550sx dual intake manifold

[cameron da river rat]

hey bill,

i found this unique lookin manifold for a 550sx reed motor. the question i have is: there is a rubber hose connecting the two intake tunnels together just under where the carbs mount. what is the purpose of this connection because i have never seen a dual intake manifold connected in any way?

the guy selling it has a pic but cant post it up here. its really cool lookin though.

[ March 02, 2004, 12:23 PM: Message edited by: cameron da river rat ]

[Bill O'Neal2]

If what you described is a crossover tube, it is there to equalize the manifold. Actually a pretty common thing on some types of intake manifolds like the oem Kawasaki 1200 uses.

[cameron da river rat]

is this equalization tube a better thing than not? or does it have its pros and cons?

[Bill O'Neal2]

It certainly won't hurt if you adjust the carbs a little richer to take advantage of it and not lean out the motor.

[cameron da river rat]

what would i need to set richer? the high speed adj or the high speed jet or every thing? thanks

[Bill O'Neal2]

Probably just turn the highs out some.

[cameron da river rat]

thanks for the info, my next question is: say i put a 125 main jet in the carb with the high speed adjuster turned all the way in. how much fuel will the adjuster flow for wot runs? just say the 125 isnt enough and i got the high turned out 1 turn would that be the same as like a 135 main jet and the high speed adjuster turned all the way in?

i guess what im tryin to ask is: is there a ratio, say for every 1/4 turn out on the high speed adjuster you could just go up in main jet size by 2? is there such a formula?

[Bill O'Neal2]

Yes there is a sort of a "ratio" for the mixture screws.

If the high speed adjuster screw is closed you will flow 100% of whatever a 125 jet will allow past it.

If you open the adjuster 2.5 turns, it will flow approximately 150%, or an additional 50% more fuel.

The needles, when closed, stop fuel from entering a bypass channel. As you open them, they allow extra fuel into the venturi through the bypass channel.

[cameron da river rat]

now thats some food for tha brain! that will help me out tremendously in dialing in this reed 550.

someone told me that the dual carbs from a pjs550 reed motor that he had, when he took the carbs off to clean them they had 2.0 n/s, a 67.5 pilot jet and a 107.5main jet on the dual 38's but a pjs motor was basicly a ported stocker so i really dont know what to start out at. i have 60, 67.5, 75, 72.5 pilot jets and 90, 125, 135, 137.5, and 140 main jets and 2.0 n/s and tons of various gram springs.

i think im gonna start out with a 67.5 pilot, a 90 main and set the high speed adj. out 3 turns and go from there.

say the 90 isn't enough at 1/2-3/4 throttle cruising, would it sieze the motor or would the high speed thats turned out compensate?

[Bill O'Neal2]

I cannot really answer that, but dropping from a 107.5 to a 90 is a big drop in main jet size.

It may very well sieze.

I'd start out by finding where too rich is, then try a smaller jet size that leans it down just enough. Better to be rich than broke and lean [img]smile.gif[/img]

[cameron da river rat]

much abliged, but have another question. i bought a motor that has been ported for racing, it is a 550 and the guy gave me his jetting, pop off, gram spring, n/s size, and turns out on the screws that he used when racing it but it is a single 44mm sbn. is there a way to convert or use some type of ratio? would i set up each carb just slightly leaner than the single for i do not have a sbn 44, just a modified bn 44 that i would rather not use.

[cameron da river rat]

because he gave me specs on a single carb set up and i dont have a 44mm sbn, only dual intake and dual carbs. 38mm sbn's.

[Bill O'Neal]

Why not just put them on using his specs and see what happens?

[Bill O'Neal]

Ok, Sorry. I misunderstood.
Try asking the question on the Kawasaki forum. I have no idea what jets you need in the twin carb setup. And, no, there is no ratio to go by.

[cameron da river rat]

i did put it in the kawasaki forum. but thanks for your time. it must not be a very good set up or else someone would know. seems everyone is sticking to the single carb set up instead of the dual. im just gonna have to take a stab at it. thanks bill o neal and bill o neal2 for the info.