Let fuel sit in the engine/carbs over the winter, I know I know, anyhow. Completely rebuilt and cleaned the carbs. Used the stock jets that were in there.

I didn't reset the Air Screws however.

If I'm in 1st at a stop and go WOT, it accelerates quickly until half way up RPMs then at around 6500, completely goes flat and feels like it's starving of fuel. It's not so much bogging of too much fuel but like it's not getting enough. The best way I can explain it is sputtering. I can feel the bike twitching back and fourth when this sputtering is occurring. This occurs in all gears.

I changed all the fuel lines and the vacuum lines when I did the rebuild.

My first guess would be the Air Screw adjustment on both carbs. I really hope I don't have to tear them apart again to fix this issue. Any recommendations?

when you figure it out let me know? I'm experiencing the same thing

No one has any ideas?

I would say float height.  Needle valve sets are touchy on the GS.  I had to buy all new OEM sets before I finally got it right.  K&L or whatever other aftermarket rebuild kits have crap for needle valve sets.

Air screw adjustment will only help idle mixture.  I would definately check float height first, and if you are still left scratching your head... Then I would suggest checking the plugs... but since it seems its fine at idle, I would go one more by doing a plug chop at WOT to determine for sure whether its lean or rich since it seems you may be a little unsure.  This would point to your next direction if a float height could not.  These two are easy and worth your time.

I can't remember exactly the details, but I remember a thread once where a member had placed the jets in wrong somehow, and it seemed it idled fine, was rich mid, and lean top (something of that nature anyway)... made determining richness or leanness impossible when only reading the description of symptoms over the web...

Anyways, my point is that you want evidence to support your next move otherwise what are you actually going by?... No offense intended, but it seems you may not be sure if it is rich or lean (and heck maybe it actually is both like the above! lol)  Making suggestions based off mixed opinion wouldn't be in your best interest. So lets get some good direction with the float height check and/or a plug chop or two at various throttle positions to point the way.  Note, that you should think in terms of throttle position (such as 1/4, 1/2, WOT, etc) when considering your fuel mixture (like richness and leanness) because throttle input is directly related to mixture whereas rpms are not.



- Bboy

Quote from: BockinBboy on May 23, 2013, 12:52:28 PM
Note, that you should think in terms of throttle position (such as 1/4, 1/2, WOT, etc) when considering your fuel mixture (like richness and leanness) because throttle input is directly related to mixture whereas rpms are not.

Not to confuse this issue further, but this is not completely true with CV carbs such as the GS's.  The throttle opens the butterfly, which allows more air to flow into the engine, but it doesn't allow it all right away.  The slide also controls air flow.  The diaphragms that lift the slide with the jet needle are raised with vacuum, which is proportional both throttle opening and RPM.  Therefore, when testing mixture at the half-throttle position, you should also be in mid-rpm, and when testing mixture at WOT, you should take it to high RPM.  At least this is how I understand it.

The problem consistently occurs at high RPMs it seems to idle okay. One issue however is if at a stop. I flick the throttle, the RPMs don't always come back down quickly, they seem to stay elevated. This also happens if coming down from highway speeds and shifting down from 6 to 1 increasing RPMs. I have to engage 1st gear and roll an inch to 'reset' the RPMs.

I think my first go is going to be check float height.

Also check your carb boots for air leaks.  Spray some starting fluid around the boots with the bike running and if it changes RPM, that is the source of one of your problems.

Quote from: bombsquad83 on May 23, 2013, 01:32:49 PMNot to confuse this issue further, but this is not completely true with CV carbs such as the GS's.  The throttle opens the butterfly, which allows more air to flow into the engine, but it doesn't allow it all right away.  The slide also controls air flow.  The diaphragms that lift the slide with the jet needle are raised with vacuum, which is proportional both throttle opening and RPM.  Therefore, when testing mixture at the half-throttle position, you should also be in mid-rpm, and when testing mixture at WOT, you should take it to high RPM.  At least this is how I understand it.

I think what he's addressing is the fact that different jets are activated at different throttle positions.

Quote from: RossLH on May 23, 2013, 01:42:37 PM

Quote from: bombsquad83 on May 23, 2013, 01:32:49 PMNot to confuse this issue further, but this is not completely true with CV carbs such as the GS's.  The throttle opens the butterfly, which allows more air to flow into the engine, but it doesn't allow it all right away.  The slide also controls air flow.  The diaphragms that lift the slide with the jet needle are raised with vacuum, which is proportional both throttle opening and RPM.  Therefore, when testing mixture at the half-throttle position, you should also be in mid-rpm, and when testing mixture at WOT, you should take it to high RPM.  At least this is how I understand it.

I think what he's addressing is the fact that different jets are activated at different throttle positions.

That's correct, and I agree.  I was just pointing out that RPM does matter as well.

You are correct the slide is not controlled by the throttle cable like with non cv carbs so troubleshooting can be more difficult. I'd check float heights, is it the same in all gears? It uses less fuel to get to 6.5k WOT in 1st than 6th so that could indicate a float set too low. Otherwise it could be either rich or lean, try pulling the choke on WOT and see if it helps or makes it worse. If it helps you are lean if it makes it worse you are rich

Quote from: bombsquad83 on May 23, 2013, 01:47:48 PMThat's correct, and I agree.  I was just pointing out that RPM does matter as well.

You'll find that RPM has little effect on vacuum unless the air filter is unreasonably restrictive. Vacuum is mainly dependent on throttle position.

Thanks for the check, guys.  Yeah, I just wanted to make sure we got some throttle postion in on the matter, because he is having mixture issues... For example if a bike has a signficant air leak, his throttle position could be lower than its supposed to be at the rpm being experienced.  I appreciate the follow-up for clarification, especially for future reads on the thread.



- Bboy

Sputtering @ 6500 rpm - and what throttle position ?

And you should think in terms of throttle position only - the fact is that the GS does have CV carbs and the throttle does open the butterflies only, then vacuum builds and lifts the slide - however all that means is you should think in terms of throttle position only after you get a stable rpm under load.

Anyway - 6500 rpm and assuming you're @ 1/2 throttle or up - needle - and main jet.
Float level will affect the thing even lower down. You wont make it to 6500 rpm and sputter.

Before we even get that far, what setup and jetting ?

Cool.
Buddha.

"The problem consistently occurs at high RPMs it seems to idle okay. One issue however is if at a stop. I flick the throttle, the RPMs don't always come back down quickly, they seem to stay elevated. This also happens if coming down from highway speeds and shifting down from 6 to 1 increasing RPMs. I have to engage 1st gear and roll an inch to 'reset' the RPMs.

Not to dispute what everyone has said up to this point but I had this very problem and it turned out that I wasn't letting the bike warm up enough. Once I let it warm up for a good five minutes from stone cold, that problem completely disappeared. I'll let someone with greater technical knowledge explain why but I know these bikes are said to be "cold blooded" and that sure was the case with mine. I replaced both the tankcock and framecock, all fuel and vaccum lines, spark plugs, measured float height, syched the carbs, and tested the carb boots for leaks only to find out that I wasn't letting the engine warm up long enough.

Quote from: dmoore on May 24, 2013, 06:57:09 AM
"The problem consistently occurs at high RPMs it seems to idle okay. One issue however is if at a stop. I flick the throttle, the RPMs don't always come back down quickly, they seem to stay elevated. This also happens if coming down from highway speeds and shifting down from 6 to 1 increasing RPMs. I have to engage 1st gear and roll an inch to 'reset' the RPMs.

Not to dispute what everyone has said up to this point but I had this very problem and it turned out that I wasn't letting the bike warm up enough. Once I let it warm up for a good five minutes from stone cold, that problem completely disappeared. I'll let someone with greater technical knowledge explain why but I know these bikes are said to be "cold blooded" and that sure was the case with mine. I replaced both the tankcock and framecock, all fuel and vaccum lines, spark plugs, measured float height, syched the carbs, and tested the carb boots for leaks only to find out that I wasn't letting the engine warm up long enough.

It's not normal to have a hanging idle that goes away once the bike is warmed up.  I believe that would indicate either an air leak, or tight valve clearance.

Quote from: The Buddha on May 24, 2013, 06:15:57 AM
Sputtering @ 6500 rpm - and what throttle position ?

And you should think in terms of throttle position only - the fact is that the GS does have CV carbs and the throttle does open the butterflies only, then vacuum builds and lifts the slide - however all that means is you should think in terms of throttle position only after you get a stable rpm under load.

Anyway - 6500 rpm and assuming you're @ 1/2 throttle or up - needle - and main jet.
Float level will affect the thing even lower down. You wont make it to 6500 rpm and sputter.

Before we even get that far, what setup and jetting ?

Cool.
Buddha.

This is the main point I was trying to get across.  I didn't mean to overcomplicate.

So, assuming I'm running too lean/rich, how would I go about adjusting this? Float height?

I know this may sound a bit novice but, the jet needles, are they "adjustable"? When I reinstalled mine, i just screwed them all the way down till stop. Also, before disassembling the carb, the bike ran just fine at high rpms/WOT. It was post-rebuild that I experienced the issues. Is it normal that float height could get borked just by removing the floats?

Thanks!