Vc tach adjustment

KirkM · 03-01-2018, 01:04 PM

Hi,
Since this is a tach thread, I thought I would ask here. I have a VC tach wired to a lifan 420 engine kill wire. It seems to read fine, but I wonder if it is only reading 1/2 the actual revs. It shows stock idle at about 600 and wide open (governed) at 2300. Not sure how fast I am going, but the engine sounds wound up.

Rooster59 · 03-01-2018, 01:22 PM

By your description it sounds like half the rpm but I thought the Lifan engines were like most others with one spark per rev of the crank like all other magneto engines.

sho305 · 03-03-2018, 02:17 PM

If its all stock it should be around 3600 max rpm on governor (engine governor). 600 is a really slow idle, the compression release would almost come on that slow. Most lawn air cooled engines stock idle 1000-1200 rpm.

Shepard · 03-05-2018, 06:11 AM

How do you have the wiring routed? Could you be having electrical interference?

KirkM · 03-05-2018, 03:22 PM

I have it routed all by itself down the drivers side frame rail. It is also reading the same as the mini tach that I had wrapped around the spark plug wire.

Rooster59 · 03-05-2018, 03:24 PM

Is it possible that the new electronic ignitions (UT2?) are using one spark for two revolutions and giving a false reading to tachometers that are set up for one spark per revolution? I'm grasping at straws.....

It might be time to call Aaron at VC. If this is happening to others it is possible he is aware of something out of the ordinary that would cause this.

KirkM · 03-05-2018, 03:26 PM

I do have a non rev-limiting honda UT2 coil installed. The readings are the same as the old Lifan coil. I just have the tach connected to the kill wire.

Rooster59 · 03-05-2018, 03:29 PM

If your Tiny Tach and the VC both read the same then could you be off in your judgement of the rpm versus sound? Have you driven it and confirmed at what speed you are seeing versus rpm?

KirkM · 03-05-2018, 03:53 PM

I will get my gps out tonight and post later.

Rooster59 · 03-05-2018, 03:58 PM

That might help confirm what you are sensing. No offense, but this is puzzling.

03-01-2018, 01:04 PM	#1
KirkM Not Yet Wild Join Date: Nov 2014 Posts: 28	Vc tach adjustment Hi, Since this is a tach thread, I thought I would ask here. I have a VC tach wired to a lifan 420 engine kill wire. It seems to read fine, but I wonder if it is only reading 1/2 the actual revs. It shows stock idle at about 600 and wide open (governed) at 2300. Not sure how fast I am going, but the engine sounds wound up.
KirkM Not Yet Wild Join Date: Nov 2014 Posts: 28

03-01-2018, 01:22 PM	#2
Rooster59 Gone Wild Join Date: Jul 2017 Location: East Central Missouri Posts: 1,955	Re: Vc tach adjustment By your description it sounds like half the rpm but I thought the Lifan engines were like most others with one spark per rev of the crank like all other magneto engines.

03-03-2018, 02:17 PM	#3
sho305 Vegas modded 420 Join Date: Jun 2009 Location: West MI Posts: 15,445	Re: Vc tach adjustment If its all stock it should be around 3600 max rpm on governor (engine governor). 600 is a really slow idle, the compression release would almost come on that slow. Most lawn air cooled engines stock idle 1000-1200 rpm.

03-05-2018, 06:11 AM	#4
Shepard Crazy Ole Man Join Date: Jan 2016 Location: Owego NY Posts: 2,758	Re: Vc tach adjustment How do you have the wiring routed? Could you be having electrical interference?

03-05-2018, 03:22 PM	#5
KirkM Not Yet Wild Join Date: Nov 2014 Posts: 28	Re: Vc tach adjustment I have it routed all by itself down the drivers side frame rail. It is also reading the same as the mini tach that I had wrapped around the spark plug wire.
KirkM Not Yet Wild Join Date: Nov 2014 Posts: 28

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03-05-2018, 03:24 PM	#6
Rooster59 Gone Wild Join Date: Jul 2017 Location: East Central Missouri Posts: 1,955	Re: Vc tach adjustment Is it possible that the new electronic ignitions (UT2?) are using one spark for two revolutions and giving a false reading to tachometers that are set up for one spark per revolution? I'm grasping at straws..... It might be time to call Aaron at VC. If this is happening to others it is possible he is aware of something out of the ordinary that would cause this.

03-05-2018, 03:26 PM	#7
KirkM Not Yet Wild Join Date: Nov 2014 Posts: 28	Re: Vc tach adjustment I do have a non rev-limiting honda UT2 coil installed. The readings are the same as the old Lifan coil. I just have the tach connected to the kill wire.
KirkM Not Yet Wild Join Date: Nov 2014 Posts: 28

03-05-2018, 03:29 PM	#8
Rooster59 Gone Wild Join Date: Jul 2017 Location: East Central Missouri Posts: 1,955	Re: Vc tach adjustment If your Tiny Tach and the VC both read the same then could you be off in your judgement of the rpm versus sound? Have you driven it and confirmed at what speed you are seeing versus rpm?

03-05-2018, 03:53 PM	#9
KirkM Not Yet Wild Join Date: Nov 2014 Posts: 28	Re: Vc tach adjustment I will get my gps out tonight and post later.
KirkM Not Yet Wild Join Date: Nov 2014 Posts: 28

03-05-2018, 03:58 PM	#10
Rooster59 Gone Wild Join Date: Jul 2017 Location: East Central Missouri Posts: 1,955	Re: Vc tach adjustment That might help confirm what you are sensing. No offense, but this is puzzling.

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