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Nov 24, 2005
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I jsut purchased a 1970 RS with the Production racing kit. I am curious about the chatter during operation. It sounds like valve noise. Is this normal? There is also a lot of vibration under 3500 RPM, especially as it decelerates. Is that pretty normal or do I have to re-adjust the isostatics? Starting question. Is there a less painful way to kick it. It takes about five kicks to start it cold. 2 with the choke and 2-3 to get her going. I am running a Mikuni Carb with Boyer ignition. Thanks!
 
Joined
Oct 21, 2004
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Excessive valve noise could be as a result of either insufficient oil to the top end or more likely that the valves simply need adjustment. Some noise is normal, but should not be any worse than a BSA or Triumph.
You may be able to fix some of the vibration by adjusting your isolastics, but if they are old you may be better off replacing them (or better yet upgrade to the later MkIII vernier isos). You will still get some vibration at low revs though. My bike has brand new isolastics and there is some vibration under 2500 rpm - smooth as silk otherwise.
Boyers need a good battery with lots of juice to work right, so if yours more than a couple of years old you might consider a new one, also make sure your charging system is working well.
Mikunis are OK, but have to be set up correctly for your bike. I run Amals so I cant help you there.

Gary
 

MichaelB

"Sons of Arthritus"
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Valve clatter could be adjustment. You say you have Prod Racing kit, do you know what cam?
The setting for a stock cam is 6 and 8, 8 and 10 for a Combat or 2S and a whopping 16 thou for a 4S. Needless to say, a 4s is noisey.

I read somewhere that a 4s can be adjusted to 8 and 10, but there would be a power drop off. I have no idea why this would happen or if this is accurate. Till someone can substantiate this it is just hear say.
Anyone know??
 
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Nov 18, 2005
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I have an Axtell 5S cam which is pretty well the same as a 4S but with different overlap and I use 8 and 10 thou clearances.
It's not particularly noisy ( compared to the supertrapp open exhausts !)

As far as I am aware tighter clearances should give more top end power and less mid range. Mine produces 58 bhp at the rear wheel at around 6800rpm.
 
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Oct 7, 2005
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If the Isolastics are "perfectly" adjusted, there shouldn't be any vibration passing through to the frame above about 1700 rpm. That was the factory target, and the prototypes all met the requirement, at least until we started to get the deformation of the spacer tubes.

The really critical adjustment is the clearance on the polyurethane discs that control lateral movement. Apparently, if they are too loose, the engine cradle vibrates back and forth sideways and if they're too tight, the vibration of the engine in the vertical plane gets transmitted to the frame.

Note that my knowledge is based on bikes from the two prototypes up to when I left N-V to emigrate to the USA in the spring of 1968. It might all be different on later bikes.
 
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