fluctuating idle/self reving?

[seidaikeishu]

I've pretty close to finishing up a restoration of a 1980 550 (thanks to all the help from here, you guys rock!), but I'm having an issue with the bike "self reving" or a fluctuation at idle. It starts fine, and will idle momentarily then start reving to about 5k rpm all on its own. ??? I'm completely stumped. Any help out there?

And yes, I'll get photos sent up soon.

 

[mike_of_bbg]

Hello and welcome. First post I see.

In all likelihood, either:

1. You're leaving the choke on. The "choke" provides an enriched fuel and air mixture to the carbs for starting. As the cylinders kick in the RPMs will rise, and can easily hit 4k. Once the RPMs start to rise you need to feather it back down. I try to keep mine around 1500 RPM until it's warm.

2. Your bike has a vacuum leak somewhere.

Did you replace the intake boot o-rings? The intake boots themselves are also known to develop leaks after 30 years or so. Petcock vacuum line? Make sure your sync ports are all plugged and tight.

Is the bike stock (particularly the airbox and exhaust)?

 

[Johnny Drummond]

Welcome to the forum,sounds like hardened "o" rings,split/cracked inlet rubbers(intake pipes to you stateside lads)-these are a bitch to detect as they usually don't crack where you can see them ie. the pipe you can see between the carbs and the head(they are made out of a steel plate with rubber bonded to it), the only real way to see it is taking off the carbs, OR the Diaphragms are holed(if it is a post '79 bike with CV carbs), here are a couple of line drawings I did for another member to illustrate what to look for



And what components are in there. If you find ANY damage like this to them-they need to be replaced before the bike will run


and this is the best way to put them back in after you have checked/replaced them
a good tip if you get new diaphragms is to put the rubber into hot water for about 45 seconds BEFORE trying to fit them, that way they will have become the right shape and really easy to fit.Also put a few small smears of grease into the channel the rib on the diaphragm fits into,it will hold it in place while you fit the spring and the top.Also double check the locating tab is in the correct place as it is easy to nip-knackering your new diaphragm!.I hope you can understand this rambling,and it of some use to you.Johnny

 

[seidaikeishu]

Thanks for the input. I had replaced the intake O-rings but only one of the pipes themselves (obvious split on that one). I'll look into those and the diaghrams.

All stock on the air intake and exhaust. And no, I'm not leaving the choke open.

 

[BassCliff]

Greetings and Salutations!!

Greetings and Salutations!!

Hi Mr.

Make sure you go over the maintenance lists in your "mega-welcome" and get everything thoroughly covered. Let me dump a TON of information on you and share some GS lovin'.

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Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

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Thank you for your indulgence,

BassCliff