your rpm's will jump up as the carb cleaner is "inhaled". Normally in automotive work I use ether to find vacuum leaks, but it is a bit extreme for chainsaws.

Using wd-40 (safer) will work just the same as you will notice the change in the way the saw runs without running the bearings dry.

 

[Golden saw]

Sounds to me as a annual buffer problem. If buffers are dry rotted or torn that would cause the ms 200T to bog or die if held in the upright position.

 

[Zippy]

... well if you've got another saw (where the other carb came from) you could try going further and swapping handle, carb boot, washer and carb over.

 

[Adamgaspo]

I agree with Saw Dr, the intake boot looks to be the culprit. In some form or fashion the boot either has a crack or is hardened enough to cause an air leak. Also check for the small vent hole on the lower right side of the intake boot where the carb mounts, if it is not in the proper location/ does not meet up with the corresponding hole on the carb you will have lean run conditions that will drive you crazy.