Pod type filters for VM 30 carbs on GS 1000 ST ( European/Australian spec)

[John Kat]

I went for a ride today.
The bike went fine but I believe acceleration could be better?
I dropped the main jets from 137.5 to 132.5 in hope to improve.
If it doesn't work I'll do a plug chop at WOT.

[John Kat]

The saga continues...
I reduced the size of the main jets step by step to get the engine to work at full throttle.
None of these jets allowed more than 1/2 throttle: 137.5, 132.5, 127.5, 122.5, 115.
The best result was achieved with 110's and very slightly worse with 107.5's but I still can't open the throttle past the 3/4 range.
My needles are on the #4 slot and the pick up is very good from 1/4 to 3/4 throttle.
Dropping the main jets to 102.5 brought total misery above 1/4 throttle.
I wonder if the VM 30's will ever work on pods???
Is it possible that one size difference could make it work i.e. going to 112.5 vs 110?
I wonder if the issue is not related to the exhaust?
It's a 4 into 2 from Kerker and when I had the OEM filter fitted to the carbs I had to reduce the size of the mail jets from 97.5 to 92.5.

[John Kat]

I read an interesting article on tuning VM type carbs:

http://forums.pstuning.com/index.php?showtopic=545

Apparently these carbs must be tuned from the bottom up thus exactly the opposite of CV type carbs.
This brings me to the next question as my bike is now running fine up to at least 3/4 throttle: should I change the Main Air Jet to get the carburation right up to WOT?
As a matter of fact I noticed that Dynojet usually provides main air jets as part of their kits.
Any experience out there?

[John Kat]

Given that I'm trying to get both the 1/2 throttle and WOT to operate correctly, I decided to follow "@posplayr" advice given here:

http://www.thegsresources.com/_forum/showthread.php?164565-AFR-Info/page3&highlight=AFR+Info

In effect at 1/2 throttle: 1 needle notch=2 jet sizes=1 point AFR
And at WOT: 2 jet sizes=1/2 point AFR

So I lowered the needles by 1 notch making the 1/2 throttle leaner by 1 point and in theory keeping the WOT AFR identical at least on CV carbs.
This is obviously not the case with the VM30's as the bike now takes full throttle for the first time but...there is an hesitation between half and full throttle.
I was expecting that and my next step will now be to increase the main jets by two sizes to enrich the 1/2 throttle by 1 point AFR while only increasing WOT by 1/2 point.
Let's see if that works?

PS: my needles are 5D36's

[John Kat]

I installed the 115 main jets but the bike will now no longer take full throttle plus a lot of hesitation at 1/4 throttle.
I'm now very close to thinking that one cannot tune a bike with pods without also changing the needles and or changing the main air jets.
No wonder Dynajet sells their kits...

[John Kat]

I believe that I'm now close to solving the issue.
There are four combinations that are close to the solution:
The two first work very well up to 3/4 throttle
Main: eitheir 107.5 or 110
Needle: #4
The two next work well at full throttle but hesitate at 1/2 throttle
Main : Eitheir 107.5 or 110
Needle: #3

This indicates to me that the mixture is too lean at 1/2 throttle.
I tried a 115 main jet with the needle in #3 but this combination does not work at all.

I now need to find a needle that provides a richer mixture.
Given that the OEM needle is a 5 DL 36 that is identical to the ones used in the VM 26 carbs, I could probably use the needles provided in the "Keyster Nencho carb kit" sold by Z1 enterprises:

https://www.z1enterprises.com/keyster-premium-nencho-carb-kit-gs1000-1978-1979.html

As I only need the "richer" needles I'm wondering if any "gsresource" member would have these laying around?
I'm ready to pay for them!