Exhaust valves NLC

[tenkfeet]

I have been working on my mates bike for him, its a dog of a carbed twin Honda Varadeero. Its had starting problems ( ok when hot) getting worse for months, backfiring badly until now it wont do anything . He said it would run with the plug out of the back cylinder. He took it to a bike shop who did a compression test , changed the plugs and said it was running lean . The back cylinder compression is low . They quoted £800 to fix , its a pig to work on . The bike is not worth that so I am doing it.

Anyway I took the head off the back cylinder and all looks ok except the exhaust valve outlets are different colours so I assume one is the trouble . I originally thought it was the black one but am not 100% . They should be the same should they not ?

Anyone got any experience of what is right or wrong ?

[robin]

Push the valves out and take a look at the valve seats ... you'll need a valve spring compressor, assuming this is a normal poppet valve type of design.

If compression is low it's probably because the valve seat isn't sealing properly ... I would guess that would be on the sooty black one (combustion taking place in the exhaust port) but cannot be sure.

Post a picture of the combustion chamber also ...

Cheers,
Robin

[tenkfeet]

Thanks, everything looks good , will get a spring compressor tomorrow. Here is a pic of the piston head and the cylinder head chamber side , exhaust valves to the bottom.

[robin]

Hmm. Nothing obvious there ... I guess you'll need to check the valve seats. Still think it must be an exhaust valve, because I assume that if there was an issue with the inlets (a) it would keep blowing up the air/fuel in the intake manifold and (b) why would that cause such a difference between the two exhaust ports .... of course it could be that they're all like that for some other reason!

Cheers,
Robin

[tenkfeet]

Hmm. Nothing obvious there ... I guess you'll need to check the valve seats. Still think it must be an exhaust valve, because I assume that if there was an issue with the inlets (a) it would keep blowing up the air/fuel in the intake manifold and (b) why would that cause such a difference between the two exhaust ports .... of course it could be that they're all like that for some other reason!

Cheers,
Robin

Again you are correct Robin . Just found out the colour is due to " (Pulsed Secondary Air inlet) which feeds air into the exhaust gallery to clean up the exhaust gasses by allowing them to burn a bit longer." I put some cleaner down it and it came out in the light one . Every day is a school day .

Funnily enough that cleaner has now leaked through the valve .

[robin]

So in that case the compression loss may not be in the head at all, but around the piston instead? Or did I misunderstand?

Cheers,
Robin

[tenkfeet]

So in that case the compression loss may not be in the head at all, but around the piston instead? Or did I misunderstand?

Cheers,
Robin

No I am talking in riddles again, its leaking through the exhaust valves . The pulsed air doofrey is external to the combustion chamber .

[mac]

De-coke and try re lapping the valves, using the course stuff first.


If it's too far gone you'll need to get the valve seats re-cut, might as well swap out the valves too if your doing that.



cheers



Mac