Installing a tach

[Charles M]

Has any one ran a tack on a 3pg motor with the gm hei mod ? Did you just pull the input on the negative side of the coil ? All the directions say the dist. has a output for the tack and I have read that is the same as the negative side of the coil. What is the red line of the motor?

[Barnsworth]

I tried to install an analog tach for either a 4, 6 or 8 cylinder engine. Just wanted to see if I could get it to work, no luck here.

Regardless of all that, the max RPM for the 3pg is 5,000 rpm. I think that is what it will do but not what it should be actually ran at.

Here is a link with performance specs. Look at page 1 specifications.

https://www.jackssmallengines.com/pd...s/1193S119.pdf

[TomStark]

You can put a tach on the - coil side of module. The issue you will have is getting it to read correct RPM. You have 1 event per rev. A 4 cylinder tach looks for 2 events per rev, so the tach would read 1/2 actual RPM. Not sure if anyone makes a 2 stroke tach. I am putting a 4 cylinder pick up where the oil pump used to be, and will have the tach set to 4 cylinder. That will have my tach read double engine RPM. If I put it at 8 cylinder it would read actual RPM, but I have a 2pg and should not go over 4000, and that is rather low, 8000 will look better LOL!
Anyway my point is will be running a tach off the second HEI module that is hooked up to the pick up where the oil pump used to live.
Tom

[Charles M]

The cart motor fires 2 times per rev you have the forward and reverse both firing per rev one is a waist spark. the tack seems to read correct going down the road but is erratic at slow speed thanking I might have a bad ground going to run the ground to the batt.

[TomStark]

Originally Posted by Charles M

The cart motor fires 2 times per rev you have the forward and reverse both firing per rev one is a waist spark. the tack seems to read correct going down the road but is erratic at slow speed thanking I might have a bad ground going to run the ground to the batt.

The cart motor fires 1 time per rev. There is no wasted spark. It fires X degrees BTDC forward or reverse, there is no overlap for a wasted spark.
Tom

[Charles M]

If you look at the pickup and the crank you will see 2 lobes one forward and one for reverse if you only had one it would be retarded in reverse

[TomStark]

Originally Posted by Charles M

If you look at the pickup and the crank you will see 2 lobes one forward and one for reverse if you only had one it would be retarded in reverse

I know it has different timing in reverse than forward (why I have no idea!) Never really gave consideration to how they do that. So what you are saying is if it is say 15 BTDC forward and 12 BTDC in reverse, it will fire in forward at 15 BTDC and then again at 12 ATDC. While 2 events per rev are perfect for a 4 cylinder tach it will never read correctly because the 2 events are so close to each other. It would give erratic readings. The easiest thing to do is put a pick up on where the oil pump was, and use a module to fire the tach.
Tom

[my1423]

http://www.ebay.com/itm/New-Digital-...ZTadfo&vxp=mtr

[Charles M]

I have been doing some reading on the net boy the gm hei is grafted to a lot of different motors . Seams this is a common problem . You can filter the rfi out but if you a use a better quality igniter instead of a cheap one they work better going to build a filter tomorrow put the stock condenser in the circuit today and it helped.

[Charles M]

Had the cart out today 4600 was about 17 mph does this sound about right. stock tires with my wife and I in the cart the tack levels out at about 2500. still need one part to finish the filtering circuit. Might try a better hei unit