MS170 is killing me!

[dyager]

Long story short, was given an MS170( go me). Rebuilt the carb, changed spark plug and fuel filter, burned out exhaust and screen. Starts on choke and revs up if I slightly move the choke lever. Switch to fast idle and it dreams. Switch to normal run position and it won’t take the throttle and then dies. Tried loosening filial CAO to no avail. Fresh fuel on board too. What am I missing? I’ve adjusted the idle screw to factory setting, 2 turns out from fully closed at counter clockwise. Stumped!

 

[dyager]

Man I need spell check! Loosened up fuel cap and no change. It’s also not a dream! Ha

 

[lone wolf]

Long story short, was given an MS170( go me). Rebuilt the carb, changed spark plug and fuel filter, burned out exhaust and screen. Starts on choke and revs up if I slightly move the choke lever. Switch to fast idle and it dreams. Switch to normal run position and it won’t take the throttle and then dies. Tried loosening filial CAO to no avail. Fresh fuel on board too. What am I missing? I’ve adjusted the idle screw to factory setting, 2 turns out from fully closed at counter clockwise. Stumped!

Carbs dont always work when rebuilt.

 

[dyager]

Carbs dont always work when rebuilt.

I hear ya Lone Wolf! Was hoping I was missing something obvious

 

[djg james]

Carbs dont always work when rebuilt.

Ditto on that. Did the saw set for a long time with fuel it it?

Mine did and disassembled and soaked the carb several times. Put a new aftermarket carb on and it ran but way too high rpms. Finally put on a OEM carb and it started right up.

 

[Clyde85]

Sounds like it is starving for fuel. I would go through the carb again make sure all the fine passages are clean, the final screen is clean. And the metering diaphragm and lever and needle are set properly. Check for holes in the diagrams and the diaphragms and gaskets are in the right order.

 

[djg james]

Sounds like it is starving for fuel. I would go through the carb again make sure all the fine passages are clean, the final screen is clean. And the metering diaphragm and lever and needle are set properly. Check for holes in the diagrams and the diaphragms and gaskets are in the right order.

As Clyde says do that first. If not done already, maybe replace fuel filter.

 

[dyager]

Ditto on that. Did the saw set for a long time with fuel it it?

Mine did and disassembled and soaked the carb several times. Put a new aftermarket carb on and it ran but way too high rpms. Finally put on a OEM carb and it started right up.

Dig james yup I believe it did. Have a logger buddy that throws me saws frequently. He’s not much into maintenance period. It takes a dump and he gets a new one. I’ll look for an OEM carb and cut through the chase

 

[dyager]

Sounds like it is starving for fuel. I would go through the carb again make sure all the fine passages are clean, the final screen is clean. And the metering diaphragm and lever and needle are set properly. Check for holes in the diagrams and the diaphragms and gaskets are in the right order.

Clyde85. I’ve taken it apart three times now and double checked my assembly. Blew wd40 through all ports and everything is where it needs to be. Swapped out fuel filters twice. I’m stumped short of getting a new carb

 

[cookies]

blow out the impulse line ...the port/line might have trash in it..also I have had success with the same symptom of not enough fuel at idle by using the butyl fuel pump diaphragms instead of the thin hard plastic ones.

 

[lone wolf]

Dig james yup I believe it did. Have a logger buddy that throws me saws frequently. He’s not much into maintenance period. It takes a dump and he gets a new one. I’ll look for an OEM carb and cut through the chase

See what shape the fuel line is in while at it.

 

[Clyde85]

Did you try backing out the idle speed screw. Or checking the tips of the high and low needless for damage.

 

[dyager]

blow out the impulse line ...the port/line might have trash in it..also I have had success with the same symptom of not enough fuel at idle by using the butyl fuel pump diaphragms instead of the thin hard plastic ones.

Cookies, good call!

 

[dyager]

Did you try backing out the idle speed screw. Or checking the tips of the high and low needless for damage.

Clyde85. From what I can tell this carb has no adjustments to high and low, just an idle speed screw

 

[djg james]

Dig james yup I believe it did. Have a logger buddy that throws me saws frequently. He’s not much into maintenance period. It takes a dump and he gets a new one. I’ll look for an OEM carb and cut through the chase

I'm a cheap SOB, so I'd rather try to fix something before buying new. Finally got tired so I purchased new OEM (Zama) off ebay for under $20. Looks like they're running around $30 now. And I've never liked to buy used carbs. To me it COULD be like you selling yours to someone. No guarantees. ebay does list some from China as OEM, but I'd not sure about that.

 

[cookies]

my next step would be a compression test if thats not the fix..when they get lower in compression they get lower in vacuum at lower rpms often they spittle fuel out of the front of the carb when they get lower compression

 

[Clyde85]

Clyde85. From what I can tell this carb has no adjustments to high and low, just an idle speed screw

Sorry I forgot they used the fixed jet carbs.

 

[SteveSr]

Man I need spell check!

You need to turn OFF Spell Check and/or proofread before you hit send!

 

[SteveSr]

What am I missing? I’ve adjusted the idle screw to factory setting, 2 turns out from fully closed at counter clockwise. Stumped!

If the saw will idle but not rev up then it could very possible by yet another Zama with a main nozzle check valve that is stuck closed. You fix these with a new OEM carb. I am assuming that you have checked/replaced the fuel line. They like to break at the sharp bend at the top of the tank.

 

[dyager]

If the saw will idle but not rev up then it could very possible by yet another Zama with a main nozzle check valve that is stuck closed. You fix these with a new OEM carb. I am assuming that you have checked/replaced the fuel line. They like to break at the sharp bend at the top of the tank.

SteveSr. Yes sir new fuel line on board! I’m shooting for new OEM carb. By the way thanks for the hot tip on spell check! Ha!