Carb float height measurement

[redrocks]

I've spent a while cleaning my carbs (1990 exup) but i'm confused about the float height. The manual and other posts say 12-14mm upside down with the carbs level however mine all measure consistently 10 to 10.5mm to the top of the float. Unless I'm mistaken one side of each float seems to a bit taller - I'm measuring the slightly smaller side of the float. I'm very wary of bending the tang but looking closely at each float assembly, there's no way any adjustment will get the float height up to 12mm let alone 14. The tangs on each carb are flat and a tiny bend would very little difference. Am i missing something ?

Now, the manual (downloaded from the site) shows how to measure the fuel level externally using a plastic tube and ruler but...........it says to get the carbs vertical. How's that possible? Does the bike need to be jacked up?

Any advice much appreciated, Andy

[Stig]

This should help... the tang should just be touching the pin in the top of the needle not compressing it. The height is measured from the top of the highest float

http://www.exup1000.co.uk/tech_info_are ... ntoobs.htm

[roadrunner]

Stig's right in what he says about the float just touching the pin set into the needle. I would add that when I did mine the weight of the float compressed the spring situated under the pin and thus gave me an incorrect measurement. In my case the only remedy was to renew all the float needles (supplied in the overhaul kits) and then I was able to make the small adjustments necessary to obtain the correct float levels.
Hope this helps redrocks

[redrocks]

Thanks for the information - I didn't actually realise that there's a spring under the float needle pin so it does look like the weight of the float is compressing it and giving a false reading. I'm pretty sure all four carbs have the same "problem" (by the way the bike has 31K miles). Measuring the highest part of the float i'm getting about 11.5-12mm. Do you think its worthwhile replacing the needles?

[Stig]

if you tilt the carbs to the point where the tang touches the pin and then set the height it should be right. You can see on the end carb if the tilt angle is right

Whilst you're in there check the emulsion toobs for wear on the central hole

[nuggitt]

I made this little video a few years back. This should help you set the carbs correctly. Like stig says do all the float heights like this and you should be ok.

Press reply to watch it a few times because the first time it plays looks a bit jerky. A bit like me at my age.

http://youtu.be/r_tLykicBY4

[roadrunner]

Thanks for the information - I didn't actually realise that there's a spring under the float needle pin so it does look like the weight of the float is compressing it and giving a false reading. I'm pretty sure all four carbs have the same "problem" (by the way the bike has 31K miles). Measuring the highest part of the float i'm getting about 11.5-12mm. Do you think its worthwhile replacing the needles?

Just found this redrocks. It shows how the weight of the float can compress the spring under the pin, just as mine did. All I can say in my case was, that after renewing the needles, the float was positioned as shown in the other picture. The float could then be pushed down against the needle using finger pressure, which would compress the spring. When finger pressure was relieved the float popped back up to it's previous position. The old ones just wouldn't do that.


http://www.exup1000.co.uk/tech_info_are ... height.htm

[redrocks]

Thanks - generally my floats have a bit of spring in them but still compress under the weight of the float itself. i've tried the idea of tipping the carbs a bit so the tang just rests on the pin - this gives better results. Anyway after re-checking yesterday I took the bike out for a good ride at various speeds and it seemed OK. Before cleaning and adjusting, the low speed running was a bit rough and the idle speed was OK at times but then dropped at other times. I might well invest in some new float needles as pat of the full "repair" kit.

[DaddyA]

Hi all, just jumping on the float height band wagon. Is this the same technique for the YZF 750 with the same measurements?

Got a few carb issues, running dyno jet I believe so going to go back to standard. New rubbers, jets, needle/tubes (Stig) and probably air filter as running the original exhaust.

Cheers

[Purity Vendetta]

When I set float heights I use a little trick to ascertain the floats are exactly at the right hight. I attach a reasonably long tube to the fuel feed, the t piece in between the central two carbs. I put the other end in my mouth and blow gently into the pipe maintaining a steady gentle pressure. As you lift the individual float you can get the exact level the valve begins to open as air starts to flow. Then measure the float heights with the dinky credit card gauge or vernier calliper. Remember don't blow too hard, just a steady very gentle pressure is all that's necessary. Best to use a cleanish pipe for obvious reasons and try not to drool into the pipe

I've found it to be the most accurate way of finding out the exact float level at which the needle valve opens and closes regardless of the angle of the carb bodies.

Hope this is of some help.

[Stig]

Thats a great tip and of course VERY acurate due to pressure dropping at the exact point the needles opens

Thanks for that.....learn something new every day

[nuggitt]

I've got a spare set of carbs in the garage so I'm going to give that a go. Good tip.