Amal float height.. An example of why it really matters.

So a friend found a bike he wanted, it was fairly cheap and the owner said it had been sitting for a couple years with Non Op tags. To be fair it's a 70 BSA A65 but this is about Amal carbs so it's all the same. The carbs were so gummed up it couldn't be started but he bought it anyway. We could tell the Right side had run leaner because that pipe was blued while the left was not at all. Took it home, cleaned the carbs changed fluids etc. Left carb flowed gas from tickler but Right would not. Despite this it started first kick, ran good on Left but Right was intermittent and weak. Cleaned the Right carb again but still it wouldn't flow gas from the tickler and ran badly. We switched float boals and the problem followed the bowl so I knew it was the float height for sure. We checked and it was low so we pressed the float needle seat down to match the good carb and it flowed through the tickler and ran like a dream. It was then obviousness to me that the previous owner never had the bike running on both cylinders. He had bought the "new old stock" original style (Non Premier) carbs when he got the bike thinking new carbs had to be all good. He most likely struggled in vain with adjustments trying to get that side to run good but wasn't much of a Brit bike guy so he knew nothing about what the real problem might be. Hence the good price. This was an extreme case because it wouldn't flow from the tickler but it does go to show that while Amals will run and are very forgiving the float height does matter more then some say.

That is a good example that the problem isn't always a clogged pilot jet.

Might as well ensure that the fuel tank petcocks do not leak, and change the carb float needle to the nice Viton tip if not done already.
I like the BAP style taps. The BSA may have a different size tank threaded hole than a Commando but thread adapters are available.

Thanks for the tutorial.

I may have a similar situation so I also have a few rookie questions.
I still run the twin, original but rebuilt amals, on my restored but rarely ridden 70.
One side sputters and is too lean per my mechanic, no matter how much adjustment.
My mechanic thought I needed to change needle position even though years ago, both carbs operated fine and currently the other side fires smooth and fine.

Does this sound like a candidate for float position?
how does one check flow by the tickler process?
what and why did you think would occur when you switched float bowls?
which leads to how did the bowl create the float height problem?

thanks.

My Commando, when I first got it last year, was difficult to start, only ran on one side until eventually the other side kicked in but not right. The carb wouldn't flood with the tickler so I stripped it to investigate. The brass float valve was so high no fuel got in at all, the float bowl was totally dry. It only picked up on two cylinders from vapour fed from the balance pipe. There's a Bushman link somewhere about carb float heights which I found useful.

The current Amal recommendation is to set the fuel level, rather than float height.


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

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

david7212 said:

Thanks for the tutorial.

I may have a similar situation so I also have a few rookie questions.
I still run the twin, original but rebuilt amals, on my restored but rarely ridden 70.
One side sputters and is too lean per my mechanic, no matter how much adjustment.
My mechanic thought I needed to change needle position even though years ago, both carbs operated fine and currently the other side fires smooth and fine.

1)Does this sound like a candidate for float position?
2)how does one check flow by the tickler process?
3)what and why did you think would occur when you switched float bowls?
4)which leads to how did the bowl create the float height problem?

thanks.

Click to expand...

1)The original poster (Gtsun) came to the conclusion that it was a float problem, (rather than a idle jet clogging) because he took the bowls off and swapped them to the opposite carb.. When the poor running issue changed sides, he knew the problem was with the parts that he swapped (bowls, floats, and float needles) Also, the tickler didn't work on the side that ran poorly which points to fuel delivery (floats,bowls, etc)

2)The tickler with slow fuel delivery was just a hint that the problem was fuel delivery, rather than the more common clogged idle jet, which leads to answer #3.

3)Switching the fuel delivery parts, (bowl, float, float need, float needle jet) to the opposite carbs proved that those parts were at fault because the engine problem changed sides with the exchanging of those parts.

4)The bowl has a seat for the float needle pressed into it. That needle seat has to be at a certain height to maintain the proper fuel level in the bowl. If the seat is too high in the bowl, then the fuel level in that bowl is low. (sometimes so low that the cylinder cuts out or doesn't run at certain throttle positions) IF the seat is too high, fuel may drip out of the bleeder.

If you have amals, you should read the info on the bushman's website. It really gives a good explanation of how amals work. I had idling issues with one carb that turned out to be the idle jet. I followed the bushman's site instructions to drill out the back of the port of that carb, cleaned the jet thuroughly, and sealed the port I drilled, which fixed my issue... good info there..

Andover Norton latest newsletter introduced a kit if you have the drain-plug type Amal float bowl.
https://andover-norton.co.uk/en/shop-details/20569
13.1688, Fuel level checking kit for Amal Mk1 & 2 carbs, £8.95 + vat (see article in this newsletter)
You could make your own.
Cheers,
Thomas

Thanks guys, all of you.

I have my work cut out...do a little testing, first of which will be to switch the bowls.
From what I gather, if the results jump to the other side then it's somewhat obvious it's fuel level / float related.

Does anybody off-hand know the thread size / pitch of the float bowl drain plug?
I would like to create a pair of the exterior tube level checker.

David,

You can mount the float bowls alone on a metal plate and watch the float level. Or as you indicated check it with a tube off the drain, if you have one. This is how I did it, but I used alcohol instead of gas.

DogT said:

David,

You can mount the float bowls alone on a metal plate and watch the float level. Or as you indicated check it with a tube off the drain, if you have one. This is how I did it, but I used alcohol instead of gas.

Click to expand...

Thanks but I'm confused what this would prove?

Do you fill up each bowl at the same time and check the difference in the float height between the two?
It seems like only one bowl has fluid in it.
How much fluid to you put in the bowl.

THANKS

CanukNortonNut said:

Andover Norton latest newsletter introduced a kit if you have the drain-plug type Amal float bowl.
https://andover-norton.co.uk/en/shop-details/20569
13.1688, Fuel level checking kit for Amal Mk1 & 2 carbs, £8.95 + vat (see article in this newsletter)
You could make your own.
Cheers,
Thomas

Click to expand...

That's a good idea, and not worth the hassle of making one at that price IMHO.

But their instructions on the web site seem vague to me. How can you measure the gap from fuel level to bowl rim so precisely when the carbs are mounted on an angle, unless you are very precise about the measuring point?

Their picture showing how to measure is too vague, and a couple of mm either side of the 'nominal position' will have significant impact on your gap measurement.

At least that's how it looks to me...?

DogT's method is pretty accurate. He could even adjust the angle to be the same as the carb. His pictures show that one level is probably lower than the other.

i have an interesting issue that might be related to float level. I set mine up by getting an accurate measurement of the float height relative to the top edge of the float bowl. My bike goes really well with no flat spots etc etc. However, there is a sign the r/h cylinder is slightly leaner than the left looking at the colour of the new exhaust pipes. As I have mentioned previously, the bike runs slightly more economically than another twin carb bike and slightly less economically than a single Mikuni. [ the difference is like 7.8 l, 8 l and 8.2 l for the same mileage ] So I presume the bike is not running too lean, but not perfectly. After a long run like 2500 miles, one of the spark plugs becomes lazy [ yes even a brand new Iridium plug does that ]/. The symptom is that on the overrun, at low throttle, one carb backfires. [ think it is the r/h one ] . This back firing is a problem because it back pressures the carb slide and in the worst scenario, causes the lower rim of the slide to break away and go through the engine, taking out the relative spark plug on the way. I did prove this on one trip and when i replaced the plug that had been stuffed, the bike ran beautifully. Haven't had any time to really sort this out but when I got back from the last run I put in a pair of N9Y plugs which I have at least 10 of. I am about to do 800-900 miles this weekend so it will be a test to see if I end up with the same problem. A thought it that one of the plugs has fouled slightly and so when i get back I will sand blast it and give it another go,.
Dereck
ps years ago, before I worked on the carbs to get the bike running economically, a lazy plug caused the l/h slide to break a 6 mm x 5 mm piece out of the front edge of the slide. That made the bike impossible to ride nicely below 50 mph so I left it in a local garage and continued the rally as a pillion. At the time, i had no idea it was caused by a lazy plug.

But their instructions on the web site seem vague to me. How can you measure the gap from fuel level to bowl rim so precisely when the carbs are mounted on an angle, unless you are very precise about the measuring point?

Click to expand...

You take the tube up at the midpoint of the bowel where the main jet is, its the fuel level that that sees that is important and confirmed by amal if asked.

david7212 said:

Thanks but I'm confused what this would prove?

Do you fill up each bowl at the same time and check the difference in the float height between the two?

Click to expand...

The object of the exercise is to check the fuel levels are within the range recommended by Amal.

david7212 said:

It seems like only one bowl has fluid in it.
How much fluid to you put in the bowl.

Click to expand...

You don't put a quantity of fuel into the bowl.
The amount of fuel in the bowl (and therefore its level) depends on the float height setting, so you adjust the float height to alter fuel level.

Here is how I check mine.

kommando said:

But their instructions on the web site seem vague to me. How can you measure the gap from fuel level to bowl rim so precisely when the carbs are mounted on an angle, unless you are very precise about the measuring point?

Click to expand...

You take the tube up at the midpoint of the bowel where the main jet is, its the fuel level that that sees that is important and confirmed by amal if asked.

Click to expand...

Thank you, that makes perfect sense!

If AN added that sentence to the page it would be ideal.

In the April Newsletter from AN:
"Our kit contains a special threaded plug to temporarily replace the float bowl drain plug. Attach the pipe to the plug’s hose an open the petrol tap and fill the float chamber with fuel. If the fuel level is in the correct range the fuel will rise in the tube to a point between 0.170" and 0.240" (4.3 and 6.1mm) below the top edge of the float bowl. Start the engine and ensure the fuel level remains within the correct parameters.
If adjustment is needed, the carburettors should be fitted with Amal "Stay Up" floats. These have stainless steel tangs which can be bent to alter the fuel level. The tangs can be easily adjusted by clamping the float in a vice up to the spindle hooks and tapping the body of the float gently in the direction required until the required level is achieved."
Cheers,
Thomas

CanukNortonNut said:

In the April Newsletter from AN:
"Our kit contains a special threaded plug to temporarily replace the float bowl drain plug. Attach the pipe to the plug’s hose an open the petrol tap and fill the float chamber with fuel. If the fuel level is in the correct range the fuel will rise in the tube to a point between 0.170" and 0.240" (4.3 and 6.1mm) below the top edge of the float bowl. Start the engine and ensure the fuel level remains within the correct parameters.
If adjustment is needed, the carburettors should be fitted with Amal "Stay Up" floats. These have stainless steel tangs which can be bent to alter the fuel level. The tangs can be easily adjusted by clamping the float in a vice up to the spindle hooks and tapping the body of the float gently in the direction required until the required level is achieved."
Cheers,
Thomas

Click to expand...

Yes, that's the text I'm referring to. It's good, but misses out the part about the measuring point being in line with the main jet, which is important if carbs aren't mounted perfectly horizontal. Well, at least I think it is!

david7212 said:

Do you fill up each bowl at the same time and check the difference in the float height between the two?
It seems like only one bowl has fluid in it.
How much fluid to you put in the bowl.

THANKS

Click to expand...

The tall upright 1X3 holds a syringe that acts like the fuel tank. The tubing takes the place of the fuel lines. The float, needle, and seat control the fuel level in each bowl.

Greg

Right, the baster is the fuel tank so the fuel goes in there. The fuel level in the bowl will reach it's own level depending on how the float is set. It will show you exactly where the fuel level is when the float needle cuts off the fuel. Like I say, if you have the bowls with the drain at the bottom, it's easier with a simple tube like the pictures shown after mine. Seems accurate enough for me. I just did one float at a time and set it to factory level.