Jetting questions (not a GS, but close)

[KEITH KRAUSE]

Well, I used to type out small novels trying to explain things but it sounds like you wouldn't really listen anyway. I just don't have time for that anymore. And don't take these words as me being angry or something because that's not so. I do remember helping you in the past...a lot. I just try to add my thoughts and the reader can use it or not.
My thoughts on the importance of throttle position and its relation to vacuum differ than yours. That's fine. I have my way of testing and that's all I can offer. VM, CV, too similar to argue about.
In the real world, you shouldn't try to gag or "confuse" the carbs by "whacking" them open. Under what conditions would you do this? A typical roll on gave you good results. But whacking it open revealed a stumble because you forced the carbs to operate in a way they're not designed to.
Whacking it open means you want to accelerate hard. You wouldn't whack it open from a dead start, you'd be revving it first as you prepare to launch. And if you wanted to accelerate hard from a cruising point you would either roll it on aggressively as you put it, or shift down and roll on, or you'd be in the powerband already and then it almost certainly would respond as you want, even if whacked open.
Maybe I'm wrong about how you're throttling this bike but you can't just whack open any bike from very low rpm's and expect perfection.

[t3rmin]

Well, I used to type out small novels trying to explain things but it sounds like you wouldn't really listen anyway. I just don't have time for that anymore. And don't take these words as me being angry or something because that's not so. I do remember helping you in the past...a lot. I just try to add my thoughts and the reader can use it or not.
My thoughts on the importance of throttle position and its relation to vacuum differ than yours. That's fine. I have my way of testing and that's all I can offer. VM, CV, too similar to argue about.
In the real world, you shouldn't try to gag or "confuse" the carbs by "whacking" them open. Under what conditions would you do this? A typical roll on gave you good results. But whacking it open revealed a stumble because you forced the carbs to operate in a way they're not designed to.
Whacking it open means you want to accelerate hard. You wouldn't whack it open from a dead start, you'd be revving it first as you prepare to launch. And if you wanted to accelerate hard from a cruising point you would either roll it on aggressively as you put it, or shift down and roll on, or you'd be in the powerband already and then it almost certainly would respond as you want, even if whacked open.
Maybe I'm wrong about how you're throttling this bike but you can't just whack open any bike from very low rpm's and expect perfection.

Well you're probably right about that. Especially with drilled slides that might be raising faster than I'm used to, I probably need to modulate the throttle more carefully.

So here's the latest: I experimented with float levels a bit. Stock spec is 25.7mm. I had 'em at about 25mm (per information from the XS forums) all along. I went up to 26mm and tried the 142.5 and 145 mains again. Way more blubbery in the middle and didn't pull as hard on the top end. 145 worse than 142.5. Did a plug chop in the soggy middle area and result was... inconclusive. Center electrode was fairly clean and grey, but plenty of soot around the edge.

Went down to 24mm and dropped 137.5 in again. Runs a little worse in the middle (agressive roll-on, 5k RPMs) than it did at 25mm with 137.5's, but it's maybe a little better off the line. Down low and up high this jet definitely pulls harder than 142.5 or 145. All signs still pointing to *rich* in the middle. Note it's easy to pull "past" the slobbery area and then it's a rocket with 137.5's, with the 145's and 142.5's you can't hardly get past it (especially in a high gear).

(Obviously float levels shouldn't have much of an impact at the throttle openings/RPMs I'm having the most trouble with, but I wanted more confirmation that what I'm fighting is a rich condition. And I was frustrated and had lots of time on my hands today.)

Also I'm wondering if perhaps the stock XS airbox flows more compared to a GS airbox, and there's not a great deal of difference between that and pods, since I'm also surprised that the stock jet runs the best. I do still have somewhat restrictive stock-style exhaust, too.

To recap:
The good: Pilot, float level (ballpark), beginning of needle circuit, mains
The bad: middle/end of needle circuit

How can I lean out the middle/end of the needle? If I lower the needle, it's sluggish off the line (begining of needle). Have to change the taper? That seems like it should be more of a fine-tuning thing...

[t3rmin]

Or another thought: maybe I should try using shims for 1/2 steps, as you mentioned. Maybe try 3.5 and 4.5?

[KEITH KRAUSE]

Since you've tried both position 3 and 4 from the top with (if I remember) lean and then rich symptoms respectively, then the most logical thought would be to use a jetting spacer (typically .022" thick) to achieve position "3 1/2". Place the e-clip at position 4 from the top with the jetting spacer directly on top the clip. Maybe that will fix things.
If that doesn't work then the air jet could factor in here. I believe those carbs have a pilot air jet and a primary air jet. Pods many times require air jet changes too.
Another thought would be to change the jet needle size or the needle jet size. You're getting in a bit deeper there. Needle jet change isn't normally needed with your mods. Jet needles often need changing. Heck, you could even have worn needle(s) or needle jets causing a problem.
I'd try position 3 1/2 first.

[KEITH KRAUSE]

Or another thought: maybe I should try using shims for 1/2 steps, as you mentioned. Maybe try 3.5 and 4.5?

Yes. I took awhile sending my previous reply about a 1/2 position change and didn't see your latest reply until I sent it.

[t3rmin]

Since you've tried both position 3 and 4 from the top with (if I remember) lean and then rich symptoms respectively, then the most logical thought would be to use a jetting spacer (typically .022" thick) to achieve position "3 1/2". Place the e-clip at position 4 from the top with the jetting spacer directly on top the clip. Maybe that will fix things.
If that doesn't work then the air jet could factor in here. I believe those carbs have a pilot air jet and a primary air jet. Pods many times require air jet changes too.
Another thought would be to change the jet needle size or the needle jet size. You're getting in a bit deeper there. Needle jet change isn't normally needed with your mods. Jet needles often need changing. Heck, you could even have worn needle(s) or needle jets causing a problem.
I'd try position 3 1/2 first.

I think you're right. I predict position 3.5 will be closer, and if I want to be right-on, I'll have to get a differently-tapered needle (that would seem to be the way to separately-tune the needle's top and bottom). Thanks.

[KEITH KRAUSE]

And I assume the carbs are completely clean.
If the old Uni's were rotting, the dinky little foam pieces will jam into the air jets and pilot circuit passages easily. After dipping/spraying, I shove at least 150 PSI through everything and verify it comes out the other end of passage.
And did you mention vacuum synching? Has to be done to accurately judge performance.

[KEITH KRAUSE]

OK I gotta go elsewhere for now.
Good luck with it and I'll try to check in later and help if I can.

[t3rmin]

Yeah they've been cleaned thoroughly. Vacuum synched as well. Yamaha put springs on the sync screws instead of locknuts like Suzuki. Sync in a fraction of the time, and with only a screwdriver. \\/

[t3rmin]

Also I believe the air jet is pressed in, so changing that isn't really an option.

The more I think about this, the more I think needle taper is what I'm fighting against. (Or needle wear, but I've examined them pretty close and they don't *look* worn.)

Here's one of 'em. They're 5GZ6



I wonder if something with a more linear taper would work better?

[t3rmin]

Ok, now I'm glad I messed with the float levels. I realized I hadn't tried position #3 with the 137.5 jets since drilling the slides, so I tried it. This time the low end didn't disappear, due probably to the richened float levels. This is the best it's run so far. I can still cause it to go rich in the middle if I roll-on fast, but with carefully-metered twists of the wrist, I can go through several gears, pulling hard all the way.

I'll try position #2 tomorrow, and if that's too lean, shim it to 2.5. But I'm going to have to call it a night now, since these test rides at 29 degrees are freezing me to death. ;-)

[LeeGS550E]

I'm following this with interest. You're doing a very good job, Matt! This thread's a nice example of the sceintific carb-tuning process at work. I'll bring the 5/7 up so you can get it dialed in next.:-D

[Guest]

You might have to tune it again when it gets warm. :?

[t3rmin]

You might have to tune it again when it gets warm. :?

Pffft!

[t3rmin]

I'm following this with interest. You're doing a very good job, Matt! This thread's a nice example of the sceintific carb-tuning process at work. I'll bring the 5/7 up so you can get it dialed in next.:-D

Hah. Actually I've made two changes at once a few times, following a hunch, which has almost always been a step backward, so I've been anything but scientific. I lack discipline...

But this thread has a been a huge help, not just the advice (which has been great, keep it coming!), but writing it all down and collecting my thoughts.

Also it's a big help not having an airbox to futz with when removing carbs, and the XS throttle cable is super easy to disconnect, and there's no choke cable (lever built-in to the carbs), and there's lots of room in that big bike frame, so they slide in and out super easy.