Hi all. Can any of you more experienced owners tell me if the reedvalve/intake manifolds are prone to leaking at all? I cant see anything obviously wrong with mine, but the erratic tickover I have on the 21 (sometimes it'll sit happily at 1500 rpm, othertimes it will sit at 3-3.5k when coming off the throttle - slides look to be returning fully) suggests an intake air leak to me (but If anyone has any other ideas please chip in). I'd like to discount an intake leak, before I start to think about crank seals so any pointers on this would be helpful. It would be nice to finally get the NSR running properly before the summer is over

Anyone know the price of a new intake manifold? If it's not too expensive, it might be worth simply replacing it to remove any doubt. I'm assuming all 21s use the same manifold? Anyone got the part No to hand? I sometimes have probs using the online manual.

Any other possible causes of an erratic tickover on a 21?

Cheers

Wb

The inlet manifolds can leak if the bolts are over tightened. You have to be quite carful.

Andys 21 used to be very bad at tickover, but his crank was shot and so were his seals. Its pretty much perfect now.

The only other cause coudl be too weak on the pilot air screw or maybe a size to weak on the pilot jet.
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If I have to take the carbs off once more...

May be a little patronising to say but double check the carbs are seated properly, they will appear to seat one "click" out of fully in (well they do on a '28 ).

And check the insulator rubber very carefully, I replaced mine when it had the same symptoms as you're talking about (the rubber was breaking up inside when I investgated further) and I was horrified at the difference.

'28 one was about £30
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Please do not PM me technical questions, if you can't find it on the Forum start a thread


Last edited by fontyyy on Thu Aug 24, 2006 9:34 pm; edited 1 time in total

Thanks, Steve. I think the pilots are stock (I'll check 'em) and the air screws are set as per the factory settings. When I got it, it had been put together without the gasket between the manifold and the cranckcase (instant gasket instead ). I fitted a new one, thinking that might cure it, but it's just the same.

I have a receipt for a full shop motor rebuild less than 1000 kms ago, but if it was them (Two Wheel Technics, Plymouth. Know anything about them?) that built it up without the manifold gasket, I don't know whether I should suspect a crank seal if the motor has just been lashed together by the YTS lad.

Cheers

Wb

Yeah I know them.
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If I have to take the carbs off once more...

Thanks Fontyyy. Don't worry about patronising - I am a total NSR newbie and any advice is good info for me. I think I'm pushing them home fully, but I'll give 'em an extra shove next time I try it. I'll have another, closer look at the manifold too I'm secretly hoping it is the manifold as I'd much rather buy a new one of them than have to try new crank seals on the off-chance. Anyone know if the 28 and 21 use the same manifold?

Cheers

Wb

Different manifold 21 to 28, you can use a '18 one though.
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If I have to take the carbs off once more...

Thanks, Steve. So whats the rep' of Two Wheel Technics, then? Should I be fairly confident that they will have fitted the crank and seals in an airtight stylee? I'm thinking that if the intake side is all present and correct, then the prime suspect has to be a sucking seal or unsealed case. It's the only thing I can think of anyway, but then I know little about the Honda motor. Though maybe that's reason enough to strip it properly? Have a look at how it all goes together. Time constraints, though, mean that I would rather not if I don't have to...

Cheers

Wb

I've had the same symptoms: sometimes, when coming from higher rpms, it idles at 3000 for a while and then settles at 1500, or goes to 1500 after a few blips of the throttle.
I asked this question on the old NSR mailing list, and 3-4 people said they had the same symptoms and a few others said it is normal for a NSR.

Someone suggested that the flat sliders in the carb, could be sucked against the groove and bind a little.

I never did anything to cure it and don't even know if it still exists but taking the cases apart because of this, sounds a little over the top.

You can test the two outer crank seals by spraying some diesel start over them while the bike is running. If the rpms change, every time you spray, then the seals are bad, if nothing happens, they're ok.
This can also be done around the manifold or along the case joints.
Use a thin plastictube, so you concentrate spray where you want it.

Oh and ehhh, its highly flammable
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Poul
"If Life Gets Boring, Risk It!"
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