Stihl MS170 Air Leak

[JimQ]

I have an MS170 in my shop. Guy brings it in and says the idle is inconsistent and sometimes dies when turned on its side. Checked the saw for leaks and found none. Threw a carb kit in it. Put the carb back on, fired it up. Runs good but seems to idle slightly high. Sprayed some carb cleaner around the area between the carb and intake. The idle dropped. Sprayed some carb cleaner on the intake on the other side of the case. No change. I took the carb back off and made sure the mounting surface was flat by running it over a flat oil stone until all original machine marks were gone. Still had an air leak. I can get it to idle down by adjusting the idle screw but that doesn't make the leak go away. Is it possible that the carb is leaking around the throttle shaft? Are these things known for bad intakes?

Any thoughts would be appreciated.

Thanks,

Q

 

[aadoublea]

It seems to me that you already have a pretty good knowledge of saws so this probably won't help but on my 064's there is a gasket between the carb and intake and I didn't see one in the picture. I'm assuming the reason for that is because you wanted to show what nice job u did sanding it down.

 

[McCulloch1-52]

I have the same problem with my lombard looks like a homelite xl runs good put dies out when you put a load on it sparyed some carb cleaner on the gasket in front of the carb kills the engine I took it a part gasket did not look that bad to cause that but I am going to make a new gasket see what happens, but do you have a brass gasket ring that go's on the boot or the box it looks like the some carb set up as my stihl

 

[JimQ]

Thanks for the replies guys.

Here's a clip from mediaCAT

The only intake gasket shown is #18. It's a white nylon ring that sits in a grove in the intake. It's there.

Heck, I even tried to use a little fluorescent oil dye to see if it would get pulled in. No luck. :confused2:

Q

 

[hotshot]

Pressure test it with air

Assuming compression, carb, & fuel lines are not contributing to the tuning problem

Pull the muffler, make blinding plates for the muff & carb face, then pressure check it at 8 psig.
May have to get creative on the nuts that snug up the carb, by using stacked washers or
spacers.

You'll quickly be able to see the slight shaft leaks (can't avoid them), but it sounds like you have
a major leak to find.

 

[blsnelling]

No gasket is used or needed. That design on the 064 was later changed to not use a gasket.

 

[turbo885]

No gasket is used or needed. That design on the 064 was later changed to not use a gasket.

Did you pressure test the carb itself i have had alot of problems with those carbs BILL

 

[blsnelling]

If vac/pressure testing a saw, you want to block it off before the carb.

 

[turbo885]

If van/pressure testing a saw, you want to block it off before the carb.

i am talking about the carb itsef if he is spraying carb cleaner at it he dont know where it is flying and sucking in may not be the intake at all

 

[hotshot]

He wants to test shafts

If vac/pressure testing a saw, you want to block it off before the carb.

Not if you want to see shaft leaks....

 

[JimQ]

Like I mentioned, I did pressure/vac test the case by blocking off the intake and exhaust. Clam shell/crankshaft seals were OK. No leaks.

I put the muffler/carb back on, had a bit of a high idle which made me think air leak between the carb and the intake. I sprayed a bit of carb cleaner at the mating surface between the two and the idle dropped. It's possible that carb cleaner made it to the throttle shaft which made me wonder about that.

I guess I was just wondering if anyone had experienced issues with the throttle shaft or intake mating surface on these little saws. Or maybe the LD screw itself.

Thanks all.

Q

 

[sefh3]

Replace the plastic ring. I have found these to be an issue with this series saw. That's the only "gasket" between the carb and the intake boot. I had an 018 that did the same thing. Once I replaced that plastic ring, the problem went away. Also, check the fuel line.

 

[roostersgt]

I had a 029 that had a worn out shaft. Tried carb kits to no avail. Presure tesing of the carb failed. Bought new OEM of feebay and solved problem. 170 carbs are a dime a dozen. Probably only $25 NEW.

 

[C George]

Whats bizzar also is that Stihl uses no gaskets on the air filter housing. Both my saw and ones that come thru the shop we gasket each side of the af housing metal plate

 

[stihltech]

Plastic ring and carburetor. Always have carbs in stock for that reason.