float height ?

[coletrain777]

Hey guys
I've got a question about setting the float height on a 1979 XS11F. Before I get tto the question I will update you to save questions later. Yes they have been triple cleaned (actually they have been cleaned thoroughly cleaned 7 times this month). They were spotless when I started except for a little sludge in the carb bowl. I have set the float height to 1.012 +/_.04 as the manual suggests. I have checked to make sure all the floats are at this height numerous times. The carbs were fine before I cleaned them, (I had so fuel leakage from the carb outlet so I cracked them open to check the needle/seat and set float height. I have distubed any setting but if I leave the carbs set to the manuals adjusted height they run horrible. If I lower the height they seem to run better. I understand that this means that they had a lean mixture before but what gives. Why isn't the manual suggested float height correct. th bike will only idle if I partially open the choke, then warm it adles at about 1350 rpms. Sorry for the long post, but I wanted to let everyone know what was going on. Thanks
Cole

[randy]

Cole,

If what you say is correct, it's disturbing because I just buttoned up my carbs and won't be installing them until some time in June. I also have a 79F and I set the float hieght to 25MM according to Clymers. IIRC, 25MM is the midpoint of the range suggested.

Are you measuring the hieght without the gasket, as specified? And, are you sure you got the pilot circuit completely cleaned out? There is a pilot passage from the pilot jet that goes to the idle mixture screw. The passage goes all the way through the carb body from the front to the back and it can be a b***h to get clean. At least I thought so. I'd be interested to hear what happens and how you solve your problem.

Randy

[Ken Talbot]

The float setting in the manual was probably ideal for these bikes when they were new, had zero miles on them, were running original stock exhaust, and were running gasoline as it was blended 25 years ago. Ditto for the pilot screw 'adjusted at the factory'. You will know if your particular setting is correct for your bike if it runs well, gets good mileage, and has ideal plug colour. It wasn't until I dropped the floats 2mm on Tsunami that I finally got it to match the 45 mpg (Imperial) that SWMBO's H has always achieved. That, plus running the needles one notch lean, plus clean carbs, plus a comprehensive tune-up, was all it took.

[pgg]

Hey Coletrain your low circuit is too lean (tell me something I don't know he mutters) if no response when cold and a high idle when warm. Might have more luck measuring in metric maybe? If everythings tweaked well - float height, pilot jets, mains, idle mix screws, idle adjuster; the old girl should fire up instant on full choke, run a bit fluffy for a couple of minutes on half choke, then settle at a low idle (below 1000) after that - with the choke off. It'll still be a bit non-responsive down low for a couple minutes more, then when warmed up, should run sweet as! - and still tick over below 1000 at idle.

[skids]

Ken, please tell me how to drop the needles in the newer carbs a notch (or equivalent). I suppose also that dropping the floats would mean raising the floats when making the adjustment in the upside down position on the bench, or do you mean literally with the manometer method?

Originally posted by Ken Talbot
The float setting in the manual was probably ideal for these bikes when they were new, had zero miles on them, were running original stock exhaust, and were running gasoline as it was blended 25 years ago. Ditto for the pilot screw 'adjusted at the factory'. You will know if your particular setting is correct for your bike if it runs well, gets good mileage, and has ideal plug colour. It wasn't until I dropped the floats 2mm on Tsunami that I finally got it to match the 45 mpg (Imperial) that SWMBO's H has always achieved. That, plus running the needles one notch lean, plus clean carbs, plus a comprehensive tune-up, was all it took.

[buffalo]

I just redid my carbs tonight, will install tomorrow. When I was adjusting the floats with the carbs upside down as per the manual, I noticed that the floats were compressing the spring in the needle valves part way. Somehow this doesn't seem right. I turned the carbs to about a 45 degree angle so the valves were closed but the springs not compressed and set the floats to the specified 1.012 setting. I then rotated the carbs back upside down and remeasured them, just out of curiosity. I got readings varying from .945 to .985. This doesn't seem right to me. I am guessing that when new the springs in the needle valves were stronger and could hold the floats up when inverted, and now they are older and weaker.
Since there is no fuel pump the fuel is under practicaly no pressure and when the floats rise far enough to shut the valves fuel flow will stop at that level. The springs only act as cushions to protect the floats, needles, and seats when going over bumps and such. Maybe one of the ex pro Yamaha mechanics in here could shed some light on this. I will let you know how mine works out tomorrow when I get my carbs back on.

[Ken Talbot]

Skids - the needles on Tsunami are the ones with the small circlips and 5 clip positions. IIRC, I worked on some of the other style needles by sliding the needle out of its plastic sleeve and filing the plastic down. This drops the needle in the jet, giving a leaner mixture. If you change your mind, you can insert some small washers to bring the needle back up again.

And yes, I dropped the floats in the bowls by raising them while the carbs were upside down on the bench. I tried the manometer method, but found that really didn't tell me anything very useful. It would certainly be impossible to get the floats all to the same level with any kind of precision without taking a huge amount of time. In my case, I knew I was way too rich, so I adjusted to a measurement that was lower (i.e. higher) than what they already were.

[pgg]

Buff the springs should be holding the valve closed when upsidedown with no variation between all 4 in float height.

[chevy45412001]

raising needles newer

My xj does not have adjustable needle. Bike shop said to use theese very small lock washers.(did i say VARY small) He even gave them to me.Made them flat with a pair of pliers.Removed tops of carbs took needles off the thingy installed washers reassembled. What a great fix.Picked up in mid range and low end a bit.Dont know if any of this makes sence or not. Thats howi had to go about moving needle height on my bike. hope it helps a lil.