Carb Spring question

[99SRX700]

Do the softer springs cause a lean condition or any disruptions in the fuel curve? I am just trying to think of why Yamaha didn't put softer springs in from the start.
Do they really make that much of a difference? Not that 40 bucks is a lot of money but I really don't want to waste my time.

 

[Turk]

Softer springs allow the primary to upshift more aggressively. Clutching has absolutely zero affect on jetting......cept if you are running a real aggresive race set up with small pilots. Yammies have very soft primary springs compared to other brands.

 

[ReX]

Clutching definitely affects optimal jetting, especially during the transitions prior to reaching a steady state rpm.

One clutch setup may allow the motor to flash with a relatively small load on it through a specific rpm while another setup might load the engine hard through the same rpm range. Unless you have a "perfect" carburator that handles transitions in an ideal way, optimal jetting always compensates for these imperfections.

My stock 05 RX-1 setup loads the motor so hard at lower track speeds that it doesn't get much over 9500 rpm for at least a few seconds. I expect Gary and Allen's setup will quickly bring the motor to peak hp rpms (~10,200) and keep it there. With the motor revving up faster softer springs make sense (BTW, I bought the kit, including the springs from them - from what I've read they seem to know what their doing).

 

[Srxspec]

I have seen zero difference in a stock air box between the green and the yellow springs. In some instances on the dyno I have seen the acceleration rate on the yellow springs to be better than the green springs. They're both about equal from what I have seen.

 

[BlgsRX-1mtn]

Allen, what about with the Stage 1 SC? I had red in with my stock air box and can't find the stock ones. I will be finishing the install later today. I am also starting at 135 mains, 25 pilots, needle in the middle and the air screws at 1 3/8 turns. I'm running the small pully down low with 91 octane + 1 gal of 100 LL Av Gas. Will the red springs be ok or should I order some stock ones?

Thanks, Jim

 

[Srxspec]

Jim, I ran stock springs, but you could give the red ones a try. I believe they will work fine as well.

What elevation are you running at? The reason I ask is because I was jetted at 137.5's, stock needle position, fuel screws out 1-1/4 turns at 1300' elevation down to about 10*F with just 91 octane with the large pulley on top.

 

[race24x]

I have a stock modified airbox the yellow springs and the 157 ( i think) main jets that came out of my sled when I did the whole ECP kit it was running great an nice improvement over stock as far as midrange but my buddy got an Apex I need every ounce of power I can get LOL I would sell the whole thing if anyone is interested make me an offer I dont know how much all this stuff is

 

[BlgsRX-1mtn]

Jim, I ran stock springs, but you could give the red ones a try. I believe they will work fine as well.

What elevation are you running at? The reason I ask is because I was jetted at 137.5's, stock needle position, fuel screws out 1-1/4 turns at 1300' elevation down to about 10*F with just 91 octane with the large pulley on top.

Allen, I'm at 3117' elevation which is where I'll be testing. My main riding will be done from 6000' to 10,000'+.

Jim

 

[whits-end]

Do the softer springs cause a lean condition or any disruptions in the fuel curve? I am just trying to think of why Yamaha didn't put softer springs in from the start.
Do they really make that much of a difference? Not that 40 bucks is a lot of money but I really don't want to waste my time.

I believe Yamaha set the Rx-1 specs for maximum fuel efficiency. Any of the mods we do to improve accelleration (including opening the needles faster) will have some effect on fuel consumption.
However, in the case of the Holtzman springs , in my observation it was very minor.