Carb floats low in bowls

I'm helping my brother getting his 81 Seca 550 running. I have gone through the carbs and cleaned all jets and reinstalled. The bike would not idle before which I figured was plugged slow jets. After clening those, now the bike runs at idle fine but after blipping the throttle the bike idles high until I turn the bike of and restart. I did see when the bowls were off that two of the floats sat higher. I adjusted those down (should have adjusted to right height to begin with!). My question is, if the floats are too low in the bowls, what will my symptoms be?

BTW: These aare Mikuni carbs if that makes a difference

Thanks in advance!

 

Uneven floats will cause all sorts of wonky issues.

The Mikuni floats are especially finicky, the tolerance on the spec is +/- 1mm. That's ONE MILLIMETER either way.

They need to be set using fuel and clear tubing, and need to be done as precisely as possible. This is critical to a good idle and crisp throttle response.

Do a good tight bench sync before returning the carbs to the bike;

then do your vacuum sync with the YICS blocked.

BUT THE VALVES GOTTA BE IN SPEC FIRST.

Follow the above advice and it will run fine. Skip or ignore any and you'll be at this for a while, honest.

 

Thanks bigfitz! I'm used to my XS650. I'm really sick of four carbs right now.
Four times the headachs! Lazy question, what is the height spec on the floats? Yeah I know there is a search function

 

Mikuni spec is 2mm, +/-1mm, "below from the carburetor mixing body edge." Quoted directly from the book.

What they mean is 2mm +/-1mm below the seam between the carb body and the float bowl.

(Measure to the meniscus of the fluid in the tube.)

There is a diagram in the PDF for setting float heights; the spec is different between Hitachis and Mikunis http://xjbikes.com/Forums/viewtopic/t=34781.html

Here's the secret to carbs: once done right, they don't need to be messed with very often at all. Once done right. If you take shortcuts or skip over things, like I said, you'll be fighting it for a while. Do it right, do it once and then it's done.

It starts with getting the carbs truly, religiously, dentally clean. Here's an exploded Mikuni for reference: http://xjbikes.com/Forums/viewtopic/t=31061.html

-Clean carbs, ensure they pass the "clunk" test.
-Replace hardened/disintegrating o-rings, clean float valve seats, etc.
-Set float levels using fuel and clear tubing.
-Bench sync. Pilot mixture screws at 2.75 turns out to start.
-VALVE CLEARANCES IN SPEC. If they aren't you won't get a good sync. Don't skip this because it seems difficult, it's not.
-Running vacuum sync with YICS blocked.
-Tweak mixtures as needed (ColorTune or by ear using the "idle drop" method.)
-If you made any major mixture adjustments, re-check vac sync.

Complete the above, IN ORDER, and it'll run fine.

 

Something I've had a question about....as the 5th picture in Fitz's 2nd link above (31061) shows, the float chamber is recessed slightly up in the carb body. Is the wet level measured from the bottom of the carb body lip or the seam where the carb body and the float chamber actually join?

 

The book says exactly: "below from the carburetor mixing body edge."

I translate that to mean "from the edge of the carb body."

 

Quoted from above....
"What they mean is 2mm +/-1mm below the seam between the carb body and the float bowl."

This is where I get confused, the actual seam is a mm or two above the carb body itself. Seems like a picky issue but the whole tolerance range is about the depth of the carb body lip.

 

The diagram in the factory book indicates that it's from the edge of the carb body; the amount that the float bowl "recesses" into the mixing chamber can vary due to gasket thickness or even how tight the screws are.

Measure from the edge of the carb body.

 

I know that there are folks here that do not agree with this method but I have used it on 3 different bikes now and it works just fine.....
Check this out.... http://www.xjbikes.com/Forums/viewtopic/t=31559.html

 

Thanks, that makes sense to me....besides the actual 'seam' is only accessible at the corners and it's not easy to get a measurement there.

I did measure from the carb body, nice to have verification.

 

Provided the actual volume of your surrogate float bowl is close enough to the real ones, it should work; but quite honestly, using the clear tube is almost as easy and allows you to perform the adjustment using fuel without making a smelly dangerous mess.

Since, if done right, it's a "set it and forget it" item, I'll stick to the book.