carburator tuning with a tachometer

[riseandrun]

I've always had trouble adjusting the carbs on the saws I work on. And for me the problems with the saws are usually carb related. I read a how-to on line and the shop uses a tachometer for their fine tuning. Does anyone use one? The post used an electronic one. Does a saw like a Super 2 have a low speed rpm and a high speed rpm?
I have a sirometer vibra tach. Anyone ever used one?
Thanks in advance!
R&R

[rowdy235]

I’ve never used a tach for tuning but I suppose there’s multiple ways to do things. I do see max no load rpm and idle rpm specified for most saws.

I’d think a tach would be useful for setting idle speed but I don’t know that I’d rely on it for the high end. Since two strokes can be burned up very easily by running them lean I always prefer to go by ear and err on the rich side if in doubt.

[5terrysupersaws]

 SUPER 2 specifications;
                                   Idle Speed: 2900-3200 rpm
                                   No Load+ : 10,000-11,000 rpm  ( + without bar and chain )
                                   Compression : 115-145 psi ..engine at operating temp.

[jselden78]

Somewhere on here is a thread with the data from Homelite with most of not all of the saws and their rpm. I will see if I can find it

[jselden78]

houseofhomelite.proboards.com/thread/5790/homelite-idle-speeds-compression-pressures

Here it is. I don’t think it’s all saws but it’s a lot of them anyway

[jselden78]

houseofhomelite.proboards.com/thread/5820/homelite-carb-adjusting-pressure-testing

There is a link in this thread to a Homelite repair manual that gives an excellent step by step procedure to carb adjustments and pressure testing. I used to have trouble with carb adjustment too but one day I put my laptop on my toolbox next to my bench. I had a saw in the vise and used this manual and went step by step. I had to do it that way a couple of times but I’ve got it down pretty good now but it helped a lot in the beginning to just go one step at a time

[riseandrun]

I appreciate all the replies and links. I will give it a try! As an extra bonus, when I googled how to use my tach, the you tube guy was tuning a yard king snowblower with one, and I’ve never been able to get that thing adjusted just right... :-)
Thanks again and Happy New Year!
R&R

[xl130]

This is a bit of an older post now but I was wondering if you ended up using your Tach? Do you like it? I bought a carb tuning kit awhile back that had a Tach in it but haven’t really used it yet. Hooked it up to my XL-2 the other day to tune the low end. It seems ok.

[riseandrun]

Shame on me!!! Yes I have used it and it seems to work pretty good. I tried it on my snow blower, but I think I have other problems with the carburator. FWIW I've read/heard somewhere that Tecumseh engines have a tendency to have a "miss".. (off topic)
I think when the saw is running and just idling the sirometer is vibrating at a very close rpm of the engine. This is based on what I was told idling rpms were. Youtube video's say they are very accurate.
If you have some idea of where it should be, you can touch the side of the saw with it, and the wire will vibrate the widest at the frequency.
Are you using this? www.youtube.com/watch?v=KIVj6Rnz3Y4 The title is in another language, but he doesn't say anything anyway..lol

[xl130]

The tach that came in my kit is just a rectangular digital screen with a wire that you attach to the plug wire.

[riseandrun]

That sounds like a very accurate way to do it. I read on-line about a shop in Washington State who said he always uses a tach, and he has tuned 1000’s of saws. He has a digital tach that doesn’t’t even need to be attached. I’ll try and find the link. Proof in the pudding, and I like it as straight forward as possible since this is just me tinkering in the garage...Why i also like pressure checking carbs. I don’t have enough experience to tell by looking....
Please report back on your experience..

[xl130]

I’ve used this tach a few times now. It seems to work ok. I think that I prefer to just tune by ear now that Ive done this a few times.

I liked the tach the first couple of carburetor overhaul and tunings. It definitely helped to teach me the proper rang and sound that the saw should run in but I don’t really bother with it too much now. I realized that if it sounded “good”, I was usually running too lean.

I would definitely suggest investing in one if you are new to this sort of thing like I am. I blew an engine to pieces the first time I tried to tune by ear.....

[sawnami]

I like to adjust the high side while in the cut. It takes into account the friction of the bar and chain and cutter depth gauge setting.
When I lift while making a cut and it four strokes, then cleans up when put it back into the cut, I know I'm at optimum.