Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Mikuni back to Amal for my A65?

As the one on the left is twelve feet long , and the one on the right 12 millimeters - comparitively ,

The darn jet wont unclear till youre at 150% throttle . or suchlike .

FLOATS can be biased to suit altitude , temp , etc , for economy or grunt ,

As in ' almost nearly but not quite level . above or below . Rich bias or lean bias . FRACTIONS . more than 1 mm and Watch It .

Had a needle drop riding - Clip gone - instantly lost a cylinder .
the pin In my pocket bent round it 360 deg. solved that .

One wonders sometimes , The loose doorhandle fitted the jamed starter motor end on evening on a mountain . An Automatic . Providance .

ANYWAY , a big long needle when ITS NOT wanted , and it Wont Run , The needle tips dangle just in the end there , Wide Open .

SO LOOK IN A BOOK for correct needle I.D. & spec.s , & alternates . Only variation would be minor variation in taper .

Monoblocks can have five positions ( clip ) . Trying Top & Bottom gets you educated .

Grease on the Lt Brown gaskets isnt a bad idea . Copper Coat isnt either . Can reuse undamadged Head Gaskets with it , even .

Your new "assembled" setup is correct for a 4t (4 stroke) Mk1 Concentric.

4t (4 stroke) needle jets have the cross drilling on the hex faces (measure about 0.035" hole) they are also more open if you look down the top of the jet and the measured section 0f 0.106" is futher down.

on a 4t (4 stroke carb) both 600 and 900 series carbs use the 2 ring needle....

on a 2t (2 stroke) bike the needle is specific to the 900 or 600 series carb, from recolection, 1 ring is 2 stroke 600 series... 3 rings is 2 stroke (or 2t) 900 series.

2 stroke needle jets do not have cross drillings of any size. the metered section also starts at the very top of the needle jet.

from your pic the cross drilling is the give away for a 4 stroke jet.

Monoblocks dont have the cross drilling, but they are a much longer jet as you can see in your image.

It should all work fine with what you have now..... Though if your jet etc is a second hand one then there is no determination of its actual size, it may have worn from the needle rattling and rubbing the sides. Also some earlier ones if you over tightened them they would crush slightly and reduce the size by upto 0.001" (I found this my self) a go-no-go gauge (aka plug gauge) would verify your jet sizing, the new jets seem to have more undercut under the hex and regardless of how tight I try to get them, I have not been able to get them to reduce in their size (not that you should be trying to sheer them anyway, but I was trying to prove a point once upon a time, some of my earlier ones - about 20 years ago, would reduce in their size with anything more than a tiny nip). Though if it was me, I would spend $10 on a couple of new jets and needles just to be sure... Not fun chasing carb problems with worn carbs...

Alan, I've confirmed that I have the correct needles and needle jets, and the needle jets are in new condition. We apparently refreshed them on the T140 just before giving up on the carbs and replacing them. We probably replaced the needles as well, cause they look new. So I won't be buying these parts. I did however order aluminum shutoff needles and a pair of float bowl gaskets.

Pushrod Tom, I'm taking your advice about checking fuel level while I'm waiting for the aluminum shutoff needles. Fortunately I have a few single-spigot fuel banjos on hand. I haven't yet poured fuel into the pipe, that's on today's agenda. And not to worry, I'm not squeezing the bowl with the vise; the vise is closed only enough to keep the bowl from tipping over.

Don't forget the carbs are tilted at around 15 degs on the bike.

Ok, good point. I'll tip them accordingly.

I also realized, after reading the article again, you're supposed to do this with the carburetor assembled, with a "vision tube" coming up off the drain plug. It would be a bit of work to make a drain plug with a fitting that doesn't leak, so I hope I can tell something this way. I may have to put a piece of tape or something over the pivot pin so it doesn't raise up out of the slot. I don't want to stake them until I get the aluminum shutoff needles.

Still no fuel added; I went to the speedway races tonight. I'm fortunate to live only three miles away from what is the only mcy. speedway track in the northeast U.S. Good racing tonight, until there was a three-way collision amongst some three-wheelers. That stopped the action for a while and we were cold, so we left.

Those hex plugs are idea for this job. Easily over tightened for normal use but a nice flat base to aid a leak free fit yet easy to fit.

Don’t forgot there is a window of accuracy. As long as both sides are as identical as possible then you have the greatest chance of keeping them in balance.

Well this turned out to be a very useful test, and I think I may have solved the mystery.

Just as the "Tuning AMAL MKI Concentrics" article warned, the brass shutoff needle drops into its seat when the float is only halfway up and the bowl only halfway full.

I repeated the test with a plastic shutoff needle, and the bowl fills all the way before the needle seats and stops the flow.

Of course the theory will be 100% proven only when the carbs are back on the bike and in operation. Since I've ordered aluminum shutoff needles, I will wait until they arrive and repeat the test again with one of those before reinstalling the carbs.

Looking at the picture it seems that you are using the plastic type of float, I don't know how well these fare over the years but would be inclined to change them for the later stay up type which has the metal tab that engages with the float needle.

The later stay up metal tab floats allow for easier adjustment of the float level as its simply a matter of bending the tab, as opposed to the earlier all plastic type which has no adjustment requiring the float needle seat to be moved.

Gunner, I've already adjusted the float levels, and I have about half a dozen plastic floats. If the alu shutoff needles (which I'm still waiting for) solve the problem, I'll just slap them back together and go without buying any more parts.

providing you used gasoline to set your float level, id say get it fitted!

Yes, just waiting for the alu shutoff needles to arrive in the mail. And I will repeat the fuel level test with the alu needle, since I'm all set up for that. Right, using gasoline.

I'll post results!

It seems to me that setting float/fuel levels by hitting things with hammers is a rather primitive way of going about things and unlikely to be very accurate. Surely it is important with twin carbs (or more) that they are balanced with equal fuel levels and I'm wondering if the best way to achieve that with accuracy is by connecting the two float bowls together (e.g. through the drain plugs) so that the fuel levels become the same. An additional feature of this approach would be that only one float would be required. Some AMAL Monobloc twin carb machines were configured with connected float bowls but not Concentrics (to the best of my knowldege). It seems to be such an obvious thing to do with a view to achieving carb and cylinder balance. I'm wondering why it isn't talked about more as an approach for accurate carburation balance.

When you park on the sidestand, fuel will run from the right side carburettor to the left one, flooding and leaking.

I have doubts about one Concentric float valve flowing enough for a Lightning being thrashed.

I agree, re the flow rate, you could always cut a bigger slot in the bowl/seat up to allow more fuel to flow.... on a slightly more serious note, you could use a methanol float bowl and needle. The needle seat is bigger than a standard bowl.




Still all sounds like a lot of work and still you will have the issues when the bike is leaned to one side.

Setting on the bike with a tube from the bottom, a wire locator holding the tube in a set location using the mounting screw should be accurate enough.

The racer trick is to cut through the wall between the needle seat and float chamber with a keyway cutter just above the seat so the fuel does not have to flow past the needle.
You do not have to use a hammer to move the seat. Besides the afore mentioned screw through the banjo bolt you can make a C frame to fit around the bowl. Two screws are needed, one for pushing up with a small shank to fit in the underside, the other down with a large enough foot to cover the seat.

DM, I was wondering if you're aware that the approximately 1/8" hole in the bowl body to access the seat is off-center with respect to the banjo bolt. It seems like it would be a tricky matter to drill a banjo bolt in exactly the right place, and then the bolt would have to be in a specific position rotationally for the holes to line up.

I wasn't planning on doing this anyway, but it piqued my curiosity. I found that I could be quite precise with a punch and a hammer, as the seat moves quite easily once the bowl is heated. I did find though that I had to move it too far up and then tap it back down from the top, where I could see how much I was moving it.

Hadn't considered the possibility of over-filling the left carb because of the sidestand issue.

Yes, I know the seat hole is offset from centre. If you mark the bolt for the fully bottomed position then drill the hole clockwise (looking at the bottom) from the mark, you can unscrew the bolt until the push pin aligns with the seat hole.

I thought these might be useful for checking float height on the bike -

Push on a piece of 1/4" clear hose and bend up next to the float bowl.

That would save a lot of messing about, how much?

Those are really nice…..your stuff always is.

BUT…….wouldn’t that be used to check “fuel” height….not “float” height.

Well, yes, fuel, not float. You can also use it to check the taps are flowing fast enough.
Made these from 3/4" cut-offs laying about so the cost was really the programming and setup so at my shop rate of $0.50/Hr, $1? Not really worth the postage cost to the UK. If there is interest over there I can include some with the parts shipment to Clive Blake, TR3OC Spares Liaison.

I’d love to have one…….$10 plus shipping? I’d proudly put it on the shelf with my other treasures.

I only mentioned the fuel thing because I know someone who got that confused one time… we all know the float height regulates the fuel height…..but they use two different measurements.

I’d love to own a clear AMAL bowl….so I could actually watch what goes on in there when the engines running. My guess it’s total chaos and nothing even resembling what goes on when you have it on the bench.

I suppose a bowl could be machined from Lucite. Or you could make windows and bore holes in the side of the bowl and use JB-Weld to glue them in. I suspect all you will see is the fuel dancing around with the vibration of the motor.