Carb balancing headache

[Guest]

This is on my 81 gs650gL

Maybe not a headache, but the smoke did give me a sore throat .. ha.

I've done a full jet replacement and rebuild of everything below the needle jet, and I went to sync the carbs. I made my own tool, which is part of the frustration, and will have a better one Friday.
In the mean time, I had them "bench synced", but they are all far from that now. I have a huge high-velocity fan keeping the bike coolish, but I am losing my cool. (Pardon my puns, I'm frustrated) The head temps were about 180, according to this IR thermometer I have.

I'm running into a couple issues I'd like advice on:

Sometimes I can't keep the bike running long enough to make adjustments, even to the idle screw. The manual says to keep the bike idling at 1750, however my gauges are more stable around 2200. With each adjustment, I am having to go back and forth a little between the idle screw and each adjustment.

What is a good starting point for the sync screws when they have been turned way out? Screwed in just barely enough to touch the spring-loaded plate? Touching plus 2 turns? With the 2 outside sync screws, 1750 sounds lopey like a high-cam car.

Adjusting each carb so that engine speed increases initially causes the flow reading on that carb to *drop*, which confused me at first.

I also just realized I left the airbox open, which is not helping things.


(Edited to remove Pilot screw question)

[Steve]

If you are questioning the position of the sync screw, you have NOT done a bench sync.

Take the carbs off the bike. No, it's not fun, but it's necessary. Hold the carbs up to a light, look into the engine side of #3 carb. Turn the idle speed screw until you see just a small sliver of light under the butterfly. Turn the sync screw between carbs 2 and 3 so that the sliver of light in #2 carb matches that of #3, then proceed to #1. Finally, adjust #4 to match #3. When all the slivers of light are as close to the same size as you can get, snap the throttle linkage a few times to see if anything changed.

While you are at it, adjust the pilot screws to three full turns out from lightly seated. This richer mixture will help it start to do your vacuum sync. After you complete your vacuum sync, turn the pilot screws IN slowly until the engine starts to slow down. Turn the screw back out 1/4 turn, move to the next carb. After all four carbs are done, do it again, but only turn the screw out 1/8 turn when the engine slows down. Verify good throttle response, then turn the engine off, you're done.

.

[WilliamGLX81]

I reluctantly pulled them off this evening because last night, I was in my garage, and discovered 3 rubber pilot jet plugs that are supposed to be in the carbs. 4 old ones would have made sense, as I tried to keep all the old parts, but 3? Nope.

I smeared a very thin film of sil-glyde brake lubricant on all the boot interiors, and it was much easier to get back together. I left things loose, and will see how it's doing tomorrow. They'll probably work better with all the parts in them. Sometimes, ADHD really sucks.

[Noreg]

If you are questioning the position of the sync screw, you have NOT done a bench sync.

Take the carbs off the bike. No, it's not fun, but it's necessary. Hold the carbs up to a light, look into the engine side of #3 carb. Turn the idle speed screw until you see just a small sliver of light under the butterfly. Turn the sync screw between carbs 2 and 3 so that the sliver of light in #2 carb matches that of #3, then proceed to #1. Finally, adjust #4 to match #3. When all the slivers of light are as close to the same size as you can get, snap the throttle linkage a few times to see if anything changed.

While you are at it, adjust the pilot screws to three full turns out from lightly seated. This richer mixture will help it start to do your vacuum sync. After you complete your vacuum sync, turn the pilot screws IN slowly until the engine starts to slow down. Turn the screw back out 1/4 turn, move to the next carb. After all four carbs are done, do it again, but only turn the screw out 1/8 turn when the engine slows down. Verify good throttle response, then turn the engine off, you're done.

.

Can you do the carb balancing without those tube tools? Is this really all there is too it?

[Baatfam]

Can you do the carb balancing without those tube tools? Is this really all there is too it?

That is to get you close enough the bike runs. You still need/should do a proper sync.