Hesitation under load

[hidesertmlb]

Just wanted to see if I could get some opinions or advice from the GS500 clan before I embark on a Saturday of troubleshooting. Here's the scenario:

I re-jetted my '94 GS w/ 125 mains and 40 pilots a couple months ago. Prior to the re-jet the bike ran well, other than it's cold-blooded mannerisms (long warm-up). After the re-jet, the bike would pop randomly during deceleration. I re-adjusted the mixture screws from 3 turns to 2.5 turns out in an effort to reduce the popping. Seems to have worked. Last week, I rode the bike to the local mountains nearby, and going up a slight grade in 6th, ~70 mph (6500 rpm), the bike is definitely holding back under 3/4 - wide open throttle. It seems to be lean.

I have a #4 washer under each needle. Bike is stock. I have been using paper air filters (HiFloFiltro-bikebandit) since I have owned it. Valves are adjusted and within specs. Tank is clean. Float height was checked using float height check trick located on the HOWTO pages-- no issues there. I can't remember when the plugs were last changed. I'm sure they have at least 4k miles on them.

Suggestions? I plan on pulling the plugs, but I have a feeling that they will be white and all of this will point back to lean. Is this all about the mixture screw? 

[scratch]

1st make sure there are no air leaks getting in.  Spray the WD40 around the airboots/carb boots trick.  And check the vacuum hose (the one between the petcock and the left carb).

Or, raise the float level, or add another washer under the needle.

[ixolas]

If its just having problems in the mountains or all the time.. if it only happened in the mountains it could be the altitude leaning it out?? Just a thought.

[hidesertmlb]

.. if it only happened in the mountains it could be the altitude leaning it out?? Just a thought.

Thanks for the input. Possible that this might happen, though I took the same ride with stock jetting in the past and didn't get the hesitation. I'm going to check for air leaks as Scratch suggested, possible that there might be a lean condition from a not-so-obvious air leak.

[rob1bike]

Altitude doesn't lean things out, it richens them...less air at elevation, same amount of gas, rich.

[ixolas]

oh ya.. had it backwards 

[hidesertmlb]

Had the day off today. Sprayed around the carbs with carb cleaner. Lo and behold, the engine picks up RPMs. Initially I thought it was the boots between carb and cylinder being a tad loose, so I loosen the clamps, double-check carbs are seated into the boots, and re-clamp. That didn't seem to make any difference, as when I sprayed carb cleaner again, RPMs would increase.

So I'm looking at the left carb and noticing the bare vacuum fitting. Could it be that I fitted the vacuum hose to the wrong carburetor? Sure enough, I spritz a little bit of cleaner on the fitting and the RPMs increase. I pulled the vacuum line off the right carb, and put it on the left carb. When I rejetted, I put the vacuum line on the wrong carb. The right carb has a fitting, it just isn't drilled.

So I put it all back together, 3 turns out on the mixture screw, and the bike is happy. No exhaust popping, either. I couldn't believe that I rode it around town for nearly a month with such a vacuum leak.

Thanks guys for your input! 

[rob1bike]

Lol, glad you found it!