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I decided to check the fuel levels in the float chambers according to the recommended settings, I have them set up on the bench with a modified drain plug with tube. One bowl needs a higher setting. While it might seem obvious to some, I'm unsure which way to bend (slightly) the stainless tang and whether the needle valve is raised/lowered to achieve a higher fuel level.

UPDATE- I've just spotted an article which says the valve is tapped down into the bowl to increase the fuel level.

Last edited by semprini; 10/11/21 1:25 pm.

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UPDATE- I've just spotted an article which says the valve is tapped down into the bowl to increase the fuel level.

Hopefully it also says use HEAT and the CORRECT sized drift when attempting to move the seat. The seat can be damaged by ham fisting it. ( ask me how I know)

Gordon


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Gordon new seats are available!

The original float was plastic and the tab rigid. This meant you had to move the seat to change the fuel level. With the new float, with the stainless ab, you can modify it to change the fuel level.

If you lift the stainles tab the slighest amount it will raise the round edge of the float. If you actually feel the tab move as you bend it, it will cause it to be too high. You don't bend it as such, but what I like to refer to as "worrying" it a bit.

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Mr Healy it’s a bit confusing for someone like me. What’s probably happened is I’ve picked up some old info and confused it with new.

Some where along the line I read something you wrote about not bending the tabs.

Probably old news.

That said I’m probably setting the level incorrectly too because it all came from that same research.

Good thing is an old seat was easy to remove and replace the damaged one and now I keep the correct drifts in with my carb tools

So it wasn’t all bad.

Gordon.

Last edited by Gordon Gray; 10/11/21 6:21 pm.

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Gordon, John, The bowl was set up on a wooden jig on a metal table, then gently heated with the torch and tapped with the correct sized brass drift.

Now the general info I looked at was from Greg Marsh Enterprises site. He says his aticle is based on the AMAL instructions. I followed his advice in using water to set the level, but then it struck me that petrol is less than 70% specific gravity of water which might mean there is a buoyancy difference with the float leading to incorrect level when filled with petrol?

Last edited by semprini; 10/11/21 9:47 pm.

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older floats were all plastic .
these tabs were not meant to be bent , so the valve seat would need "drifting"
to adjust float level .
newer floats have bendable stainless tabs .
so float can be set by adding a slignt bend in the metal ( seat does not need drifting )

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Some where along the line I read something you wrote about not bending the tabs.

Yes, that's true! I still believe that. But for good reasons I will leave it at that.

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Originally Posted by John Healy
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Some where along the line I read something you wrote about not bending the tabs.

Yes, that's true! I still believe that. But for good reasons I will leave it at that.


Thank you Mr Healy for all you do/have done for this hobby.......we are truly blessed to have you around.

I'm guilty of sitting at the back of the class but I try to listen.

Grateful in NC, USA Gordon Gray

Last edited by Gordon Gray; 10/11/21 10:34 pm.

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Originally Posted by semprini
I decided to check the fuel levels in the float chambers according to the recommended settings, I have them set up on the bench with a modified drain plug with tube. One bowl needs a higher setting. While it might seem obvious to some, I'm unsure which way to bend (slightly) the stainless tang and whether the needle valve is raised/lowered to achieve a higher fuel level.

UPDATE- I've just spotted an article which says the valve is tapped down into the bowl to increase the fuel level.

HI Semprini -

The fuel height should be set at 6mm below the top edge of the float bowl. I measure the distance and score the center of the side of the bowl so I have a permanent mark. You can make a tool to check the fuel height by drilling a hole in a drain plug, glue in some brass tubing and attaching some aquarium hose and then turn on the fuel and see how high it goes up the center of the bowl to your mark.

I really like the stay up floats for this as you can bend the fingers of the metal that fit about the shutoff needle. Now nothing is perfect. The stay up floats tend to sit higher in the float bowl than the standard plastic floats. If they get too high the carb body can stop them rising before fuel shutoff happens. So if you have 6mm fuel height in the bowl to start with but the fuel keeps rising and starts to flood, then set it a bit less intill it wont flood. Closer to 6mm is better then way farther down.

I've tried driving the needle seat up and down for the white plastic floats. It would really be nice to have the proper tool. Even with heat the brass seat is quite brittle and will get tiny cracks so that the needle will seat but fuel will still leak slowly past.

Good luck.

Last edited by Semper Gumby; 10/16/21 8:22 pm.
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ok thanks semper, I've been working on it! I set the bowl up in a jig as you suggested and proceeded to alter tang/needle seat with a final setting of 5-6mm.

I found I had to remove the seat (a bit of heat and a 0.125/6 drill end) as it would not tap down. Reason for that was the bottom of the seat hole was not quite milled cleanly (perhaps because its a Wassell?), so I carefully scraped out the roughness and put a slightly more pronounced chamfer on the seat, so now it sits down about 16 thou below the top of casting. As you say, when the float is too high, it floods!

I've used white sprit for tests, similar S.G. I believe.

I now have them about right and weather allowing, will test later today.


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Cool. If you see the fuel slowly rising either the float is just too high, or the seat is cracked chipped from tapping. You need a strong magnifying glass to see if that is the case as I could not see it with my now old eyes.

FWIW - White spirits (I should know what this is but I don't - kerosene?) will have a different density than the pump fuel you are using. Apples and oranges I'm afraid. Sooo......

Last edited by Semper Gumby; 10/17/21 7:52 pm.
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White spirit is mineral turpentine.

I'll leave the fuel tap on, this should check for any leakage.

The SG of petrol is given as 0.7-0.74, white spirit as 0.78, so not far away. Kerosine is about 0.8.

I have misfire on the engine at the moment, its nothing to do with the carb work as it was developing before that, so I have to rectify it before I can run the bike properly.


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Heres my take on float bowl fuel levels.
So long as the bowls are not overflowing leave well alone. Fiddling with bowl level falls into the category of " senseless waste of human effort"

There is more chance of damaging the float bowl / float than there is of making any appreciable difference.

In service the float level is continuously varying due to demand and vibration, its not a millpond in there, its barely controlled chaos.

Most BSA twins have an intake balance pipe, this is to iron out small irregularities with induction bias, it works.

When i run out of fuel the bike runs fine until it stops, during this running fine period the bowl level is continuously falling.


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Originally Posted by gavin eisler
Heres my take on float bowl fuel levels.
So long as the bowls are not overflowing leave well alone. Fiddling with bowl level falls into the category of " senseless waste of human effort"

There is more chance of damaging the float bowl / float than there is of making any appreciable difference.

In service the float level is continuously varying due to demand and vibration, its not a millpond in there, its barely controlled chaos.

Most BSA twins have an intake balance pipe, this is to iron out small irregularities with induction bias, it works.

When i run out of fuel the bike runs fine until it stops, during this running fine period the bowl level is continuously falling.
#

+1, I have found little to be gained by adjusting the floats on the new AMAL prems (don't know about wassel carbs). Ensuring that the float level on twin carb models is matched would give more benefit than changing the height from the manufacturers predetermined setting.

You could be more anal and fit a matchbox remote float and remove the internal floats. you could then adjust the float level in the carb bowl much more simply by raising or lowering the matchbox float bowl.

Just a thought.

Last edited by Allan G; 10/18/21 6:26 pm. Reason: “Is matched” was added

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Gentlemen - I respectfully disagree.

I argued with my 1969 Firebird for a couple of years until I set the proper fuel height. It was like night and day when done. After setting the fuel height on the Rocket 3 three carbs, Richard Watley told me that it was the best idling triple he had ever heard.

But there is truth here. You cannot hamhandely go changing the fuel heights without being extremely careful. Stayup floats make the process much easier. But even with stay up floats there can be interference with the carb body above. Tapping the shutoff needle seats up and down for the white plastic floats must be done with heat and great care for the brass seat is brittle and easily damaged. And what is worse you can't see the damage with the nakked eye.

All carbs are designed to work at a certain fuel height in the bowl. It behooves you to know what that level is. Just ask Wade about his Goldstar out in Peteluma all those years ago.

FWIW - I check the fuel height on every carb I get just like I check the gap on new plugs I'm about to install.

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I daresay there are occasions when the float level needs adjusted in a Mk 1 conc. perhaps after another DPO has fiddled with it.
Maybe its an American thing to fiddle with fuel levels, perhaps previous experience with japanese multis encourages this , I know these are more critical, and I have past history of helping out others , particularly kawasaki triple owners, with float level issues. maybe I have been lucky with concs.

Goldstars are a different kettle of fish, the steep downdraft angle makes for a pernickety set up.

Last edited by gavin eisler; 10/18/21 4:08 pm.

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Originally Posted by gavin eisler
When i run out of fuel the bike runs fine until it stops, during this running fine period the bowl level is continuously falling.

I've often wondered about that. I've run out of fuel plenty of times, and while I'm doing it, the fuel level in the bowl isn't just "low" by a millimeter .... it's low by 10 or 20 millimeters, depending on what kind of carb it is. And while it's happening, the bike doesn't seem to run one bit differently than it does when the float bowl is full. It's obviously not cut off until the fuel level gets below the jet, because when I put gas in the tank, I have to wait quite a bit for the bowl to fill back up ... ?

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Awhile back there was a link to a video a fellow made about the fundamentals of how a carb works. One of the things that sticks out in my mind reading this thread was what was happening in the bowl with the engine running. He made the bowl out of a see through material. All I can say is it was very interesting watching the fuel in the bowl.

All that said. I adjust fuel height by moving the seat. Only damaged one but that was all on me and was an easy fix ( as long as you have good spares).

Does it NEED to be done? I can’t answer that question but the people I listen to say yes.

Gordon

Last edited by Gordon Gray; 10/18/21 6:39 pm.

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When I first checked the levels with the plastic tube, they were high near the top of the bowl, thats why I decided to proceed even though the engine was running ok, except a bit rich. It is a lengthy job though and care and patience is required, but I do have a good range of small engineering equipment such as end mills, measuring tools, drills, punches and all the rest.

Due to the pivot height being fixed, it's a trade-off between the tangs and the seat height.

The mis-firing issue I was having appears to have been a blocked pilot jet, that waxy stuff presumably from the fuel, although I do use 4 star.


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Moving the seat the tiniest of bits will have big changes. You will probably find your self going back and forth till you get it close to right. Resist the urge to not reheat the bowl between taps.

I strongly suggest contacting these guys for the right tool. https://surreycycles.com/contact-us/

Your neck of the woods and always been really helpful. Drill bits tend to be hard on the brass. Perhaps they have something softer.

Last edited by Semper Gumby; 10/18/21 7:24 pm.
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You're right on all counts, although, when bowl is warm/hot, the seat fell out with a gentle tap.

Thanks for the info on Surry cycles.


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Originally Posted by Semper Gumby
Just ask Wade about his Goldstar out in Peteluma all those years ago.

I remember that, it was me who got it started at the rally. I think Wade had dropped the bike or something?? I can’t remember exactly what lead up to it prior to the rally but the engine was definitely flooded. Took a lot of WOT, good use of the decompressor to help get that flywheel spinning and one hell of a lot of kicking. But it did fire up eventually.

I’ve adjusted the float seats on the older plastic float carbs and it did help with leaning the mixture off a little (lowered the float) certainly at idle. Though I’ve yet to find the need to with the stay up float. I think these are probably set more accurately at the factory now than they were 15 ish years ago by Burlen.
Not saying they don’t need to be adjusted, but I’d leave it as a last resort.

Just my 2c


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Well That is interesting. Paging Wade!

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I went through this a couple of times with the VM Mikunis. The first time I was setting height to the wrong reference point. I got it right, but it didn't change much after I re-jetted.
As for the MkI AMAL, I always checked and set them according to the service bulletin. However, my new Premiers came with the floats set even with the top of the bowls, so I left them there and they work well. Could be that the newer floats and needles cut off fuel flow better? Could also be that the original bulletin assumes the use of the stock nylon float needles, which require more pressure to shut of fuel flow?
Perhaps someone could compare the actual fuel level between an old and new carb.


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