Hi i have a problem with my 21 and i need some help with it...

In high rpm's (after 10k) and usually in 3-4-5-6 gears the bike seems to run out of mixture.With the choke on its a little better but still 5-6 gears do the same.After lots of tests it seizured but fortunately only a piston change...

It runs spliced, modded airbox and premix.The main jets are bigger than m-max suggestions.
I thought that maybe its the power jets but they were clean.

Now, i bough the hrc jet suggestions and i am ready to install them and test it.I will leave the power jets as they are just to be secured.

Could it be something else causing the problem or something i should do?
I dont want to seizure it again so any response would be great!

Check your float heights. My MC18 used to run dry just before the braking zone at Ruapuna and just after the entry road at Teretonga, cos I had the float heights wrong (like that when I got it).

you're wide open for less time in 1st/2nd than the other gears, less time to suck the carb bowl dry.

Check your splice. If its spliced to first or second gear, the ignition advance is more than the other gears.

And finally, look over all your carb gaskets etc, make sure that you aren't sucking air in somewhere else. My little brothers IT200 siezed or holed pistons about 6 times before we finally fixed the problem (twice with me on it ) too much compression leading to the base gasket blowing out, leading to air being sucked in leading to . Solution: thick, wire reinforced industrial gasket material. Made it gutless, but reliable...
_________________
The Chopster

Also check that your fuel tap isn't semi blocked

This could cause the same sort of problem as having the float adjusted incorrectly due to the engine drinking more than can trickle into the bowls.

But, it still sounds like a jetting issue. If its over rich, it will loose power top end from flooding.
_________________
Winning isn't everything, but loosing isn't anything

80XAR wrote:
But, it still sounds like a jetting issue. If its over rich, it will loose power top end from flooding.

NSR-LOVER wrote:
With the choke on its a little better...

Sounds more like it's going lean, but Kieran's advice is sound; make sure everything is 100% (i.e. check for air leaks, everything is clean etc.) before you start messing with jetting.

If you want to discuss jetting specifics however, it will need to be done in the "Setup Discussion" section of the Supporting Members area.
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!


Last edited by Andy on Sat Dec 13, 2008 3:32 pm; edited 1 time in total

80XAR wrote:Also check that your fuel tap isn't semi blocked

Upon removing a tank & fuel tap assembly for the first time, I couldn't believe how much dirt & debris had collected around the stem filter. Semi-blocked, more like 3/4 blocked.
_________________
Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

Thanks for the infos, they will help.

Well i fitted the big jets and it does the same...

The tank filter is clean so now i will check the suspicious intake manifold it has some small cuts and maybe its this.

The first 3 gears rev good but i think it shouldnt rev because of the big jets and the power jets.

Tests continue...

Now, i bough the hrc jet suggestions and i am ready to install them and test it.I will leave the power jets as they are just to be secured.

You are fighting a losing battle if you don't fit the kit (or anything else for that matter) as HRC intended.

I've seen it dozens of times. If you don't fit all the kit and set it up as it's supposed to be, then it simply doesn't work. As Kieran says, 1st and 2nd aren't a good way to tell what's going on, as the motor is in the high RPM zone for a lot shorter period of time, and under a lot less load. You should be confident the motor is free from air leaks and a little rich, and then do a plug chop in top gear. Either that or take it to a dyno where they know NSR's and how to set up an HRC kit.

As stated in the tuning guide, the HRC base settings are NOT to be considered as the definitive setting. They are for use with (amongst other things) pre-mix, HRC race pipes, HRC heads, and open carbs, and under the same atmospheric conditions as stated in the HRC manuals. They are also only base settings for SP and SS applications, which both allow tuning of the engine internals to a different level, which can also effect the jetting requirements.
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!