'80 550L Gutter on Decline: Petcock?

[GSinDC]

My idle on my 550 would drop when I had the bike running on the center stand then pushed it forward to knock it off the center stand. Problem was simple, Floats were set just a smidge too high. Gas would splash up into the system and temporarily drown the bike.

If a complete cleaning is a bit out of your reach at the moment, start with a small task like resetting the floats to factory settings. You don't have to take the carbs all apart, but it will get you used to taking them off.

This sounds exactly like my problem. Truth be told, guy who sold it to me said something about "carbs.... floats.... when i got it...", but at the time I didn't even know what those things meant (even less than I do now, if you can imagine it) so it just made no sense to me.

Its possible he got the carbs cleaned and assembled, or had the float set a little too high... the quote above sounds exactly like my problem.

My Clymer guide doesn't give a lot of detail about setting the floats- is there a guide for that somewhere? Outside of doing a complete carb rebuild?

[mike_of_bbg]

There are a few potential causes for the old "idle stumble". Let me offer a few suggestions - though you should clean your carbs and check your float heights (do some forum searches on the subject of float height - you can use a thin clear sharpened tube shoved in the bowl drain plug threads). You should also verify the proper operation of your petcock - particularly that there is no fuel in the vacuum tube.

Check your voltage at the coils. The stator puts out less power at idle, and the bike voltage can drop because of it. If you're already low at the coils you can get weak spark. The ever-so-common coil relay mod is an easy fix. Go through the whole stator papers test procedure. Maybe it's just me, but the smaller 4 cyls seem to charge high, and this can cause burned out ignition components; particularly ignitors. You'll want to head that off if you can. You should also check the resistance on your plug caps. Stock ones ran about 10k ohms, most of the NGKs we use as replacements are 5k ohms. When they go bad the resistance can jump up into hundreds of thousands of ohms and really restrict your spark.

You need to do a vacuum sync (when was the last valve adjustment? if it's time that needs to be done first). At idle the butterflies are BARELY open. Just having them off a little bit can cause one of your cylinders to be too far closed, suck in too much fuel and foul out. Pull your plugs and have a look (feel free to post your pics here and have the masses take a look). If the insulators are turning charcoal grey this is a good bet. Combined with a rich mixture this gave me headaches (plus low coil voltage, which didn't help the stumble and made the bike a bear to re-start). This will be more pronounced too when the air is hot and less dense.

If only the #2 plug seems very rich that could definitely indicate petcock issues.