MS170 is killing me!

[Snowchaser]

Slap an adjustable carb on it and be done with the fixed jet. Itll run way better and more power. Lots of threads here on the minor alterations.

 

[PV Hiker]

Did you pull the needle and spray carp cleaner through all the ports? How does the needle and seat look? Is the needle seat arm adjusted at the right height to allow the proper fuel flow? Check that you have the proper vacuum to pull on the diaphragm through the impulse hose. Run on choke those could be some of the issues.

 

[PV Hiker]

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.

Yes! As above...

 

[L34]

Had nothing but trouble with fixed jet carbs.
Done 2x trimmers and 1 ms170 with chi adjustable carbs
All good.

 

[Cliff R]

Been a while since I worked on one but had the SAME issues. I try to avoid "low-end" models especially those that used "fixed jet" carburetors. I just bought a new OEM carb for the one I had in here, replaced the missing fuel line (fuel melted it to nothing) problem solved. I was surprised at how lean Stihl has those set, it would rev to the moon and never even think about "four stroking". I thru some extra oil in the tank and gave it back to the customer with my exclusive "Arkansas Warranty"......."IF you break it in half......you get BOTH halves!".....LOL

 

[Vintage Engine Repairs]

The fact it starts and runs on choke and dies on high idle tells me you have an air leak. I’d suggest a vacuum and pressure test is the next logical step forward.

 

[dyager]

Slap an adjustable carb on it and be done with the fixed jet. Itll run way better and more power. Lots of threads here on the minor alterations.

Sounds like the direction I’m headed. Thanks, never knew about an adjustable carb for these boogers

 

[Chainmale]

The fact it starts and runs on choke and dies on high idle tells me you have an air leak. I’d suggest a vacuum and pressure test is the next logical step forward.

Hi Tom. I know you've become pretty familiar with pressure/vacuum testing now. I've just picked up a mityvac to test a couple of saws. I was wondering if you could point me towards a thread with some pointers for plates and fittings in a general sense. Searching “pressure vacuum test” doesn't seem to be finding any Info that I remember reading in the past (I have a feeling you may have been involved lol).
Thanks in advance!

 

[cookies]

use the impulse port as your access to test, cut out sections of bicycle inner tube to use as sealing gaskets between the carb and muffler

 

[Vintage Engine Repairs]

Hi Tom. I know you've become pretty familiar with pressure/vacuum testing now. I've just picked up a mityvac to test a couple of saws. I was wondering if you could point me towards a thread with some pointers for plates and fittings in a general sense. Searching “pressure vacuum test” doesn't seem to be finding any Info that I remember reading in the past (I have a feeling you may have been involved lol).
Thanks in advance!

use the impulse port as your access to test, cut out sections of bicycle inner tube to use as sealing gaskets between the carb and muffler

Sure thing. There isn’t an impulse line on the ms 170, it’s a drilling in the carb.

take the exhaust muffler off and slip in some inner tube and bolt it back up.

take the carb off and and slip in some inner tube and bolt it back up.

then make one of these adapters - it’s the most usable method of testing across a whole range of saws.

Here are a few methods to make the adapter.

https://www.arboristsite.com/commun...plug-pressure-vacuum-testing-adapters.282737/

 

[Yukon Stihl]

If you make a testing port out of a spark plug, get rid of the flat cruch washer on the plug and use an o ring as a seal Ask me why.

 

[Chainmale]

Awesome. Thanks heaps guys

 

[L34]

I put a bit of grease on the threads.
Seems to work.

 

[Woodslasher]

Or buy one of these like I did:
https://************/attachments/s-l1600-jpg.293845/

 

[Jasonrkba]

Those 170's are the least liked of saws I have kept. I use it to cut stumps in the dirt.

 

[cookies]

Sure thing. There isn’t an impulse line on the ms 170, it’s a drilling in the carb.

take the exhaust muffler off and slip in some inner tube and bolt it back up.

take the carb off and and slip in some inner tube and bolt it back up.

then make one of these adapters - it’s the most usable method of testing across a whole range of saws.

Here are a few methods to make the adapter.

https://www.arboristsite.com/commun...plug-pressure-vacuum-testing-adapters.282737/

then get a m 14 or m 12 bolt with 1.25 threads then drill a hole through it and pop in a impulse port on the head side, wrap the threads in teflon tape and screw it into the spark plug hole to run your tests, you can also get the 8 dollar test plate from any still dealer that you remove the carb to use.

 

[Chainmale]

I've got a compression tester I don't use without the Schrader at the end I could Rob the fitting from, hopefully can find a hose connector with the right thread. Is the pressure/vacuum enough to have to hose clamp the tester hose to either end?

 

[dyager]

Finally modded the muffler a bit and put on the WT-215 carb. Second pull everytime! Boom!! Thank you everybody for the advice and tips. It’s still a crap little saw but now the wife has her own!

 

[birdhunr]

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.

I agree with clyde85. My MS170 was mostly doing the same thing as yours. 2nd time I cleaned the carb I made sure I removed the needle valve held in by the spring/ lever and cleaned out the hole below the valve with a small wire then dprayed out the hole. Also I removed and cleaned the threaded brass piece and hole below it. I stripped the plastic off a bread tie to have a wire small enough to clean all the ports / holes after removing what I could. Use a small wire to clean all holes and also sprayed each one out with pressure from a fresh can of carb cleaner wit. Not just soak the carb. After getting a wire into every hole I also used a plastic nozzle on a spray can of chemtrol B12 to spray out all holes. Replaced the o ring on the carb that fits into the air filter housing. 1 yr earlier I had replaced the plug and fuel filter. Before cleaning the carb it would crank and rev once or twice then it would start to dye with any throttle. After my very tedious cleaning and setting left hand idle screw to 1.5 turns open, it started and ran great. Earlier I had also used pb blaster lmt (lawn mower tuneup) in a can to clean carbon out of the piston. When used a couple of years earlier that did seem to help but last year it wouldn't run and this year I decided to clean the carb thoroughly and it worked. You can try the lawn mower tuneup in a can and chemtrol B12 and sometimes they are enough but my carb really needed a thorough cleaning even though it didn't look dirty. I'm sorry i can't remember who I was watching on YouTube who showed me how to clean the carb but he also recommended to dump out almost all the unused fuel and then crank and run the saw until it totally runs out of fuel before storing the saw. So, I'm trying that now to hopefully avoid needing to clean the carb each time I need to use the saw. And of course...only mix fuel oil mixture using non-ethanol gasoline!!! Good luck. Hope you get it fixed. It is a great little saw when it works but a pain in the a when it doesn't run. Also i Love my MS 290 for larger jobs.