Topic: big engine trouble

[mlinder]

Phi:

Is your advance working properly?
Are we assuming you left out a 0 after the decimal point correctly?
Are you running on all 4?

Lets get confirmation on these things before you start rejetting..

[phi]

I'm sorry, I have left a zero out, the valve clearance is of course 0.05 mm (0.002 in) and 0.08 mm (0.003 in)
You may have a point with the airfilter, I have just cleaned it with pressurized air and inspected it. A new stock airfilter is on its way.
In the meantime I have read the plugs by killing the engine on the troublespot, and they are white. I need more gas, not more air as I assumed. I have, based on this knowledge, dropped the 900 carb idea and start by jetting the original. It is definitely not running too rich, so I will try to bump the slow jet one step up, and the main jet 2 steps up.
Just interesting info: I wondered why the bikes pistons and valves was fine with so lean a mixture, so i contacted the seller. It turned out that the bike had been running some big CR carbs in the past, but those had been used for something else, and had, without further concern, been replaced with the stock ones and never run again. No wonder it is lean.
Thank you for help and inputs.

[willbird]

Can you raise the needles ? My bike when I put the header on would act sort of like yours does, the plugs were white, raising the needles one notch cured the lean condition.

In my case easing in some choke made the problem go away at cruise speed (55 mph) so I suspected a lean condition, checking the plugs confirmed it.

Bill

[phi]

Update:
This is magic: I raised the needles one step from the original position, and the problem spot raised to around 6500 RPM. A 130 main jet took care of the rest. I am one happy guy! Now I just need to adjust the embarrasing high idle when hot. Adjusting the airscrews will probably take care of that.
I feel like a evil engine genious right now, so once again, thank you all for inputs and ideas.

[MCRider]

Update:
This is magic: I raised the needles one step from the original position, and the problem spot raised to around 6500 RPM. A 130 main jet took care of the rest. I am one happy guy! Now I just need to adjust the embarrasing high idle when hot. Adjusting the airscrews will probably take care of that.
I feel like a evil engine genious right now, so once again, thank you all for inputs and ideas.

You ARE the evil genius (positive reinforcement). 

Those big cylinders just needed a little more go juice.  Have fun.

There is an idle jet in the carb that can be changed IIRC. May need to go there.

Of course all the usual suspects, air leak, hanging cables, etc, should be checked.