Amal Floats and needles

I’ve been having a bit of trouble with my G15-

It had been fouling its plugs (particularly the left one) when run slow, as in traffic and stop and go. If held to a happy 3-4K and run like I was escaping a tornado it ran terrifically. I concluded the float levels were too high and installed a new set of stay-up floats and viton tipped brass needles.

Now the bike would run out of fuel unless both taps were open, and it seemed the heavier needle valves were not opening as they should without as much head pressure as the tank could provide.

As an experiment and because the proper aluminum needles are weeks away, I skeletonized the brass valves to reduce their weight- stock plastic units are 4g, the full brass are 1.7g, and the hogged out ones pictured are .7g.



The lighter needles worked better but unless caning the bike it still wants both taps open- I presume when run hard the increase in vibration is helping to jiggle the needles free.

Have any of you encountered a similar problem? What was your solution?

Well, I may have solved it- flow through the peacocks was robust but flow past the sintered bronze inline filters was about half.

So- filters are removed and another test is pending.

I should have known better as this isn’t the first time I have had fuel starvation from restricted (but by no means blocked) fuel filters. I chased a set on a BMW R100RT for a lot longer than I should have- in that case the bike would stumble at a constant 80 if the tank was below half, but ran normally otherwise. It seems so obvious in hindsight…..

In your first post you said the bike sent OK at higher RPM which wouldn't really point toward fuel delivery issues. But you never can tell.

I have had a few battles with stayup floats on two bikes now. Getting the fuel height right can be a hit and miss affair. You do need those aluminium needles although your machined out brass ones look like they should work. I found you need to be painstaking checking for gasket interference, fuel height and cleaning out the carb internal passages.

To be frank I havnt found a foolproof method yet. I just keep cleaning and adjusting and eventually things come right. I set by the book and it still takes a few goes. Rather frustrating.

I think that the low flow of the fuel was contributing to the needle remaining seated- but that’s just a guess. Once the valve opened there was sufficient flow to fill the bowl, so at higher loads (and greater vibration so perhaps the needles were “bounced” open) there was plenty of fuel to keep the motor running.

Still, that’s all just speculation.

What is the orifice size of the needle seats ......??
Are you running the chopped Monoblocs....??

See https://www.accessnorton.com/NortonCommando/flow-measurements-on-ewarts-fuel-tap.21225/

The orifice of the needle seats is the principal determinate of fuel flow. My Atlas has a non-stock orifice of 0.200 inch and does not suffer from fuel starvation. I think the stock orifice size of 0.125 inch is insufficient.

Slick

A follow up- the G15 just ran 25 miles without hiccup, using only the left petcock. So- between the lightened needles and ditching the fuel filters, all seems well once more. Most of the running was at lower speeds and throttle settings and it wasn’t fouling plugs, so it would appear my original assessment of the float heights being too high was correct.

I think the aluminum needles are needed and the brass units are to be avoided- hardly controversial advice here, which I would have known if I had looked a bit deeper. I’m new to Amal Concentrics and had not even considered that the needles are upside down compared to most, and need to be lifted up to allow the bowl to fill. On a Bing/Mikuini/Delorto/Keihin the needle falls down to open the fuel flow, so a small bit of fuel restriction upstream won’t matter. I considered popping the plastic units back in but wanted the Viton sealing tips- and would have ordered up a set of aluminum needles if I hadn’t had a mill sitting over in the corner of the shop.

TexasSlick- thanks for the link. I have a 64 Atlas in restoration right now and it needs a new petcock- the original was replaced with a brass stopcock so has no reserve.

Elfix said:

TexasSlick- thanks for the link. I have a 64 Atlas in restoration right now and it needs a new petcock- the original was replaced with a brass stopcock so has no reserve.

Click to expand...

It is hard to find a petcock with reserve that also can deliver a pint per minute.
Pingel makes one with a NPT thread that can be modified to BSPP. Expensive, but that is the way I would go if I need to replace my Ewarts.

Slick

When using methanol my fuel consumption is doubled when compared with that of petrol. With my Mk2 Amals, I have never had a fuel starvation problem. Also my carbs are rubber-mounted so I do not get flooding. If you get flooding, it is probably due to the fuel frothing in the bowls, rather than a the float needles bouncing.

Another advantage I have noticed with the aluminium needle is it tends not to react as much with my local fuel as does brass which becomes a bit sticky.

elefantrider said:

Another advantage I have noticed with the aluminium needle is it tends not to react as much with my local fuel as does brass which becomes a bit sticky.

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Tell more about your local fuel.

Pump gas?

Brand?

Grade?

Non-ethanol?

AVGAS?

VP 110?


"Sticky" is usually the result of fiberglass resin breaking down.

91 octane Chevron or Shell in Southern California.
Had similar results in steel tank, nylon, and Caswell- lined fiberglass tank.
The same stickiness has caused new reproduction fuel taps to lock up also.
That is what happens after a few months with the fuel here.

Our fuel in Alaska seems much less prone to turning into goo than fuels in other states- I don’t know if its base stock, formulation, or average ambient temperature and humidity- but I’m very thankful that a carburetor needs to sit unattended for years before anything bad seems to happen to it.

elefantrider said:

91 octane Chevron or Shell in Southern California.
Had similar results in steel tank, nylon, and Caswell- lined fiberglass tank.
The same stickiness has caused new reproduction fuel taps to lock up also.
That is what happens after a few months with the fuel here.

Click to expand...

Interesting results from EPA mandated E10 like the rest of the US.

I'm pretty sure California gets a special blend compared with the rest of the US.