NEWS FLASH "Amal Float bowls might suck(air)!"

Realizing that some air seeps through tickler, I am wondering how important the sealing of the float bowl is to smooth running with emphasis on the pilot circuit?

When testing the float level on a wooden jig and scribing the .020 and .017 on the side of the bowls and gauging with the meniscus method, I applied slight air pressure to the hoses and saw much weeping around the float gasket. When I removed it and put it to a flat surface it was like a teeter tater rocking on the screw ears.

These ears are soft and just like mounting the carbs to the head will warp when over tightened along with the carb body ears. I worked all surfaces flat, reassembled and concluded my adjusting session.

With all the talk of not being able to get our machines to settle down and after trying everything that we can think of, I think that we should add this to the list of things to check.

I am sure that this has been brought up before but then again maybe not. With so many of us going for the new float, we best give them a sound condition to function properly.

I think there has to be some air getting in the bowl or wouldn't it cause a vacuum?

In my experience, removing the float bowls whilst the engine / carb are hot (usually trying to trace a misfire that turns out to be ignition ! ) will often result in the chambers distorting as they cool and leaking when they are replaced.

Figures of eight on the plate glass have always got me out of trouble.

Quite why they skimped and only used two screws is a puzzle to me.

the tickler is a vent for the float bowl, just as the gas cap is vented they both must equalize to atmospheric pressure.

if the float bowl does not have a good seal than it COULD have a leak where it COULD have trouble drawing fuel into the pilot circuit. if you look at the float bowl there is 2 passages that lead up to the pilot circuit and depends on which handed carb as which side is used to supply fuel to it.

Actually Ludwig , that picture is of an F-14 Tomcat , but your point is well taken

Ron

There was a thread a while ago on the question whether jets suck or blow gas. It's semantics but I find it's easier to understand jetting by thinking that the gas is getting pushed through the jet by the relatively higher pressure, (atmospheric) in the float chamber. Amal saw the elegant simplicity of the tickler/vent. Either way you look at it the pressure in the bowl has to be vented to atmospheric.

pvisseriii said:

Realizing that some air seeps through tickler, I am wondering how important the sealing of the float bowl is to smooth running with emphasis on the pilot circuit?

With all the talk of not being able to get our machines to settle down and after trying everything that we can think of, I think that we should add this to the list of things to check.

I am sure that this has been brought up before but then again maybe not. With so many of us going for the new float, we best give them a sound condition to function properly.

Click to expand...

Amal (Burlen) address this very point in their technical article "Notes On Rebuilding the Amal Mark 1 Concentric Carburetter"

http://www.amalcarb.co.uk/TechnicalDetail.aspx?id=11

Actually, that article tells you pretty much all you'd want to know about Concentrics and their various configurations. After reading it, while working on my carbs, I flatted the bowl surface with 1500 grit wet-n-dry on a sheet of glass to make sure there were no air leaks to the pilot circuit.

Regardless of venting to atmosphere...it seems poor practice to have it leak at the bowl gasket! Now, how about around the pilot jet screw and the idle adjust screw? How important are those O-rings? Or are they there just to prevent the screw turning with vibration?

Russ

well if you read the Bernouilli principle it basically says if you create a venturi (restriction), no matter if it's water, air, anything, the speed goes up and the pressure goes down at that point. understanding that, the term "vacuum" is throw around very widely and is known as the absence of everything, this scientifically has yet to be proved on the planet. outer space, now thats a different issue. what most people don't understand and this is kind of hard to grasp is that EVERYTHING IS PUSHED, NOT PULLED.

You take a straw and you suck up your favorite beverage right? No, what actually happens is you are creating a pressure difference in the straw from your lungs expanding and the atmospheric pressure of 14.7psig PUSHES down (gravity), pushing the beverage up the straw into your mouth. You take a "vacuum" leak on an engine, air is not sucked in, rather being pushed into the area of the pressure difference. Everything wants to equalize. Just like the pressure above the fuel in the float bowl and gas tank, they are vented. You increase or decrease that pressure and it's going to have a major influence on how fuel is metered.

This is the whole concept of a carburetor, you create a venturi (restriction), the speed goes up and the pressure goes down at that point and the fuel in the float bowl is PUSHED up to the main/pilot to wherever it goes.

pvisseriii said:

Realizing that some air seeps through tickler, I am wondering how important the sealing of the float bowl is to smooth running with emphasis on the pilot circuit?

When testing the float level on a wooden jig and scribing the .020 and .017 on the side of the bowls and gauging with the meniscus method, I applied slight air pressure to the hoses and saw much weeping around the float gasket. When I removed it and put it to a flat surface it was like a teeter tater rocking on the screw ears.

Click to expand...

It finally dawned on me that your question may be about the seal of the gas side of the pilot circuit at the gasket and not anything about the venting of the bowl at all? Could you describe the setup you used for checking fuel level? When you pressurized the hoses was gas coming out of the pilot orifices, needle jet, and tickler too?

What is NOT a news flash is that Amal carbs suck eggs :mrgreen:

and that aint no yolk :wink:

Jean

The following is from the Amal web site...

Inspect the gasket surface of the float chamber carefully for damage. The gasket surface should also be inspected for flatness. Light damage and irregularities can be remedied by dressing the surface using fine abrasive paper on a flat surface, or fine grinding paste on a plate of glass. If the surface is reduced too far however, the depth of the slot for the float spindle will become too shallow and may cause difficulties with the operation of the float. Over-tightened Allen bolts, which are a popular modification, can bend the lugs and cause an air leak within the float chamber into the idle circuit. If the lugs are bent the float chamber should be replaced.

I believe the highlighted sentence is what our friend was trying to alert us to.

and by the way, the question about the O-rings was serious. Are they intended to seal or are they to secure the screws, or both?

Russ, my vote is that they do both, seal and secure. With more emphasis on secure, seeing as how the Mikuni screws seem to get by without an o-ring and use only a spring.

About getting off point on thread, hey, it happens. I'm pretty sure it was Ludwig's picture that did it

bpatton said:

pvisseriii said:

Realizing that some air seeps through tickler, I am wondering how important the sealing of the float bowl is to smooth running with emphasis on the pilot circuit?

When testing the float level on a wooden jig and scribing the .020 and .017 on the side of the bowls and gauging with the meniscus method, I applied slight air pressure to the hoses and saw much weeping around the float gasket. When I removed it and put it to a flat surface it was like a teeter tater rocking on the screw ears.

Click to expand...

It finally dawned on me that your question may be about the seal of the gas side of the pilot circuit at the gasket and not anything about the venting of the bowl at all? Could you describe the setup you used for checking fuel level? When you pressurized the hoses was gas coming out of the pilot orifices, needle jet, and tickler too?

Click to expand...

I mounted the carb on a wooden platform vertically, hook a hose the inlet of the carb and a hose to the drain plug via a nylon elbow. I raised the drain line along side of the carb to act as a site glass to see the level. On the inlet side I hooked a weed sprayer and applied just enough pressure to keep the hose filled as it demanded(just a pump or two). I drilled a small hole in the drain hose to simulate usage. As it would empty I could watch the level drop then the sudden rise to the required level as the float activated.
I blew on the drainhose (not sure why) at some point at which point I saw fluid and bubbling coming from the float bowl/body gasket. Hence the posting. Although fluid would come out of other places(tickler) my concern was for the float bowl area and pilot circuitry due to the warped ears.

pvisseriii said:

When testing the float level on a wooden jig and scribing the .020 and .017 on the side of the bowls and gauging with the meniscus method, I applied slight air pressure to the hoses and saw much weeping around the float gasket. When I removed it and put it to a flat surface it was like a teeter tater rocking on the screw ears.



I mounted the carb on a wooden platform vertically, hook a hose the inlet of the carb and a hose to the drain plug via a nylon elbow. I raised the drain line along side of the carb to act as a site glass to see the level. On the inlet side I hooked a weed sprayer and applied just enough pressure to keep the hose filled as it demanded(just a pump or two). I drilled a small hole in the drain hose to simulate usage. As it would empty I could watch the level drop then the sudden rise to the required level as the float activated.
I blew on the drainhose (not sure why) at some point at which point I saw fluid and bubbling coming from the float bowl/body gasket. Hence the posting. Although fluid would come out of other places(tickler) my concern was for the float bowl area and pilot circuitry due to the warped ears.

Click to expand...

Cool method. It's a very good example of a case where the need for a seal is more than aesthetic and the design has everything going against it. I asked a guy that's retired from the biz and his answer was to get the bowl flat, never try to reuse a gasket, don't overtighten the screws, and use loctite on them. The part about reusing the gasket was that a dry fiber gasket swells when they get wet forming the seal you need, not so much the clamping force itself. It only happens once.