MS290 High RPM Only. Help!!!

[ButcherGY54]

Hello All.

I am trying to fix this saw for my cousin. His construction crew was using this saw when it died. To make matters worse, it's a borrowed saw. The air filter got dirty so they poked holes in it. The summer/winter gate was in the winter position on a nice 100* day. They put on a new air filter after it died.

The carb was full of saw dust. I cleaned and rebuilt the carb. Same thing, will only run at high RPM. It is also a little hard to start. The spark plug is also good. I have checked the impulse line and intake boot under vacuum. Pass. Replaced the crank seals. Cleaned the fuel filter. All to no avail. What am I missing?

Any help is greatly needed and appreciated.

Thanks.
David

 

[Lakeside53]

Did you do an end-to-end pressure AND Vacuum test? Not sure exactly what you did from your description. If you're sure it does not have an air leak then look inside the carb again. Remove the welch plug and check the low speed jets...

And dump the fuel filter... A new filter only cost $5,or $2 for the insert. Get a genuine Stihl filter. Make sure the fuel line is clear of debris or it will have just blocked the inlet screen again.

 

[cbfarmall]

So, they borrowed a saw, poked holes in the air filter when it got dirty, continued to run it, and expect to give it back to the owner with no compensation??

Sounds to me like they owe somebody a new saw.

As far as fixing it, I can't add any more to what the other fellow offered.

Chris B.

 

[ButcherGY54]

The way I tested the boot and impulse line was to take them off the engine and seal one side. Then use a vacuum pump to check them. They each held 20in. with no bleed down. I put the engine under a vacuum after I did the seals with the intake and exhaust blocked off. It bleed down from 15" to 0 in about 3 seconds. I have not checked the engine under pressure. I also checked the muffler to make sure it was not clogged. It is clean. I replaced the fuel filter. No good. I pulled the engine from the chassis. I do not see any evidence of an air leak. This engine also put out 175psi worth of compression. The jug and piston look good.

When I rebuilt the carb I took out the welch plug, cleaned out the passages with the screws out. I have blown 100psi air in every hole of this carb. It appears clean. Do you think it could have a clogged port in the carb? If so, and this is only an idea, could I "cook" the carb? Either boil or bake the debris out.

As I said, this saw will run good at high RPM only. 3/4 to full throttle only. You can keep it running if you play with the thottle, but it will not Idle.

David

 

[Lakeside53]

Bleed down to zero in 3 seconds? You have a bad air leak. If it's real good it will not budge for an hour, and if marginal, maybe down to 0.2 Bar Bar in 30 seconds... The max test vacuum should be about 0.6 bar, or 8-9 psi..

Blowing 100psi Air into the carb main jet will almost always destroy the integral check valve. Air blowing should be very gentle with the nozzle a few inches away from any hole.


Block off the exhaust and carb connection to the cylinder. Apply 8 psi pressure to the Engine via the impuse hose. Drop the entire engine in a bucket of water and watch for bubbles.

 

[THALL10326]

The way I tested the boot and impulse line was to take them off the engine and seal one side. Then use a vacuum pump to check them. They each held 20in. with no bleed down. I put the engine under a vacuum after I did the seals with the intake and exhaust blocked off. It bleed down from 15" to 0 in about 3 seconds. I have not checked the engine under pressure. I also checked the muffler to make sure it was not clogged. It is clean. I replaced the fuel filter. No good. I pulled the engine from the chassis. I do not see any evidence of an air leak. This engine also put out 175psi worth of compression. The jug and piston look good.

When I rebuilt the carb I took out the welch plug, cleaned out the passages with the screws out. I have blown 100psi air in every hole of this carb. It appears clean. Do you think it could have a clogged port in the carb? If so, and this is only an idea, could I "cook" the carb? Either boil or bake the debris out.

As I said, this saw will run good at high RPM only. 3/4 to full throttle only. You can keep it running if you play with the thottle, but it will not Idle.

David

Hmmmmmmmmmm. Are you using the flange that fits the saw to do the vac/pressure test on the engine itself? A crankcase should hold 4 bar of vac and pressure for at least 20 seconds. Without the proper flange that fits in place of the carb to do the tests with its almost impossible to do those tests at all.

Also when this saw runs at 3/4 to full thottle do you know what RPM's its turning? A bad crank seal will allow air in the crankcase and cause the saw to scream. Is this saw screaming at full throttle?

 

[Lakeside53]

Hmmmmmmmmmm. Are you using the flange that fits the saw to do the vac/pressure test on the engine itself? A crankcase should hold 4 bar of vac and pressure for at least 20 seconds. Without the proper flange that fits in place of the carb to do the tests with its almost impossible to do those tests at all.

Also when this saw runs at 3/4 to full thottle do you know what RPM's its turning? A bad crank seal will allow air in the crankcase and cause the saw to scream. Is this saw screaming at full throttle?

Ur.. make that 0.4 BAR!!! (6psi on the ordinary guage).

 

[THALL10326]

Ur.. make that 0.4 BAR!!! (6psi on the ordinary guage).

You count the 0. ? Heck I put that needle on the 4 and never see the 0.,lolol

 

[Lakeside53]

You count the 0. ? Heck I put that needle on the 4 and never see the 0.,lolol

Tough to find the seals inside the saw after that!


New way to remove seals. Install protective body armor, snap 150psi connector onto on the engine, flip the air switch. Bam!:hmm3grin2orange:

 

[THALL10326]

Tough to find the seals inside the saw after that!


New way to remove seals. Install protective body armor, snap 150psi connector onto on the engine, flip the air switch. Bam!:hmm3grin2orange:

Shhhhhhhhhhhhhh Lake, we gotta make some money somehow,,:hmm3grin2orange: :hmm3grin2orange:

 

[Ekka]

Personally, I hate those 290's.

(I feel sorry for ya trying to to fix it) junk.