Trying to test 261c on my dyno. Tach is funny???

[chadihman]

I have a tach I attach wrapping the lead wire around the plug wire three times tightly securing it with a zip tie. The 261c is giving funny rpm readings. If the saw is running wot with no load the rpm reads correctly but as I increase the load and the saw decreases rpms the tach increases to 15,000 rpm range when I'm guessing the saw is really at 9-10 k. Is the cm screwing it up or do I have a faulty tach. I think I have another tach in my stash somewhere I'll try.

 

[Stihlman441]

I have had issues with MTronic and tachs in the past.

 

[chadihman]

I have had issues with MTronic and tachs in the past.

I wouldn't have thought there would be an issue. Doesn't the carb adjust according to rpm from the coil. Hmmm I wander if the coil sends out some extra sparks to ignite unburnt fuel on exhaust delivery? Discuss.....

 

[Terry Syd]

Could be it has a multiple spark discharge circuit to help ensure combustion, but those circuits are usually more useful when the engine's throttled back, not at WOT.

If anyone ever finds a circuit drawing of either Stihl's or Husky's electronic systems, please post it so we can figure this stuff out.

 

[DexterDay]

What type of Tach? I have heard some give funny readings on AT/Mtronic saws.

 

[chadihman]

What type of Tach? I have heard some give funny readings on AT/Mtronic saws.

Hardline product # 5644491

 

[DexterDay]

My Stihl EDT-8 does fine on my two Mtronic Saws (362C-M and 441C-M)

 

[Brush Ape]

Could your dynamometer be causing electromagnetic interference?

 

[Mastermind]

My FastTach sometimes acts weird with M-T saws.

 

[struggle]

rev limited? hitting it.


Sent from my iPad using Tapatalk

 

[chadihman]

Took care of the issue. I ordered a nice shaft rpm sensor a while ago and it was sitting on my shelf and almost forgot about it. I installed it this evening and I'm impressed it reads in every rpm with a resolution of one rpm and it has a super fast refresh rate. I have no need to measure saw rpm. I just figure the ratio whether I'm running a 7 or 8 pin sprocket on the saw to the permanent 24 pin in the dyno. I'm going to make a laminated sheet with shaft rpms to obtain saw rpms from 6000-13000 in 500 rpm increments.

The big test with Randy's 261C against my stock 261C will have to wait till tomorrow night.

 

[Mastermind]

I'll make a prediction.....my 261 will not have impressive HP numbers, but it will have a wide band of usable power with no sudden drops on either end.

 

[Stihlalltheway]

I'll make a prediction.....my 261 will not have impressive HP numbers, but it will have a wide band of usable power with no sudden drops on either end.

How many of them have you done so far? Do you think you have this model "down"? Just wondering.

 

[Mastermind]

I've done over 50......probably closer to 75 of them.

I'm done "tweaking" the numbers on it. Very happy with the way they end up.

 

[chadihman]

I've done over 50......probably closer to 75 of them.

Impressive!

 

[MustangMike]

This should be interesting, and I just had to post something so I will get e-mail alerts when more is posted.

 

[weedkilla]

I've got a prediction - mastermind is being modest and his 261 will pull more than a 20% improvement in peak hp, and 30% more peak torque. The big bet is on how much extra width (in rpm) the useable power band is?

 

[redfin]

This should be interesting, and I just had to post something so I will get e-mail alerts when more is posted.

Use the watch tab top of the page.

 

[KG441c]

Stihl edt 8 designed to read mtronics rpm

 

[blsnelling]

If anyone has one of my strato gutted 261s, I'd pay shipping both ways if you'd let Chad test it.