GL1200 Stumbles at High RPMs

[garywyoung]

My 1984 GL1200 stumbles at high RPMs on hard acceleration. This is most noticeable if I'm making a quick acceleration in first gear once I hit about 5500 RPM, or if I'm doing a high speed passing maneuver in 3rd gear, again, at about 5500-6000 RPM. Basically, the engine starts to bog down once these higher RPMs are reached. Other than this issue (which, admittedly, isn't something I experience frequently as I don't generally ride the bike that hard), I notice no other issues with the bike.

The carburetors have been recently rebuilt using Radakk's kit (I did this hoping that the problem would go away) and synchronized.

So, is this a fuel delivery issue, a carburetor issue, or a spark/ignition issue?

Thanks in advance for whatever insight you folks can provide.

[virgilmobile]

One of the things the 1200 suffers from is voltage drop feeding the ignition coils.Add a large demand on this circuit from high rpm and the spark can get a bit poor.
Some will bypass the oem ignition wire at the coil by using it to operate a relay.The relay contacts are then fed from the battery direct(15 amp fused #12 wire) and tied to the coils.This provides full battery power and maintains all the safety features.
Do also verify that the battery volts are staying up above 14 volts at that rpm and preferably not exceeding 14.5 volts at any time.
Fuel flow and volume is a consideration along with a clean air filter and proper operating vacuum slides in the carbs.

[garywyoung]

Those are interesting things to consider. The coil bypass procedure, however, seems a bit unclear to me. I’d be intrigued to learn more about whether that’s a widely successful procedure. As for carb slides, they’re good, as are the fuel and air filters. So I guess that leaves fuel flow, as in fuel pump output. Or could it be float bowl levels instead?

Anyway, I very much appreciate your thoughts and suggestions.

[Rednaxs60]

The coil mod where you feed a 12 VDC wire to the coils from a relay works well. Did it on my '85 LTD almost two years ago after reading a lot of the threads on this forum.

Cheers