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PR: Proprietary Items GP advice & suggestions


Mike 40M

Well Known and Active Website User
VOC Member
Sorry to make another Gardner note in the AMAL GP thread.
Mine came with a grub screw on top, probably for idle adjustment. When it decided to drop down jamming throttle at about 1/4 open was not a good experience. Just to change it to a hex head screw.
 

vibrac

Well Known and Active Website User
VOC Member
Well after much searching and asking I have found little on the slide size to start my 1 1/4 GP2 tuning on the racer. The Gold Star owners seem a well informed bunch even if they use huge holes so I guess I will start with a No4 slide. commensurate with a 105Db silencer
The next shock is the price £75 each ! (but thinking about machining their shape I can understand it -3D printing anyone?)
So if I need larger I guess its out with the file. In that context I think I remember cutaways start at the center line as per the sketch can anyone confirm?
1581170873598.png
 

greg brillus

Well Known and Active Website User
VOC Member
I use a surface plate and linish the cut away to size using number drills to check. I think you are right with the center line as in your picture above. I have spoken to Ron Gardner a few times and he is going to make me up a type "C" carb with a 40 mm choke size. Great guy to talk to, very helpful and sounds quite with it, for a bloke in his 90's.........
 

Cyborg

Well Known and Active Website User
VOC Member
This sad looking paper weight is a number 5. Not all that accurate measuring with callipers, but was moving safety gap screws yesterday, so chucked it in the dividing head. Lined up the edge of the cutaway with a pointer and the other edge is 180 degrees away, so yes starts at the centreline. At least it does for a #5. EDB7EBBB-E0F0-477C-BEEA-8A5809BAD3CD.jpeg
 

davidd

Well Known and Active Website User
VOC Member
Tim,

I think that you are correct. I found a diagram years ago, but there was no explanation of the measuring std. So, I measure relative to the slide itself, but I contour the slide with the diagram contour in mind. I am not certain if it makes a difference, but you have to have a plan.

Slide Cutaway Angle.PNG
David
 

Phil Davies

Well Known and Active Website User
Non-VOC Member
Well after much searching and asking I have found little on the slide size to start my 1 1/4 GP2 tuning on the racer. The Gold Star owners seem a well informed bunch even if they use huge holes so I guess I will start with a No4 slide. commensurate with a 105Db silencer
The next shock is the price £75 each ! (but thinking about machining their shape I can understand it -3D printing anyone?)
So if I need larger I guess its out with the file. In that context I think I remember cutaways start at the center line as per the sketch can anyone confirm?
View attachment 32344
The number of the slide refers to the height of the cutaway in sixteenths (of an inch!), so a number 4 has a cutaway height of 4/16" from the bottom of the slide, 4.5 slide represents 9/32", and so on.
As DD indicates the cutaway start is side centered and arcs to the front centre (air side) of the slide. The arc is important as aids to present a progressive 'analogue' increasing signal to the spray tube and hense fuel take up, rather than a straight lined cutaway that presents a 'digital' signal increase with poor fuel pick up.
 

davidd

Well Known and Active Website User
VOC Member
The size of the throttle valve can be confusing. Phil is correct from the Monobloc on with 1/16". Before the Monobloc the size is measured in steps of 1/32". Thus, the Grey Flash with a No. 7 slide in a 10TT9 would be a 3.5 slide in the Monobloc and later world. I used a No. 6 slide in my 32mm TT.

The slide No. 6/4 for example is a "6" for the "6, 76 & 276" model carb and a "4" meaning 4/32". This was done because the slides were interchangeable within the same model range. You would find the number "29" on the "29, 89 & 289" models, such as 29/4.

The forward edge of the slide performs much like the fit of the slide in the bore. They both determine how and where the vacuum occurs inside the carb bore. A poor fit of the slide or an improperly formed forward edge on the throttle valve will make the fuel delivery inconsistent.

David
 

greg brillus

Well Known and Active Website User
VOC Member
Racing carb's only........the slides on 276/289 carbs' the slide cut away is in 1/16ths of an inch.......My guess is the fine tuning of a race engine needed more selection than the large jump from say a 3 to a 4 slide by 1/16" at a time, which for a road engine is a massive jump on it's own. Example.......a 3 slide on a shadow will be too rich, whereas a number 4 is on the lean side these days.
 

davidd

Well Known and Active Website User
VOC Member
I am not sure it makes much of a difference as long as you measure it at the time. Amal says that all throttle valves prior to the Monobloc are 1/32". The Amal literature says that a 276 slide stamped 6/4 is 1/8" from zero. Burlen also says the 276 is measured in 1/32" stages. but they are fuzzy about the change to 1/16". Burlen says that the GP is measured by 1/32", but Amal says they are 1/16". Finally, looking in the original Amal TT9 carb brochure, it says the throttle valve increases in 1/16" stages. If you believe either one or both...you are correct!

I know that Greg is correct about the tuning. Just make sure you know what you want from measuring your throttle valve yourself.

David
 

vibrac

Well Known and Active Website User
VOC Member
Oh joy! The cutaway is an arc and not a flat and Amal and Burlen disagree on something as fundamental as the unit of measure on a GP slide and I thought the cost of slides and the lack of a ball park figure was bad
The only bright spark is the lamba sensor on the rolling road(•‿•)
 

Magnetoman

Well Known and Active Website User
VOC Member
Oh joy! The cutaway is an arc and not a flat
The following has nothing to do with GPs but I don't think it counts as off-topic. In making measurements when converting a 2-stroke 1036 Concentric for a 4-stroke Gold Star I found that the cutaway isn't an arc but rather a straight cut from the leading edge to the center of the slide. Geometry required Amal to mount the slides at different angles to produce the required cutaways.

Cutaway_SlideNumber.jpg
 

Phil Davies

Well Known and Active Website User
Non-VOC Member
I found that the cutaway isn't an arc but rather a straight cut from the leading edge to the center of the slide.
Just to clarify a statement of mine in a previous reply,
MM's comment is quite correct, what I was (poorly) trying to illustrate was that the cutaway is cut as per the illustration in DD's response illustation and thus appears as an 'arc' when viewed front on (to the slide) by nature of the curve of the slide.
What I was trying (very badly!) to convey was that the cutaway is NOT at a uniform height to the centre of the slide body (don't laugh I have seen it done).

BTW, thanks David - every day is a learning day - I was unaware that TT slides were 1/32" nominated as I never had the opportunity (TTs were bonkers money at the time, if available!) - I raced with heavily modified 'smoothbore' clip fitting 32mm monoblocks - made for a two stroke!, so I started on first principles from waaaayyy over left field on a dismally small cutaway (with a big help up from Bill Thomas's knowledge - "Keeping filing until it stops 8 stroking", then measure!, thanks mate).
I then raced moderns on Miks and eventually Gardners.
 

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