MS170 x 2 fuel run issues, need repair advice?

[Okie]

go buy 2 wt215's and put them on and don't look back,, they are fully adjustable

I previously asked in this thread about maybe getting the walbro adjustable as a replacement carb instead of the OEM Zama and odds were to get the OEM. I prefer the Walbro carbs but:

Reasons why to go get the OEM Zama:

These two saws are not mine and I wanted minimum time spent on repairs. (only needed replacement carb for one of the saws)

The guy that owns these two saws has two good ole Redneck teenage boys (and the apple did not fall far from the tree) that use these saws in the woodlot and when dad is not watching and they will take a screwdriver to a saw carb in a heartbeat. (they have seen dad do such) I suspect they had been twisting on the one saws idles adjust and got it way off. I'm going to plug the idle adjust holes in the side of the case so I can tell if the saws have been DICKED WITH BY A REDNECK if I ever see the saws again.

These two MS170's don't have any access holes in the side of the case for adjusting the H and L Walbro. Have to mod the case drilling access holes and I did not want to mod a saw that was not mine. The saw that needed the carb looked almost new, no faded color to the plastic and bar paint still very good. I think they had stored the saw with probably ethanol gas mix in the tank and in a hot building and gummed the carb. I asked the guy if he tried to use non-ethanol gas for his eq and said no, his son's use what ever is readily available, might even be kerosene.

 

[a. palmer jr.]

I didn't recommend the aftermarket adjustable carbs, bc i have no experience with them. Are they decent?

Gonna find out, I have two ordered. I also have two 170s sitting in my shop with the same problem as original poster..

 

[a. palmer jr.]

I tried cleaning those carbs before and the saw ran exactly as it did before cleaning so I ordered fully adjustable ones to replace the Zamas. Note that the air filter housing has holes to accommodate the adjustable carbs also but I suppose you have to remove the top cover to adjust.

 

[Okie]

I tried cleaning those carbs before and the saw ran exactly as it did before cleaning so I ordered fully adjustable ones to replace the Zamas. Note that the air filter housing has holes to accommodate the adjustable carbs also but I suppose you have to remove the top cover to adjust.

What I noticed on these saws:
Yep, I noticed that the plastic air filter housing had the holes for the H and L adj but no holes thru the outer side of the plastic case to the outside for a straight in screwdriver adj of L and H jets. except one small hole for the idle only and it was not straight into the adjustment, had to go by feel for the screw slot. (and the side cover not easily removed)
I did not want to drill any holes in the outer case of a saw that is not mine or try making L and H adj's adjustments with a 90 degree ratcheting screwdriver on a running saw.

I bought a $6 Zama carb kit from flea bay and have a Ultrasonic cleaner but did not try the kit mainly due to the Zama jets not being removable for a good cleaning thru the jet holes and suspected the kit might be a waste of time/effort. I'll let the owner of the saws try the kit on the old carb if they desire. A OEM Stihl Zama carb kit was listed at around $18-20 and new carb at $29

One of these MS170's will drop easily if you pick it up by the pull rope, with very little pause between compression strokes, the other one feels normal and both saws have been at rest for 3 days and the one with weak rope feel starts and runs slightly easier than the one with good felt pull of the rope????? (usually running within not more than 3-5 pulls from cold start) If going by the rope drop test I would have bet that that saw would not even start just going by compression feel. (compression did check little low at 120psi) I did not test the compression on the other MS170 with good rope compression feel as a comparison of the two saws.
It also cuts with good power and accelerates good. I seen a little homelite awhile back acting the same and no compression release when starting. (probably about worn out and on it's last leg would be my guess)
I'll tell the owner if it gets weaker and won't cut the mustard just save it as a parts saw for the other one.

 

[a. palmer jr.]

If nothing else, you could bolt the carb on the saw without the airbox and adjust it then put the airbox back on it.

 

[Okie]

If nothing else, you could bolt the carb on the saw without the airbox and adjust it then put the airbox back on it.

Is that what you are going to try (no air box) with the walbro adjustable carbs? (still going to be a close 90 degree screwdriver adjustment or might be able to use just a driver screwdriver end and adjust by finger pressure???))

Give us a report back when you get one installed as to what you find, etc?

 

[SteveSr]

Here is a new carb off of the ms170.
View attachment 524480

That is a BIS (Balanced Idle System) carb. I thought that Stihl got rid of them a decade or two ago!

 

[davhul]

I haven't read through all the post but if no one said the compression is to low at 100 psi to idle than it is. When it gets to around 90psi it probably won't start at all.

 

[a. palmer jr.]

Is that what you are going to try (no air box) with the walbro adjustable carbs? (still going to be a close 90 degree screwdriver adjustment or might be able to use just a driver screwdriver end and adjust by finger pressure???))

Give us a report back when you get one installed as to what you find, etc?

I will do that. Still haven't received the carbs in the mail, should hopefully be this week.. From what I see it looks like you can adjust these carbs right through the airbox but with top orange cover off. If I can't I'll just take the air box off and adjust it without it. Looks like this air box has holes for both types of carburetor..

 

[a. palmer jr.]

I haven't read through all the post but if no one said the compression is to low at 100 psi to idle than it is. When it gets to around 90psi it probably won't start at all.

That's not the problem with the two saws that I'm working on, seems like they have plenty of compression. They will run if you squirt a little fuel mix into the air box.

 

[a. palmer jr.]

That is a BIS (Balanced Idle System) carb. I thought that Stihl got rid of them a decade or two ago!

That's what's on both of mine. They're too small to make a door stop out of so I guess they go into the dumpster..

 

[HarleyT]

That is a BIS (Balanced Idle System) carb. I thought that Stihl got rid of them a decade or two ago!

That carb is off of the new style ms170.

 

[Okie]

I haven't read through all the post but if no one said the compression is to low at 100 psi to idle than it is. When it gets to around 90psi it probably won't start at all.

I agree that anything less than 100 is suspect but I take compression reading with a grain of salt, especially on the itty bitty engines.

I've seen some of the little Homelites that took several pulls even with oily jugs to get to 80 and they start, idle and piss rev and cut good. (and this is using a good 2 cycle comp gauge setup especially for small displacement engines)

Lots of comp gauge setups will indicate low compression and therefore misleading to the operator (and won't read good compression) on small displacement engines!

 

[Okie]

That's what's on both of mine. They're too small to make a door stop out of so I guess they go into the dumpster..

Might use the little carbs as sinkers for catfish jug lines. I've considered using Poulan saws as trot line weights, but they pollute too much with a oil slick and catfish don't like their smell and also Poulans leaves a bad taste in their mouth and I've noticed the same.

 

[davhul]

I agree that anything less than 100 is suspect but I take compression reading with a grain of salt, especially on the itty bitty engines.

I've seen some of the little Homelites that took several pulls even with oily jugs to get to 80 and they start, idle and piss rev and cut good. (and this is using a good 2 cycle comp gauge setup especially for small displacement engines)

Lots of comp gauge setups will indicate low compression and therefore misleading to the operator (and won't read good compression) on small displacement engines!

True. A cylinder leak down test is way better. Here's a new ms170 off the shelf pushing 150psi. I have a Polaris 90 that stock is 80psi and its runs great but that engine is designed to run with that. That engine sir is toast.

 

[Okie]

View attachment 526914
True. A cylinder leak down test is way better. Here's a new ms170 off the shelf pushing 150psi. I have a Polaris 90 that stock is 80psi and its runs great but that engine is designed to run with that. That engine sir is toast.

Your compression tester appears it might be homemade or modded by looking at the bottom connections to the gauge . What type of setup or what does it look like on the input to the gauge?

 

[davhul]

I can guarantee its correct and not homemade. It's made with a quick coupler. Also have the hose for the 10mm thread cylinders.

 

[a. palmer jr.]

I agree that anything less than 100 is suspect but I take compression reading with a grain of salt, especially on the itty bitty engines.

I've seen some of the little Homelites that took several pulls even with oily jugs to get to 80 and they start, idle and piss rev and cut good. (and this is using a good 2 cycle comp gauge setup especially for small displacement engines)

Lots of comp gauge setups will indicate low compression and therefore misleading to the operator (and won't read good compression) on small displacement engines!

A lot of that has to do with the reed valve on the older Homelites and others. I don't think any of the newer ones use a reed valve and require higher compression. I've been using an old Lawn Boy mower for years that barely has 90 psi compression.

 

[davhul]

A lot of that has to do with the reed valve on the older Homelites and others. I don't think any of the newer ones use a reed valve and require higher compression. I've been using an old Lawn Boy mower for years that barely has 90 psi compression.

I don't know a lot a about law boys or Homelites. But his saw has 2 piston rings and doesn't have reeds. It will get to the point where your going to have to pull the rope faster and harder to get it to start at all. I hope the carb fixes it but I doubt it.

 

[a. palmer jr.]

I don't know a lot a about law boys or Homelites. But his saw has 2 piston rings and doesn't have reeds. It will get to the point where your going to have to pull the rope faster and harder to get it to start at all. I hope the carb fixes it but I doubt it.

What I was trying to convey is that if your engine doesn't have reed valves it will require over about 120 psi. compression to run right. Most newer designed chain saws carry around 150.