Carb for a big bore spree

[mr pibbs]

Interesting. I learned something new today.

So on the Sportster, a 30% increase in displacement = 20% increase in jet size.

So for a 10% increase in displacement, 7% increase in jetting. That's a 68 --> 72 or so.

Sound close?

I'm not sure your math is correct.

If my understanding of the jet numbering is correct it is a measure of the diameter of the hole in the jet. And based on the sportster an approximate equal ratio is appropriate.

1200/883 = about a 35 or 36% increase of displacement

Because the jet actual size is determined exponentially (pie*r^2) the increase from a 155 to a 182.5 is about 39% increase. close to spot on.

In that same light a change from 68 to 72 is actually a 12% change in size of the hole in the jet. That is, if the size is directly proportionate to the diameter of the hole.

[Wheelman-111]

Greetings:

You can drive yourself crazy doing the math, think you have it all worked out and........

It doesn't.

This is one area where theory and practice diverge. There are just too many variables. 2-stroke, 4-stroke, fluid dynamics, volatility, viscosity, surface tension, AAHHHHH!

Just because the ratio worked on a Sportster it's no guarantee that it'll apply to a Spree. The holes are twice as big. It's a starting point for testing at best. Better still, ask someone who's done it without BBQing the bore. And even then, trust only what you see for yourself.

Even if the main jet issue can be addressed, there's still the little matter of that pesky tiny and non-adjustable pilot circuit.

Were I to experiment on my own Spree, I'd consider the purchase of the 17.5 Arreche, whose dimensions and bystarter bore match Honda's in all the critical elements. At least there'd be the option to insert a pilot jet correctly-sized for an open pod.
Scooter-Center.com had them not long ago. Get the Vision one and be prepared to address a shock mount issue.

[Bear45-70]

Everyone doing mods needs to remember that no two engines are identical. Every single engine is an individual. What worked for somebody else may or may not work for you. You have to check or a seizure is sure to be in your future. And that is a truism.

[Lunytune]

.. the dealership in my area is over 200$ for the repair parts. so taz's kit seems the better option.

Sad part about this is that sometimes more power is not necessarily wanted. My 99 Elite bit the dust, and I don't really want more power, but stock kits are not out there. Also, seems most of the kits are 50mm/80cc. So I'll probably end up with daywot's 6mm over, 66cc. I don't really need it, especially since I will now need to eat up that extra power with faster gears.

[mkluvin]

well here's where I'm at, I'm using the 95 jet that came with the kit and it seems to be a pretty ok match. as I have a 65,68,78,85, and the 95. I tried them all I"m sure that 78-95 is the range that most spree's would fall into. As Bear say's "each bike is a bit different" I used this tuning time to heat cycle the engine .

I have 4 - 3/8 holes in my air box cover

I ran the exhaust through the wood stove and reduced the weight by almost 1/2 pound this helped

first off I'm running between 24:1 - 26:1 for a bit to make sure I wear the biggie in nicely . At first I was getting 27 mph(after break in) but there was mad low end power I'm 200 lbs. now Im not saying I have It right but its close. feels like I could use more throttle cable. but untill I go to 32:1 I'm not going to be to stressed.

Idle is an issue. Idles fine then drops off. I plan on buying a new bystarter . and I have yet to mist the crankcase with wd40 to see if I have a leak sucking air.

I also did the pulley mod on the front. I lost a bit off the bottom but made it up on the top end now I'm at about 30-32 on the flats and making good power in the midrange

I'm going to find a larger rear tire and see where that puts me

http://www.hondaspree.net/phpBB3/viewto ... 16&t=11550

[Wheelman-111]

Greetings:

Very nice summary MK! Your idle issues may have more to do with the carb's fundamental limitation - no option to enlarge the stock idle circuit - than with bystarter malfunction. I'm guessing you needed to screw the idle mixture almost all the way in? In any case, cleaning the carb is hardly ever a bad idea.

Thanks for sharing.