I have an 85 GS and it has the infamous 3k hesitation. I was reading a sticky about it last night explaining that the hesitation is caused by the delay of the ecu switching the fuel pump to full power before the secondaries kick in, and during that time, the primaries are not getting enough fuel causing the stumble/ hesitation.
So my question is, could I cut the spring in the secondary diaphragm and pull it out to the original length which would cause the secondaries to kick in sooner. Would this get rid of the stumble due to the secondaries kicking a few rps before the fuel pump switches over to full power?

 

If it is a gs there is no ecu. The secondaries are vacuum controlled. The gsl-se was the only first gen with an ecu.

 

Ah, ok I was mistaken.

 

Do you think having the secondaries come on sooner would alleviate the hesitation?

 

I don't think so. Driving with mechanical secondaries has taught me that there is no upside to opening the secondaries under roughly 4000 rpm.
With 4 85 GS or S models since 1988 I have never experienced the hesitation of which you speak. Some maybe at 1500 to 2000 starting out, but carb rebuild has always cured it.

 

^ this guy has it right. Carb rebuild seems to solve the majority of these types of issues.

 

Good News Everyone! I figured out the stumble! I had to remove the distributor and shift it over one gear. I re-timed it and the car runs like a top now. Super stoked! No stumble and smooth acceleration through the entire power band. This also fixed a weird chirping noise under heavy load which I was told was most likely pre detonation, which would make sense. Thanks for everyones help and suggestions!

 

Splendid! Thanks for reporting the fix.