mixture screw, which way for richer ??

[boo86]

Hi guys I'm having trouble with my race sv. I've had her dynoed @ 70.16 rwhp which is great but when I was at the dyno we couldn't find the mixture screws and we settled on it running a little lean. As it's running a little on the lean side it's giving me a big hole at 7-8. I can put it back to run rich with a standard bmc fiter and it makes 64rwhp. But 64 is less than 70.
Soo..... I've now found the mixture screws (cheers Haynes) but I'm unsure if I go clock wise or anti clock wise for richer, any ideas ? I'm guessing it's anti clock wise as per my rd250 but 'm unsure. It's running only slightly lean with an air ratio of 14-14.5:1 so i reckon half a turn will do the job nicely. I know another dyno run would be good but money is tight.
Sp for richer clock wise or anti clock wise ??????

cheers in advance, Boo86.

[Jase22]

Think it's inwards to richen, but I don't think that will do much at 7-8000 rpm?

[boo86]

if I've done this right I should have attahed the dyno chart for you guys to see. If I havn't done it right, help !

http://img211.imageshack.us/img211/3612/marksbikexn1.th.png (http://img211.imageshack.us/my.php?image=marksbikexn1.png)

[img=http://img211.imageshack.us/img211/3612/marksbikexn1.th.png] (http://img211.imageshack.us/my.php?image=marksbikexn1.png)

[boo86]

as you can see there's a real hole at 8k. It's killing me coming out of corners.

[NedSVS]

No, it's outwards (or anticlockwise) to richen the idle/low speed mixture. I'm afraid it won't make any dfference at all at 8k though. I'm suprised the dyno shop didn't advise you of this! Either you need to lift the needle a notch or a larger main jet, or even both.

[northwind]

Ned and Jase are both spot on, it's not a master mix screw, it's an idle screw. What dyno shop was it? Their operator's useless. It's not like these are an uncommon carb design...

I would stick bigger jets in straight off. Not massively bigger. There's no point at all in playing with needles unless the jets are right.

[Dangerous Dave]

what dyno shop was it? Their operator's useless.
+ 1

there's no point at all in playing with needles unless the jets are right.
+ 1

[boo86]

so this may a daft question, but there isn't a master mixture screw ? I'll have to play with a selection of jets ? It allready has a dyno-jet kit and I checked last night the slide holes have been drilled out as per dyno-jet specs. I wonder if the previous owner was running a different filter. When I run a standerd jmc with a 45mm inlet the mixture is so rich it drops off the chart on the gas analyser. When I run a jmc fiter with the top cut open it runs as per the chart above. The difference in power is 64 vs 70.16. but the differnce in drivability is massive as the power curve for 64 has no dips at all. When it gets to 8k running lean it feels like it's mis-firing, it sucks.

[yorkie_chris]

Bigger main jets.

There's a few different circuits in the carb all of which affect different rpm and throttle ranges. 8k wide open is main jets mainly and also slight affect by the needle taper.

Mixture screw is anticlockwise to richen, but only really affects tickover and the very slow speed.

[zadar]

unscrewing(counterclockwise)is richer.
you are to lean,should be right around 13:1.
before you change main jet you need to richen up everything else.
mixture screw will not do it.start with needle.also check float level.

[boo86]

thanks guys you are awesome. check out http://www.nemcrc.co.uk/pages/gallery/86348.php

for pic of the bike in question in actionat Croftat the beginning of this month

cheers again.

[NedSVS]

Northwind is correct in saying you should go for correcting the main jet first - any good dyno/tuning shop would start with getting the main jet correct, but they would normally have a selection of jets to hand. If you don't have any suitable mains it is probably worth trying lifting the needle 1 notch (to raise the needle you are moving the circlip down). The irratic bit on the graph is below peak power, so the needle may be the way to go anyway.