GL 1200 Carb Model Ignition Control Module Musings

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Rednaxs60

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This is a theoretical thread to replace the OEM ignition control module on the GL1200. EarlyGWCollector posted on my '85 Limited Edition ECU replacement thread about his GL1200 carb models seeming to have a speed limiter.

Don't want to go off topic regarding my ECU replacement project.

I did a bit of reading about the GL1200 carb models ignition timing and how it operates.

In a nut shell, as per Clymer manual, the timing is adjusted in relation to engine speed when using 1st through 3rd gear. When in 4th or 5th, the control module switches to an ignition pattern that is varied according to engine vacuum. I notice that there is a vacuum hose from a cylinder to the control module. Fuel is set by the carbs.

A person can change/test different carb jets, but without being able to adjust the timing to suit it will never be quite right. An example would be taking a modern day Camaro/Mustang at say some 350 HP and pumping up the volume to say 600 HP and expecting the OEM ECU to take it I stride and perform well - doesn't happen. Not designed for the new conditions.

I have mentioned that the proliferation of add-on/piggyback units are out there to address the symptoms for a perceived need. We love to play/tweak and I'm no different. My point is that a person can play/tweak as much as necessary, but the OEM designed its vehicles to do "X" and we want the "Y" - chasing the holy grail so to speak.

Thought about what a person could do to replace the GL1200 ignition control module. Not as daunting as one would expect, but the "want" has to be there.

The ignition control module can probably be changed to an aftermarket ECU that can control ignition timing from idle to full throttle. From what I have read and looking at the schematic, you would need to install a MAP sensor, two 4 wire spark igniters (use the ones from an '85/'86 FI model), a new trigger wheel (use a 1500 trigger wheel 12-1 - fits on the crank shaft output between the timing belt crank pulleys). Would only need one crank trigger wheel sensor - the ones fitted will work well. Take the gear shift out of the equation. You could install the new unit using the existing wiring harness so that you can revert back to the OEM system if you choose. Unfortunately the carbs would have to stay initially. This could be a stepping stone to an EFI conversion.

EFI conversions are discussed and some come to fruition, but not many. These are a long term and most times, an expensive proposition.

Once a person becomes comfortable with the new ignition control module, the next step to a full EFI system is not a major step. Parts and pieces are the issue; however, in perusing the aftermarket EFI forums -specifically the Speeduino forum, it is mind boggling how many different manufacturer parts are cobbled together In some of the builds. The point is that if the parts being used are compatible with a specific aftermarket ECU, all is well. Auto wrecking yards are the shopping place for these type of projects. We are fortunate in that Mr Honda designed the GWs with an automotive flavour.

A person can change/test different carb jets, but without being able to adjust the timing to suit it will never be quite right. An example would be taking a modern day Camaro/Mustang at say some 350 HP and pumping up the volume to say 600 HP and expecting the OEM ECU to take it I stride and perform well - doesn't happen. Not designed for the new conditions.

I have mentioned that the proliferation of add-on/piggyback units are out there to address the symptoms for a perceived need. We love to play/tweak and I'm no different. My point is that a person can play/tweak as much as necessary, but the OEM designed its vehicles to do "X" and we want the "Y" - chasing the holy grail so to speak.

A project such as this could breathe new life into an older GW. The OEM parts are not going to be around forever, and when available are still old parts, and probably not inexpensive.

For info and thoughts only.

Cheers
 

claydbal

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so, after all that/. if your attempt to get into the oem ecm, whos software will you use? and do yohave access to a eddy current dyno? and is so, is there any reference data to get you some insurance before you destroy a few engines while tuning (BASE MAPS) etc.
btw, i owned 2 dynos and built and tuned v-twin bikes for performance..............yeah, it happens. lol
 
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Rednaxs60

Rednaxs60

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Since this is a theoretical discussion, you could get into the OEM ignition control module. What's in it don't know. The GL1200 ignition control module is probably less complicated than the OEM ECU for my '85 Limited Edition FI model.

The basis for this discussion is a theoretical replacement. Many change OEM ECUs for aftermarket, inexpensive units without having access to a dyno and do not destroy their engines. Trying to modify a carb to get better performance when all you are doing is changing the amount of fuel flow into the engine, and after this, not having the ability to change the timing characteristics is, in my opinion, a lot of work for no real return. More or less fuel with the same engine timing profile could also be considered an accident waiting to happen.

This theoretical discussion is not to achieve a change in the OEM design intent - might happen, but to have a replacement alternative should the ignition control module go south for whatever reason. A new replacement for the OEM ignition control module may very well provide much better performance and still be within the OEM design intent.

This thread is also about the realm of possibility. Dreams never die, just the dreamer.

Cheers
 

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