650sx carbs

[jesutton3]

I own a 89 650sx with pjs head and exhaust manifold, supertrapp water box, polished ports, and it been bored over some not exactly sure how much. I was wondering if dual 38 mikunis would give better performance or a single 44 SBN?

[Dan DePardo]

Hi;
With your current engine set-up I doubt that you'd see much of performance increase going from a single 44 SBN to dual 38 SBNs, at least not enough to justify the $$$ and effort.

The available dual 38 SBN 650 intake manifolds tend to be race oriented, and are typically not very good for low to midrange performance.

Obviously a single carb is also much easier to tune than duals.

Are you running a PJS tuned pipe or just the exhaust manifold?

For a good performance increase, I suggest looking for either a Coffman's or Factory Pipe aftermarket exhaust system for your 650. A tuned pipe will provide a substantial power increase, and a 650 will typically pick up a 3-4 MPH in top speed after swapping out the OEM pipe.

I also recommend going back to a stock 650 waterbox. The Supertrapp 'box isn't helping your power output, and will generally only make your boat loud and annoying, especially with the '89 650SX side exhaust outlet.

Dan

[ January 24, 2003, 08:29 AM: Message edited by: Dan DePardo ]

[jesutton3]

I bought the ski with all that on it and to rebuild the motor. It has the factory pipe but a pjs manifold. I will probably leave the supertrapp since I'm not to comfortable with trying to close up the hole and cut new ones since the outlet has been switched from the left to the right. If I go with the 44 about where do I need to start with the jets, screws, and I have heard something about a restrictor in the return line. Whats the restictor all about?

[ January 24, 2003, 09:23 AM: Message edited by: jesutton3 ]

[Dan DePardo]

Hi;
What does it have for carburetion now?

You won't need a restrictor in the fuel return line with "SBN" Mikuni carbs, only with the old style "round body" carbs. A fuel return line restrictor controls the fuel pressure, but the SBN already has one cast into the fuel pump outlet.

Dan

[jesutton3]

It has two old style 38 mikunis and i have access to a 44 SBN that I am planning on putting on. It will be running at about 100ft above sea level. Just out of curiosity a friend of mine is running dual old style 44s on a 650 is that overkill?

[Dan DePardo]

Hi;
Why do you want to replace the 38 round body carbs with a single 44 SBN?

Dual 44mm Mikunis would be more carburetion than most 650s could use, but a lot depends upon how much your friend's engine has been modified.

Dan

[jesutton3]

I haven't made up my mind about which I'm going to put back on. I was considering the 44 because of easier tuning or would there be a noticeable drop in power from the switch from dual 38 round bodys?

[jesutton3]

How much would a westcoast exhaust help out or are they not worth the money?

[Dan DePardo]

Hi;
The Factory Pipe exhaust that you said was on the Ski is a much better system than the Westcoast 650 pipe, which is out of production, difficult to install, and simply doesn't make as much power as the Factory brand pipe for the 650.

Dan

[ January 29, 2003, 09:44 AM: Message edited by: Dan DePardo ]

[jesutton3]

The exhaust on mine is the stock not a Factory sorry for the confusion. Would the westcoast be better than stock or are they still not worth it? I know Factory is about the best you can buy but there kinda pricey.

[Dan DePardo]

Hi;
Sure, adding a Westcoast pipe will improve power over a stock pipe, but that particular pipe is tough to install, since the headpipe and divergent cone are cast as one piece. You'll also have a problem finding replacement rubber couplers since Westcoast no longer makes PWC parts. My advice is to look around for a used Coffman's or Factory Pipe 650SX / X-2 pipe. You should be able to find one for $200 or so.

Dan

[jesutton3]

Got any suggestions on where I can find some good used ones on the internet or some places that part out jet skis? What about the difference between the dual 38 round bodies and a single 44 SBN would the switch to the single bring a noticable change in power?

[Technical Support]

Try these guys.

[jesutton3]

Thanks. What about the information on the carbs?

[wetracer14]

Re: 650sx carbs

A Westcoast pipe for a 650SX is not hard to install and it is 2 pieces and if your coupler gets bad you can use a plumbing pipe coupler that you can buy at ANY hardware store. Mike
www.Northwetpowersports.com