Top out at 80mph

[SCAT]

Just bought a new carburetor as the sliders would not spring back...
really hoping that fixes it!

[SCAT]

still not working.. got fed up, took it to a dealership (where i passed my test)
they recommended a compression test?

[CMSMJ1]

Where are you based?

They are simple beasts.

If it can rev out in the early gears then the carbs work. If it is a speed related thing then the air flow, the bike heat or something that is causing fuel starvation?

Be thorough, work on one thing at a time and you'll sort it.

[bikemonkey]

My money is on airflow, had a similar problem myself and it was that.

[SCAT]

Thanks, I called them and told them to leave it in bits I will go to see what they've done sometime this week.
They should have known i reckon charging me £1200 for nothing is ridiculous anyways spoke to Honda they said they would elevate the matter.. I have another motor on the bench (if you follow my other post about supercharging the motor).

[SCAT]

OKay so the bike is back home, took it for a ride and put a smile on my face for sure. After 2.5months it didn't matter if it was 1deg C with small snowfall, i needed a test ride.

Compression test result:
120PSI (3cylinders) and 140PSI (4th cylinder) I can provide cylinder order and compression per cylinder.
Honda told me that for the stock 11.3:1 compression ratio I would have been expecting about 150 to 215 PSI

They unfortunately had NO idea why compression was low, as all valve clearances where within spec.

Any ideas?

[bikemonkey]

Could be the valve seats out of shape? I.e you need to grind them in.

Could also be your piston rings? Replacement jobby.

If that is the problem then try re-seating your valves first

[thunderace]

Low compression can be caused by many things.

Lack of oil causing the rings to be overworked.
Old (worn) and weak rings.
Crack or opening in the head - but that doesn't always mean you'll get water in the oil or oil in the water.
Cracked cylinder
Burned, warped or cracked valve
Burned or cracked piston
Cylinder worn or out of round
Blown or leaky head gasket
Sticky valve
Broken or worn valve spring
Bent/worn pushrod
Worn camshaft, or a broken lobe on the cam
Worn or bent rocker arm
Collapsed lifter


Take your pick

[bikemonkey]

And I was trying to keep it simple! (Not that I didn't know half of that stuff anyway )

[SCAT]

* When I said NO idea - I meant they suggested stuff like ultrasonic scans or what not (which is when I said forget about it I want it back)

would they not have noticed worn piston / valve seats when they took carbs to bits, valve clearance and compression test?

I wish I had my own garage for my bike, then I would know exactly what's what: I asked if they would let me in the workshop but no.
Unfortunately I can only use university tools for the project supercharged NC30..

Thank you for the input. I had thought of cracked head cams etc but dismissed them as worst case...
to be honest at this stage would it not be better to source a new block for £350? Although I might be buying into a similar problem.

Is there a way to figure out if the cylinders are leaking, or if the cylinders are simply not being filled up fully ? (to narrow down the list)