pe reivers

Some years ago, in the late 90-ies, I had several ST2300 engines, so I could experiment with the way the carb should be modified in order to get the most out of these superb engines.
I just found the drawing I made when I started my own web pages, and thought it would help many ST 2300 and big tigre users.
The mods do:
1) provide better total fuel flow capacity
2) adjust fuel mixture strength over the whole range.

In the drawing, the lower part of the spraybar is with original dimensions. The upper part is the modified dimensions.
The end of the almond shaped cutout should be sharp (dull tools produce rounded ends)
The fuel passages should have no burrs. These reduce fuel draw capacity.

Kweasel

My Feedback: (29)

Nice work. I never modded the spraybar but had excellent success by boring the body to match the barrel and cutting the slot to (more/less) match the 9 degree ramp. It had a very slight fourcycle at 3000 rpm but was perfectly linear everywhere else with 5% nitro. An OS 7D and 7M showed no advantage and were removed after testing in favor of my modified stock one.

vasek

My Feedback: (4)

Has anybody else wondered why after all these years of proven mods ST hasn't made these changes at the factory? It would seem as being simple "adjustments" in the production line

pe reivers

The 5° ramp was determined by measuring the amount of barrel displacement neede at half throttle that was needed to correct the mixture.
This was done using the idle needle, and measuring the distance that the idle needle had to travel for correction.
With this mod, the idle needle is in control up to at least half throttle. A rich idle setting will result in a rich mid setting and vice versa. I have yet to see an other carb that does this. OS7D comes very close though, but is shamelessly expensive, and has a smaller venturi bore as well.
I too did match both bores in my primary setup, but later found that just modding the spraybar and drum displacement worked just as well.

@ Vasec,
At that time, ST was cutting on all costs, and in the process of transferring assebly to China. They had goofed with the dogleg mod, but saw no reason to further investigate. Even the tools for milling the spraybars were dull! With the China production they alsoreintroduced the straight 9° groove. People stopped whining and everybody (?) was happy again.
The ST barrel is very hard, and the 9° straight groove is a simple milling operation. The reverse dogleg ( 5° / 9° ) is more machining work and tolerance sensitive. Not a real cheap production thing.

rc34074

My Feedback: (5)

There's no need for them to change the 2300 carb - the chinese version of the 2300 carb works fine just the way it comes now - at least it has on the ones I have.

Ed