Carb work with vacuum gauges

[kungpaodog]

I have done a complete tear-down, cleaning, and rebuild of my carbs on my '81 gs650GL. I set the air jet screws to the recommended 1.5 turns out from full close.
I adjusted the air screws a little on 1 and 2 since it seemed to be running WAY too rich (exhaust smelled like gas) until it smelled less like gas and didn't smoke.
I also set the float levels with a caliper (with the gaskets on) to the recommended level, but I think I'll set them with the clear hose method tonight.
I synced all the carbs with a vacuum gauge.
It revs great in my garage, but it still has issues getting past about 5000 rpms on the road. It will, but it requires some ginger throttle control, otherwise it sputters and won't accelerate under full throttle. Once I get past 5000 it revs up to redline just fine, so I believe it is a bad mixture on the idle circuit.

My questions are these:
1) Where should the fuel level be if I use the clear-hose float level method?
2) Can I hook up the vacuum gauges and adjust the air-mixture screws until they give maximum vacuum? I feel like if a carb is too rich or too lean, the vacuum would be less than at ideal mixture, but I'm not sure if this theory is correct.

Any good ideas, gurus of the GS?

[dabe]

rough running

how doo... was the bike running ok before you did the carbs? because the symptoms you describe are consistant with an advance and retard timing problem, my gs1100 has a "bob weight" mechanism on the timing end of the crank and you get the same symtoms if these weights are stuck, also my repair manual states that the fuel level should be in line with the carb body where it meets the fuel bowl, most carbs are set the same way so you cant be far out, hope this helps good luck.....

[Dave8338]

You may find, that after all methods of testing for air leaks at the various connections and finding none, you may need to bump your jet needles up slightly...I did on mine and it is a bone stock engine/air box config. I'd first check all fittings, the intake boots at the head (may be o-rings), and the air box, to see that everything is sealing tightly and all of these areas are ruled out. If they test out perfect, the next thing to try would be to raise the jet needles by one notch.

[kungpaodog]

It was running OK before the rebuild, but it was doing the same thing. I hadn't made any adjustments on anything ever, and wanted the peace of mind that the needles were clean, floats adjusted, etc. I haven't looked into the timing yet, though. I'll check that out tonight. Thanks.

Also, what about using the vacuum gauges to fine tune the air mixture screws?

[kungpaodog]

...and yes, the boots and airbox seem to be air tight. Can I make adjustments to the needles without rejetting?

[Nessism]

I don't think you want to adjust your mixture screws based on smell of the exhaust or anything to do with the vacuume readings. Set idle mixture to 1.5 turns out and then tweek slightly to achieve best idle - should be within 1/2 turn of where you are.

[Dave8338]

...and yes, the boots and airbox seem to be air tight. Can I make adjustments to the needles without rejetting?

Sure can...sounds like you're running lean in the midrange then.

[kungpaodog]

Thanks! I wasn't even aware that I could adjust the needles! I take it that I pull the clip holding them in place and move them more open, so essentially what is in the main jet is a shorter amount, right?

[kungpaodog]

how doo... was the bike running ok before you did the carbs? because the symptoms you describe are consistant with an advance and retard timing problem, my gs1100 has a "bob weight" mechanism on the timing end of the crank and you get the same symtoms if these weights are stuck, also my repair manual states that the fuel level should be in line with the carb body where it meets the fuel bowl, most carbs are set the same way so you cant be far out, hope this helps good luck.....

That makes perfect sense for some of the symptoms I'm seeing. Sometimes it runs poorly, and then, like someone threw a switch (usually at high rpms) it will run great. Then, sometimes the "switch" gets flicked off and it runs poorly. I'll let you know if it's sticky when I pull it apart tonight. I REALLY hope it's that bob weight, because I REALLY don't want to pull the carbs off AGAIN (4 times and counting...sigh...) Thanks to all for the input!

[Steve]

The needles in your '81 probably don't have the extra grooves necessary to adjust them easily.
They pretty much disappeared after the '79 models, due to EPA regulations forbidding you to tune the carbs to peak efficiency. 8-[

I have found two ways to get around this:

1) When you remove the needle, you will see a thin metal washer just under the circlip,with a thicker nylon washer below the diaphragm. Switch the two washers, it will raise the needle by the difference in the thickness.

2) Go to your favorite hardware store and get some small washers to add to the thin metal washer. I have found that rivet backing washers work well. Might have to ream out the hole just a bit, depending on the size of your needle.

If you have digital calipers available, measure the washers you are putting in to find four that are close to the same thickness.


.

[kungpaodog]

I just made myself a custom extra-long snap ring tool and got out the snap ring to adjust the needle height, and was suprised to see no extra grooves to move the clip to. So I swaped the nylon washer around to the top...and then logged on to see the tip about moving it to the top! Thanks for the feedback... I may need to try adding some custom washers like you suggested. I don't know if I would have thought of that for shortening the needles even further.

And sorry, Dabe, but the timing advance mechanism is nice and lubed, not sticking at all.

With the help of you guys, I'm sure I'll get this sucker running well! I'll update you tomorrow about how shortening the needles worked.

[kungpaodog]

I raised the needles by moving the nylon washer to the bottom instead of the top of the clip on the needle, and it's running a lot better, but it still isn't pulling as hard as it formerly has. If I tweak the idle air mixture screws, will this help with higher rpm acceleration? I can't really tell if it's running too rich or too lean. How do fine tune it now?

[Dave8338]

I raised the needles by moving the nylon washer to the bottom instead of the top of the clip on the needle, and it's running a lot better, but it still isn't pulling as hard as it formerly has. If I tweak the idle air mixture screws, will this help with higher rpm acceleration? I can't really tell if it's running too rich or too lean. How do fine tune it now?

Do a plug chop at the point that it seems to fade/bog out. This will tell you if you're still running lean or rich. Lean = white plug. Rich = black plugs.

[kungpaodog]

Do a plug chop at the point that it seems to fade/bog out. This will tell you if you're still running lean or rich. Lean = white plug. Rich = black plugs.

OK, I give up. What's a plug chop? I tried to search GSR for instructions, but no luck. Thanks!

[Dave8338]

OK, I give up. What's a plug chop? I tried to search GSR for instructions, but no luck. Thanks!

Run the bike (after completely warmed up) out on the road and when you reach the RPM/speed where you notice that you're having the bog condition, run it there for a few seconds and then hit the kill switch and pull in the clutch. Take out the plug wrench that you'll need to bring with, and remove the plugs one at a time and note the color (you may want to bring along a note pad so that you can record which plug is doing what). This is the most accurate way of reading plug color as you will be doing it at the exact moment in time, that the problem presents itself.