TT-20K tach problem after muffler mod 6401

[cbr929rr]

I muffler modded my makita 6401. I enlarged the existing 5/8" muffler hole to 13/16 which is 74% of the exhaust port area. When I fired her up she was lean and hit the rev limiter ( I warmed the saw up with a few cuts in 14" wood), so I richened up the high screw and the max recall showed 10,500. I then cut a couple of cuts in wood and leaned her out a bit 11,500. I cut a couple more cookies and leaned out more and more never hitting the rev limiter and the max rpm never went above 12,500 under no load with bar and chain. I used a hot exacto knife and removed the limiter tabs so I have full adjustment. What am I doing wrong. I never actually saw max rpm but the recall function put it out on the second display. The idle was 3,300 and the chain didn't creep and excellerated great from idle. In the wood it cut just like stock. I have never used a tach before or tuned by ear but the rpms constantly jumped all over the place.
Can someone help me out?

 

[cbr929rr]

bump

 

[Lakeside53]

"Jumping all over the place" is because you are hitting the rev limiter. It's not a nice smooth or instant transition and you can't use a tach to max. Wecome to tuning rev limted saws... you can't do "by ear" either.

 

[cbr929rr]

If i can't tune by ear or use the tach how would I go about it. I thought you must use a tach when tuning rev limited saws?:monkey:

 

[Lakeside53]

There will be a factory approved process for doing so - I'll let a Dolmar guys speak aout that.

With the very few Stihl that had limited coils, it was to set a low point (like 11.5k) then 1/2 turn CW (H) more. Rough, and conservative.

Me... I set it conservatively, listen to the saw in the wood, and make small adjustments. If you want to race, do a series of timed cuts and read plug color. PITA...

 

[timberwolf]

I would put quite a bit of effort to get rid of the rev limiter coil, not that it's going to make big performance gains, but at least the mixture can be set without difficulty.

Like lake said, it's a PITA, but set up to do timed cuts, set it way rich and then slowly lean it and watch the cut times, once you have where it cuts fastest, back off a hair towards rich to give yourself some safety margin.

 

[romeo]

The rev limiter is set ridiculously low on Dolmar/Makita saws. But like the others say, start on the rich side and go up from there making test cuts. The limiter shouldn't matter unless your saw is capable of busting 12.5k while in the cut, that takes more than a muffler mod.

They are a :censored: to tune, they can sound like they are four stroking and still be way to lean.

 

[cbr929rr]

well I went way rich and used the wire leads and got 13,200 (no jumping around)with bar and chain no load. I cut like that for an hour, seems ok but sounded a little lean at times. I will test with cuts in a couple of days. Thanks for your help.
PS. I wish I never bought this tach, I know it has nothing to do with the manufacturer but I spent $88 and I doesnt work on 2 of my saws!!!!

 

[Haywire Haywood]

I'll give you 45 for it... :greenchainsaw:

Ian