Tiny Tach Club - saws running high

[spudulike]

I trust tuning by ear more than the tach, buts thats because I know what to listen for.

Tuning by ear allows you to understand whats happening and warning bells sound when it doesnt make the right noises when you expect, showing there might be problems to address. The tach is OK to double check but should not IMO be used on its own,(what if its inaccurate?) but thats just my opinion.

 

Sorry to contradict but here are my observations - on older saws, they are easier to tach as they have lower max revs and the fourstroking is more pronounced.

 

On the later saws revving out at 14K +, it is much harder to get the fourstroking at the right level and is easy to tune 500 - 1k below where perhaps you should be - not damaging but you do lose chain speed.

 

I have noted that if you vid a saw you have tuned by ear, it sounds different if played back on a vid - much more pronounced fourstroking when viewing at a distance!

 

Here is the last but very important point - many modern machines have limited coils - when tuning by ear, it is very easy to think you have done a great job and the saw is fourstroking when in reality the saw is bouncing off the limiter. I had this with a members 372 recently. It wasn't pulling as it should and found the H screw in too far and was fourstroking of the limited coil but the tach sorted it as you can bring the revs up to near max and when th etach goes crazy, back the H screw back down to a stable setting just below the limiter.

 

By ear is fine as a rough cut setting that will get a saw running safely and OK but the Tach is a technicians tool to get the maximum performance out of a saw.

 

The tach is also great when porting and tuning saws:thumbup1:

 

That is my opinion - I can do both and both have their place, sorry Barrie, no offence intended, we all have our own working practices:thumbup:

[GardenKit]

Very well put Spud and I dont disagree. I do however feel that a tach should not be used in inexperienced hands, without a basic feel for whats going on. It is IMO as you say a technicians tool to be used in conjunction with his skills.

 

And, I am not offended at all.

[spudulike]

Very well put Spud and I dont disagree. I do however feel that a tach should not be used in inexperienced hands, without a basic feel for whats going on. It is IMO as you say a technicians tool to be used in conjunction with his skills.

 

And, I am not offended at all.

 

Cheers:thumbup:

[blazer]

I will split the last two comments a bit no offence meant - if caused.

 

How can you tell 14k rpm if you don't have a referance? After seeing many photos on here of siezed saws and reading Spuds posts on tuning, I stopped guessing and brought a 'tiny tach'.

 

My day job is medical engineering, so it's all relying on calibrated instruments, but I see a place for 'working by ear' as an approx check only (I used to set up 132kv switches and could guess the operations times to within a few 1,000ths of a second) - problem is it's so far out when tested against a tacho.

 

Example one, I fitted a twin port to my MS460, so I knew it would be too lean, I warmed it up and set it to 13.5k with slight 4 stroking, which evened out under load - so that worked.

 

Example two my MS280 (10yr) sounded much the same with the H screw in or out, so it could be at risk. I removed the restrictor and set it to a max of 13.5k - yet to try it on some wood.

 

Example three my lads new MS200T, now running a bit high at nearly 15k, it sounds a bit fast but most of the MS200T I've heard do scream a bit. Now set to 14k does sound a bit slow for what I'm used to along with his MS260 at 14k.

 

Hopefully later I will test out the 'tiny tach' against my sons XT660 but that's at say 7K. If not I may set up something using an oscilloscope to check it out.

[GardenKit]

I think one of my issues in relying on a tach alone comes more from brushcutters than saws.

 

The length of cord or size of blade plays a massive part in governing max speed. An inexperienced person could well try to achieve stated speed by tuning to the lean side, when he should actually be correcting the cord length and tuning to run rich enough to survive. I find this much easier by ear.

 

The same applies , but to a lesser extent, with the tightness of a chain.

 

Others may disagree, and if so I will not take offence.

[blazer]

Well I take great offence - only joking, had enough of everybody being nice:thumbup1:

 

I tend to be a 'rule of thumb' person, with say sawchains tension I think we may all vary a bit about whats correct (adjusted my son's XT660 chain before he went down to the 'Ace cafe' and was told by a copper it was too slack)

 

With the +1k rpm on the Tiny tach, I have adjusted to the book Max but will test again when the saws have been running for say 30 min, so the fuel will be vaporizing better to give me a clearer idea.

 

Either way it's brought out a lot of debate on saw tuning, which can only be good:thumbup:

 

Have a good Sunday afternoon everybody

[spudulike]

I think what we are saying here is that the bar and chain should be in good condition and the chain tensioned correctly to tach a saw - I always ask what bar length is to be used on saws I tach or ask for the bar and chain to be supplied with the saw.

 

I tuned by ear for quite a while but now only tune by ear to do a rough cut tune and use the the tach for the final tune.

[Stubby]

Spud is right . anyways the bike chain should be tensioned with the rider sat on it as things like swing arm pivot position ans suspension travel can affect it .