>>>> The first production run of slide throttles is complete. I will be
>>>> shipping them out starting next week. As soon as I do, I will post some
>>>> pix of them.
>>>>
>>>> The machinist has the drawings for the 20B slide throttles. I expect he
>>>> will be making a prototype sometime in the next week or two. Any
>>>> interest?
>>>>
>>>> Doc Custer
>>>> Retired Software Engineer and sometime Audiologist
>>>>
>>>> Here is what it looked like at Sun n Fun.
>>>>
>>>> Paul Lamar ...No rotor no motor.
>>>
>>> Those are the prototypes. The production models are lighter by removing
>>> the
>>> rectangular end and making it rounded. Also slightly shorter. And the
>>> cover
>>> plates are now 0.125 instead of 0.250, a good saving.
>>>
>>> Anodizing is optional.
>>>
>>> Doc Custer
>>> Retired Software Engineer and sometime Audiologist
>>>
>>> If you don't mind Doc I am going to make a new Teflon
>>> slide and use your housings to test the mech fuel injection
>>> on the p-port RX8 dyno engine. Other than a couple of 1/16th holes
>>> in the spacer nothing else will be modified.
>>>
>>> Paul Lamar
>>
>> OK with me. I have thought some on this. Here are some of my thoughts.
>>
>> The Teflon has a much higher coefficient of expansion than AL. I found
>> that
>> the Teflon expands 0.02 inches in 2.5" more than the AL when heated to
>> 200F.
>> I would recommend that you reduce the width of the slide to permit this
>> expansion and install springs between the edge of the slide and the inside
>> of the spacer so as to force the slide up against the fuel hole. This will
>> allow a better seal between the top of the slide and the point where the
>> fuel enters the slide throttle. Of course it would be better to enlarge
>> the
>> spacer and covers, but that means a whole new throttle. Maybe you can put
>> the springs where they won't interfere with the induction holes.
>>
>> I also used 0.01" total clearance between the slide and covers, i.e.,
>> 0.005
>> on each side. This amount is for heat expansion and the Teflon tends to
>> curl
>> slightly and without this clearance the slide tends to be hard to move,
>> especially when hot. This gap may not interfere with the sealing of the
>> fuel.
>>
>> The Teflon I get varies in thickness from batch to batch, even though it
>> is
>> all 3/8" nominally. I specify the clearances and provide the Teflon to the
>> machinist, so the spacer thickness varies from batch to batch. I think the
>> Teflon in the throttle you have is 0.400" and there is no clearance built
>> into the spacer, so Teflon 0.390" would be good, if you can find some. I
>> think the side clearance is not critical as long as there is enough for a
>> pure throttle. A carb might be different.
>>
>> Incidentally, coarse 3M scotch brite works great for deburring Teflon
>> after
>> machining. It doesn't tend to gouge like a deburing tool.
>>
>> Good luck. I think you will have a difficult time with sealing.
>>
>> Incidentally, my machinist friend needs a carb for his truck. He is also
>> thinking of doing what you propose, only with a single hole. I'll let you
>> know what he finds out and vise versa.
>>
>> Doc Custer
>> Retired Software Engineer and sometime Audiologist
>>
>> Good advice. Thanks Doc.
>> Well if worse comes to worse and I don't have room for a race track
>> shaped groove and Teflon O-ring around the slot I could go to a 1/2 inch
>> thick slide. I was thinking of a flat or wave spring, like the apex seals,
>
>> under
>> the Teflon slide.
>>
>> BTW the O-ring groove is not shown yet in these 3D's.
>>
>> Why don't you guys fly cut the Teflon to all the same thickness?
>>
>> Paul Lamar ...No rotor no motor.
>
snips...
>
> The kind of spring I was thinking of is shaped like a recurved bow as in
> archery. Put two or three in the bottom and they will force the Teflon up to
> help seal the sliding joint.
>
> I hope the O-ring works. And you have a lot of success. How are you going to
> deal with the left over fuel in the system after the engine shuts down?
> Maybe a positive shut off valve right at the slide throttle?
>
> I know my machinist is interested in the problem. As I mentioned previously,
> he plans on making one for his truck instead of buying a new carb. Would you
> like to be put in touch with him?
>
> Doc Custer
> Retired Software Engineer and sometime Audiologist

snips..

This addresses the sealing and expansion rate of Teflon issues.

Maybe this is what Doc had in mind. Larry suggested we machine the springs
in the spacer all in one operation using 7075 T6. A high strength aluminum
alloy. I used to build race car wings out of it and it is like razor blades.
I will contract Larry to make a new spacer and Teflon slide for the
all mechanical low pressure  fuel injection.

BTW It recently became crystal clear to me the difference in a venturi
and intake manifold pressure. The venturi does a much better job of measuring
the mass airflow. Not as good as a mass airflow sensor however. I digress.
Consequently the new Teflon slide will be 1/2 inch thick instead of
3/8th and the large holes will have a slight venturi shape.
We are building a new 7075 T6 spacer anyway. The rest of the slide throttle
parts will be the same as what Doc is producing.


Paul Lamar ...No rotor no motor.

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