Fuel flow through 32mm amal bowl

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jseng1

jseng1

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Does anyone know how many ounces of fuel will flow through a 32mm amal bowl in one minute with a full tank of gas? You would need a bowl with a removable plug to check this (or drill a hole though a junk bowl to test).

I'd make the test but I no longer have any amals to check.
 
Trixie only had 1/2 tank gas right now but if no one pings back will top off and measure. What ever it is it is not enough to feed a good BSA on the boil so they did this to Amals as I did the pair on Trixie so will not apply to un-opened Amal anyway. Amal float flow restriction is fuel passing by the top of needle area so here's how that's bypassed.

Fuel flow through 32mm amal bowl
 
Fuel flow is sometimes limited by the single hole in the banjo bolt that holds the filter and fuel line connection to the bowl. A common modification (probably advisable as a routine) is to drill a second hole in the banjo bolt (just drill through the existing hole and out the other side). Stock petcocks can also be another area of restriction to fuel flow; I've had crud in them cause lean running; I look for the rebuildable ones with a circlip. There are better aftermarket petcocks out there as well if you don't care about keeping the bike stock. I run with one petcock most of the time to have a reserve since there is no fuel gauge or odometer;I open both petcocks for more spirited riding. Judging by how quickly I can drain the gas tank, two gallons or so in less than a minute; faster than I can burning it through running the motor.
 
If you're getting less than 300 ml/minute from each bowl when BOTH drain plugs are removed,there's room for improvement.More is better.The slot in the float bowl can help,or you can carefully drill a hole in the same place.

The engine will only consume about 1/2 that much,but you need it.When the float needle is fully open,the toe of the float has dropped about 6mm.That's the position you tested it.You don't want it open that far,and the fuel level in the bowl that low.You want to be able to flow enough fuel and still keep the fuel level in the bowl close to a normal setting.
 
If you need more fuel flow with a MkI concentric, you can buy the float bowl and needle designed for alcohol. The needle and seat are larger in diameter to allow the larger flow volume required to run on alcohol. I think Burlen can still supply them. There was also a float bowl available with a larger seat than standard, but not as large as the one in the alcohol bowl. You still might need to do the other mods if you're not getting enough flow with the larger needle seats. I don't have any experience with these parts, but I remember them being available back in the '80s when I was looking at using carbs to run an alcohol/gas blend.

Ken
 
I just want to know how much fuel a standard unmodified Amal 32mm carb will flow through the bowl in one minute with a full tank of gas.

If no one knows this - someone please send me a carb and I'll measure it, post the results and return the carb. But the carb needs a drain plug or a bowl I can drill a hole in and leave that way.

send to:

Jim Schmidt
JS Engineering
4480 N. Academy
Sanger, CA 93657

include return address.
 
OK- Using a Interstate tank with 5 gallons of 92 octane inside, clean screened BP fuel tap, clean 1/4" fuel line, good performing 32mm Amal concentric with removable bowl plug I got:

9 oz or 250 ml in one minute.

I hope this helps.
 
Bob Z. said:
OK- Using a Interstate tank with 5 gallons of 92 octane inside, clean screened BP fuel tap, clean 1/4" fuel line, good performing 32mm Amal concentric with removable bowl plug I got:

9 oz or 250 ml in one minute.

I hope this helps.
Click to expand...

Yes - that's what I'm looking for.

1. Is the carb stock and unmodified? (float level not modified?)

2. What is the distance from the top of the carb bowl to the top of the tank fuel level (gas cap) on the interstate tank?
 
Additional info:
The now-vintage Amal is stock with float height set per the book (good idle), Viton tip float needle, and stock fuel line banjo bolt with the stock one-side only hole.
I measured the top of the float bowl to the top of the Interstate tank at 13".
 
I suppose I should ask why you would want to know. I have Amals on all my stock Brit bikes. They have been used on many race bikes and land speed bikes over the years. Probably not the "best" carbs, but simple and effective.
 
Sometimes they starve for fuel - sometimes they don't. Probably depends on the float needle orifice. I'm looking for a fuel flow requirement minimum that I can compare to. I sell carbs and so its important to me.

Can anyone tell me the standard float hole orifice diameter (check by fitting in a number drill)?
 
I measured the orifice at about 2.95 mm and I measured 120 mL/min of fuel through one bowl with float and needle in situ but tank was only 1/2 full. WTH, I may just send you a spare to examine.
Some Amal problems were due to the flexible plastic of the float that flopped around (fixed by using a StayUp float or an old hard float) and some were due to the float pivot pin being loose and held in place by just the bowl gasket (fixed by lightly tapping or staking next to the pin). Float height varied a lot from one carb to the next direct from the factory, so each carb should have the height set properly (heat the bowl and tap the brass seat). The Concentric was introduced as less expensive to manufacture than the Monobloc and the result was rapid slide wear, erratic idle, no replaceable idle jet, etc. Looking at your website, it looks like I am unlikely to make a convert out of you. A local group is taking a blown Honda to Bonneville and they can't get their Mikuni set up right. I offered them an Amal, but they don't believe I could set one up right for them, either.
Anyhow, carbs are carbs.
 
jseng1 said:
Sometimes they starve for fuel - sometimes they don't. Probably depends on the float needle orifice. I'm looking for a fuel flow requirement minimum that I can compare to. I sell carbs and so its important to me.

Can anyone tell me the standard float hole orifice diameter (check by fitting in a number drill)?
Click to expand...

For Mk I Concentrics the standard is .100", the high flow is .125", and the alcohol is .156". Not sure about the Mk II concentrics, but I think they are significantly larger.

Ken
 
Hi Jim

You got so use to your own carbies :lol: and forgot about the old ones.


Ashley
 
Jim, I mailed you a spare concenric blowl wtih (floppy white) float and viton tipped needle. Play with it all you want, then let us know what you think. I believe the bowl is the same for all 900 series concentrics. Carb bodies vary by size of orifice, but needles, needle jets, slides and main jets are interterchangeable. I have fiddled a lot with Amals on bikes being run at 6000' altitude (where I live) and higher. This causes standard setting to run too rich up here. The advice from the shop manual about changing main jets is useless. I lower the float height , sometimes lower the needle a notch and use a different slide.
My most recent carb project was a triple Del'Orto pumper setup. Very complicated and fiddly. I almost thought about swapping them out to a triple Amal setup.
 
Thanks Chris for sending the bowl.

Testing with water it flows 8oz min with 11" head.

It flows 9oz with the float needle removed.

The needle orifice is .098" in diameter.
 
This is something that had stumped me for over a year. The bike would run well for a short while, then stumble.
I checked the fuel flow through the tank, lines, jets & vent hole in the tank, it all seemed to flow well.
I took the bike to the dyno & the operator confirmed there was a fuel flow problem. But where? I had checked everything.
I took the carb apart again & quite by accident I looked at the needle jet hole size & it was very small, I had found the problem!
The carbs had come off an engine that was used in a sidecar & was fed by an electric pump. The smaller float valve hole was not a problem with a pressure feed.
I wasted a whole race season & winter fixing that one!
 
I hadn't heard of that one before. I've been fiddling with and cussing at Amals for 40 years without coming accross this issue. Did you replace the bowl(s) or drill out the seat? I don't know if you can get just a replacement float valve seat. It is common to have the wrong needle jet (or one without a hole on the side) or needle if you have a carb of unknown origin.
 
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