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Old 11-14-2009, 05:02 AM   #31
tennessee thumper
now in Mt. View, AR
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Location: Arkansas Ozarks
Oddometer: 739
I had the smokey start up on my /5. I cleaned out the choke units on each carb and the smoke went away.
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Old 11-14-2009, 11:33 AM   #32
I'm working on it...
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Joined: Jul 2004
Location: Rome, GA
Oddometer: 510
Originally Posted by More_Miles

Well, I tore into the airbox tonight. Guess what I found?

Oil in the crank case breather tube. Enough that there was a drop or two forming at the end of it. The intake was also oily... I cleaned it all up, and I think I know why the left cylinder was smoking more than the right. The tube that runs from the Tee to the intake was sloped down towards the left. Gravity's a bitch.

I also took the starter cover off. It looks like there has been some oil getting out into this area. I cleaned it up as best I could, and since I'm almost into the winter cabin fever season, I'll tackle that later. For now, oil is fresh, and I'm going to keep an eye on it. I am pretty sure I know why it's smoking, just need to figure out now why it's blowing oil.
I'm not too surprised cuz that's what I found in my RS (and why I suggested at least looking, back in post 11 ). You will find some oil droplets in the breather tube, as a big twin moves a lot of air around in the crankcase.

When you get around to it again, check out the internals of the crankcase breather. My '78 RS had the older one, which apparently doesn't work as effectively as the new style. The older one is a fibre washer and a coil spring, while the newer one is like a reed valve. My RS puffed quite a bit of oil when warm, and the new style breather virtually stopped it.

Check an on-line parts fiche (like and view section 11, diagram 11_1725. Assembly #2 is the older style, and #3 is the newer replacement part.

If you have the older one, try upgrading to the new one as it's only $30mumble bucks.

If you already have the new style (and the diaphragm is intact) then I'll hush and let somebody more experienced speak up .

Ride it.
If it breaks, Repair it.
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Old 11-14-2009, 12:42 PM   #33
Joined: Nov 2009
Location: Seattle, WA
Oddometer: 5,165
A few thoughts:

The crankcase breather could be a problem (worn reed valve allowing a bit too much venting into the carbs). However, too much oil past the breather could also be caused by more serious problems such as worn rings (compression blowing past the rings, into the case and out the breather).

When I had worn valve guides on my 78 R100S the most noticeable symptom was smoke on deceleration esp. going downhill (cut the throttle and the piston starts sucking through every possible opening such as the valve guides which sucks oil into the compression chamber).

Hard tellin', not knowin'. A compression check is step one.

Keep at it!
Forging ahead, down a false trail.
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Old 11-20-2009, 05:24 AM   #34
More_Miles OP
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Joined: Aug 2009
Location: New Brunswick Canada
Oddometer: 312
Sucess, of a sort


Post oil change/air filter change/cleaning of the breather system followed by 700 km at or above 110 km/hr (does that count as blowing the snot out of it?) and the bike hasn't acted up since...

I'm not saying it's cured, since as soon as I do the problem will be back with a vengeance.

Thanks one and all!

Larger than life and twice as ugly!
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Old 11-20-2009, 08:05 AM   #35
C Squared
Now with TURBO!
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Location: FDL WI.
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A compression check will probably not show worn valve guides as the valves will probably still seal on the seats.

R bikes have guides that have alot of clearance and no valve seals.

Check into new guides and valves if you find this to be the problem.

Matt at Motor West in Milw. WI. Sells some "tighter" guides and seals. (high quality)

I am sure others sell the same ones.

But give Matt a call.
I can explain it to you, but, I can't understand it for you.
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