Tk22 pilot jet question, '81 GPz550

So after getting my carbs dialed in as well as possible with my current jetting I find that my airscrews are turned almost all the way in.
All 4 are running about 1/4 to 3/8 of a turn from being bottomed out.
As I understand on the tk22's the airscrew is just that, a screw that controls airflow. Turning it clockwise means less air, or richer, am I correct?

I assume that means I should try a larger pilot jet?

The stock pilot is a 32, I have the set thats in the bike and a spare set to drill out.

Stock airbox, 4 into 1 exhaust (mac I think) and a yosh pipe from who knows what.

You are correct on the air screws. There are no sources for larger pilots, so drilling is the only way to get bigger pilots.

Since you have the stock airbox, I would not expect the jetting to be changed a lot, but I have found a Mac 4-into-1 does seem to require low end jetting (pilots and needle). It seems to breather a lot more at idle (which is why it's pretty loud at idle compared to systems like the Kerker's, etc.). But it doesn't breathe a whole lot at wider throttle openings.

However, I have found that precisely shimming the stock needle can sometimes work in place of using larger pilots. The tk-22 website has details on how to properly shim the needles without binding them. IT requires a shim wire on the perimeter of the needle retaining hardware.

But before going into any jetting, it's important to make sure there are no vacuum leaks. Also, all four plugs should look the same, so you are not chasing a local cylinder problem rather than actual jetting problem.

I would start with a .55mm shim with .026 wire. Second try would be .63mm shim with .028 wire. (The shims can be +/- .03mm or so, and still use the same wire.) Obviously, shimming can be undone, whereas drilling can't.

BTW, 1/4 to 3/8 out is not way far out if it seems to run ok. It does indicate leanness in the pilot, which might make for longer choke times etc., but if it starts and runs ok after warm up, then the screw setting, alone, is not a huge worry.

Here ae some notes on shimming.
gpzweb.s3-website-us-east-1.amazonaws.co...shimmingNeedles.html

Here are some notes on jet drilling.
gpzweb.s3-website-us-east-1.amazonaws.co...22jetsAndDrills.html

Thanks Lou, I think I've got it sorted enough to start jetting and needle adjustments, plugs all look even, just tracked down a bad plug wire and fixed that yesterday.
Synched the carbs, no leaks, and the carbs respond as expected to air screw changes.

I've got 4 rebuild kits with adjustable needles and #92 mains and #32 pilots, I've read most of your info on the tk22 and its been very useful. Used the drill bit size chart to bump up the main jet to the correct for GPz #34.

I'll read over it again but off the top of your head do you have an idea what size I should shoot for on the pilot?

Thanks

MadShad wrote: ...
I've got 4 rebuild kits with adjustable needles and #92 mains and #32 pilots, I've read most of your info on the tk22 and its been very useful. Used the drill bit size chart to bump up the main jet to the correct for GPz #34.

I think you mean 94 for the main. 94 is correct.

Have you seen my posts on the no-name rebuild kits? The needles are not useable, and I haven't gauged out their jets.

Here's how to identify the fake Keyster kits.
gpzweb.s3-website-us-east-1.amazonaws.co...TK22rebuildKits.html

And here is the problem with the needles from those kits (they are too skinny to use at all):
gpzweb.s3-website-us-east-1.amazonaws.co...K22threeNeedles.html

I recommend you get some really tiny washers and see how the adjustable needle compares to the factory needle. If it's off by more than 3 mm in vertical position, (skinnier), it cannot really be used. It will be too rich, but more importantly, it will be super rich in the off idle range.

MadShad wrote: ...
I'll read over it again but off the top of your head do you have an idea what size I should shoot for on the pilot?

The drill kit I suggest has a 34.3, which is where I would start. Normally, I wouldn't go any bigger unless you go to pods. The next size up is 36.8, which is the biggest I've ever used, and that was for pods, and possibly for use with Dynojet needles (which are tapered very lean off idle, compared to stock needles), but again, the Mac system is pretty lean at low RPMs, so it's not out of the question for you as well.

The needle shims I recommend are less than one clip position different. If you go near a full clip change on the needle, it will be rich, but the problem is that the lean-cruise range moves too far toward the power range of the throttle. You end up with a rich cruising range, and a lean spot at around 1/4 throttle. This gives you less mileage. The factory (adjustable and non-adjustable) needles are designed to have a lean-cruise position at about 1/16 to 1/8 throttle. That's when you're doing about 50 to 70 mph steady. When you change the clip position, you change the position of the lean-cruise portion of the throttle.

Here are some recent AFR readings for a standard KZ550 with a Mac system that we modified slightly to reduce noise. We basically pinched the reverse pipes very slightly (they are the pipes in the canister).

Notice the setting we ended up with in green. It's not ideal, but the bike runs great. The only problem with it is the lean bump happens at 1/4 throttle instead of 1/16~1/8. This is due to the .63mm shim on the needle. Notice with smaller shims, the same needle has the lean bump earlier in the throttle range.

The purpose to that setup was to test if it was possible to get a workable jetting by using stock jets. It worked, and the main advantage is that all changes are done from the top of the carbs so they don't have to be removed. The only downside is the gas mileage will be a little lower than ideal unless you do a lot of cruising at 80 or 90 mph.

One upside of having richer 1/16 and 1/8 throttle is that you can come off choke much sooner.

You can also see the AFR readings with the fake needles (in red). The AFR goes the opposite direction from what you want... not good. The bike still ran, but the plugs got very black.

The blue trace has a good shape, but the overall AFR is too rich.
The green trace has less than ideal shape, but the overall AFR is pretty good.
The magenta trace has a too broad of a lean bump, and the overall AFR is a little too lean.
The red trace is not a useable shape at all. and is too rich overall.

If we had more time, I would have tried less shim, with bigger pilots as indicated by the note.

The kits I have are original keyster kits, made sure I didn't get the no name ones after reading your info.
And yes I did mean #94 on the main.

Thanks for the graph, really good info.
Sure woukd be nice to hook up the laptop and datalog, lol.
Although I have enjoyed every second of wrenching. I've got the next 5 days off so should be able to find time to do some testing.

Thanks!

If you mess up and ruin a pilot jet I have a few extras. Good Luck.

You won't tune out all the cold-bloodedness, but you are on the right track.

Just an update here, I drilled the pilot jet out one drill bit size to a 34.x.

cold starting is now predictable and I can come off the choke much sooner. I turn the choke till it hits it's detent, back it off just a bit and hit the starter button. The bike starts and hits a high idle of about 1500 rpm indicated and will hold that rpm throughout the warm up. I can come off the choke much sooner than I could before.

Now to be fair it's been warmer these past few week so it's not as cold as it was when I first picked the bike up, overall I'd say it's still a noticeable improvement, I don't have to babysit it while it warms up.

You may have also seen the fast-idle mod. It lets you independently control the fast idle setting of the choke system. It is so you can easily set the idle speed for different seasons.

gpzweb.s3-website-us-east-1.amazonaws.co...astIdleScrewMod.html

Where did you get the shims Lou. I see a 4-1 in my future. R

I think I found some at Grainger. I probably found some others laying around at work. I might have even dug some up at Menards. The Dynojet kit came with some as well. They are all varying thicknesses, usually between .4 and .8 mm.

If you do get them at a supplier, always get like 20 or 30. Even the same source will vary slightly in thickness, by a few hundredths, so you will probably want to mic them out.

You can see from the chart the difference that .07mm made. The .56 shim was very useable, but the .63 shim put it in the sweet spot for mileage without going too lean on cruise. With the .56mm shim, a really strong gust of crosswind might have caused a little hesitation at light cruise (which is one of the complaints people make about pods). Just going to a .63mm shim eliminates that. Had we gone to the next clip on the needle (which is what you would do if you are jetting by seat-of-pants method) it would have been too rich for sure. It would run fine, but the plugs would be darker, and the mileage would suffer a little.

I don't know where I got most of my shims, but here are three sources I know of (though they are on the thicker end):

0.77mm to 0.82mm
Source: Menards
Brand: Handi-Pack
SKU: 738287877069
Part# 87706
#4 flat washer USS
Aluminum
2 pcs

0.69mm to 0.79mm
Source: Menards
Brand: Handi-Pack
SKU: 738287812411
Part# 81241
#4 S pattern flat washer
Brass
3 pcs

0.64mm to ??
Source: Grainger
Part# 2DNL5
#3 screw flat washer
AN960-C3 flat washer
Stainless
100 pk
Listed as .75mm to .89mm, but actually thinner.

When you're ready, let me know. I think I might have a few extras laying around I could throw into an envelope.