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I have a Strada 350 which starts and runs well at low speeds, but seems to run out of puff above 50mph. I have balanced the carbs etc., but can't get the top end performance which the bike should have. With a really long run up, it will (just about) reach seventy, but then seems a little hesitant. At a stand still, out of gear, it will rev to the red mark quite easily.

The bike has standard jets and sprockets, though I wonder if it may be something to do with the jets?

Anybody with more expertise than me have any ideas?

MikeT

Hmmm, everyone's hesitating to reply. Starts & run well at low speeds, revs up to the limit in neutral but not on the road.

First off, count your blessings - it starts! Remember running up to the limit without load is very different from running under load.

Second, check your plugs: are they black from too rich a mixture or white from too weak (or too advanced ignition)? Morinis seem to be very tolerant of ignition timing (I speak from experience) so if the static timing is set according the manual look elsewhere to start with. Fit new plugs (they're cheap) then check the valve gaps (shouldn't be a problem but methodical works best).

Third, check the manifolds between carbs & heads for splits & leaks and that the hoses between carb & airbox are fitted properly.

Fourth, remove the air filter from the airbox, but leave the airbox in place, and take it for a short run. Any difference? I have a Kanguro which is notorious for a sleeve in the airbox which really chokes performance; removing it makes a world of difference. If this makes a difference replace the filters - the bike should work fine with new filters. If new air filters don't help check the float heights in the carbs.
I had a different problem, more to do with starting but I replaced every jet & grommet in the carbs for my Sport without luck until I replaced the carb floats. Dell Orto have manufactured completely different floats (different material & you can't adjust height) which made a world of difference. I suspect that a lot of the apocryphal tales about the rear carbs needing different jets from the front are due to problems with the floats.

Fifth (beginning to get desperate), check the valve timing. This is difficult to get absolutely accurate, but that's not necessary. Is it within a few degrees of the factory specification? (by switching keyways on the pulleys and teeth on the belt it is possible to vary the timing by only a few degrees).

Sixth, are you sure the engine isn't worn out? Get a friendly bike shop to do a compression test on the cylinders. I can't say what figures to expect but with a nominal 10:1 compression they should be high. You might have busted piston rings or burnt out valves.

Check the resistance of the ignition coil on the stator - if it's less than 200 ohms it's time for a rewind (but this usually upsets starting not just fast running). Likewise the problems with transducers are not usually limited to fast running.

If this doesn't find the problem it's time for serious work. Have you got a slipping clutch, binding brakes or twist grip & throttle cables which don't open the carburettors fully?

If you've got this far without a solution it's certainly time to check the ignition sender on the left hand end of the camshaft. My Kanguro not only had the hub rattling on the camshaft but also the magnet loose on the hub giving me very variable ignition timing (it would still run, mind).

Good luck, keep posting!