Some may find this useful. Wet sumping comes from two areas, either past the anti-drain valve or through the pump into the primary or crankcase. The easiest check is to leave out the primary drain, sump plate and the filter and cap and see (obviously, with oil in the tank). Seepage through the pump will need a rebuild or replacement but putting anaerobic sealer between the sections might be sufficient. Putting a seal on the output shaft will stop the oil into the primary but not the sump. A 1 x 8.5mm O-ring can be put between the feed and return sections to stop both. Two problems with the anti-drain valve: 1) the hole the ball sits on and the seat were made with drills, not too sharp drills at that. The ball sits on the edge between the cone face and the hole so any irregularity such as a score mark will cause a leak, 2) the spring is too weak. Density of oil is 0.504 oz/in^3 so a 24" column generates 2.027 PSI (rho * g * h). The hole above the ball is 1/4" so the force on the ball is 1.59 oz. The ball itself weighs 1.8 oz and the spring compression gives 3 oz so the force on the seat is 1.2 oz. I measured the ball and spring on a gram scale. Since the valve is on the pressure side a stronger spring or a spacer to increase preload can be used. Check that the ball will clear the down stream passage under full compression.
Hi Dave, Yes, the metric system is great except when people use kilograms as force (kgf). You do not hear of people using slug force, do you? Of course the foot and finger system messes it up by using pound mass (lbm) which is just as stupid. A kilogram only produces a certain force under a particular acceleration. Keeping to the metric system, density of oil is 0.871 gm/cm^3, acceleration of gravity is 981cm/sec^2, column height is 61 cm.
So the pressure at the bottom is 52241.2 gm/cm/sec^2 or dyne/cm^2 1 dyne = 1e-5 N and 1 N = 0.2248 lb (lbf to be clear) That makes the pressure 52441.2 * 1e-5 * 0.2248 = 0.1174 lb/cm^2 = 0.7577 lb/in^2 - so you are right, I screwed up somewhere in the oz/lb/ft/in conversion I misread the scale, the ball (7/16") is 0.18 oz. I did check the scale against a good condition UK penny (3.5 gm). So the oil is pushing 0.595 oz and the spring minus ball is pushing 2.82 oz so 2.22 oz against the seat. Glad to see someone is checking for my stupid mistakes.
Dave, you make me laugh with "slug force"! This is my OCD checking stuff! Alot of this came out with my analysis of brass float needles in mk1 concentrics, which is generally disbelieved, but so? Everyone needs checking mate, that's technology, not gossip! Dave
The original design used the light nylon needles which had there own leaky problems, the later needles with a viton tip are much better in this regard. The early upgrade was brass/viton, latterly aluminium/viton have been introduced. Either can be made to work, the light aluminium/viton doesn't result in any change in float bowl function from the original design, however the much heavier brass/viton results in a lower fuel level in the bowl. Some engines tolerate this better than others, but ideally adjustment should be made to the mechanism to achieve the correct FUEL level, as there is now a different relation between FLOAT level and FUEL level, the latter being the important factor.
"AMAL Mk1 Concentric float needles" - try a search using this on Triumph board for much detail and debate. Here I will only give a nutshell. 1st of all, it is vital to note that the float needle setup is unusual in the world of carbs, in that gravity tends to pull the needle down onto its seat, in most carbs gravity tends to pull the needle away from its seat. And that the float tang has a lot of vertical slack in its niche in the needle, so the float has to drop a long way from where it is pressing down on the needle to where it is pulling the needle up. The nylon and the aluminium needles are pushed off the seat by a small head of fuel as soon as the float tangs release their downward pressure. However, the much heavier brass needles need >37cm head of fuel(which they never see on a bike) so they stay put until the float level has dropped(5+mm) to where the tangs start to lever the needle off the seat. This changes the operation of the valve from a "push to close" to a "pull to open" system, and then the slack of the float tangs comes into play. All carbs that I know of use "push to close", as do toilet cisterns, as its a much more positive stop, and this is how this carb originally worked with the nylon needle.
interesting. i honestly never paid attention to which way the needles are oriented in any carbs i take apart, and i can't remember what most of them were. mikunis and fcrs lift the needle to shut off fuel.
obviously the weight of the brass needle in a Concentric is greater than the nylon or aluminum, and if they're installed without changing the buoyancy of the float to lift them, they will require the fuel to be lower before the lifting force of the descending float balances the increased mass of the needle. if you made the needle out of lead, the fuel would have to drop way farther down before the float would begin to pull the needle up.
i don't know of any specs for actual fuel level in a Concentric, as everybody just ignores it and set the float instead. shouldn't be hard to figure out, though. the easy way would be to level a bowl/float/nylon needle assembly and then just use a burette to slowly feed fuel into the bowl through the needle valve. when the burette level stops falling, the needle would be closed, and you then measure the fuel in the bowl, ignoring the float. then swap needles and change whatever you need to do to achieve the same fuel height with the new needles
the stay-up floats seem to be the same shape as the old nylon ones. are they the same mass? they would have a similar effect on fuel level, shutting the needle off at a lower level if they floated higher in the fuel.
of course, the place to look for fuel levels in an AMAL carb would be the AMAL website:
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..
The correct fuel level for all Mark 1 Concentric carburetters is 0.21" plus or minus 0.040" below the top edge of the float bowl. Thus when the needle valve is being held shut by the tangs of the float, the level of the fuel will be between 0.17" to 0.24" (4.33mm to 6.35mm) from the top of the bowl.
thanks for that
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.