Problems with blowtrough carbs..help

[Richard.]

Hello,
let me introduce myself.
I'm Richard from Holland and I have a gsxr 1127 turbo.It's been dyno'd at 297.5 rear wheel hp...

I only have a "little" problem with setting the carbs up right.I'd thought my best bet would be to ask round here.

First I'll explain my setup;
It's a blowtrough 1127 with lowered compression.Turbo is a td04hl-16t without a intercooler.The fuelsystem is a Bosch fuelpump with a highpressure fuelfilter and a malpassi fuel regulator.
The system is build by a friend of mine and he also prepared the carbs (40 mm) for boost.
the floatbowls are pressurized via a pitot-tubes (each set of carbs has its own pitottube) in the middle of the airstream.
There's a 3 mm hole drilled from the venturi to the underside of the diaphragm of the slide.The stock breather system (below the diaprhagms) is closed up
In the slide there's 1 hole (the standard one) the springs are stock,as are the needles.

The problem is this;
at 4500-5000 rpm I can only open the throttle as much as 25% or else it will stumble and stutter...
On the dyno it turned out to be extremely lean (off the scale!)
Below 4500 rpm it's great and above 6000 rpm it's like a missile.Yesterday it lifted the frontwheel in 4th gear on the throttle

I hope someone here has a solution for my problem

Please reply in english if you can,thanks

Greetings Richard

Here's a link of last year before I streetfightered it,it's a 221 hp run

http://members.home.nl/peterhin/run1.wmv

 

[andersbrink]

Please describe how you've pressurized the carbs, in detail. Which circuits gets pressurized air - and from where?

 

[Richard.]

I hope I can clear this up using a picture;
the blue arrow points to the lines that pressurize the floatbowls. They're attached to 2 angle cut tubes in the airstream just below the plenum.The lines are 4mm in diameter.

the yellow arrows point to the stock breather system below the diaprhagms,these are blocked off.Instead there's a hole drilled (3 mm) in the venturi (red arrow) wich comes out below the diaprhagms.This way it also gets dynamic boost.

It uses stock needles and springs,and 1 hole in the slide (also stock)

One thing someone else mentioned;maybe the choke has something to do with it,on higher boost it sometimes pushes the choke out.It doesn't gets pushed out(to the first click) on anything lower then 10 psi,but maybe it does gets slightly actived....

 

[andersbrink]

I'd seen that kind of modification before but you should really consider unplug the diaphram vents and connect them to the pre-chamber of the plenum. You don't need to plug the 3 mm holes you've already done.

The reason is that you get a too weak "raise" signal to the throttle. Also consider changing the pilot jet size one or two sizes. You might need to lower the throttle needle a clip or two to compensate in the low rpm range.

 

[Richard.]

I also thought about the 3 mm hole being to small.....will it help if I drill them slightly bigger,say like 6 mm or even bigger if I can get away with it?

I'm asking 'cos I don't have the T's from the original breather system anymore

And about the pilot jet; In wich rpm range does this work in combination with the needle?

Excuse me for all my questions,but this carb issue is almost starting to be a obsession

 

[andersbrink]

The pilots works from about 1/16 to about 3/5 trottle opening. Usually in the low to low midrange around 2000 to 5000 rpm.

An easy way out is to install a set of CV34 from a 1986 gsxr1052. They'll support at least 400 horses. All you need to do is to seal them and increase the main jet size to 132.5 (I think 127.5 or 130 is stock) and pressurize them through their stock openings, i.e. diaphragms and floats. Any dynocrap-kit installed is a BIG no-no. The CV34 comes with sheet metal caps above the throttles and are secured by 4 screws, not the usual 2.