chasing a problem

[cwillson]

Would appreciate any suggestions on following:

1984 R65 with 26,000 miles
Throttle is 'bogging' (best word I can think of) on roll on - particularly in 3000 RPM range.  On hard roll-on it is much smoother.  The bike is new to me and maintenance unknown (appears to be well cared for but also ridden.  As part of getting to know the bike I have:

Changed plugs and plug wires.
Replaced coil (just because - it was the original)
Changed air filter
Confirmed no water in fuel
Balanced carbs at idle, 2000 RPM and 3500 RPM
Confirmed timing is set correctly
Confirmed values correctly adjusted
Been through various carb mixture settings from stumble lean to stumble rich and everything in between
I have not disassembled carbs for proper cleaning

I welcome any suggestions as to what I might try next.

Thanks
Craig

[Luca]

First thing I'd check are the carburetor diaphragms.  A tiny little leak in one of those and the bike will act like it isn't getting enough fuel (because it isnt... at least not out of the carburetor)

[cwillson]

Luca

Thank you.  Added to the list to check.

Craig

[nhmaf]

+1 with Luca - an ill fitted or cracked diaphragm will cause great reluctance to rev over ~ 4000 RPM in these bikes.   Check the diaphragms CAREFULLY with a bright light - it only takes a small slit in it to raise havoc.   Also, the later versions have a small tab that fits into a slot on the inboard edge of the carb top - if the diaphragm isn't well seated in place, it will also cause vacuum leak.

[montmil]

[smiley=thumbup.gif] I'll make it three votes to check the diaphragms.

The Bings require a vacuum to lift the slides. If one or both diaphragms have a tiny hole or slit, the carb slides will not rise properly and the result is the "bogging" you're experiencing.

Strongly encourage you to use the OEM Bing replacements, if required. This carburetor component is not the place to cheap out on parts.

[cwillson]

Three votes it is!  Ordering carb kits as soon as I can source here on our wee island.  If anyone knows of a reliable Canadian source much appreciated.

Craig

[Luca]

There is a place in Canada called Shail's that a member here, Quixotic, used... but they are in BC.

About the same distance in the opposite direction you can get kits from motobins.co.uk  Like Monte said, get the genuine deal, not the pattern stuff.

...and he will swear to you that their shipping is reasonable