Carb Flooding, need advice (Following the guide)

[Derek2k3]

Hey all,

I have a '79 650 Special, Hugh's PMA kit, running like a dream. It was parked over the winter with stabilizer in the tank, got it out and the thing ran like a freaking champ. Was beautiful, red-line in 4 gears without a miss.

Anyway, after a couple weeks of riding, I ended up with gas coming out of my left airbox a pretty extensive clip. The carbs had just been rebuilt before I parked it last year, but from what I can tell it is a floats problem.

I'm following the carb guide, gonna take it apart and clean/measure tonight. But, wanted your guys' advice on what exactly to keep an eye out for. The "inside information" that you experts have. Below are the facts:

1979 650 Special, stock carbs
Gasoline leaking out the left side airbox
Gasoline does NOT leak when the bike isn't running. Petcocks seem to be fine.
Vacuum style petcocks


Any opinions/advice/tips are welcomed! Thanks!

 

[TwoManyXS1Bs]

Hey Derek2k3,
There were some posts here discussing rubber float valve tips coming loose, possibly from non-gasoline chemicals. Try forum search: 'float valve', 'viton', 'alcohol'.

 

[Derek2k3]

Hey Derek2k3,
There were some posts here discussing rubber float valve tips coming loose, possibly from non-gasoline chemicals. Try forum search: 'float valve', 'viton', 'alcohol'.

Ah, thanks!

Based on my searches, I'm going to check:

Floats

• Are they "sticking"? Look for varnish/crud etc
• Are there any holes/cracks/perforations allowing gasoline to weigh them down?
• Are they set correctly/moving freely?

Float valves

• Are they clear of crud/debris?
• Is it sealing properly (looking for grooves etc)

I'm also checking every single o-ring/seal on the thing, make sure they're all ok. I'll check any float valve tips, but I'm not sure if mine are rubber or steel, comments in other threads lead me to believe these older style BS38's have steel tipped float valves? Either way, I'll know when I get 'em off the bike in a couple of hours.

Thanks again! I'll update here with my findings, that way anyone having a similar problem can see what process I go through to fix it.

 

[5twins]

Yes, you have steel tipped float needles. The viton tipped float needles only came in the BS34s. When you check the floats, make sure you measure twice, once from each side. Each float "bulb" needs to be at the same height and often they will be different due to the pivot bracket being "racked" or twisted. It's no big deal, you simply twist it back so both sides sit the same.

 

[Derek2k3]

Yes, you have steel tipped float needles. The viton tipped float needles only came in the BS34s. When you check the floats, make sure you measure twice, once from each side. Each float "bulb" needs to be at the same height and often they will be different due to the pivot bracket being "racked" or twisted. It's no big deal, you simply twist it back so both sides sit the same.

Ah, so even if one side was correct, the floats could be "whopperjawed" in there, causeing the spill. Thanks!

I got the bike to my shop, kind of an adventure. Could hardly get over 35-40mph, gasoline dripping onto my foot. Fun!

 

[Derek2k3]

Welp, got the carbs out and immediately found a problem

Yup, that would adversely affect the functionality of the floats. Sucker was full of gas, absolutely was a sinker.

 

[TwoManyXS1Bs]

Woah, I fell outta my chair when your pic scrolled up!

Finally, a carb problem that makes sense...

 

[jetmechmarty]

You will find new brass Mikuni floats at a good price here:

www.siriusconinc.com

Posted via Mobile

 

[gggGary]

A nice picture of the common "radial cracks" in the floats. At that point I would replace both floats. Too bad no one has seen fit to make a foam float for bs38's. Then again with a 30 year plus MTBF it's not likely you will have to do the job again.....

 

[Derek2k3]

You will find new brass Mikuni floats at a good price here:

www.siriusconinc.com

Posted via Mobile

Thanks! Would you get them through Sirius as opposed to MikesXS?

A nice picture of the common "radial cracks" in the floats. At that point I would replace both floats. Too bad no one has seen fit to make a foam float for bs38's. Then again with a 30 year plus MTBF it's not likely you will have to do the job again.....

Gary,

What causes these cracks? Is it just age?

Thanks for your comment about replacing the other one, I was thinking of being a cheapo and only replacing the one. However, every time I take a shortcut with this bike it haunts me. Slow learner

 

[5twins]

The brass floats from Mike's have been reported to spring leaks rather quickly. I wouldn't buy them (or their BS34 foam ones either for that matter, those fit poorly).

 

[Derek2k3]

Thanks 5, I ordered from Sirius.

Appreciate all the input, guys.

 

[gggGary]

I would guess the floats are stamped out of sheet brass, the edges get a stretched quite bit by the die. Added age, thermal cycling, vibration, cause them to crack.

 

[5twins]

Yours don't appear to be in the best of shape. It looks like they sat for some time covered with old gas varnish and residue which ate into the brass, weakening it. I'll bet that was a factor as well.

 

[buddy]

Mine leaked too. On the left side. Took off float bowel removed floats. One was full of gas. Drilled 1/8 hole in float to get gas out then soldered the leak and the drilled hole. Worked for me.

 

[Derek2k3]

Got the new floats in, set them to 24mm, bike is back to starting on the first kick

Thanks for all of the help! On that note, I bought 4 gaskets and only used 2. Anyone that really needs a couple of gaskets, I'll make you a great deal.

 

[5twins]

Spare float bowl gaskets are something I like to keep "on the shelf". Chances are that if you pull a float bowl and accidentally tear a gasket, it will happen on a Sunday when the shops are closed.