MS180 fixed jet carb drilling out main jet to drop 15400 max rpm

[trains]

Hi Chaps,
I finally got around to putting in a new carby kit in my 180, its the fixed jet carb, I did order some chinese WT215 carbys to swap it and another over to a fully adjustable carb, but the ones I ordered did not look that good re quality, I took them apart, and felt that I would stick with the original one.

Even so, it tached out at 15200-15400, so I thought that was a bit too high. The metering arm was incorrectly set, probably by the previous owner, or maybe it was like that from the start, either way, everything was now correct but it was running far higher than I was comfortable with.

I had a look at the IPL, and the jet size is 0.45mm, high altitude jet option is 0.42mm.
I used to play around with race cars some years ago now, and would rejet the carbys depending on conditions of the day so I got out my verniers and realised I did not have any small jet drilling bits this size.
Further thinking found some needles at 0.46, then I came across one at 0.50, it was a needle that I would use for injecting grease into or past seal lips.
Gently rotating the jet on the needle caused the hollow end to ream out the jet orifice, taking out very small flakes of brass.
Once through, I checked the jet orifice under a magnifying glass, and it was smooth, and not rough, so back together it all went.

Warmed up and now it tachs at 12000, good 4 stroke out of the cut, and clean in the cut and dosent bog like it did previously, very pleased with how it ended up, still I think that an 0.47 or 0.48 would have been a safer start if it was available to me.

Hope that might help others who have a screaming 180.

Cheers

T

 

[Overkill338]

A good, informative post. But I keep laughing everytime I read "carby" lol

 

[trains]

A good, informative post. But I keep laughing everytime I read "carby" lol

Hey, thanks for the feedback, of interest is there another meaning for carby that us Aussies are unaware of ?

And whilst were talking of ms180s, some of you may remember when I did some plastic welding with a soldering iron to fix the case where the oil pump drive gear arm had damaged the case and worn through to the oil gallery and where the oil pump is pressed into the housing, it went so deep that it actually moved / twisted the oil pump so that its outlet did not align with the oil gallery in the housing.
its still working fine

T

 

[Overkill338]

Hey, thanks for the feedback, of interest is there another meaning for carby that us Aussies are unaware of ?

And whilst were talking of ms180s, some of you may remember when I did some plastic welding with a soldering iron to fix the case where the oil pump drive gear arm had damaged the case and worn through to the oil gallery and where the oil pump is pressed into the housing, it went so deep that it actually moved / twisted the oil pump so that its outlet did not align with the oil gallery in the housing.
its still working fine

T

That's awesome about the plastic welding. Do you have any before and after pics?

Also, there is no other meaning for carby. That's the first time I've seen it used. I really didnt mean any offense by it. I'm sorry if it appeared I was making fun of you.

 

[jltrent]

I bought a MS170 that would tach at 15200 and apparently had been that way as the bar was worn out and the cylinder was discolored for getting red hot. It still had like new compression as they must be tough little saws. I put a MS250 fully adjustable carb on it and maxed it out at 12500.

 

[trains]

That's awesome about the plastic welding. Do you have any before and after pics?

Also, there is no other meaning for carby. That's the first time I've seen it used. I really didnt mean any offense by it. I'm sorry if it appeared I was making fun of you.

Hi Mate, no offense taken, not the first time I have been caught up using a word or term that is acceptable in Aust, but not elsewhere.

Link to oil leak fix here

https://www.arboristsite.com/commun...-from-crack-how-to-repair-the-plastic.304229/
https://www.arboristsite.com/commun...-from-crack-how-to-repair-the-plastic.304229/

Jltrent, I have 2 of those carbs to suit a 250, as that was my first thought of fixing the problem, I think I would need to at least rekit them with a proper carby kit, even tho they were bought new.

I realize that Stihl specs for those saws are 14000, but I think it runs far better a bit richer.
Of interest I also tried out the 250 side adjuster on the 180, even tho its a $4 chinese part, it proves concept, and will replace it with a genuine Stihl part when it finally fails.

cheers
T

 

[SteveSr]

Hello,

One other possibility... Rather than mess with reaming fixed jets... What happens if you adjust the metering lever up some to richen the mixture somewhat. Anyone ever try this? This technique seemed to work on vertical Mikuni bike carbs by adjusting the float level. Wondering if this would also work on a saw carb. It shouldn't take much to drop the RPM to within a good range.

My $.02,
Steve

 

[TBS]

Hello,

One other possibility... Rather than mess with reaming fixed jets... What happens if you adjust the metering lever up some to richen the mixture somewhat. Anyone ever try this? This technique seemed to work on vertical Mikuni bike carbs by adjusting the float level. Wondering if this would also work on a saw carb. It shouldn't take much to drop the RPM to within a good range.

My $.02,
Steve

I did that on an 017, dealer put a new carb on it and it wouldn't run still so they gave up on fixing it. I noticed it was getting way to much fuel so i pulled the carb apart and readjusted the needle lever. It took a lot of Time and repeated disassembly to get it right.

 

[CR888]

Buy a $3 set of micro drills from EBay and have some JB weld on hand for mistakes & you can drill your jets out or reduce them to whatever size you want. And get a pin-vise to hold the drill bits. Just have some calibers around to check drill sizes should the little buggers get mixed up.

 

[trains]

Have not come across any drill bits that would do the job for 3 a set yet, closest was 25, had 30 drills in usable steps.
Jets are not just a metered hole, tho that is an important part in metering fuel, some jets have a lead up and ramp off from the measured final diameter, and this has a large impact on the flow of fuel through the jet.
Quite a science behind it if you care to look into it.
Dont get me started on emulsion tubes and their drillings, and air corrector jets.

cheers

T

 

[jltrent]

Hi Mate, no offense taken, not the first time I have been caught up using a word or term that is acceptable in Aust, but not elsewhere.

Link to oil leak fix here

https://www.arboristsite.com/commun...-from-crack-how-to-repair-the-plastic.304229/
https://www.arboristsite.com/commun...-from-crack-how-to-repair-the-plastic.304229/

Jltrent, I have 2 of those carbs to suit a 250, as that was my first thought of fixing the problem, I think I would need to at least rekit them with a proper carby kit, even tho they were bought new.

I realize that Stihl specs for those saws are 14000, but I think it runs far better a bit richer.
Of interest I also tried out the 250 side adjuster on the 180, even tho its a $4 chinese part, it proves concept, and will replace it with a genuine Stihl part when it finally fails.

cheers
T

A $5 carb and it runs great. I ordered 5 Chinese MS250 carbs and 4 of them worked as good as OEM and the other I took the carb kit out and used it in another. About a 15 minute fix for those MS180/MS170 and makes a good saw out of them. The OEM carb that comes on them are junk.

 

[blsnelling]

While 15,400 is way too high, 12,000 is way too rich. The normal approach taken on the 170/180 is to raise the needle height.

 

[Chainsaw Jim]

The C1Q S137 (ms180) is a factory 15,500rpm carb.
C1Q S137a is 14,000.
C1Q S152 is 13,300.
C1Q S286a is 13,000.
The WT215 carb (ms210/230) is 12,500.

 

[trains]

While 15,400 is way too high, 12,000 is way too rich. The normal approach taken on the 170/180 is to raise the needle height.

Hi David,
Yeah, ideally 12500 would be better, but it 4 strokes out of the cut, and is clean in the cut, dosent bog anywhere like it did before, will keep an eye on the screen and see how it goes, can always get another jet and then play with the metering lever height, tho the reason I did not was that it was already proud of the carb, and looked like someone had already tried that before, but it was still 15400, correct setting is level with carb, and it was still up at 15200-15400, so thought I would look at the jet.
Might try a 0.46 or 0.47 drill on another jet and report back. jets are only a few dollars.

Cheers
T

 

[trains]

As an update on the 180 fixed jet carb.

I ordered a 0.48 jet, but when it arrived, we discovered it had superseded to a 0.50 instead.
Thought that it was worth trying anyway, as the drill I used earlier to open up the original jet was not super accurate.
When taking out the old jet, I wore my glasses this time, and noticed the jet was 0.46, not 0.45 as per the IPL listing.

Put in the stihl 0.50 jet, and it tachs out at 12800, clearly my drilling was over 0.50, maybe 0.52, anyway, helps to wear glasses and not assume things are as you think they are.
Happier with the 12800 compared to the 12000, tho both are better than over 15000 and boggy.

Jet cost au $10 ish.

 

[a. palmer jr.]

My approach is to change the non-adjustable Zama with an adjustable Walbro. To adjust it initially you do have to take the stuff off of it so you can get your screwdriver in it but I always start at one turn on the H and L screws and that gets it pretty close. I've seen one or two of those little saws that came out with an adjustable but don't remember the model.

 

[trains]

Just an update, the saw has a bit of time on it now, and very happy with the results, saw runs strong, fine cutting, idling etc, no bogging, stalling etc.
Had a branch fall from the tree last night, and cut it up before it got too hot today.
It really is a toy sized saw, but nice and light, easy to use, and great for limbing.

 

[rayjay257]

Jet drilling is a lost art and many are not comfortable doing it for some reason. It's not rocket science and there is no need to worry about lead in angles and other nonsense that they use to try to discourage drilling and encourage jet buying. The lead in angles etc are already there.

 

[trappermike]

rayjay is right. You can buy a mini drill set(I wouldn't buy a $3 ebay set),then get a "pencil drill" tool to hold the bits,you can get them at a welding supply store cheap(used to clean welding tips).
A good mini drill set includes #61 (.039") to #, 80 (.0135"),sorry I don't have metric conversion on that.
You can rejet or cure other carb faults with it,very handy.

 

[rayjay257]

The holder is called a 'pin vise'. My drill set goes up to #61 !! The smallest is .0145" iirc. When I was doing a bunch of Holley carb mods for customers the first thing I would do is drill out the pump shooter to .039" for racing use.