T150 Trident carb float and fuel levels

Hi guys - I have a friend's T150 4-speed in my shed at the moment. It's not running right, so I whipped the carb assembly off to check the throttle slide sync, clean the pilot jets and check the fuel and float levels. I have checked the ignition beforehand and all is good in that department. Also, I know that the carbs are in good nick. As a note, even thought the choke slides bottom out, it doesn't seem to make any difference whether the chokes are up or down (which could indicate richness across the range). The pilot jets are embedded in the body of the carbs, as in the Commando and I have plenty of experience cleaning out those damn things.

I decided to see if the float levels corresponded to the actual fuel levels. I read - please correct me if I'm wrong - that the fuel level across all Amal 928s is 0.21" +/- 0.040". In the case of the float bowl in the pic below, the fuel level is 0.275" and the back edge of the float is almost at the level of the float bowl's top edge but not quite parallel. Something doesn't seem right here, since if the fuel level was adjusted to the stated level of 0.21", then the float would be above the top of the bowl. Surely that would be way too rich? I have seen 0.080" below the level of the bowl mentioned for float height but your comments and advice would be welcomed on what you have found works best in practice.

Should I just adjust the float levels and forget about the fuel levels?

Dave

daveh said:

I decided to see if the float levels corresponded to the actual fuel levels. I read - please correct me if I'm wrong - that the fuel level across all Amal 928s is 0.21" +/- 0.040".

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Yes, although standard T150 Concentric carbs would be (27mm) 626.

daveh said:

In the case of the float bowl in the pic below, the fuel level is 0.275" and the back edge of the float is almost at the level of the float bowl's top edge but not quite parallel. Something doesn't seem right here, since if the fuel level was adjusted to the stated level of 0.21", then the float would be above the top of the bowl. Surely that would be way too rich?

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At the moment the fuel level is apparently too low, so how will raising the fuel to its correct level (by raising the float height) make it too rich? It's the fuel level you need to concentrate on setting correctly, not float height.

daveh said:

I have seen 0.080" below the level of the bowl mentioned for float height but your comments and advice would be welcomed on what you have found works best in practice.

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Amal changed the needle seating depth in the float bowl, also different weights of needle can affect the float height (see Amal link/quote, below) so the original 0.080" float height setting (originally adjusted by raising or lowering the needle seating) is no longer considered accurate by Amal.

http://amalcarb.co.uk/optimising-mark-1 ... uel-levels

Because there have been changes to the float chamber since the Concentric carburetter was introduced, and because there is no way of knowing what alterations may have been made by a previous owner, measuring the fuel level is the best way of setting up the float chamber.

Needle Valve

If your float chamber is fitted with a brass needle valve, you may find the valve sealing under its own weight, before the float has risen far enough to press it shut. Symptoms of this problem can be that the carburetter takes a long time to tickle, hesitates on pickup and does not idle reliably. A Viton tipped aluminium needle valve is now available that overcomes this problem. It is now fitted as standard equipment to all new Mark 1 Concentric carburetters.

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daveh said:

Should I just adjust the float levels and forget about the fuel levels?

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The whole idea of adjusting the float height is to set the fuel level. If you cannot set the fuel level correctly for that particular carb without having to raise the float higher than would be expected then there has to be something different about it. I suggest you measure the needle seat depth and compare that dimension with the other two float bowls.
Did you hold the float pin down in its groove when you did the check as you won't get an accurate result otherwise?

Les, thank you for your detailed reply, much appreciated!

So I will go ahead and adjust the fuel level as per your suggestions.

Cheers, Dave

P.S. Yes, I did hold the float pin down initially. It stayed obligingly in its groove long enough for me to take the photo. And, yes, I will cross check the needle seat depth with the other two carbs.

Good luck with your attempt at setting the correct bowl fuel level.
I think that if the top of the float rises above the bowl flange to achieve the correct fuel level, it is not a problem.

Bob Z. said:

Good luck with your attempt at setting the correct bowl fuel level.
I think that if the top of the float rises above the bowl flange to achieve the correct fuel level, it is not a problem.

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Bob, I agree. I've set all three now, and they are all exactly the same (which is important) and I am happy with the result. It helps that they are the new floats with adjustable tangs. Next is the road test!

A quick road test today confirmed that the poor low speed running has been cured (touch wood). However, since the jetting is for a stock Trident (.106 needle jets; 150 mains) and this bike has short velocity stacks instead of an air filter, it is running a bit lean throughout the range. Has anyone found through experience what jet numbers work best for an otherwise stock Trident without an air filter? (I am assuming here that an air filter would make some difference on a Trident with stock 1972 style silencers.)

Your comments would be welcome.

The http://www.triplesonline.com/ forum would be the best place to get that information, however, the website is experiencing some technical difficulties with an upgrade at present but which hopefully, won't take much longer to resolve.