Fuel Height

[Steris]

Morning all.
I am having slow running problems, bike runs fine above about 3000 rpm, but wont tick over and has no power when pulling away. The plugs are all sooted up. When i set the float height to 22mm
the fuel over flows on all 4 carbs. Needles are on the third groove down. I have got the carbs off and stripped and ultrasonically cleaned them and all the jet etc.  I have set each carb up on the bench with a sight tube so i can see the fuel level. At 26 mm float height the fuel level is 10 mm below the float bowl lip, and when drained into a beaker there is 50 ml in the float chamber. I seem to remember reading that this is right, can anyone shed any more light on this for me please.. Its driving me mad 

Many thanks Andrew

[Nurse Julie]

Did you set the float heights correct Andrew. I'm sure you did but I'm just checking 😊
http://www.sohc.co.uk/index.php/topic,23233.0.html

[Steris]

Hello Julie

Yep, I have set them just like you describe, this time I've set them individually ie off the bracket. I'm wondering if the springs in the needles have become weak, hence the need to make the float height greater, from 22 to 25/26. This would allow the float to exert slightly more pressure and seal the fuel flow.  I have know read that the fuel should be 3-4mm from the top of the float bowl so i will adjust again tonight and see what i get.

Thanks for your reply

[Bryanj]

I have seen needle with "sticky" pins, i cleane them in acetone and it improved them

[K2-K6]

Clean / polish the taper seat of the inlet by using a small dowel sharpened like a pencil with something like t-cut to make sure it promotes a good seal. You can either spin it with you hands or in a drill slowly to improve any surface imperfections. 

It usually helps the valve shut off easily with just the minimum of pressure.

If the moving  valve tips aren't rubber (brass) you can also polish these the same. 

[Steris]

Hi oddjob

No they are the original's.  I bought 4 repair kits but the needles are slightly longer than the original's and with them in you can't get the fuel level  high enough. 

[Steris]

I've set one carb at 22mm and one at 26mm both with sight tubes attached, and there is only a slight difference in fuel level. I left them over night with a good head of fuel feeding them and the level was still the same this morning  so i will go back to the 22mm float height and fit them back to the bike, but I'm sure they will leak again once I've refitted them  . If the level is too high will this make the bike run rich on tick over (on the pilot jet)?

[bruxby-clive]

Hi Andrew

I had similar problems when I restored my KH, just couldn't get it to idle or run properly even with the carbs having been blasted in an aqua jet and then ultrasonically cleaned. After the 2nd or 3rd ultrasonic cleaning and out of desperation, I put them back into the cleaner again for an hour each turning them half way through at 75 degrees, I was amazed at how much muck came out but after this the bike would idle and pull cleanly. I would try cleaning them again. I came to the conclusion that some of the airways in the carb must have been blocked with old fuel. 

[K2-K6]

"If the level is too high will this make the bike run rich on tick over (on the pilot jet)?" Yes but it's not a drastic change and more of an influence than absolute.  Obviously it's ideal to be as close as possible to judge.

Picking up on what bruxby-clive noted,  the idle circuit is drawing mixture from the float bowls by vacuum drop in venturi. This is modulated by the air adjustment screw to change the mixture ratio, but if the air passage leading to the screw is impaired then the vacuum pulls "full" fuel through the pilot jet. So in effect it's easily too rich if they are not fully clean.

One way to give an indication is with it running,  then try each airscrew individually to see if that cylinder will range from rich (fully closed by turning inwards) to essentially too lean at about 3 full turns out.  If you can't hear the cylinder changing much then that's an indication of the air passage still being partially blocked. You're dealing with very small volumes in these carbs,  with any impairment making quite a % difference to the mixture.

You could end up with different settings on each airscrew and different from manual spec too.  If you give each cylinder what it needs then discuss if they look really wonky as to what may be affecting it.

[Steris]

I think I will give them all  another hour in the ultrasonic Bath then try again,  thanks for all your help so far, I will let you know how I get on over the weekend 🙂🙂

[Steris]

Well all 4 carbs have had 2 hours in the ultrasonic bath. I have checked and re checked all of the jets and ports and everything is clear. I have blasted acetone through the slow pilot ports and its shooting through great, out the little jet in front of the slide and out the jet port and air intake port. Rubbers all replaced and float height set to 22mm checked and rechecked. I have balanced the carbs and rechecked the timing and valve gaps, it know ticks over at 900 with the air bleed screws wound 3 turns out but has no guts below 3000 rpm it just dies if you don't rev the nuts of it which suggests its only running on the main jets. I am now at a loss. Might have to spend some money on a another set of carbs    Any advice would be greatly received

[K2-K6]

Turn the air screws to 1 1/4 out and try it as straight comparison with nothing else altered to see what it does.

[Steris]

Hi and thanks for the reply

I have had the air bleed screws set from 0 to 3 turns out and 3 turns out seems to be the best, it even runs with the air bleed screws completely removed

[K2-K6]

Have you verified all air "vent" passages into the float bowls? 

Try blowing into the overflow tubes to see if they are clear.

Something's odd, but must become apparent through inspection.

[K2-K6]

Ignition advance and retard operation verified as ok?