Keihin PWK slides - notched vs. not.

[scot_douglas]

I'll try to get photos later, but I noticed something when I was swapping needles in a 36mm PWK. The slide has a 1mm X 1mm notch cut out of the bottom face of the slide, right behind the needle. I have another slide that I purchased from sudco, same cutaway (7.0) and it does NOT have the notch.

I have searched but cannot find a reason for the notch. Looking at my slide "inventory", I have a 6.5 and 7.0 that are notched and a 7.0 that is not. AFAIK, the 6.5 and 7.0 that are notched both are from OEM KTM airstryker carburetors.

Any idears? This has got me quite curious! ?

[scot_douglas]

wealth of knowledge here. ?

[Wayward Son]

nice pictures ?

[scot_douglas]

nice pictures

DAMMIT!

I knew I forgot something! OOps I've been busy with work, and I think the cheeze slid off my cracker this week.?

[scot_douglas]

nice pictures ?

HA HAAA!!!!!

I finally had time to snap some photos...

Notch:

No notch:

[Wayward Son]

ah,makes for better idle with out cranking the slide hieght up.

[scot_douglas]

I wondered about that as it seems that when I ran the slide *without* the notch, the idle was very hard to set - either too fast or too slow being separated by a few degrees turn of the idle screw.

[Wayward Son]

exactly!

[jaguar57]

it focuses the idle flow closer to the center where the idle nozzle is and of course a few millimeters back is the needle/needle-jet which also contributes to idle fuel flow

[EmpireofDerp]

Decided to revive this thread for its 10 year anniversary? [emoji529]

[Evan03]

How bought another rebirth of this thread.

 

Thinking about notching my 38mm keihn on my 125

[DEATH_INC.]

I tried it on the 'striker on my 500 and it screwed it up, couldn't get it running right 'till I replaced the slide again. Maybe the 500 has too much vacuum for this?

I did a bunch of reading on it before I tried it, the KTM guys seemed to like it.

Edited November 18, 2023 by DEATH_INC.

[Evan03]

I just did it. Had dremel disc that was about 1.5mm wide. Seems to maybe idle alittle better. 

Doesnt appear to have messed anything up doing some brabbing in garage to set air screw.

 

Will report after tomorrow ride

[Taffy]

its going to create a stronger signal over the atomiser and pilot hole.  So, the slide will be set lower than without the notch and all the air going through will be centralised.  

The bike will run richer.  The idea is that you now change the jetting to take advantage of it.  so it requires that you realise that it takes two moves to be successful.  

Most people can't think of two moves.  Chess players understand this completely and chess/jetting is a great euphamism on life.  
a consistant idle and pick up will be better.  But again, only if you tested and jetted downwards to take advntage of it.  

This is why people don't use octane booster - two moves.

its why people who raise the compression of an engine and then leave it alone often pay dearly for thewir mistakes....they only did the first move.

Taffy

[Evan03]

If i could tune a carb in two moves id be in somekinda heavon. Havent put the jets away yet.

On move 40ish now and just kinda getting in the ball park now the weather is turning bitter cold. Ugh

Edited November 18, 2023 by Evan03

[Evan03]

Id say the little groove i did did virtually nothing on my kx144. Idle screw is more effective is all

 Bougght 80 mile ride today

[Doc Brown]

On 11/19/2023 at 5:27 AM, Evan03 said:

Id say the little groove i did did virtually nothing on my kx144. Idle screw is more effective is all

 Bougght 80 mile ride today

 I am not surprised as smaller engines may react less than bigger engines. The notch can help to get a more stable idle or just help to keep the engine running with a very low idle which many riders prefer.  In my opinion, hardly any further steps are needed to get this right, apart from setting the air screw correctly, of course.

Doc