Factory Performance Pipe

[jesutton3]

I just bought a used Factory pipe for my 650sx and I can't figure out how the tunable head pipe works . I read the guide at the Factory website and I was wondering what screws they are referring to when they talk about the injection screws? Any help on how you tune this pipe would be greatly appreciated.

[Bill O'Neal]

On the cast aluminum portion of the headpipe, you will see one or two allen head screws with a small stainless steel lock nut that is tight against the headpipe. By adjusting these screws in or out detirmines the amount of water sprayed into the exhaust stream. These are very critical adjustments to gaining performance and rpm at WOT ( high water pressures ) because of the amount of water put into the system. A turn of 1/8th can be a couple of hundred rpm when you get it close.
I find that they only need to be opened less than a turn from seated. When your pipe chamber starts to get so hot it cooks the couplers, you need to open them slightly to cool the couplers. Best performance is where they run as hot as possible without cooking the couplers. For rec riding, go a little more, or carry extra couplers.

[jesutton3]

I looked all over the head pipe and all I can see are the two nipples for the water jackets around the head pipe. There is a hole in the lower one that goes through and into the pipe. Where on the head pipe should the screws be or is there a model for the 650 that does not have the screws?

[Bill O'Neal]

Sounds like you have an earlier pipe without the water injection adjuster screws.

That hole under the brass fitting is your only water injection point. The trick to adjusting the amount of water that passes through it is in the use of a bypass on that water line that feeds that portion of the pipe. If you lower the water pressures to that hole, you pass less water through it. A "bypass" is a tee in the line with a waterline running overboard. The size of the restriction at the water thru hull fitting will effect the water pressure in the headpipe, thus changing the flow through the internal injection orfice. A simple gate valve in the bypass line that is adjustable can save you alot of time. As you close the valve, you add pressure which equals more water entering the pipe and vise versa.

Or you could drill and tap that hole for a Mikuni mainjet, then install your own orfice size restrictor to cut down on the water passing through it.

The idea is to run the pipe as warm as possible without burning couplers.

[ February 20, 2003, 09:54 AM: Message edited by: Bill O'Neal ]

[jesutton3]

Is it possible to install my own set of screws in the head pipe to tune it like the newer models?

[Bill O'Neal]

It would be if you bored a large enough hole in the outer waterjacketed portion of the headpipe to give you room to weld a boss into the inner pipe, then weld up the outer pipe so it wouldn't leak water in either direction. Then drill and tap it for a needle adjuster.
Not too feasable, IMO. Why not try it the way it was made?

[jesutton3]

I probably will I just figured they put the different water injection on it cause it was better for a reason. Do you have to worry about buring up the couplers with it in stock form?

[Bill O'Neal]

Not if the pee hole that allows water into the exhaust stream is not clogged up. It should work fine. Actually those water injection needles can be a pain at times. They get frozen up with corrosion and cannot be adjusted as the small allen sockets get stripped out.

[jesutton3]

Thanks