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

[trappermike]

When modifying Holley carbs I simply purchase the shooter size I want,any size is available,quite cheap,and 1 screw to replace.
I use the mini drills to modify all the circuits of various saw carbs.

 

[Johnsonlong]

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

Just for archive and information purposes I just measured 2 factory carbs I have. The ms180c OEM non-adjustable carburetor jet sizes pin check at .011 on the low jet and .017 on the high jet this is Sae inches not MM.

 

[chainsawredeemer85]

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

Where are you talking about drilling? Photo please? Are we talking the inlet needle here or what?

 

[trains]

sorry dont have any photos of it, just the main jet in the carb, search it on the web if you need to know what it is.

 

[chainsawredeemer85]

sorry dont have any photos of it, just the main jet in the carb, search it on the web if you need to know what it is.

The main jet meaning the the jet that sprays fuel into the venturi? So we are not talking about changing the inlet needle then? I thought the main jet has a tiny diaphragm in it?

 

[trains]

The main jet is behind what poke out into the venturi, and that piece is called the fuel delivery nozzle, that has a small one way valve or disc so it allows fuel to be drawn out into the venturi under vacuum, but does not allow air to be drawn back into the fuel side of the carb.

The inlet needle is yet another different piece that is actuated by the metering lever diaphragm and maintains the correct fuel level behind the main jet, sort of like a normal carbs fuel bowl. does that clear it up ?