Float height effect

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Apr 7, 2008
After reading various posts I believe the normal float height on the standard concentric MK1 should be 2 mm below the float bowl edge.
It has also been stated that lower float level settings will give a leaner mixture and a higher level a richer mixture.

My question is how much effect the float level actually has?
Is the effect over the entire range or only at certain levels?

My bike has a very lean mixture on small trottle openings and requires choke until properly warmed up (10 miles or so) then it gets better but it is still on the limit and I might need to change my 3.5 cut away for a 3 but I was thinking that maybe a higher float level might do the trick?
Would a change from a 106 jet to 107 make any change at low trottle openings?

Any suggestion/comments would be appreciated.

Best regards,
Thanks guys!

I have a few spare parts for the Amals so I will prepare a pair of floats with 1 mm float level and see if that makes a difference or not.

Right now I have the air screws 1 turn out and last thing I did last night was to turn it further in (approx 1/16 turn) and it felt more responsive on the trottle but I did not get a chance to ride and try it.
What is the richest position you can use, 3/4 turn out or can you adjust it further in :?:

The guy who modified the carbs for me is using a 107 claiming the re-sleeved carb is running to lean on the 106. I believe this has no or very little effect on small trottle openings?

The carbs are resleeved so the trottles are not standard dimension but I will see if I can borrow a pair of trottles with a 3 cut away but I want to try other options first.

Cheers, Per
Adjust the air screws as required by your engine. I suggest using vacuum gauges and adjusting both idle speed and air screws so that both carbs are pulling equally and the idle is smoothest at the desired rpm.

I don't understand how a set of carbs can be removed from an engine, sleeved to reduce excessive clearance (read: air gap), and the result is a lean running with the same jetting? I would think if anything the sleeved carbs would run a bit richer as less air would be sucked in from around the slide. What am I missing?

I agree with Ron, the sleeving should make it run a little richer asumed nothing else is touched.
Be aware you do not ajust the float height on floats but you adjust the brass insert in the bowls, heat the bowl in hot water or use a heat gun.

I have to agree, the less air's leaking by the trottle should actually give a richer mixture so the 106 to 107 makes no sense if he didn't do something else to the engine. I have to ask him about it!

Reading somewhere (don't remember where) that the effective adjustment range of the air screw starts at 1 turn out , looks like it's wrong?
But I have also seen stated that the float hight should be 1-2 mm over the edge (not below) and that's probably not correct, is it?

When time permits I will do more testing and report back on the progress.

Float level does not affect mixture unless it is way low ,starving the engine or way high and flooding the engine.
Hi Per

You could have a look at the links on this homepage. http://www.nortons.dk/links/
There is some good links to pages explaining how the amals work + a dozen of other usefull links to Norton stuff.

Thanks for all comments provided :)

Tested the air screws and now running 3/4 turn out and yes, it's getting better :D

As time permits I will try further and also use my Carbtune for final adjustments. I plan to try the higher float level, seems to be a bit different opinions on the effect of that.

Best regards,
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