I put on a Stewart-Warner Tach on my blaster, and I have to set the tach on 2 ppr (pulses per revolution). If I set it on 1 ppr it reads way to high. When I set it on 2ppr it seems about right.

What's up with that? Does the Blaster really spark 2 times for each revolution? That doesn't make sense to me, and it's driving me crazy trying to figure it out.

Can anyone help me with this? Thanks, Izord.

 

What range were the RPMs in when on 1 ppr?

I have heard of people having problems with tachs on 2 stroke motors but I thought the problem had to do with tachs that didn't have a low enough range. I noticed that Stewart-Warner sells tachs with ranges down to 1 ppr (as you tried). I might have to check out a tach from them. Up till now I thought you always had to get a aftermarket ignition to get the right 12v tach output.

As for your problem, I'm pretty sure the blaster would not have wasted spark like twin cylinder 2 strokes. So I have no idea what the problem would be... other than it not being able to understand such a fast/dirty tach feed. I also don't know if the feed off the blaster's CDI to the coil is a sold 12 volts or not.

 

When it was on 1ppr the rpm's were reading twice what they were on 2ppr. The stewart-warner tach has 3 wires.

I already had a rick-stator with a floated ground and a cap, so from the tach the red wire went to +12v, the black wire went to ground, and the green signal wire worked on the (+) coil side. In the stewart warner directions it said the green wire should go to the (-) coil side, but it didn't pick up anything there. So I tried it on the (+) side and it seemed to pick up well there, except for I needed to put the tach on 2ppr.


The tach is pretty small, and mounts pretty good on the left hand grip where had taken off some lever I didn't need, and still had a bolt in there I could use to mount the tach.

 

Anyone else have any ideas on this? Thenks, Izord.

 

Is the tach for a 2 stroke or a 4 stroke or either (switch for 2 or 4).
The only thing that makes sense to me is that ppr is the wrong term and should be pulses per cycle and not pulses per revolution and the tach is for a 4 stroke.

 

Here's what the directions say:

CALIBRATION (PPR/Number of Cylinders): Until recently, tachometers were calibrated based on the number of cylinders in the engine. Now, there are all types of engine control modules (ECMs - on-board computers) and distributor-less ignitions and the old standard rule --"half the number of cylinders equals the pulses per revolution (PPR)" -- no longer applies. "Pulses per revolution" relates to how many times the ignition fires per crankshaft revolution. The tachometer outputs from the ECMs can range from 1-PPR to 4-PPR for a V-8 engine. So, the new standard is to refer to PPR instead of the number of cylinders.

SIGNAL INTERFACING: The Ultra-Shift Light is also designed to work with a wide variety of ignition types, including standard inductive [coil (-) connection] and any ignition system with a clean tachometer output signal.
The input level can range from TTL 5V (outputs from newer engine control modules) and 300-400 volt pulses from coil (-) on most inductive ignition systems.
Ultra-Shift will operate on most traditional capacitive discharge ignitions when connected to the ignition primary circuit. However, for high-output CD's (such as MSD) only connect to the tach output terminal, never the coil primary.

Here is the link to the whole instructions page: http://www.racerpartswholesale.com/stewarn1a.htm

 

Do you have one of their digital tachs? I noticed they are very sneaky in the manuals for all their tachs. They all talk about settings down to 1 PPR but, it is only the higher priced tachs that have such settings.

 

rruser, yup it's the digital ultra shift light. it has 1, 1.5, 2, and up to 12 for 12 cylinder engines. Here's the one I have: http://www.racerpartswholesale.com/stewarn1.htm

Any idea on why I have to set it to 2 ppr?

 

cant remember the modle but yamaha does indeed fire twice per cycle once at tdc and once at bdc before someone says it would blow up.ive already thought the same thing no compression at bdc so no combustion why yamaha does this is a mystery to me? But been working on the big 4 for 30 years most 2 strakes fire at tdc only

 

I have a YFZ450 and it sparks twice per revolution, this is because everytime the piston goes up and down the flywheel only makes 1/2 turn. If the rpms seem like they are doubled with the 1 signal per rotation setting then most likely your engine is setup the same way.