Float Height

[Bob Falter]

What is the float height supposed to be for my 79 Special? My manual gives me the fuel level and I may check that once I get the carbs together but I would like to have a starting point. Did a search and found a lot of info but no list of float heights for different models. Found a setting of 29 mm but not sure that is for the 79 Special.

Thanks for any help that you can give.

[Snow]

I am not absolutely sure, but I *believe* the 79 standard and 79 special might have the same float height, and the 79 Standard's height is 25.7 (what an odd number) mm, unless Haynes is lying to me.

[MartyA]

Yup, that's what Clymers says, 25.7 +/- 1.0mm, or 1.012 +/- .04 inches for you non-metric folks. Measure from the bottom of the float to the float bowl gasket surface.

[RiskyBusiness]

Originally posted by MartyA
Yup, that's what Clymers says, 25.7 +/- 1.0mm, or 1.012 +/- .04 inches for you non-metric folks. Measure from the bottom of the float to the float bowl gasket surface.

This brings up an interesting point. Measuring floats seems like really tricky business. There is a lot of range of motion on these floats after the valve has seated or come unseated, depending on the direction of movement. If you visualize the float on the bike with fuel coming in there is a range of active motion. At the top of this range the valve stops fuel from flowing and at the bottom of this range it starts letting fuel in. The float is physically able to move higher than it actually does in normal motion and it is also capable of moving lower than it typically does in normal operation. The crux of the issue is what position do we measure from? When balancing my floats I eyeballed it by holding the carbs in the position they are on the bike but with the bowls off. I then pushed a float up until the valve seated. I would then balance the float on the next carb to match the same height. This is tricky because neither float is fully up or fully down. Is this the point where we are supposed to measure from? Or are we supposed to flip the carbs upside down and let them bottom out (beyond fully closed) and measure from there?

After I eyeballed my floats, I measured using a tube and I was almost exactly right on. One small adjustment had to be made.

And speaking of balancing using tubes, do you all balance using water or gas? In the tech tip it looks like water (too clear to be gas). I thought about this but was afraid to use water as, I believe, water is more dense than gas so my floats would float higher in water than in fuel. I made a helluva fuel mess doing it with fuel, however.

-J

[beechfront]

i was asking myself that same question this weekend. The first time I measured, I would lift the floats up (away from the carb body) and gently let them down until they came to rest and measured there. Then I pushed the floats down (toward the body) and let the spring push them back up until they stopped. There was about a 1.2 mm difference between these measurements on each float. Not sure which method is correct - but I ultimately ended up using the latter.

[Snow]

What I've ended up doing was putting the bank of carbs on its side (careful if you put it on the choke lever side) with a slight tilt upside-down so that there is only minimal gravity being excerted on the float valves - not sure if that is a good way or a bad way to do it, but that's what I've been doing lately.

[MartyA]

If necessary (and legal?) I can scan the Clymer's drawing and post it here. Comments?

Also, note that for the 1980 model, Clymers says "The float adjustment procedure is the same as on previous models but the correct height is 0.906 +/-0.020" (23.0 +/- 0.5mm). "

I think they were trying to tighten up the emmissions. This model also had different inside and outside jets.

It also says you can adjust the float bowl level from the outside using clear vinyl tubing. More if anyone is interested.

[RiskyBusiness]

If you want to scan it and put it in a PDF, I can post it on my work website and then post the link. We will just assume it is part of the "fair use" clause in the copyright laws.

Email it to me if you don't mind doing the scanning: James_agrisk @ hotmail.com (remove the spaces, of course)

-J

[Bob Falter]

Thanks for all the info. Being impatient, I decided to set them at .95” (24.13 mm) because that was about the average of what they were when I started. Must be close because after syncing and playing with the idle mixture it runs great. I used a caliper locked at .95” and set each float so that it would spring down and come back up to the .95 with the carbs turned upside down. I did get some difference between the left and right side of the float. I had planned on checking the level with a clear plastic tube but didn’t because I couldn’t find a fitting that would replace the drain plug and connect to a tube. Was going to make one but, like I said, I am impatient. I, too, was wondering whether to use water or gas. Water is safer, but it is heavier than gas.

Next question. Does anybody adjust the idle screws or do you just leave them back out about 1-1/2 turns? I turned the idle speed down to about 700 rpm and tried to adjust each for best idle but it didn’t seem to work all that well.

Thanks again,

[RiskyBusiness]

I opened up to 2 turns to richen the mix at idle. I was too lean down low and this helped. This was with k&l rebuild kits which have a different length idle screw, so your results may vary.

-j

[beechfront]

Risky - this will be a tough question to answer - but how different were your idle screws? out of the four kits i ordered, three of the screws were much, much different and one of them looked similar compared to what came out of my carbs - although you could still see a difference visually.

I never thought to look at them, but when I was turning the new ones in I noticed that when turning in the screws they all turned in fine except for one which I had to push down to compress the spring past the threads before it would catch.

just curious - i'm trying to figure out if i got one wrong screw or three. from the looks of them i would guess i got three bad ones.

[RiskyBusiness]

Originally posted by beechfront
Risky - this will be a tough question to answer - but how different were your idle screws? out of the four kits i ordered, three of the screws were much, much different and one of them looked similar compared to what came out of my carbs - although you could still see a difference visually.

I never thought to look at them, but when I was turning the new ones in I noticed that when turning in the screws they all turned in fine except for one which I had to push down to compress the spring past the threads before it would catch.

Well here are my long winded and too verbose ramblings. I am learning like everyone else, but in typical male fashion I have strong opinions after only a little experience. *grin* (My girlfriend says that strong opinions with little experience is a trait brought on by the presence of testicles) Hmm.. reminds me of a joke.

I can't help but wonder if you possibly got some incorrect rebuild kits. This could explain why your float valves don't seal properly and you are having some other issues.

The new idle mix screws I got were about 1/32 or 1/64" different in length than the original. But if they are shaped exactly the same backing either length screw out 1 1/2 turns would produce the same mix. I mentioned the different screw just to point out that possibly the shape could be a little different (shorter needle on the end maybe?) and make the mix different than stock.

If the parts are different among four rebuild kits, by all means don’t use them until you get a matching set. If you rebuild carbs with mismatched parts you are guaranteed to have issues keeping the carbs balanced and smooth. If I were you I would not even think about other trouble shooting until I did the following process:

-rebuild all four carbs with matching rebuild kits

-balance the floats and ensure that each float valve is shutting off. To determine if the valves are shutting off blow into the fuel line with the bowls off and manually move the floats and you will feel them open and close. Also when using the tube type balancing method with the carbs off the bike you will be able to see exactly which carb is leaking. Look for the carb with fuel running out the throat.

-Bench sync the carbs using the “bread tie wire” method

-Make sure the idle screws are all adjusted out the same amount. Error on the side of slightly rich and lean it up if your bike darkens plugs at idle.

You can chase a lot of carb problems and joust a lot of windmills, but until you are sure you have matching carbs that are balanced your chances of success are very limited.

With respect to rejetting, remember what Blaine Hoopes says in his FAQ: “Also, if you start rejetting to solve a problem that is actually caused by something gummed up or leaking (or even an ignition or cam timing problem) you have thrown in a whole new set of variables that make it really hard to find the real problem. I say leave the jetting stock, get the bike running correctly and adjust the floats to get the spark plug color right.”

I am probably going to change jets because I have my floats as high as I am comfortable with and it is still a little lean. But prior to screwing with the jets I spent a LOT of time getting the bike running balanced and even. Now I can dink with the jets and not be afraid of masking some other issue.

[beechfront]

way ahead of you on that... I've put everything back to stock. I have new mikuni pilots (stock, 42.5) new main jets that came with the kit (stamped 137), and new float valve/needle. Everything is running perfectly aside from a slight delay coming off of idle which I believe is nothing out of the ordinary. I also thought I may have the wrong kit - but I don't believe so as the gasket is correct and the kit is marked for an xs1100. I think somebody was just in a hurry when putting them together.

From what I can tell, carbs 1 & 4 are the only ones leaking.

Hopefully the fine folks at dennis kirk will make things right.

[Bob Falter]

Rode the XS11 to work today. It was a nice day and it was 51 miles to work. Normally it is only 20 miles. Funny how warm weather stretches that distance. Got home a couple of hours ago and left the XS setting in the driveway with the gas on. No leaks so far.

I went one step further then the blow test when I put my carbs back together. I did the blow test in the garage but when the weather got warm I took the carbs out to the drive way and hooked them to a plastic bottle filled with gas. Also hooked a cheap vacuum/pressure (bought it many years ago) gauge into the line. Filled the carbs with gas (tipped the carbs toward the air inlet end until gas ran out to make sure all were getting gas). The plastic bottle had two opening (like gas stabilizer) so I could vent the bottle to air while keeping gas to the carbs. Holding it above the carbs about as high as I thought a full gas tank would be I got a pressure reading of about ½ pound (just off zero). By closing the air vent cap and squeezing the bottle I could get the pressure reading to go up. I held it at 2.5 –3.0 psi for a few minutes, several times, while looking for leaks from the carbs. I had put a new needle and set in the #1 carb which was the one that was leaking when I got the bike. Left the old ones in the other carbs. Never had any leaks. Now if I go back out to the driveway and find a big puddle of gas all of that will have been a was of time, but I’m hope’n.

[RiskyBusiness]

Marty was nice enough to scan the float sectons from his aftermarket manual. I have converted these to PDFs and you can get them here and here.