nsr125 track bike pin RC valve open

[salem1987]

Just wondering if anybody has tried pinning the RC valve wide open and disconnecting the servo?

From what i've read on the geneva racing docs the RC valve on my engine will only open to 90-95% under normal running.

On my old TZR125 i had it set up like this and the top end power was great.

I know the engine will lose most of its bottom end, but i'm not really bothered as the bike is gonna be ridden in the "powerband" most of the time.


Asking as the bike is not on the road and can't test it out without going to the track first!


Thanks for any advice

[alains]

we have tested the valves openning on french & uk bikes and the result is near 80% due to the electronics , so a valves controler & CDI is the best solution
you may lock the valves fully open , the only unconvenience is reaching 8500 rpm especially in the winter
if you need some more infos send PM
already you may download https://www.geneva-racing.ch\~alains\NSRtips.doc
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the worst day fishing is better than the best day working

[MarJay]

As a slight aside to this, I'd say having a 125 as a track bike is a crazy idea. At least go with a 250 two stroke...
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[salem1987]

thanks alains.

marjay i agree completely and i ride 400's and thous on big tracks. This is for a bit of fun on some short go kart style tracks racing my mate on his aprilia!

[skatefreak]

My NSR came with a pinned power valve.
Just disconnect the cable for the servo and put a wood screw through to hold it open (that's what the previous owner did, in fact no... they CUT the cable for god-knows what reason, leaving the servo in there?!?!).

I'm not 100% sure if it makes the top end that much more balmy or if the lower/mid range is just that pants that it seems that much faster.

What I do remember is pulling the throttle way back just to get moving and once I hit the power band having to throw my hand forward so as to not slam the car/van in front.

Completely impractical and an absolute arse for road going use but if your on a track and planning to live in the power band + it only takes 30 seconds to do/undo certainly worth a punt!

Let us know how you get on!

-Jvr

[salem1987]

thanks for the advice skatefreak. I pinned it open and took the bike out last night to teesside autodrome for a track evening. The bike ran good and handled amazing for what it is.

Having the RC valve pinned open seemed to let the bike rev out to 12000rpm (ish) in all gears apart from 6th where it hit 10500 and stayed there.

Did a plug chop on one session at full throttle and rolled into the pits. Plug was perfect colour so got the mixture right at least.

Think the next thing to play with is the gearing!

[skatefreak]

Out of curiosity did you change the jetting or stick with the standard de-restricted jetting?

Best regards

-Jvr

[salem1987]

sorry for the late reply..

Its running on the de restricted jetting. Have had the bike out a few times now since originally posting and it runs better overall with the RC valve connected.
Max indicated speed of about 85mph.
6th gear totally useless on standard gearing (actually slows down in 6th).

I believe it is due to my poor swiss CDI, can tell the ignition curve completely tails off at around 10K RPM.

For anyone reading the swiss CDI has model number CI626A

CI626 is whats needed.


Definitely have to get a UK spec CDI as its driving me crazy!