ms660 has slow throttle response

[Jim Fuss]

I have a ms660 with the tolloston carb on it. it fires right up , but there is a lag in the throttle response. when you pull the trigger, it takes a second to spool up. but then revs like all get out. and it takes a few seconds to return to idle after you release the trigger. the idle seems to be set around the 2700rpm mark. i feel like there is an air leak somewhere in the system causing the poor throttle response by not letting the diaphram in the carb do its job. but not sure if anyone else has had this problem. or is it just a very temper mental carb setting. or a bad crank seal or leaking decompression valve. any help is greatly appreciated.
Jim

 

[CR888]

Have you tried adjusting the L screw richer/leaner? Fresh mix? Is your air filter clean & spark arrestor clean and not clogged with carbon? Are fuel lines not kinked and healthy? Fuel filter pickup clean? Have you been inside carb lately and replaced metering lever or adjusted it? Symtoms don't directly indicate air leak (its possible) but a pressure/vac test could varify. The things I mentioned would be where I'd look first, there esay to check & then we can go from there.

 

[Jim Fuss]

yessir. ive been all around the L , and La ranges to find where it will idle best. the carb is new ( i also took it apart to clean it for good measure just in case), fuel mix new . now are you talking the lever that adjusts the needle ? should i bend it a little up so the diaphram touches it sooner? no fuel flow issues either, and the hoses are not kinked

 

[BobL]

Have you done a crankcase pressure test?

 

[Jim Fuss]

no sir. i am not sure how to either. can you enlighten me?

Have you done a crankcase pressure test?

 

[BobL]

no sir. i am not sure how to either. can you enlighten me?

The easiest way to do this is via the service manual instructions.

It involves sealing the exhaust and removing the carby and attaching a way of applying positive and negative pressure to the crankcase.
For the 066 the saw must hold 7psi on the pressure and after applying 7psi of vacuum it must not rises to more than more than 0.3 bar (4.25 psi) within 20 seconds. The pressures should hold even when crank is moved.

Usually enough pressure can be obtained using a hand pump.


Components
A: tubeless tyre valve - just go to a tyre shop and ask - I was given a couple for no charge.
B: on/off valve. Any air tight tap will do.
C: Pressure gauge. Shown is a 100 PSI pressure gauge, but I now have a -10 to 20 PSI pressure/vacuum gauge.
D: Adapter plate to attach pressure line to cylinder inlet port.
E: Alternative Adapter to attach pressure line to spark plug hole - if this is used the inlet port must be blocked. This is not the best way because it does not allow you to pressure test while moving the crank.
F: 14 x 1 mm blocking bolt for a compression release valve
G: Blocking plate and rubber gasket for exhaust port. Hole in the middle is not required. Easiest way is to slip a bit of rubber between exhaust and port and retighten exhaust bolts

For vacuum as opposed to test, remove the tyre valve and just suck with mouth - you can easily reach the vacuum normally required for most testing i.e. 6/7 PSI and then close the tap. Taste of crankcase not very nice so I keep a beer handy to rinse your mouth!

 

[BobL]

Another question is how well do the revs hold up under load i.e. bar buried in wood?
If it holds up it is unlikely to be the crankcase pressure.

 

[Jim Fuss]

thanks for your tester parts list..

Another question is how well do the revs hold up under load i.e. bar buried in wood?
If it holds up it is unlikely to be the crankcase pressure.

I have not had it out cutting yet. it is not reliable enough to try. its scary inconsistant

 

[CR888]

Another thing is to make sure your carb bolts that secure the carb to intake are tight. I like Bob's press/vac tester and advice on tasting crankcase!