Topic: Some CB650 questions

[Scott S]

 Do the CB360/400/450 sprockets fit the SOHC4 bikes?

[Scott S]

 Found a new 40T sprocket on ebay for $25 shipped! That's a third of the price that Sprocket Specialist quoted me.

 Now...about those carb questions...

 I'm running these carbs (VB44A):


 ...with these filters...


...and this exhaust...


 I know that trial and error is probably in my future, but do you  think I'll need to re-jet?

[trueblue]

I haven't played too much with the CV carbs, but I would be expecting you would need some rejetting.  I would put it together and see before I played too much with the jets.

[ShermanPain]

Do you know what brand exhaust that is?

[Mainerider]

Scott,


The CVs are indeed more forgiving, up to a point. Because the piston slide only rises in conjunction with a proportional rise in intake pressure, the air/fuel mixture is essentially self-regulating.

You are probably using "re-jetting" in the generic sense of the term, so if you are, please disregard this...
A rough breakdown of what carb parts control what load and speed regions is this:

0-1/4 throttle is pilot jet and pilot air jet.

1/4 - 1/2 throttle is top part of your jet needle, needle jet and air jet.

Acting as a bridge between the above regions, the air slide cutaway and bypass circuits help to smooth the transition from idle to just off idle.

1/2 -3/4 throttle is lower part of jet needle, needle jet and air jet.

3/4 -full throttle is main jet and air jet.

These are approximations that vary from bike to bike and there is always transition overlap from one throttle region to the next.  I just point this all out as a reminder that for a good chunk of your throttle position, the position of the jet needle, and the needle jet and air jet characteristics, actually dominate carb performance more than the main jet. It's just a handy reminder for if and when you have to re-tune the carbs. Hope this is a little help. Good luck.

[Scott S]

Do you know what brand exhaust that is?

 It was listed as Jardine and a guy over at the CB650 forum has one just like it and he said it was Jardine as well.

[Scott S]

 MaineRider....yes, I'm familiar with the carb function. I've done jetting and tuning in the past. Just trying to get a feel for these carbs and maybe some real world experiences from people modding the CB650.

 I can't remember if the needles are adjustable in these or not. I don't think they have clips, so I'd have to use a washer. If that's the case, what thickness would you suggest?

[Mainerider]

I wouldn't venture a guess at this point. If it was me, as suggested by Trueblue, I would assemble it all and see if you have any running issues with the stock settings and if so, in which throttle region. That would then serve as a guide to which components you should initially focus on.

Given the fact that the stock filter setup seems to be too restrictive on the CV-equipped 650, you might be pleasantly surprised with how well the stock carb setup works with the  aftermarket parts.

[ShermanPain]

Okay thanks! my left side header is getting pretty rusty so im thinking i will have to replace it this year or next. Just looking for options that fit the 650

[trueblue]

Okay thanks! my left side header is getting pretty rusty so im thinking i will have to replace it this year or next. Just looking for options that fit the 650

There are a few options out there depending on what you want and how deep your wallet is.  The ones I looked at when I bought my new system were Mac, Marshal Deeptone (I really wanted this one, but it was expensive) and Motad, this is the one I bought.  The price of the Motad wasn't much more than the Mac and it has a really nice tone, nice and quiet and crisp .

[ShermanPain]

I had looked at the Mac ones before and they were the ones I was considering. Marshal is a bit too pricy for me but maybe when the time comes to order them ill have more money sitting around. Ive never heard of the Motad ones, thats good its quiet because i dont want it to be too loud, my stock pipes are already pretty loud IMO. Did you have to rejet? im running the stock airbox and will probably be keeping it that way.

[trueblue]

Nope didn't need to rejet, goes much better than with the old exhaust.  The Motad ones were available through Dave Silvers, that's where I bought mine .

[fmctm1sw]

I can't remember if the needles are adjustable in these or not. I don't think they have clips, so I'd have to use a washer. If that's the case, what thickness would you suggest?

You have to shim them.  I tried one and had to drill out the seemingly threaded retainer holding the needle in place.  I left it as is for now but I have .5mm and 1mm thick washers I bought from a RC car place.  I'll see if I can find it...

Edit:  I can't find it right now, I'll look at them when I get home.  They may have been "axle spacers."

Edit again:  Like these:  http://www.amainhobbies.com/product_info.php/cPath/1_25_1468_611/products_id/22652/n/XRAY-Aluminum-Set-Up-Shims-10mm-20mm-30mm  I bought a bag of 10 (I think) 0.5mm thick and a bag of 1.0mm thick.  I figured that would give me .5, 1, 1.5, 2.0, etc mm increments.