I had to replace an '81 BS34 needle valve and seat that hung open on a ledge worn into it. I naively assumed the new would measure the same as the old, so I didn't check the float level. Fired it up and tons of black smoke out that side. Looked at the float and it was set to float a couple of mm too high. Changed it to 21 mm, on a gasket that's compressed to about half its original thickness. Still a small amount of black smoke. Tomorrow will give it an additional mm or two, to account for the thin gasket, which I think will eliminate the smoke. The jets in it are marked stock size. I had no idea you could richen that much with just the float.
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Why even bother with jets?
- Thread starter xjwmx
- Start date
Classic
rackin' up the miles
Sounds like the fuel is just overflowing into the venturi... not good.
It was shooting out of the air jet originally and that cylinder would not fire. Made a 150 mile trip with no problem the day before. The needle was worn and got trapped at an angle in the seat. No leaking now, just still rich from a high float a mm or so high I think. The point is I'm surprised it can be rich enough to smoke from just the float.
Before you run it again get a tube on the float bowl drain and check the actual fuel level. I am guessing it's something other than just float height.
Such as?
Sure ask that question. Not sure just a hunch I guess but I would check actual fuel height vs. just setting the float. This is foam floats? I have been setting 22 with no issues. Finished up a set of foam float BS34s today but had to untangle a wiring nest and do the oil filters thing before I can hang em and see how it runs.
LOL. That's not a bad idea. I will try to scrounge up a bit of clear hose; and then if my drain screw isn't frozen.... I'm visiting friends and am on my emergency tool bag. Considering the thinness of the gasket I think my true float height is 20-20 1/2. It's reading 21. Figured that should be good enough, but it's still smoking black, just barely detectably if you're looking for it. I'm very happy the smoke cleaned up with the first adjustment as much as it did.
The manual is clear as mud on this, the H supplement claims 27.3m +- .5mm I believe I have been using 22 on foam floats from a chart someone made up. (what I used today.) A clear battery overflow tube works fine as a fuel level tube.
The chart is the one on page 27 of the carb guide www.amckayltd.com/carbguide.pdf and even that has some confusing (to me) wording on the G and H float heights I always have to read it at least twice before I set the foams to 22mm
The chart is the one on page 27 of the carb guide www.amckayltd.com/carbguide.pdf and even that has some confusing (to me) wording on the G and H float heights I always have to read it at least twice before I set the foams to 22mm
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The flat "measuring area" on the foam floats is at an angle to the carb body so you can get different heights depending on just where you measure. I measure about the middle of the area.
I don't believe the H supplement refers to a height at all, just the tube technique. The 27.3 I believe pertains to the G, with brass floats. I was going by 5twins spec of 22 on the plastic floats, from the gasket to the top of the round part of the plastic float. I wish I had a calipers with me, to compare the new set with the old one. They look the same, just by eye.
http://www.xs650.com/forum/showthread.php?t=4302
http://www.xs650.com/forum/showthread.php?t=4302
If I have been doing it wrong I apologize to anyone involved. Here are excerpts from the G and H manual updates and the carb guide.
I will do a fuel height check on the set of plastic float BS34s I have on the bench along with some pics of my float height setting technique (so far). If we can get this clarified so much the better. We stand on the shoulders of giants, for all the hard work on the carb guide!
I will do a fuel height check on the set of plastic float BS34s I have on the bench along with some pics of my float height setting technique (so far). If we can get this clarified so much the better. We stand on the shoulders of giants, for all the hard work on the carb guide!
I'm wondering if the drawing in the H supplement that shows the level using the clear tube method is wrong. Measuring from where it says, the bowl would be completely full, and the level would be into the top of the carb a little bit. For a bs34 for a different bike I had the point to measure from was the bottom of the lower flange, where the screw heads are. I wonder what clymer or haynes say about the tube.
P.S. The H does say 27.3 after all, but the table looks like it's just carried over from the brass float G. I suspect that's wrong for the H, at least unless they're measuring to the very highest point on the plastic float. To add to the uselessness, the table calls it "fuel level" not float height...
Also, I'd like to know how the 22mm +-1mm was arrived at...
P.S. The H does say 27.3 after all, but the table looks like it's just carried over from the brass float G. I suspect that's wrong for the H, at least unless they're measuring to the very highest point on the plastic float. To add to the uselessness, the table calls it "fuel level" not float height...
Also, I'd like to know how the 22mm +-1mm was arrived at...
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Yeah I am airing this out to try to get to the bottom of "correct" settings of plastic floats. At or slightly above the bottom of the carb seems fairly normal for fuel height.
The H supplement does show a different carb number than the G supplement but I agree that something smells wrong there.
I refuse to even look at much less believe Clymer or Haynes manuals unless I have NO access to a factory book.
First off, you measure the floats from the gasket surface of the main body, not the gasket or any of the lips or flanges. If you go off the gasket, you should subtract about 1mm from your spec. For instance, if the spec is 22mm, set the floats at 21mm if measuring off the gasket. The gasket is raising your ruler about 1mm from where it should be.
The plastic floats should be measured to the top of the lower rounded "ball" part of the float, not the higher flat portion by the metal hinge bracket. Here's some set to about 21mm .....
The 21mm is at the high end of the spec but I bench tested these and they didn't leak. I also did the sight tube test which looked good. These haven't been run yet but if we encounter overflow or richness problems, we'll just re-set them.
When Yamaha introduced the plastic floats on the '81 H models, unfortunately they didn't update the float level specs in their H and G shop manual supplements. In fact, I don't know if they ever did. I found the spec in of all places, the '83 SK parts manual (look at the carb diagram) .....
http://www.biker.net/83_650sk_parts/650sk_parts main.html
All the specs in that chart I made up were taken from various official Yamaha shop manuals, parts manuals, and service data sheets. Nothing came from aftermarket books like Clymer and Haynes.
The plastic floats should be measured to the top of the lower rounded "ball" part of the float, not the higher flat portion by the metal hinge bracket. Here's some set to about 21mm .....
The 21mm is at the high end of the spec but I bench tested these and they didn't leak. I also did the sight tube test which looked good. These haven't been run yet but if we encounter overflow or richness problems, we'll just re-set them.
When Yamaha introduced the plastic floats on the '81 H models, unfortunately they didn't update the float level specs in their H and G shop manual supplements. In fact, I don't know if they ever did. I found the spec in of all places, the '83 SK parts manual (look at the carb diagram) .....
http://www.biker.net/83_650sk_parts/650sk_parts main.html
All the specs in that chart I made up were taken from various official Yamaha shop manuals, parts manuals, and service data sheets. Nothing came from aftermarket books like Clymer and Haynes.
Thanks, I see the spec down there in the corner. There's a multilingual 'B' manual that says the measurement in it is without the gasket. Only place I've noticed that said explicitly. Have you checked to see where the 22mm corresponds to on the carb body if you use the tube method?
"Have you checked to see where the 22mm corresponds to on the carb body if you use the tube method"
If yer talkin to me, I should get there this afternoon yet.
If yer talkin to me, I should get there this afternoon yet.
The only 34s I've checked with the tube test were the set above @ 21mm. They looked good, right around the seam line between the bowl and body, but this was a non-running bench test. Tested when idling may be a whole different ball game what with the engine shaking around and vibrating, lol. They may be puking gas all over, lol.
I never tested the 38s on my '78 with a tube. I need to make a drain plug w/ a nipple on it to do so. Their spec is 24mm +/- 1mm. I found them right at the 24mm setting but tried both extremes (23 and 25mm). The bike just seemed to run best using the 24mm setting. It wasn't leaking fuel or running lean at the 2 extremes, just didn't seem to run as nice overall. I find accurately setting the levels on the 38s to be easier. There's no main and pilot jet "tower" between the 2 float halves so you can place the rule on the far side and sight across the tops of both float "bulbs". This eliminates the "parallax" factor and you get a nice accurate measurement. Here's a set of '77 carbs set to their 25mm spec .....
I never tested the 38s on my '78 with a tube. I need to make a drain plug w/ a nipple on it to do so. Their spec is 24mm +/- 1mm. I found them right at the 24mm setting but tried both extremes (23 and 25mm). The bike just seemed to run best using the 24mm setting. It wasn't leaking fuel or running lean at the 2 extremes, just didn't seem to run as nice overall. I find accurately setting the levels on the 38s to be easier. There's no main and pilot jet "tower" between the 2 float halves so you can place the rule on the far side and sight across the tops of both float "bulbs". This eliminates the "parallax" factor and you get a nice accurate measurement. Here's a set of '77 carbs set to their 25mm spec .....
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Pics of tube tests after the floats were set at 22mm pretty much by the 5twins method.
I will reopen the carbs and confirm settings, RH carb looks a little low.
Couple of notes:
It is important that there are no air bubbles in the tubes the air will throw the gas level off. It helps to open the drain screw rather quickly.
If you move the tube once you have opened the drain you have to shut the drain screw, drain the gas out of the tube and start over. There is no place for excess gas to "flow back to" and the indicated level may be higher than the actual float setting.
HTH!
I will reopen the carbs and confirm settings, RH carb looks a little low.
Couple of notes:
It is important that there are no air bubbles in the tubes the air will throw the gas level off. It helps to open the drain screw rather quickly.
If you move the tube once you have opened the drain you have to shut the drain screw, drain the gas out of the tube and start over. There is no place for excess gas to "flow back to" and the indicated level may be higher than the actual float setting.
HTH!
