Amal Premier Float Test with Fuel on Jig--Way High!

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Tinkerbell

Tinkerbell

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Hi Everybody,
This is a continuation of my AMAL COLD and SOOTY thread. I built a test jig to hold a bowl level and retain the float pivot bar whilst filling it with fuel from a similar hydrostatic head as it would be filled from a gas tank. I took an old Amal bowl with the brown plastic float which mechanically measured reasonably close to .080" to .100" below the lip. On the test jig, filling it with fuel, the actual fuel fill was about .220" below the lip. So far so good... I next took the bowl from my COLD and SOOTY right hand Premiere. It is fitted with the aluminum needle and black Stay-Up float. It mechanically measured in the realm of .080" below the lip . On the fuel jig, fuel filled to almost exactly the same level --or .080" below the lip. There was almost no difference. This is certainly above the Amal spec that the fuel fill should be .210" +/- .040" below the lip. Maybe this is related to my cold and sooty troubles.
Thank you,
Kara
Additional test on other bowl with Stay-Up float and aluminum needle: static mechanical level .080" below lip--with fuel on jig the fuel comes up to almost the same height--perhaps .020" lower , but still really high. Now--I tried bending the stainless tangs on the float to lower the fuel level and I got it down, but the geometry seems off and there is almost no allowable movement in the needle. As fuel comes in the needle is tapping like its close to shutting off. It did shut off at an OK level, but there is very little range in either the float or the needle and this does not inspire confidence. The old style float has a generous range of movement and yet rises to the correct level. And the needle does not hammer until near shutoff. I am coming to the conclusion that bending the tangs on the Stay-Up does not really work well and that Amal changed the buoyancy of the new floats and did not do anything to compensate for the change in geometry that this creates.
 
Last edited:
Tinkerbell said:
Hi Everybody,
This is a continuation of my AMAL COLD and SOOTY thread. I built a test jig to hold a bowl level and retain the float pivot bar whilst filling it with fuel from a similar hydrostatic head as it would be filled from a gas tank. I was writing about high fuel levels, but there was a glitch in my methodology so if you read this post in its initial form , I apologize for jumped conclusions. I am still working on the rich and sooty issue with one of the Premieres.
Thank You!
Kara
.
Click to expand...
 
Some people make a lot out of the float height. IMO, It's not that critical. There's a good range in float height adjustment that will work fine.

... if your engine is idling, the fuel height in the bowl effects the delivery of fuel through the idle circuit at low RPMs/low vacuum pressure. WTBS, If you can adjust the idle air screw position to compensate for a slightly lower fuel height, then for the most part things are equal.

The worst mistake is too high of a fuel height which can mean leakage out the bleeder port, which will have you taking the bowls off again micro-adjusting the float height again. There's no reason to get your fuel height as high as is possible. The idle air screw position is there to compensate for your the variation in fuel height in your bowl... so set it low enough so you know the float needle will seat solidly in the jet.

The other thing that is commonly said is that if the fuel level is too low you will run out of fuel faster than the float jet can replenish it... Somehow, I can't see that happening in a normal commando engine if the fuel level is only 1/8th" below the highest possible setting. Sure, dragsters burn 5 gallons in a quarter mile, but something tells me the flow rate of the float jet in a commando is greater than the consumption rate of the carb at WOT... you only need to have enough fuel in the bowl to overcome the lag in flow of fuel as the float begins to fall, then it catches up pretty quickly I suppose.

Some people here spend a lot of time measuring float height. I did mine by eye, then adjusted the idle air screws to compensate for the fuel level... The big deal with amals and their clones (premiers) is seeing the big picture of how the chosen components interact with the other components and knowing how to diagnose which elements are at fault when there's a problem by the RPM range in which those problems occur.
 
Tinkerbell said:
I am coming to the conclusion that bending the tangs on the Stay-Up does not really work well
Click to expand...

Your conclusion jibes with what I have heard and read. The correct way to set float height is to move the float needle seat up or down. You do this by heat via a heat gun, at some point the seat will respond to a drift. Given the geometry a small movement of the seat will produce a much larger movement of measuring point on the float.


o0norton0o said:
Some people here spend a lot of time measuring float height. I did mine by eye, then adjusted the idle air screws to compensate for the fuel level..
Click to expand...

I don't disagree, but your eye and judgement may be more learned than others, including mine. It is not easy to move the seat, but getting it to spec may allow more judgement to be spent riding safely, just saying.

Best.
 
RoadScholar said:
I don't disagree, but your eye and judgement may be more learned than others, including mine. It is not easy to move the seat, but getting it to spec may allow more judgement to be spent riding safely, just saying.

Best.
Click to expand...

yeah I agree, drifting that seat up or down is a pain in the ass. I think those new "bendable" tangs on the new "stay up" floats spare us all from the old method of moving the seat up or down to change the float height.

My contention is that all you have to be is close in adjusting the float height and then the air idle screw compensates for the A/F ratio of the idle circuit based on the fixed proportions of the idle circuit ports and the height of the fuel in the port leading to the idle circuit mixing chamber.... Trying to get the fuel level as high as possible is tedious, problematic, and unnecessary when the idle air screw compensates for fuel height if you get the height "close enough".

I don't see how riding safety is effected by knowing how to adjust the idle air screw to obtain a good A/F ratio at idle. That one you might have to explain...

Best, back at ya!
 
First, I have no problem with the old white (now yellow) floats or brass needles. In fact, I replace the premier stuff with the old stuff and move the needle seat up or down as needed. I am willing to trade 6 brand new stay up floats for the old ones. As for the needles I want the extra weight of brass to shut off the flow. I made up a small drift for the needle seat and use a small C-clamp to shove it up or down. As for fuel level I use the small plastic tube from the drain plug and have the fuel level at the bottom of the float bowl flange and try to make both as close to each other as possible. Check several times.
Andover Norton makes a great tool for checking fuel level height. Buy two, one for each carb. After matching both levels then connect one tube to both outlets. Also, if it takes longer than the count of 5 to make the tickler flood the carbs that can be solved. I cut a very short piece of 1/16" rod, tapered one end and shoved it into the tickler roll pin using the same C-clamp. Make sure it ends up above the float bowl.
 
Andover Norton makes a great tool for checking fuel level height. Buy two, one for each carb. After matching both levels then connect one tube to both outlets.

Would this not cause flooding if the bike was leaned over, say left on the side stand? Fuel flowing from the high bowl flooding the low bowl then into the cylinder?

Dave
 
I agree that the OEM plastic floats/brass float needle valve gives me a warmer feeling than the stay-up floats/AL valves. That being said, I haven't had any trouble with the Premier floats or valves...yet. But my experience with automotive carbs in the past means I expect the foam floats to eventually quit "floating" and that float level will slowly drop/fuel level rise over time.

FWIW, the foam floats also do not have consistent formulation since they now recommend that they be checked "wet" with a tube to measure fuel level as opposed to the much simpler method of measuring float drop. The fact that they can't state a "height" spec indicates that the fuel level can vary too much from float to float for a spec height to produce the same fuel level.
 
Interesting Mike. I’m also coming more and more to the conclusion that the stay up floats might present more problems than they solve.

If they are inconsistent and not 100% impervious to fuel that makes them rather troublesome IMHO. Personally I don’t think I’ve ever had a ‘normal’ float give me any trouble. But I think they would be very easy to identify if they were.
 
The stay-up floats are more bouyant, so float higher on the top of the surface of the fuel.

I think the only way to truly test fuel height is with the bowl off the bike, and using a piece of perspex over the bowl to replicate the body of the carb.
With the top of the float hitting the carb body it may be in some cases that the float needle is still not seated properly stopping fuel flow as desired.

It's a very delicate area to set up - remember it was only a couple of years ago when they switched from brass float needles to aluminium ones, because they were finding that the weight of the brass ones shut off the fuel flow too early, resulting in the fuel level being too low in the bowl!
 
gtiller said:
It's a very delicate area to set up - remember it was only a couple of years ago when they switched from brass float needles to aluminium ones, because they were finding that the weight of the brass ones shut off the fuel flow too early, resulting in the fuel level being too low in the bowl!
Click to expand...

Yet the plastic floats/brass needles were used for 50+ years with no such problems. ;) Timeframe-wise it seems that the needle valve material became an "issue" when they went to the foam floats. :rolleyes:
 
MexicoMike said:
Yet the plastic floats/brass needles were used for 50+ years with no such problems. ;) Timeframe-wise it seems that the needle valve material became an "issue" when they went to the foam floats. :rolleyes:
Click to expand...
Have to admit 'til I came here 'float height' had never crossed my radar in over thirty years of running Amals!
Interestingly the NOC Commando service notes don't broach the subject in three pages of carburettor trouble shooting..
INOA Tech Digest gives it three lines.... recommending any adjustments to be made by heating the float bowl and moving the seat..
 
EstuaryBoy said:
Have to admit 'til I came here 'float height' had never crossed my radar in over thirty years of running Amals!
Interestingly the NOC Commando service notes don't broach the subject in three pages of carburettor trouble shooting..
INOA Tech Digest gives it three lines.... recommending any adjustments to be made by heating the float bowl and moving the seat..
Click to expand...
I remember trying that on a mk1 fitted to a tiger cub.... after repeated attempt in getting the brass sleeve into the correct position I gave up, bending the tangs on the float is without doubt the easiest way to go
 
I use wood dowels that fit the top of the float needle seat and the bottom.
Then place in a bench vise to move the seat in the desired direction. So much more 'feel' through the vise when the seat moves a tiny bit.
The heat and hammer method is frustrating because the seat can be over-adjusted then needs to be knocked the other way.
 
Bob Z. said:
I use wood dowels that fit the top of the float needle seat and the bottom.
Then place in a bench vise to move the seat in the desired direction. So much more 'feel' through the vise when the seat moves a tiny bit.
The heat and hammer method is frustrating because the seat can be over-adjusted then needs to be knocked the other way.
Click to expand...
Yep... and then the other way again just for good measure :D
 
olympus said:
I remember trying that on a mk1 fitted to a tiger cub.... after repeated attempt in getting the brass sleeve into the correct position I gave up, bending the tangs on the float is without doubt the easiest way to go
Click to expand...
Was this with the old type float?
If so how did you get the plastic to stay in place?
Cheers
 
baz said:
Was this with the old type float?
If so how did you get the plastic to stay in place?
Cheers
Click to expand...
It was indeed the plastic float that's why the brass sleeve needed to be adjusted
This was a number of years ago before the stay up floats with bendable (sorry adjustable) tangs were available.... I had an old float chamber that I usd as a replacement in the end
 
YEP, you can't "adjust" the tabs on a plastic float so if adjustment was needed you had to move the sleeve BUT, if required, it was a one-time adjustment. You never had to do it again since plastic (or brass) floats don't slowly lose their buoyancy and require re-adjustment. ;)
 
I think the main problem with the stay up float is that the made the metal piece from 0.7mm stainless. That and the inherited design doesn't make it easy to bend just the tangs. Thinner Brass would have been sufficient and much easier to adjust. They are without doubt the hardest carbs I've ever set the fuel height on.

You can see my rig here..

www.accessnorton.com

Premier Carb help please

Having fitted to a 1973 850 and followed your advice on 19 pilot jets the bike is now running and so far covered 300 miles. Plug colour is light coffee colour both sides. It starts and ticks over comfortably. But on the road between the 3rd and 4th throttle position it is IMO not pulling very...
www.accessnorton.com www.accessnorton.com

Cheers,

cliffa.
 
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