Add Advance To 20hp Kohler Ignition

bcroe · 02-14-2008, 04:59 PM

I am not happy with the performance or economy of my 20 hp Kohler twin , TORO 520 xi. I am sure the torque can't be optimum over the operating rpm range of the engine. There is NO spark advance mechanism, and I'm wondering if anyone has seen a way to add this. There is a fuel injected version of this engine, but complete conversion looks to be impractical.

thanks,
Bruce

bcroe · 07-24-2008, 11:16 AM

I made a little progress. Needed are manifold Vac and spark timing inputs to drive spark advance. I decided to start by putting a Tach and Vac gauge on the tractor. There were no taps on the intake manifold, and removing it for drill/tap means removing the air shroud, which means removing the engine. Instead I drilled a hole through the very thick carb gasket and glued in a fine tube for Vac to the gauge. I noted bosses for fuel injectors, later.

The ignition is 2 modules driven direct from the flywheel. Where to pick up signal might be an inductive pickup (stolen from a timing light) on a plug wire. I tried this and got a pretty good scope signal, 200V. However I also checked the KILL wire connected to both modules, and there was a nice 30V pulse for each of the (odd fire) cylinders. With a bit of electronic conditioning, I had a 4000 rpm tach.

The gauges got me started on what the engine was doing. The odd fire wouldn't do much more than 15 inches of Vac, with 5 at moderate load and zero for heavy load. The tach idled about 1500 rpm, and hit 3800 max, lossing a little with load. I found that very heavy load was best delt with by slowing the tractor enough to maintain 3000 rpm. Going slower risked stalling and didn't get much done.

There is enough info here to drive a spark advance system. I could time a revolution to get rpm, then modify the spark timing for the next revolution. The original modules would supply crank position info as before, but I would develop a new spark output from HEI components (built in dwell control). It would be waste fire as before, so no cam sensor needed. Or I could put a magnetic pickup on the flywheel teeth for resolution, may not be needed.

The MANUAL choke on this engine has annoyed both drivers, I'd like to get rid of it. With an oil temperature signal already in place, this might not be too hard. Maybe blip it on with the starter. Bruce Roe

02-14-2008, 04:59 PM	#1 (permalink)
bcroe Registered User Join Date: Feb 2008 Posts: 3 OS: apple	Add Advance To 20hp Kohler Ignition I am not happy with the performance or economy of my 20 hp Kohler twin , TORO 520 xi. I am sure the torque can't be optimum over the operating rpm range of the engine. There is NO spark advance mechanism, and I'm wondering if anyone has seen a way to add this. There is a fuel injected version of this engine, but complete conversion looks to be impractical. thanks, Bruce

07-24-2008, 11:16 AM	#2 (permalink)
bcroe Registered User Join Date: Feb 2008 Posts: 3 OS: apple	Add Advance & Auto Choke To 20hp Kohler Ignition I made a little progress. Needed are manifold Vac and spark timing inputs to drive spark advance. I decided to start by putting a Tach and Vac gauge on the tractor. There were no taps on the intake manifold, and removing it for drill/tap means removing the air shroud, which means removing the engine. Instead I drilled a hole through the very thick carb gasket and glued in a fine tube for Vac to the gauge. I noted bosses for fuel injectors, later. The ignition is 2 modules driven direct from the flywheel. Where to pick up signal might be an inductive pickup (stolen from a timing light) on a plug wire. I tried this and got a pretty good scope signal, 200V. However I also checked the KILL wire connected to both modules, and there was a nice 30V pulse for each of the (odd fire) cylinders. With a bit of electronic conditioning, I had a 4000 rpm tach. The gauges got me started on what the engine was doing. The odd fire wouldn't do much more than 15 inches of Vac, with 5 at moderate load and zero for heavy load. The tach idled about 1500 rpm, and hit 3800 max, lossing a little with load. I found that very heavy load was best delt with by slowing the tractor enough to maintain 3000 rpm. Going slower risked stalling and didn't get much done. There is enough info here to drive a spark advance system. I could time a revolution to get rpm, then modify the spark timing for the next revolution. The original modules would supply crank position info as before, but I would develop a new spark output from HEI components (built in dwell control). It would be waste fire as before, so no cam sensor needed. Or I could put a magnetic pickup on the flywheel teeth for resolution, may not be needed. The MANUAL choke on this engine has annoyed both drivers, I'd like to get rid of it. With an oil temperature signal already in place, this might not be too hard. Maybe blip it on with the starter. Bruce Roe