Hi, Thank you for having a look at my thread.

So firstly my sincere apologies, I know there are at least 57 forum threads relating to the adjustment of RC valves (probably many more) but I just can't seem to find the info I want!

I can confirm the valves are minty clean and without the actuators fitted they easily move by finger pressure, they open fully and close easily.
I have fitted and adjusted the RC back plate and actuators as per described in the tuning section with a little slack play in the cable.

When I go through the cycle procedure they open and close, no excess noise from the servo. The pointer lines up with the index mark and the dowel pin holes look to be aligned as well... all good so far.

But when I look up the exhaust port the valves don't seem to be fully open, they do not sit flush against the port wall and I can't see how they ever would be...there just doesn't seem to be enough movement in the servo.
Maybe this is right? but I thought I read that the RC valve petal should sit recessed when open?

So can anyone advise how far open/closed the petals ought to be when the servo actuates? any images or measurements would be greatly received!

Cheers
Max
👍

Have you followed this procedure?

NSR250 English Service Manual - MC21 RC Valve Adjustment by NSR-WORLD.COM
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Andy.
NSR-WORLD.COM

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Forgive me Andy but your link just takes me to the Forum header page...

This is what I have followed from the tuning section of the nsr-world.com website.

Strange. Can you see the list of available manuals at this link?

http://nsr250.net/forums/members

The Tuning Section you've referred to is basically the same information as the Service Manual, with the finer HRC tolerance recommendation tagged onto the end. In fairness, without extremely accurate measuring systems, i.e. a dyno really, it's very difficult to get it much more accurate than with the Service Manual method.

It's easy to adjust the RC Valves badly, unless following those instructions, and lose power by not keeping on top of maintenance, but to eek out the very last of the gains is, I would say, almost impossible without a dyno and being able to see on a graph any gains or losses during adjustment.

Maybe I should remove the HRC part in the Tuning Section to remove any ambiguity.
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Andy.
NSR-WORLD.COM

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Hi Andy, so after correct adjustment what position would you expect to see the valve petals to be in? should they be flush against the port as I suspect?
Or do they sit out about 5mm even on the disconnected TPS setting.

Cheers for any input

Well it's a good question that I cannot answer just from memory, and I don't have access to an MC21 barrel to check, so someone else will have to chime in.

I suspect you're probably making a bit more out of it than necessary though, but if you are indeed feeling up into the barrel in the correct area (which is actually pretty difficult to judge), then no, I wouldn't expect it to be 5mm!

I've just had a look at an HRC MC16 barrel here, but the port's too small to get my fat sausage finger up, so hopefully someone with an MC21/28 barrel can have a look.

As a side note, are you sure you're not confusing the back of the RC Valve (the part closest to the expansion chamber) that can often protrude into the exhaust port...


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Andy.
NSR-WORLD.COM

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aahhhh maybe! (I love that diagram BTW )
Ill take some photos tomorrow and post them up.....then we can all have a good laugh at my stupidity! (won't be the first time and I doubt the last)

Max wrote:
aahhhh maybe! (I love that diagram BTW )

I modified/redrew the HRC diagram to illustrate the more common way of feeling for the valve position. HRC shows doing it with the head removed, which isn't very practical for most situations. My OCD sees me recreating poor quality images/scans a lot.

Max wrote:
Ill take some photos tomorrow and post them up.....then we can all have a good laugh at my stupidity! (won't be the first time and I doubt the last)

Can't beat having a laugh at someone else's expense! Looking forwards to it!
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Andy.
NSR-WORLD.COM

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OK, so I finally got a look at this yesterday...what I can see is that (with the TPS disconnected and the servo in the Hi position) is that the "body" of the RC petal is flat and in line with the port edge but because the petal is cup shaped the edge of the petals rise up into the port at the mouth of the outlet...if that makes sense.
On balance I realise that the port is oval and the petal is not as oval, so its edges look to block the outlet a little...would I be right in thinking that this shapes the charge as it exits the barrel?

Honestly I preferred my RS125 that just had a carb and a spannie !