The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Clutch on March 26, 2007, 05:53:27 PM

Title: high revs when wet
Post by: Clutch on March 26, 2007, 05:53:27 PM

hello all,

I've noticed that when I don't have my bike (1981) covered and it rains, that the next time I ride, the engine idles high (~3200 rpms)... kind of like it would if I had my choke on.  The interesting thing is that I've noticed this engine behavior is correlated with the sound (and sometimes sight) of water boiling within the right-hand engine valve cover (I park using the sidestand, and I think that keeps water from getting into the left side as easily).  Before you freak out, what I mean is that water falls into that hole on top of the engine head where the valve cover meets the fins, and then has to boil itself out when the engine heats up.  After that water is gone, I don't have the high rev problems.  I've read in previous threads about how air leaking past the rubber hoses connected to the carbs can cause high revs, and so that got me wondering if this water could somehow be affecting some seal to cause the rpms to rise.

Any ideas?

Title: Re: high revs when wet
Post by: Semper Gumby on March 26, 2007, 06:03:17 PM

Check the rubbers between the carb and the cylinder head.  If they look anything other than perfect - replace them.  Doesn't your bike have emissions hoses from the airbox to the carb.  My 1980 doesn't have such things.  Check your exhaust valve clearence to see if it is tightning up.  .008" I think is the right clearence.  What moisture has to do with this I do not know.

I holed a piston on the CB350F because of (air) leaky carb isolator.  Lovely melted stuff on the plug followed by oil smoke out the exhaust.  Of course I was running it wide open at the time.   :-/

Title: Re: high revs when wet
Post by: nhmaf on March 26, 2007, 10:22:11 PM

I would also recommend looking for possibly cracks or gaps where air and/or water can get into
the intake tract or carbs.  If it runs erratically/misses/runs rough I'd look for cracks/gaps etc in the plug
wires and/or ignition components.

Title: Re: high revs when wet
Post by: Clutch on March 27, 2007, 09:36:26 AM

thanks for the comments!

I'm going to be checking valve clearances and balancing the carbs probably in the next few weeks, so that'll eliminate some things.  I replaced the spark plug wires about 4 months ago, which helped a cold starting problem I was having.  I'll thoroughly inspect the rubber hoses between the carbs and the heads too.  It just blows my mind why it only happens after it has rained...strange.