Getting away from my previous thread regarding potential carb issues and getting straight to the issue, which is electronic. With the engine cold and only cold, and the choke pulled, the engine fluctuates rapidly a few hundred rpm. The choke can be pushed back in and using any throttle what so ever causes the issue to return. The engine will not rev past a fluctuating 1200 rpm. You can turn the engine off and restart it and everything is normal until the choke is pulled again. Once the engine has ran for a few minutes the choke will work fine and the engine will rev fine after the choke is disengaged.

If I unplug the electronic portion of the choke, everything is fine other than the choke not staying engaged. Moving down the line, I did the same with the ECU and the same result. Unplug it and everything is fine. Plug it back in and the issue persists. Moving on to the Choke and Check Relay, if I unplug the alternator portion, the problem stops but the tach and warning lights do not work. Unplugging the choke portion does nothing to change the issue. I then adjusted the throttle switch per the FSM. I replaced the choke switch, ECU, choke and check relay with known good units and no change. I'm pretty stumped. Any help would be appreciated.

 

Any thoughts?

 

I wonder if the computer is cutting the trailing plugs at 1200 and the leading plugs' spark isn't enough umph for the engine to run cold and on the choke (mad rich y0).

When I had my '80, I had to change the spark plugs every 3k before I installed the MSD.

 

I could test that and get back to you. Feel free to swing over and have a listen to it!

 

It'll have to be after the weekend. Mom's coming up for Thanksgiving this year and staying until Sunday.

 

Whenever you have time is fine with me honestly.

There are plenty of things to work on here to keep me busy, lol.

 

Still hunting for ideas

 

Still looking for a lead on this.

 

Vacuum advance? When was the last time the Nikki was serviced? Maybe a valve or something is stuck. Hot start assist motor? (Sorry, just throwing stuff out there).

 

I rebuilt the carb thinking that it was a mechanical issue. There was originally very little fuel from the front primaries. It runs exceptionally well after the rebuild except the issue still persists.

 

Kudos to your perseverance Dave!
Will be very interested to see how this gets solved. At least the rebuild wasn't a total waste of time.


Stu Aull
80GS
Alaska

 

Just thinking out loud.

Could it be something with the TPS?