GS1100E and Mikuni 33 smoothies

[sharpy]

They have different Throttle Slides in them aswell. Kawa and suzi. The throttle Valve is 1.5 on one and 2.0 on the other. Pic below (green highlight).

Carb Info.jpg

[GregT]

They have different Throttle Slides in them aswell. Kawa and suzi. The throttle Valve is 1.5 on one and 2.0 on the other. Pic below (green highlight).

The air jet size is significant too. 1.5 slide (rich) has a 1.2 air jet (lean) to match - and vice versa for the other version.
I have struck a case of used 33's where it became apparent the wrong combo had been installed.

On another thread about 33's some time back, Ray encouraged vacuum syncing of 33's. I'll endorse this heartily.
For a racebike, bench syncing of the slides is good enough. For a road bike, use a vacuum sync.

[pete]

Since posting that I revisited the bench sync which I only gave a cursory glance to... it's far more important than I realised! My lack of a stable idle was due to them being way out of sync, fixed that and most of my idle woes are solved. I also discovered by the use of an AFR gauge that the 17.5 pilots weren't lean at all after the bench sync, so I've gone back to them.

The carbs have the 1.5 throttle valves which I already knew meant the carbs were likely set up for a Kwak (but thanks Sharpy!), but as best I can tell the impact there is initial cracking of the throttle from what I've read, and 2.0 valves are NLA now.

The carbs are set up as tested in the garage with 0 kms so far, this is just to get it registered when I can then tune on the road:

Pilots - 17.5
Air screws - 3/4 turn out
Needle - Middle position
Mains - 122.5
Air jets - 0.6
Throttle vavles - 1.5

The jet needle and needle jet are as outlined in the Sudco screen shot Sharpy posted.

I haven't vacuum sync'd them yet but going by the tuning guide (in addition to Ray's advice now I know it), they say sync the carbs manually but use a vacuum gauge to set the pilot air screw, typically the highest vacuum point is the correct air screw setting.

Another month or so and I can get some real kms done and know how the carbs truly are...

[GregT]

The slide number is simply the height of the cutaway. If you need a 2.0 slide a 1.5 can be converted by raising the height of the cutaway.
Conversely, to convert a 2.0 to a 1.5, material is machined off the flat bottom edge of the slide.

Done a lot of this over the years. Pre internet, carb bits were hard to find in NZ so you made stuff...

[pete]

Yep cool Greg, while I understood that referred to the cutaway I didn't think about modifying them... hopefully something I don't need to consider as that's a daunting prospect for me!

[fastfrank]

Getting close to reinstalling my carbs. Have a few pics of the process, and I’ll post one here. I’ll do the (PITA) tank cleaning routine before I get that far, and use an inline filter for awhile afterward. I’ll go through and check the valves, while I have everything out of the way. Glad there aren’t shims.

Been spending most of my time getting my 99 ZRX going, after rebuilding the stock CVK carbs, and it’s running great now. Nice to get back on a liter bike; it’s been awhile.

Once I get these two running right, I’m on to my KZ750 Twin - just ordered some VM34 carbs for it, instead of futzing with the BS38s.

A0CA9741-EC81-4AD7-8E08-E0F0D3A57D84.jpg

[GregT]

Yep cool Greg, while I understood that referred to the cutaway I didn't think about modifying them... hopefully something I don't need to consider as that's a daunting prospect for me!

If push comes to shove, post the slides over here and i'll do them for you.

[pete]

Cheers Greg, good to know! Right now I know my needle seems to be in a pretty good position but after dropping the mains to 115's I'm still too rich up top so need to go lower yet, just gotta decide if 112.5's are enough or if I need to go 110's. The 122.5's had the AFR gauge reading 10:1 (limit of rich on it) and the 115's get to low 11's and I'm aiming for around 13, so dropping at least another 2 sizes sounds like the best next step.

I still have the idle higher than I'd like as a nice setting for the air screw still eludes me, but to be honest I haven't given that the proper amount of attention I should just yet as I've wanted to really get the motor run in rather than idling.

[GregT]

Be aware that the pilots have an effect higher up the range than you'd think. Too rich on them and you get fuel bleeding through them well into what should be the needle area. On the smoothbores - and Keihin CR's - it can be easy to go too rich on the idles to get response and pay for it with problems further up.

[pete]

Ah interesting! What I was seeing with the needles was low 14's at 1/4 throttle, around 13 at half throttle, then 3/4 throttle and over is where it dived down to 11.

I was actually contemplating another quarter turn in on the air screws to get that 1/4 throttle area just a touch richer, but that might be too much? I can only try it and give it a go right?

[GregT]

So what size pilots are in it now ?

[pete]

I have 17.5's in there now, tried 22.5's when I thought it was too lean before I properly bench sync'd them but they were way too rich (even at 1.5 turns out on the air screws).

[GregT]

I have 17.5's in there now, tried 22.5's when I thought it was too lean before I properly bench sync'd them but they were way too rich (even at 1.5 turns out on the air screws).

It is starting to sound like it needs bigger slide cutaways - more air - IE leaner at that point. Once you run out of adjustment on what can be adjusted, it's time to look at the cutaways.

[pete]

Ah ok, I've only read through the Sudco tuning manual but that's about it aside from a bit of Google searching, and understand how/when that cutaway comes into play is a little confusing to me. Cheers Greg!

[pete]

Well I'm pretty convinced it's the throttle valves causing me grief. I spent some time with the idle adjustment and air screws and got it down to a reasonable RPM with a reasonably steady idle, but now way too rich around 1/8 throttle, and the 2.0 throttle valves would in theory make a difference there.

I'm not sure about another symptom though but I suspect same cause... if moving along with the throttle in the 1/8 to 1/4 range, then closing it to downshift or roll into a corner with engine braking, there's a big delay when I open it again before the engine responds, something like a second. If I crack the throttle even more it kicks in sure, but that's a big kick in the pants mid corner so can get a little scary. If I keep the throttle just partially open, the issue goes away completely.

So, is there a template or measurements or something to copy to adjust the throttle valves from 1.5 to 2.0? I just remembered yesterday I still have a mate's stock Kat carbs here that should only be missing the main jets, so I'm contemplating giving them a once over and installing them to let me put some time into the VM33's.