Sprint - Sprint Sport Hits A Top Speed Wall

lol. just sayin, so it goes to within 20 mph of top speed, well thats approx 110 mph or so,mmmmmm.
you say it revs ok in all gears except top 2 so i wouldnt think it was fuel or it would be the same in all gears surely.
not sure about the pipercross filter and jetting, would guess main jets aint right,maybe blocked as it runs good lower down.
guess you tried running it with the tank cap open to see if there is a vacuum
last guess but a bigger job, valves? but if it starts ok and runs ok probably not that

 

Take it for a run minus the air filter. It may be over oiled. This will tell you one way or the other.

 

Exactly. I am suggesting in a roundabout way that you eliminate possibilities. If it is not 'muzzled' and the ignition checks out you have either got a fuelling issue or maybe poor compression. How is oil consumption? You might need a rolling road re-tune.

 

To be honest, it could be a number of things from clogged petcock on the fuel inlet side to an exhaust a bit furred up with corrosion (unlikely!). For a vehicle that has sat I can only suggest you systematically work through fuel supply, air supply and exhaust.
I cleaned my own carbs ultrasonically but tank rust particles in the mesh petcock filter were part of the problem, as was the inline filter and a slight kink in the fuel hose that limited flow at full chat.

 

This is getting confusing as there are two threads with the same name both by the same person asking the same question ........

This one under Tech Help
And one under Sprint & Trophy

Amalgamating the two would probably yield less confusing answers and save people doubling up on suggestions

 

Silly question - have you checked the throttle ' throw ' by that I mean when on full throttle does the carb move fully open?

 

Going back to my reply earlier, stupid advice from me, dont try riding with tank open, that is for static test only, I realised after. sorry

 

I remember seeing a fella gazing into his fuel tank - with a cigarette in his mouth - I moved away quick like

 

It's welding in the vicinity of fuel tanks that makes me twitchy!

 

Be honest now ......... why do bikers always stop at a petrol station to light up and smoke, often whilst topping up the tank ???

 

Death wish ???

 

I do it to get warmed up

 

Because they forgot to shave?

 

I remember looking in my Tiger Cub tank with a match when I was 16 .... Never done it since