How to check rpm

[humpo48]

Yep, thats the one I linked to. Totally wireless, just point it at the plug/ht lead and it gives you the revs. A lot less messing about.

 

 

Use mine on the quad bike as well to get the idle right just hold it near and picks up the revs

 

 

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[Kevm]

Those fast-tachs are about £70, I think I will use the mechanical one I already have.

What I am not sure about though is if it will "rev out" more without the chain.

[spudulike]

Those fast-tachs are about £70, I think I will use the mechanical one I already have.

What I am not sure about though is if it will "rev out" more without the chain.

 

 

If you are going to rev the saw up to 13Krpm and stick your machanical tach on the end of a small crankshaft end spinning at the same speed you are braver man than me.

 

For starters, these old saws bounce all over the place when revved, secondly, I only rev the saw flat out for a second or two at a time - you will be doing it a lot longer, thirdly, it may be accurate on slow shafts but I would be surprised if it is THAT accurate at these rpms on a non fixed position engine/shaft.

 

If you must - buy a cheap one off ebay that picks up the induction off the HT lead,. The ones we have mentioned on here are the correct and safe ones to use with the machine fully assembled and safe - your method defies my safety standards and WILL NOT tach the saw correctly as it should have the typical bar to be used fitted - the drag of the chain should be factored in when taching a saw.

 

Your choice but I wouldn't do what you are attempting to do.

[Eddy_t]

Those fast-tachs are about £70, I think I will use the mechanical one I already have.

 

What I am not sure about though is if it will "rev out" more without the chain.

 

 

You're a brave man, clutch issues aside, different bar lengths affect the saw differently - a longer bar requires a leaner mix to reach the correct rpm. A shorter bar requires a richer mix, so if you have a longer bar already, you could toast the top end, so £70 vs £300 for a new p&c, I know where my money went. If you tuned it to 13k rpm with no bar, you could find sticking a bar would drop it down below 12k rpm, coking the exhaust, piston crown and cylinder head quite quickly (you're not creating enough heat to burn off the oil significantly, instead, it welds itself to the insides).

It'll run sluggish and down on power to boot!

Another question is how you operate the throttle, adjust the carb AND hold the tach in place all at the same time considering each is on a different side.

 

 

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[spudulike]

Where are you, I have tach tuned saws for peope on this site as favours and others may do similar if local.

 

Better than causing injury.

 

Listen to good advice from the experienced!

[Kevm]

Spud,

My old mechanical tacho only goes to 12000 anyway and it probably would have been a bit dodgy trying to hold it on at full revs!

Anyway you have answered my question of how it's done, I never knew those little induction pickup tachos existed till today.

I am in Aberdeenshire so a bit too far for your services, thanks anyway.

Kev

[spudulike]

Spud,

My old mechanical tacho only goes to 12000 anyway and it probably would have been a bit dodgy trying to hold it on at full revs!

Anyway you have answered my question of how it's done, I never knew those little induction pickup tachos existed till today.

I am in Aberdeenshire so a bit too far for your services, thanks anyway.

Kev

 

Many aftermarket rev/tacho meters work on induction as it is the simplest way to measure rpm on an engine, just got to make sure the gauge is set up for single cylinder engines.

 

Some need a wire wrapped round the HT lead which can be a PTA if done on many saws, the better ones do both wire wrap or simply place it near the HT lead.

 

Things to look out for are 0.5 second refresh for a fast accurate readout and 20krpm maximum reading - the refresh is important

[Eddy_t]

Things to look out for are 0.5 second refresh for a fast accurate readout and 20krpm maximum reading - the refresh is important

 

 

The tiny tach is by far the cheapest in the range of inductive tachometers, there's another few American tachs which are priced up to about £150... And then there's the DET/PET series of tachometers, which are what Stihl, husqvarna, echo and dolmar say to use... Prices start from £200! Although they measure up to 30k rpm, so should you have a mcculloch kart saw, you can tach it

 

 

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[GardenKit]

The TT20K seems to be the industry norm. I have one, as well as Stihl one, but use the TT in preference as it seems to pick up an inductive signal at a greater distance. It has a rubber case and can sit happily on the bench beside a firmly held MS200T revving at 14K!

[SawTroll]

I think the tachometer mentioned here count the spark impulses as you aim them at the plug top . Could be wrong ...........

 

 

That's how most current tachs work.