The Beast Lives! But those pesky carbs - now what?

[dbs]

Long term readers (like, 20 years or so) will have heard tales of The Beast, my 1978 GS850. It's been chatted about on rec.motorcycles, NEDOD lists, and occasionally here. It's time for another chapter in the project.

I just uncrated the bike again and I'm ready for my next round of repairs. About 10 years ago I thought I had the proper handle on the carbs, but I want to do it Right this time. Age is not making this easier, neither is my only sporadic use of the bike (2-3 decent trips a summer).

I give you, the beast's guts. (The rest of this photo set is http://www.flickr.com/photos/planet-geek/sets/72157600189486787/ )

The question is, what do I tackle first... I have to preface this with "It starts!" - Put the key in, a little choke, and it starts right up. Choke down after 5 minutes of warmup and it's ready to go.

I'm doing a couple basic things first:
1) Replacing that amazing air filter. How beautiful is that, eh? NOT!
2) Draining and refilling the oil, and putting in a new filter - basic stuff there.
3) Draining and... what? with the gas tank. The tank sits for the winter half full, I've heard mention that rust in the tank can cause needle valves to stick - what's the best procedure for cleaning out an almost 30 year old gas tank?

Here are the things I must fix before I can have confidence in riding it any distance though.

1) The petcock is leaking. I hadn't noticed it before, but turning it to reserve or primary causes it to be drippy. I've seen mention of petcock rebuild kits
- shoudl I just go ahead with that?

2) The dreaded overflow leakage. This has been a problem for years. My understanding is the basic job is to pull the carbs, do a rebuild on them, and put them back together - this is just the needle valves sticking with gunk on them. Should I try just running carb cleaner through them first?

3) This seems minor, but it keeps bugging me. Why does my choke cable slip? I can't choke without wrapping something around the pull lever to hold it up. Just replace the choke cable?

All of this is before I've gone for my first checkout ride. I really want an engine that doesn't leak gasoline everywhere. IS that too much to ask?

Anyone in Boston wanna do a weekend or two of repairs with me?

 

[deves3000gt]

ok, well i wouldn't bother with the petcock rebuild kit just spend the extra 15 or 20 dollors and get a whole new unit. please get rid of the filter..lol.as far as the overflow does it only happen when the bike is running or will it still leak while off either way by the looks of the airbox you should at least pull the carbs and clean them in not overhaul them (see didnt say rebuild) i dont know much about the workings of the choke so can;t help you there but deffinantly buy a new petcock. good luck
steve

 

[SqDancerLynn1]

Replace the petcock, most likley the float seats have an O ring-leaks replace that & clean them No need to rebuild them. Try pulling the choke cable up & turn slightly to left should stay up

 

[dbs]

Replace the petcock, most likley the float seats have an O ring-leaks replace that & clean them No need to rebuild them. Try pulling the choke cable up & turn slightly to left should stay up

Where would i get those o-rings for the float bowls?

I see petcocks new on ebay for about $40 (seems a little steep), or a 'used' one for $25. Sounda bout right?

 

[robertbarr]

The 850 wasn't imported to the US until 1979. So you don't have a '78.

You have VM carbs, which do not use O-rings on the valve inlet seats.

Keep that filter! Just clean it properly.

Looking at that bike, I'd be astonished if your carbs DIDN'T leak... just sayin'... a little cleanliness might be called for.

 

[dbs]

The 850 wasn't imported to the US until 1979. So you don't have a '78.

You're right... I'm not sure where i got the date wrong. I even just went down to the garage and checked, and the plate on it says '5/79'.

You have VM carbs, which do not use O-rings on the valve inlet seats.
Keep that filter! Just clean it properly.
Looking at that bike, I'd be astonished if your carbs DIDN'T leak... just sayin'... a little cleanliness might be called for.

The bike has had a long and busy life, with admittedly not fantastic maintenance. I'd like to fix that now. So what I'm hearing you say is "clean everything first". I'll do that with the airbox and filter, pull the float bowls and make sure the needle valves are all happy and moving and all ungummed - no amount of lceaning is going to fix the petcock though, so I'll replace that.

Any other suggestions on how best to clean those carbs? (You say 'VM' carbs - i've always just said 'mikumi carbs' - is there a difference I don't understand?)

 

[robertbarr]

Any other suggestions on how best to clean those carbs? (You say 'VM' carbs - i've always just said 'mikumi carbs' - is there a difference I don't understand?)

Well, I generally recommend the full disasssembly and chemical dip, but at least clean up the bowls and hit the inlet seats with some carb spray. If it runs OK, who am I to argue? If it keeps leaking, I'm afraid surgery will be necessary.

Mikuni made VM carbs, and these were used on earlier GS's. Mikuni also made CV carbs, which are used on later GS's.

VM's are, in my opinion, superior and far more tolerant of neglect. They are ugly, but they just work and work forever without complaint. They also have no hideously expensive diaphragms to go bad.

I had the exact same model and color of '79 GS850. The only minor difference is MINE WAS KEPT IMMACULATE. Not that I'm fussy about maintenance...

My tank also turned pink like that after a few years in the sun, so I had it repainted twice more during ownership. The bike stayed in good shape in part because I kept getting hit by people with insurance. Brand new exhaust systems, a brand new seat ($82 back then... including the chrome along the sides). New handlebars, rack, mirrors, fairing, it just kept happening.