MS260 muffler mod / high speed tuning

[MS260 Fan]

I read a great post by Timberwolf on opening up the muffler. I think it was an 026. I tried the same on my MS260. Carb was reset by myself to factory original settings before I knew any better prior to doing the mod. The saw ran great prior to the mod.

After the mod I bought an Echo PET 1100 Tach and started the saw to tune it. I cut a few slices to get the saw warm. Outside T was about -2 deg C. Here's what I noticed.

1. The saw was idling much higher than normal at idle. Chain was turning. I measured 3800-4000 rpm. I adjusted the LA to get close to factory spec of 2800 rpm. When warm the idles surged to 3000 every 10 seconds or so but stays pretty close to 2800 overall.

2. At WOT I'm at 15,800 rpm with 18" bar and 0.325" chain. The saw ran through 16" ash beautifully. No bogging. Problem is the factory max rpm is 14,000. Can you really get this much out of them by opening up the exhaust? After warming up and LA adjustment the tach showed idle at 2800-3000 rpm so I think I'm good there.

3. I tried to richen the H mixture with H adjustment by turning it counterclockwise. The H won't turn any more. Fully closed is 10 o'clock and fully open is 2 o'clock. Counterclockwise from 10-2 is less than 3/4 turn. I thought there would be multiple turns.

Any suggestions on getting the rpm down? Should I not have more turns on the H? Without the tach I wouldn't have known any better and just run the saw. Now I'm concerned I'll burn it up by running too lean. I checked the plug and after 10min the base was tan on one side and black/tan on the other. Am I missing anything here?

 

[Erick]

15,800 is way high for just a muffler mod, you need to remove the limiter cap so you can tune (turn) the high side.

 

[timberwolf]

Yep, get in there right away quick with a little hook or dry wall screw to pull the HS limiter cap and turn the HS further counter clock wise.

It should end up above factory RPM to give a nice 4 stroking mix. Would not surprise me though if it was in the upper 14K 18 inch B&C even pushing into 15K range with a 16 inch B&C.

 

[K9-Handler]

2. At WOT I'm at 15,800 rpm with 18" bar and 0.325" chain. Problem is the factory max rpm is 14,000. Can you really get this much out of them by opening up the exhaust?

When I was young and dumb -- a couple of weeks ago -- I did the same thing you did on my MS260 Pro. Modified the muff (I think I posted some pics on it) and let her rip. Man, that thing would scream! Didn't cut with it though until I checked. Whew! Did something right for a change.

When my tach finally came in I warmed up the saw and tried it again. Yep. That sucker was winding up to 17,100! Nothing but a muffler mod, and me twisting the screw the wrong way... I had removed the H limit caps at the same time as the muffler mod, anticipating the need for adjustment. I just didn't adjust it the correct way.

After being corrected by Lakeside I got it down to a more respectable 14,100, but now it sounds slow!
Cuts OK, though.

I guess they make limiting coils for guys like me.

 

[PA Plumber]

A few weeks ago, I opened up the 026 muffler a little more.

Turning 14,200 and still getting a little 4-stroking (burble).

The saw runs nice and strong. Planning to leave the high side alone, unless there is carbon buildup on the spark arrestor screen.

 

[MS260 Fan]

I was hoping it was going to be something simple like this. I didn't realize the plastic caps were removable. I removed the H limit cap last night. It wasn't pretty but it came out. Based on the attached picture I don't think I'll be putting it back in anytime soon. Now that I have more adjustment, I'll turn it out another 1/2 turn or so (to 1-1/4) today before I start it up. Let it warm up and then play with the tach.

Thanks for the help!!

 

[2000ssm6]

LOL, I have done the caps the same way. Get it tuned and make a few cuts to see how she runs. You want to replace the caps before she goes back into service, they keep the carb screws in place from moving. Just cut the tabs off so you can adjust without having to pull them out again.

part # 4203 121 2700, should not be more than $.50 each.

 

[MS260 Fan]

LOL, I have done the caps the same way. Get it tuned and make a few cuts to see how she runs. You want to replace the caps before she goes back into service, they keep the carb screws in place from moving. Just cut the tabs off so you can adjust without having to pull them out again.

part # 4203 121 2700, should not be more than $.50 each.

Son of a gun. I had myself convinced I wouldn't need to put them back in. Oh well, $0.50 for the cap is well worth the aggravation I saved trying to make a tool to take it out in one piece. Thanks for the part number!

 

[MS260 Fan]

I let the saw warm up a bit and turned the H out almost 2 turns. RPM's at 14,400 and cuts great. I'll fine tune it when I get the limiter cap (without tabs) installed.

Is it normal for the rpm to surge at idle between 2800 to 3100? How stable should idle rpm be?

 

[kiwiguy]

My MS260's idle fluctuates between about 2700 and 2900 (before reading this thread yesterday, from the service manual, I thought its idle was supposed to be 2500 - so it pays to keep reqading these forums!).