High revs on the right cylinder when idling

[trolle]

This is a severe problem: The right cylinder has just started to develop a bad habit of revving up to 2000 rpm when it should be idling at 900. I cannot find the cause; at first I suspected that the exhaust valve was too tight, but it was not that. Then I cleansed the carburettor and that did not help neither. Now I am at my wits end (and I am in no mood for stupid jokes about that   ), Please help me out here  :-?

greetings from a warm and sunny north

trolle

[Clutch]

make sure the cables (throttle and choke) aren't binding up somehow.  Also check to see if you aren't getting an air leak around the carbs (cracked rubber hoses connecting the carb to the head/loose hose clamp on those rubber hoses)

[trolle]

Cables are ok, clamps ok but the airleak sounds like a probable cause, I will check that.

greetings from a warm and sunny north

trolle

[Bob_Roller]

Is this happening all of the time or just after a long high speed ride? It's not uncommon to develop a high idle if the bike wasn't warmed up to operating temperature when the carbs were adjusted for idle mixture, idle speed and synchronization. It's happened to me a few times in the past. Tight valves will usually cause the engine not to idle, or to idle poorly. If you have not done a full carb adjustment in a while, this may be the time to do it.

[trolle]

It is happening all the time: When cold it revs to about 1100 with no choke and after a 20 minutes ride, ie being warm it revs to about 2000. Normally it won't run without choke when cold and runs with a 1000 rpm when warm. The condition evolved rather suddenly.

greetings from a warm and sunny north

trolle

[Bob_Roller]

I don't remember what year bike you have, but it sounds like the 'choke' or enrichment may not be closing all the way. Have you tried loosening the 'choke' cable adjusters at the carbs to make sure they are returning fully to the 'off' or normal position. If you have the 'choke' lever on the handle bar, you may want to check the cable 'splitter' under the tank to make sure something hasn't come out of place here as well. I know my bike won't start without the use of the 'choke' if the air temp is under 75 F., and won't stay running without it being on for a mile or two of riding.  

[Clutch]

Did you happen to leave your bike out in the rain just before this high reving occurred?...I'm just curious because my bike revs high after it gets rained on, and after the engine head dries out the idle goes back down to normal.  I haven't figured out what my problem is, and was wondering if anyone else has had this problem.

[nhmaf]

It does sound like it might be an air leak, or perhaps, the vacuum hose is pinched or cracked /leaking somewhere ?

[trolle]

Now I have checked everything, and I mean every thing. It still revs up to 2000 rpm when warm. The plug looks slightly warmer but nothing alarming, I have changed the membrame, checked the rubber hose connectecting the carb with the head for leaks, checked choke and throttle which are ok and finely adjusted, checked and adjusted airscrew (idle) but nothing helps!§!!! :-?

greetings from a warm and sunny north

trolle

[Semper Gumby]

If the Carb hoses are not perfect replace them.  Cheap insurance.

[Ed Miller]

Which carb hoses do we replace?  The hard plastic elbow, the softer hoses on either end, or all of them?  I should be thinking about that, I guess.

[Justin B.]

As those that connect carb-to-head get old they get hard and cracked and sometimes won't seal properly.  If this happens you get a sown-stream airleak which leans everything out and makes it impossible to get a good adjustment.  The test is to spray like WD-40 around the connections and if the idle speed changes you've found your airleak.  A vacuum leak will cause idle to raise as it is just like cracking the throttle a bit.

[trolle]

Thank you for all your inputs, sorry but they have not helped. I switched the left and right vacuum hoses, but the right cylinder continued to rev: Now it has settled into a pattern. When cold it runs at about 1400-1500 rpm and when warm about 2000 rpm but sometimes it goes as high as 3500 rpm. If I then give the throttle a blip up to 6000 rpm it settles at 1300-1500 rpm.

I do not think it has anything to do with the carburettor but suspect some valvetrouble. Has anybody experienced anything like this?

greetings from a warm but soon cooler north

trolle

[Chris_in_BC]

trolle,
 How do you know it is just the right cylinder reving too high?

I would try what Bob suggested. Go for a ride and get it really hot (not just a 15 minute cruise around the block)

Then adjust the idle on the carbs back down to the level you want.

You also don't mention if you changed anything prior to this sudden change. ie you didn't rebuild the carbs or something similar? With the carb intakes to the airbox off, and the throttle closed, do the butterfly valves look tightly closed?

[trolle]

done that, been there - believe me, I have tried everything suggested. That is why I find it so annoying.

Status so far: Probably no leak because after doing 30 miles at high speed between 90 and 100 mph, the plug on the right side shows no signs of overheating. All cables have a tiny amount of slack, idling screw does not touch the throttle lever, ie idling is as low as possible, airscrew is set to optimum, membrane is OK, butterfly closes - (when I wrote the word butterfly, I thought that it would not harm to check them just one more time. Now I am back after having had both carbs off, checking the position of the butterfly - and lo and behold, the right one was just a tiny bit askew - pressing the throttle lever arm down to its full extent and letting it pop back a few times set the butterfly right). Tried starting the engine which ran straight and after a couple of minutes managed to idle at 800 rpm without choke. Now I only have to go for a ride to warm her up and to see if my correction of the position of the butterfly lasts.

Strangely enough the butterfly was the first item on my suspicion list, but I dropped the thougt because the butterfly is in a rather fixed setting - or is it? Evidently this one was able to fly away, must be the spring.

Thank you for your advice and to Chris in BC: I mount a threaded pin on the tap of the plugs at each side. This way I can short either one of the plugs with a screwdriver and find out which of the cylinders is revving. I always carry the pins with me.

My wife says that I tangle too much with the motorcycle - I do not agree, it is one of the charms having an old bike like the r65, she's like a lady demanding your attention and being the gentleman I am, I give it gladly.  

greetings from a sunny, cooler and windy north

trolle