BS34 carbs stutter at 4k

Hi, I have a set of BS34 carbs with #40 pilots and 130 mains. I have a Kerker with a 2" comp baffle and stock air box.
I moved the needle clip to the very bottom. I have the air mixture screws out 2 1/2 turns. The bike use to pop on deceleration but not anymore with the above settings.

I have a stutter now at or just before 4k rpm if I hit the throttle. The bike pulls hard now but for that.

At 4k rpm that would be the needle and I think I'm running rich? Should I move the needle clip up one to get rid of the stutter or should I turn the mixture screws out another half turn?

4k rpm stutter when I hit the throttle.

I moved the needle clip one from the bottom and the stutter at 4k is gone. The popping noise on deceleration is still gone as well.

Going to order one of those Colortune tools to dial the bike in right. I'm not to good by ear half deaf I think. lol I already have the Carbtune Pro and it works great well worth the money.

KZ1100 Bully wrote:

I moved the needle clip one from the bottom and the stutter at 4k is gone. The popping noise on deceleration is still gone as well.

Going to order one of those Colortune tools to dial the bike in right. I'm not to good by ear half deaf I think. lol I already have the Carbtune Pro and it works great well worth the money.

sounds like youre on it.....g/l......

Don't waste your money on the colortune. It's interesting and educational at best, but doesnt help all that much.

If your running the stock airbox the origional 37.5 pilots will suffice. You'll find your cruise throttle position will widen, and the bike is smoother and easier to control at small throttle inputs and lower speeds.

The needle clip can be left in the default/middle position or 1 down, whichever gives best power at 1/2 throttle.

The main is a guess based on the max power output at WOT.

Your jetting is entirely dependant on throttle position.
To test the main jet you need to blast the bike full throttle. Anything below 3/4 throttle doesnt rely on the main that much.

1/2 throttle pulls for the needle. cruising is on the pilot, and the mixture screws are for idle.

The mixture screws are not all that important other than to produce a nice idle and make for smooth transition to accelleration (on the needle).

They arenet supposed to be X number of turns out. They are supposed to be set just slightly rich of the point that they produce the highest rpm.

With the bike good and hot, turn all four screws in until you hear the idle drop, then stop and screw them out till the idle drops again while counting how many turns it took. Then turn them back to the halfway point of your count. Thats a good ballpark setting, then you can fine tune each one using the same method individually.

GL!

TeK9iNe wrote:

Don't waste your money on the colortune. It's interesting and educational at best, but doesnt help all that much.

If your running the stock airbox the origional 37.5 pilots will suffice. You'll find your cruise throttle position will widen, and the bike is smoother and easier to control at small throttle inputs and lower speeds.

The needle clip can be left in the default/middle position or 1 down, whichever gives best power at 1/2 throttle.

The main is a guess based on the max power output at WOT.

Your jetting is entirely dependant on throttle position.
To test the main jet you need to blast the bike full throttle. Anything below 3/4 throttle doesnt rely on the main that much.

1/2 throttle pulls for the needle. cruising is on the pilot, and the mixture screws are for idle.

GL!

dont let OMR hear ya talk smack about the colortune....its a key part of the anal-retentive tuning guide.....:woohoo: :laugh:

TeK9iNe wrote:

With the bike good and hot, turn all four screws in until you hear the idle drop, then stop and screw them out till the idle drops again while counting how many turns it took. Then turn them back to the halfway point of your count. Thats a good ballpark setting, then you can fine tune each one using the same method individually.

GL!

This is the part I don't understand even thou it is pretty straight forward.

It is to bad the morgan Carbtune does not do mixture screws. I really need a tool to adjusted the settings.

I just find it hard to hear the drop.

Thanks for the info TeK9iNe, I will try to dial them in.

KZ1100 Bully wrote:

This is the part I don't understand even thou it is pretty straight forward.

It is to bad the morgan Carbtune does not do mixture screws. I really need a tool to adjusted the settings.

I just find it hard to hear the drop.

Thanks for the info TeK9iNe, I will try to dial them in.

If you turn all of the screws at the same time (eg: turn carb 1 2 3 4 all in 1/2 turn, then listen), you will clearly hear an increase/decrease in rpms.

You can also use the carbtune at the same time, it will display what your hearing! As you change the mixture screw the combustion on that idling cylinder will decrease/increase, thus changing the vacuum, thus changing the readin on your carbtune.

Setting carbs by carbtune: Turn an individual carb mixture screw in until the carbtune drops 6cm vacuum for theat cylinder.
Then turn the screw the other way while counting the turns.
When the vacuum falls from the highest point it reaches by another 6cm, stop.
Ruturn the screw back to half the number of counted turns, and your done!

GL!

keith1 wrote:

dont let OMR hear ya talk smack about the colortune....its a key part of the anal-retentive tuning guide.....:woohoo: :laugh:

:laugh: :laugh: :laugh:

I have one and have used it to diagnose some problems on cylinders, but for mixtures I find the "by ear" method best to set initally, then "by feel" for power/smoothness of transition.

I just ordered a "colortune" today. I don't know why people keep on messing with the pilot jets on these carbs. Going to a larger pilot jet with BS34s is not at all necessary and ill-advised. I have found that on my built 1150 with cams pod filters and header I am actually way too rich at the lower end. This will manifest itself as a "popping stutter" between 1500-3000rpm. a stutter at 4000rpm is indicative of wrong or maladjusted needles. Because these needles are not adjustable, they must be shimmed. Usually about 1-1.5mm up. If you have adjustable needles than they are not OE Kawasaki and most likely Dynojet bring the needles back up to the center position.

otakar wrote:

If you have adjustable needles than they are not OE Kawasaki and most likely Dynojet bring the needles back up to the center position.

They may well be OEM, the pic below is copied from my FSM that specifically mentions which groove the clip should be in.

Might be a Euro model thing, I don't know, but it would seem that some Kaws came with stock BS34s with adjustable needles.

canada has adjustable needles too

In a few countries there were adjustable needles incorporated. However not in the USA. The needles actually come into play at about 3500rpm. This can be changed WIT a needle adjustment by almost 500rpm down and 1000rpm up.