Drill vacuum throttle gpz750?

Hi,

I have a problem with a KZ/GPZ 810 engine that breaths thru GPZ750 Mikuni BS carburetors and a homemade foam filter.
When I come into a corner at 5-6 krpm and slowly getting on the gas it initially bogs because of lean mixture and after a second it’s good again.
Will increasing the vacuum hole diameter help or worsen this problem? 
AFR is good all the way from idle to wot except from when getting on the gas slowly in the middle of a corner.

Kr
Sixten

Sixten wrote:

Hi,

I have a problem with a KZ/GPZ 810 engine that breaths thru GPZ750 Mikuni BS carburetors and a homemade foam filter.
When I come into a corner at 5-6 krpm and slowly getting on the gas it initially bogs because of lean mixture and after a second it’s good again.
Will increasing the vacuum hole diameter help or worsen this problem? 
AFR is good all the way from idle to wot except from when getting on the gas slowly in the middle of a corner.

Kr
Sixten


 

I don't know a lot about CV carbs, but I was under the impression that increasing the vacuum hole under the diaphragm was mainly used to raise the slide quicker. That modification is in the instructions for all DynoJet kits. I don't believe that increasing it will solve your issue. Once you drill those slides there is no going back.

Have you checked your float levels? There is no mention of that, just a thought when you mentioned going into a corner.

When you say AFR is good, how accurate are your numbers?

At the RPM you are having that issue your at the top of the tuning range for the needles so maybe richen up the needles by raising them (if adjustable or with some shim washers) and leave the main jet alone - See what that does for you.
 

As a result of your free-flowing filters, the carbs diaphragms cannot react accurately at low rpm.

You will absolutely solve this by installing these:
See posts by user forum zed1015...

(Can't post an ebay link but below is the description)

Air corrector jet kit. CV Carbs . Kawasaki Z650,Z750L3,Z750 CUSTOM,GT750,GPZ750
H.

kzrider.com/forum/23-for-sale/611992-air-corrector-jets-

"Homemade foam filter" sounded like he still has the air box.

Does the engine hesitate when rolling on the throttle slowly in a straight line?

A picture of the filter might also help with diagnosis.

Thank you for the advices.

Instead of experimenting with the hole diameter I did the easy solution and covered the filter with thin fabric to increase the vacuum.
now the bike runs great but a bit rich on top so I have to rejet.
I use the front part of a GPZ air box with the rubber runners and then a square foam filter over that.
 

Sixten wrote:

Thank you for the advices.

Instead of experimenting with the hole diameter I did the easy solution and covered the filter with thin fabric to increase the vacuum.
now the bike runs great but a bit rich on top so I have to rejet.
I use the front part of a GPZ air box with the rubber runners and then a square foam filter over that.

 

That does not sound like a sealed air box, could you post a picture?

Injected wrote:

Sixten wrote:

Thank you for the advices.

Instead of experimenting with the hole diameter I did the easy solution and covered the filter with thin fabric to increase the vacuum.
now the bike runs great but a bit rich on top so I have to rejet.
I use the front part of a GPZ air box with the rubber runners and then a square foam filter over that.



 

That does not sound like a sealed air box, could you post a picture?

You could do something like this

 

Not quite what Kawasaki Engineers signed off on.

Injected wrote:

Not quite what Kawasaki Engineers signed off on.

I like the yellow!  

Injected wrote:

Not quite what Kawasaki Engineers signed off on.

Do you mean like putting an 1197 motor in a 650 chassis   the stock unit wouldn't fit with the mono shock and to be fair it was so restrictive it's ridiculous. I have never seen a stock air box on anything with so much baffling (I quite like induction roar)