Smoking Pipe

I recently started having issues with my '71 R75/5 when cold. It smokes out the left pipe for a good long while, far beyond getting warm. It only started this since I used the side stand once and most people's comment is that its residual oil from the lean...but it still does after a 4 or 5 mile ride. It's not blue, its white.

I used an infrared thermo to measure the temp on the header just in front of the exhaust nut. The left, one is markedly hotter than the right side while the engine is warming up.

Balanced the carbs with Twinmax after a good warm-up ride and by all accounts, its running and idling very well.

The smoke is white and trails for 10-15 feet before dissipating. After it is really good and hot, the temps on the headers are the same within 5 degrees.

The valves sound good and the bike runs well, but I'm thinking this is the first place I need to look (adjustment and/or valve job).

Of course, the exhaust nuts are frozen (and they are the old /2 leftovers with the dimples), so I'm soaking them thinking I may need to consider a valve job soon.

Hoping to generate a few ideas to look into, even though I think I should know what's causing this--I don't :-(

what was the old test... white smoke under acceleration = valves; blue smoke under deceleration = rings

or was it the other way 'round?

Might be coolant ... .

I'm betting valve guide?

White smoke/vapor usually indicates moisture. Consider dropping the float bowls and checking for water in the bottom. If that is the case, run som Iso-heet through the tank to remove the moisture. Also, since the left side is the low side on the stand, any moisture would accumulate in the left side exhaust, especially if you're doing just short trips and not thoroughly warming everything up.

Agree -- I'd also suggest emptying the tank so you can pull the petcocks to completely drain what is likely an accumulation of seam-rusting water along the bottom of the tank.

On the difference in temp between L/R during warm-up, followed by equal temps/good ops when fully warm, that suggests the right side choke is not supplying fuel -- possibilities include a blocked jet at the bottom of the right float bowl choke well, or a damaged/collapsed paper gasket under the choke housing.

manicmechanic said:

White smoke/vapor usually indicates moisture. Consider dropping the float bowls and checking for water in the bottom. If that is the case, run som Iso-heet through the tank to remove the moisture. Also, since the left side is the low side on the stand, any moisture would accumulate in the left side exhaust, especially if you're doing just short trips and not thoroughly warming everything up.

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Funny you should mention that Manic, that describes my use of this bike at least so far. I also just got a tank in somewhat better condition (paint) than mine and was about to rebuild petcocks, new screens etc. Might as well bite the bullet and rebuild the carbs. I just got this one a few months back, so no history.

Lmo1131 said:

Might be coolant ... .

I'm betting valve guide?

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Aha! Coolant, I never thought to check the water pump condition. Thanks Lew, you clever man.

mneblett said:

Agree -- I'd also suggest emptying the tank so you can pull the petcocks to completely drain what is likely an accumulation of seam-rusting water along the bottom of the tank.

On the difference in temp between L/R during warm-up, followed by equal temps/good ops when fully warm, that suggests the right side choke is not supplying fuel -- possibilities include a blocked jet at the bottom of the right float bowl choke well, or a damaged/collapsed paper gasket under the choke housing.

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Mark, I think you are up to your usual self: right on the money, like Manic says.

...damn I hope Lew isn't right this time too!

Thanks guys.

...damn I hope Lew isn't right this time too!

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Like checkin' the point gap right on a diesel .. . ?