My MK3 does not rev beyond 4500rpm

Cam one tooth off the proper spacing (on it's chain) with the drive sprocket?

As others have alluded to, it's sounding awfully like that's the problem. Only a 1-hour job to correct.
 
You are clearly getting nowhere and it is time to find someone local to you who is very familiar with Norton heavyweight twins, especially Commandos, to actually examine it. By “familiar with” I mean with longstanding, practical experience, not someone who knows what colour the side panels should be painted. They will probably identify the problem within minutes.
 
hybridracer said:
You are clearly getting nowhere and it is time to find someone local to you who is very familiar with Norton heavyweight twins, especially Commandos, to actually examine it. By “familiar with” I mean with longstanding, practical experience, not someone who knows what colour the side panels should be painted. They will probably identify the problem within minutes.
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just makes me wonder how many people like that are left in the whole world, and then how do you find them….?
 
MexicoMike said:
DOES it rev beyond 4500 in neutral or not? Efficient troubleshooting steps are different based on whether it will or won't.
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Yes!

Once that is answered, state what happens with a timing light at 3500, 4000, and attempted higher. Are the marks stable or do they move all over the place.

Assuming you learn nothing from those two things, take the timing cover off and check the cam timing - it's a simple thing to do but you'll probably need a new gasket and I would replace the oil pump to cover rubber seal.

There are over 125 posts and nothing definitive so everyone, including me, is just "taking a stab at it".
 
Yeah...another stab:

I haven't had it happen on a motorcycle but HAVE seen it several times with cars - collapsed/clogged mufflers will cause the symptoms you describe - won't rev, engine gets very hot. Seems really unlikely in this case but since we're all stabbing in dark, there's another knife wound!! :rolleyes:
 
When the amal drain plug fell out of one carbs, my motor would barely run, running on one cylinder, shakey and no power. 😁
 
OP probably figured it out and is too embarrassed to admit what the problem was. :)

javi what's the scoop?
 
Rich_j said:
Cam wear? Would have to be pretty catastophic and I've never heard of a cam wearing that badly.
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I think that might've been ruled out by noting "uppy-downy" goings-on at the business end of the rockers...

(but I could be imagining that)

...and, oh, by the way, perhaps you've never seen a photo of one of the late cams that were purported to have been cut from softened cheese?

1757359317713.png
My MK3 does not rev beyond 4500rpm
 
Perhaps the OP replaced the throttle cable with one which is too long ? The question should always be 'what has changed ?'. If he has bought a bike with the problem, he might need to rebuild the motor. It is not wise to take things for granted. The problem is probably that often that the owner might never have reassembled a motor and lacks confidence. One of my mates had old motorcycles for years. The first time he pulled a Bridgestone 350 two-stroke apart he really freaked-out - but all the internals just fell into place as he put it back together. A Commando engine is not fool-proof, but is not really difficult.
 
Old British motorcycles are usually owned by real motorcyclists. For me, the joy is in building a motorcycle and proving it works better.
 
grandpaul said:
I think that might've been ruled out by noting "uppy-downy" goings-on at the business end of the rockers...

(but I could be imagining that)

...and, oh, by the way, perhaps you've never seen a photo of one of the late cams that were purported to have been cut from softened cheese?

View attachment 121635 View attachment 121636
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Yeah that would slow things down.

I bought an SS cam from Bob Raber in the early 1990's (I think) and Radford warned me about a batch of SS cams that could have been soft. I asked Raber, and he said what he sold me wasn't one of the soft cams. However, what else would he say. I put about 6K miles on it before replacing it with a JS2 and associated hardware. The SS still looked good. I also just recently removed the JS2 and put flat tappets and SS back in my 750. Living on the wild side. :)
 
grandpaul said:
I think that might've been ruled out by noting "uppy-downy" goings-on at the business end of the rockers...

(but I could be imagining that)

...and, oh, by the way, perhaps you've never seen a photo of one of the late cams that were purported to have been cut from softened cheese?

View attachment 121635 View attachment 121636
Click to expand...
Almost as bad as some modern KTMs...
 
I've had several Cams like that, You can hardly tell , speed wise There is more noise and you can see a rocker arm or two doesn't travel as far But I turned decent 1/4 times with one in my MK2A and My MK3 suffered 2 cam failures and It went pretty good. Like I have said my racer friend Gary, Had to wick up his Ex race bike powered by a 750 hopped up motor and he was surprised when he saw the cam. When I sent to Web Cam they said they never saw one as bad. All my bikes can rev over 7 K, some faster than others. Bad cam or not.
My MK3 does not rev beyond 4500rpm
 

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