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Re: 56 DBD34 Amal woes [Re: Magnetoman] #772951 05/07/19 9:55 pm
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Brid Caveney Offline OP
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MM -- Hehe!! Beat me to it - I just pulled a VM 36 out of stock to take a pic!! As far as I can remember, it's always been on there -- even with the levers that have black plastic sheaths on them.
So -- Mikuni can 'talk out of both sides of their mouths at the same time' - with their description, and the article in question!! Funny stuff!!
And -- I think to completely simplify matters, we should do as Koan58 does -- and just call them all 'Cold start systems'!! Doesn't roll off the tongue quite as well as choke though - does it?
"Hey Billy -- did you put the cold start system on" ---!!

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Re: 56 DBD34 Amal woes [Re: Brid Caveney] #772958 05/07/19 10:22 pm
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Originally Posted by Brid Caveney
just call them all 'Cold start systems'!! Doesn't roll off the tongue quite as well as choke though - does it?
Personally, I prefer descriptions that contain at least a hint of the physical principle involved. If I asked for help because my 'cold start system' isn't working it would be hard to get any meaningful suggestions for a fix until someone realized my cold start system is my DocZ rollers.

When the lever on a Mikuni is up it opens a separate circuit that provides a richer mixture than the main circuit so it functions as an "enrichening" lever. When the slide is lowered in a Monobloc it reduces the air flow in the main circuit so it functions as a "choke." There are fundamental differences in the way these provide richer mixtures for starting so it seems reasonable, to me at least, to use the terms that actually indicate how they work. However, I'm beginning to choke on this discussion so I'll give up now.

Re: 56 DBD34 Amal woes [Re: Magnetoman] #772965 05/07/19 10:58 pm
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"When the lever on a Mikuni is up it opens a separate circuit that provides a richer mixture than the main circuit so it functions as an "enrichening" lever."

Hang on there - now you're confusing matters even more!! It's just the opposite on a Mikuni!! When the lever is up, the enrichening piston is down - and the circuit is closed, as the actuating lever is pivoted!!. That is however unless you are using one of their pull up choke systems - and then when that is up, the circuit is open.
Well -- I guess we sort of know now - hehe!!

Re: 56 DBD34 Amal woes [Re: Brid Caveney] #772969 05/07/19 11:18 pm
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MM quote "Personally, I prefer descriptions that contain at least a hint of the physical principle involved."

even if your description is incorrect? Was it not the GP carb that was under discussion? and that you were clarifying all of our cloudy minds about?
So "When the lever on a Mikuni is up it opens a separate circuit that provides a richer mixture than the main circuit so it functions as an "enrichening" lever." is exactly the distinction between an enrichener and the choke in the GP which blocks an air passage.

I wouldn't blame you for having given up.

Re: 56 DBD34 Amal woes [Re: Brid Caveney] #772986 05/08/19 1:36 am
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Originally Posted by koan58
"When the lever on a Mikuni is up it opens a separate circuit that provides a richer mixture than the main circuit so it functions as an "enrichening" lever." is exactly the distinction between an enrichener and the choke in the GP which blocks an air passage.
I do my best to ignore all the incorrect information koan58 writes in his various posts, even when he's sniping against what I post, and I'll try to continue to do so. But, in a moment of weakness, I'll respond to this.

In a trivial sense all three carburetors might seem to be the same because a "choke lever" is moved for starting. However,:

The Mikuni has a completely separate circuit for enrichening the mixture for starting. The lever operates a plunger that either completely closes off that separate circuit, or completely opens it. When open a separate air passage from the front of the carburetor picks up fuel and delivers it directly into the main bore. When the bike is running the plunger is closed and that separate circuit no longer has any effect.

A Concentric has a slide that is dropped down into the main bore to restrict air flow and enrich the mixture via the same circuits that are active at all other times and throttle settings.

The GP has an air compensating passage, as do both the Mikuni and the Concentric, that delivers air to the cavity between the needle jet and the spray tube. The main jet is chosen such that the bike runs best with full air flow through that compensating passage and like the compensating air passages in those other carburetors this circuit is active at all times and throttle settings. However, unlike either of those other carburetors in a GP a plunger controls the air flow through this passage allowing it to be used to give the desired richness for starting. This also allows the GP to be set up for large changes in altitude, since the richness can be adjusted using the plunger without restricting the air flow through the main bore of the carburetor. That cannot be done with either the Mikuni VM or the Concentric, further indicating the operation of the air lever on a GP is different than either the separate starting circuit of the Mikuni or the blocking choke of the Concentric.

Three carburetors, three completely different ways of controlling the starting mixture, only one of which is a choke. OK, back to ignoring koan58.

Re: 56 DBD34 Amal woes [Re: Brid Caveney] #772995 05/08/19 3:33 am
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I am glad that ignoring my comments worked so effectively!

" However, unlike either of those other carburetors in a GP a plunger controls the air flow through this passage allowing it to be used to give the desired richness for starting."

which is exactly what was being discussed. That is an air choke. It was a small issue and I'm surprised that you made so much of it.

I have been dignified and respectful in my posts, yet the remarks about myself, by yourself, seem less than polite:

"I do my best to ignore all the incorrect information koan58 writes in his various posts, even when he's sniping against what I post, and I'll try to continue to do so. But, in a moment of weakness, I'll respond to this."

"OK, back to ignoring koan58."

Reminds me of pompous supposed experts throughout history. Are you so sure of your facts? The GP plunger eliminates the subsidiary air supply, effectively choking it. What is so hard to understand about that? No need to divert to high altitude compensation to run away from the matter. I hate to say it, but that is just scientific bull. And please go back to ignoring koan58.

Re: 56 DBD34 Amal woes [Re: Magnetoman] #772997 05/08/19 3:46 am
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Originally Posted by Magnetoman
Originally Posted by Brid Caveney
when regardless of what a starting aid does - manufacturers call it a choke!! I have been a Sudco Mikuni dealer for many years, sold many hundred carbs and spares, and also used their carbs on all my race bikes. The Mikuni VM 'choke' is actually an enrichener -
Not to argue, but the 1975 Sudco manual explains that "In place of the choke the starter system is employed for Mikuni carburetors. In the starter type, fuel and air for starting the engine are metered by entirely independent jets..." The explanation goes on to make make it very clear that Mikunis have a "starter system," not a "choke." It's because the system is completely different than that of dropping a slide into the main passage that Mikuni calls it by a different name, and why defaulting to calling both "chokes" isn't a good idea.

Calling something a condenser or a capacitor is irrelevant because it's the same thing by two names. It might cause some minor confusion until someone figures out they're the same thing (like trunk or boot, tire or tyre), but the name has no effect on troubleshooting. It's different for a choke and a starter system because, unlike a condenser and capacitor, they don't operate in the same way

There's a lot to be said for Villiers' use of 'strangler' for their system of partially blocking the intake to the air filter, though that does raise the spectre of 1980s punk bands

Re: 56 DBD34 Amal woes [Re: Shane in Oz] #772999 05/08/19 4:21 am
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Originally Posted by Shane in Oz
There's a lot to be said for Villiers' use of 'strangler' for their system of partially blocking the intake to the air filter,
I spent a few minutes going through my books and literature, but so far 'strangler' wins the award for best description. Of course, I may be overlooking something...

Attached Files Amal_Mikuni.jpg
Re: 56 DBD34 Amal woes [Re: Brid Caveney] #773002 05/08/19 4:42 am
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"This also allows the GP to be set up for large changes in altitude, since the richness can be adjusted using the plunger without restricting the air flow through the main bore of the carburetor."

So is that done by tuning initially at low altitude, or initially for high altitude? With the plunger at which position (air channel open or closed, or a few thou either way?).
I can only imagine that you're talking of something like the Isle of Man mountain circuit, where perhaps one would set the carb for altitude and need to apply the "choke" for most of the ordinary part of the circuit at moderate altitudes. That's hard to swallow.

Re: 56 DBD34 Amal woes [Re: Brid Caveney] #773022 05/08/19 2:58 pm
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That's hard to swallow.


But sometimes one just has to.

The main purpose of this air bleed is to compensate the fuel mixture for altitude, throttle position and load. It changes the depression in the GP's choke (aka as venturi).


Re: 56 DBD34 Amal woes [Re: John Healy] #773032 05/08/19 4:59 pm
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Is this all some sort of gag?

JR

Re: 56 DBD34 Amal woes [Re: Brid Caveney] #773034 05/08/19 5:03 pm
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Thanks John, so how would that facility actually be used in the heat of battle?

Would you do the low altitude sections with the plunger blocking the air bleed, then open the bleed at high altitude to counter the richness up there?

Re: 56 DBD34 Amal woes [Re: Brid Caveney] #773035 05/08/19 5:10 pm
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It's interesting, and possibly relevant to this thread, that the pilot circuit of the original GP limited downdraft angles to 15-deg. to avoid fuel draining straight into the engine, especially if the float level was set just a little too high. In 1961 AMAL introduced the GP2 with modified pilot circuit to allow for steeper angles. The reason it's interesting is the DBD Clubman head, with its ~15-degree downdraft angle, was introduced five years earlier. I wonder how many Gold Star cylinders filled with gasoline during those five years. I wonder how many are still filling with gasoline today because of incorrect float levels.

Re: 56 DBD34 Amal woes [Re: Brid Caveney] #773042 05/08/19 5:50 pm
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Is this all some sort of gag?


AMAL GP manual: "COMPENSATION on this G.P. Carburetor is obtained through the medium of the primary air which passes through a slot (4) in the Mixing Chamber and then, via the air jet (2) previously mentioned, atomizes the liquid fuel passing from the needle jet (1).
As the engine supply increases or decreases at a given throttle opening with a varying load, so compensation will take place. The mixture strength supplied the engine will vary as the air supply falls off, or increases according to whether the R.P.M. decreases or increases, due to the lesser density of the air compared to the petrol. This dampening effect on the flow of liquid results in a COMPENSATED mixture being maintained."

Yes, it was used by some in the TT to compensate for elevation, or other conditions.

While most AMAL's have a fixed compensation air circuit, Mikuni VM, AMAL - MKII, TT and G.P. models use an air jet supplied in a couple of sizes.



Re: 56 DBD34 Amal woes [Re: Brid Caveney] #773068 05/08/19 9:57 pm
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That extract could, with trivial modifications, be a general description of the functioning of most ordinary slide carburettors.
They all require compensating air passages in some form to maintain a reasonable air/fuel ratio at varying RPM and throttle openings.
A carb that was just a venturi with no supplementary compensation air passage would tend to gross over-richness at high RPM/throttle opening. This is what the compensation is all about, and it applies to carbs in general.

The extract isn't referring to compensation for altitude, though that may be something that the GP open/closed air passage may have been used (or even hijacked) for?

In this case, what I find difficult to understand is that when the passage is closed the mixture is richer, which would only be useful at low altitude (if it has been set up for best performance at high altitude with the passage open).
Thus the racing at low altitude would be with the passage closed.

Alternatively, if the carbs are set up to run at low level with the passage open (normal I hazard?) then the facility to close the passage at altitude confers no advantage at all, quite the opposite in fact.

So how was this air passage control actually used to adjust the carb between low and high altitudes?

Re: 56 DBD34 Amal woes [Re: John Healy] #773107 05/09/19 3:41 am
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Jerry Roy Offline
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Originally Posted by John Healy
Quote
Is this all some sort of gag?


AMAL GP manual: "COMPENSATION on this G.P. Carburetor is obtained through the medium of the primary air which passes through a slot (4) in the Mixing Chamber and then, via the air jet (2) previously mentioned, atomizes the liquid fuel passing from the needle jet (1).
As the engine supply increases or decreases at a given throttle opening with a varying load, so compensation will take place. The mixture strength supplied the engine will vary as the air supply falls off, or increases according to whether the R.P.M. decreases or increases, due to the lesser density of the air compared to the petrol. This dampening effect on the flow of liquid results in a COMPENSATED mixture being maintained."

Yes, it was used by some in the TT to compensate for elevation, or other conditions.

While most AMAL's have a fixed compensation air circuit, Mikuni VM, AMAL - MKII, TT and G.P. models use an air jet supplied in a couple of sizes.



Thanks for the explanation John.
My statement was a poor pun.

Gag,,,,, choke..... strangle....r.....?

JR blush

Last edited by Jerry Roy; 05/09/19 3:47 am.
Re: 56 DBD34 Amal woes [Re: Brid Caveney] #773224 05/10/19 9:14 am
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I do my best to ignore all the incorrect information koan58 writes in his various posts, even when he's sniping against what I post, and I'll try to continue to do so. But, in a moment of weakness, I'll respond to this.


Funny you should say that.
When he was being arguementative for no reason other to have an arguement on the Ariel thread, I had a second look at all of his poswts right across all of the sections I browse.
Now I believe that every one has the rights to express their opinions & ideas, no matter how wrong or demeaning that are.
However every one has the same right to ignore said same people and BritBike has a nice little feature called "Ignore this poster".
Thus I no longer see anything he posts.
This is the very first time I have felt the need to do this & I like to think I am a very tollerant person but some people are just a total waste of time.


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