Looking for a more fuel efficient carburettor

For Information: it was mentioned earlier in the thread about issues if your shovel has the internal-throttle piano-wire cable and thinking about a carb swop to a cv and wanting to keep internal setup, and why wouldn't you? Possibly you're thinking of going to an early/internal setup for the cleaner look. i dug out my old photos of when i did mine.

this is how i tackled it.


i took a piece of 8-10, maybe 12mm? stanless-rod, chopped a little section off, drilled through for the cable(s) and drill/tap for the locking cap-screw. i made it as big as possible for integrity. that cap-screw is likely M5 or M6. I wanted as much purchase/grip on the cables as possible.

i had an inner cable kickin' about off somehting, a lambretta i think whose nipple fitted the k-cv perfectly, save chopping up the existing cable if it didn't work out. chopped a piece off long enough to couple the piano-wire to the throttle-linkage with room to spare. i think i initially made it super-long and trimmed it back once i knew where i was with it.

i thought of making a second-version 'swaging' the cables together and silver-solder/braze too make it bomb-proof and make a less bulky coupling. but it's never happend as above has, and works 100%.

firstly, setup 'loose' i backed off the cv-butterfly so it was fully closed; the idle-screw backed off so a gap between screw and throttle-cam as i'll call it. adjust the cables so you take up as much slack, but without opening the butterfly.
bit if dickin' about, snipe-pliers are your friend here. but straightforward enough. plus once you've had the carb on/off a few times over time. you get proficient at it.

now that it's setup off throttle. when you adjust the butterfly to be slightly open to obtain correct idle, it'll introduce a small amount of slack in the cable, so when off-throttle, it's definitely backed off and NOT held open slightly. leading to unstable idle, as i found first dealings attemping to setup with butterfly at idle-position.

Now, concerns of that little pig-tail, as seen above fouling on the spring of the idle-screw and giving hassles led me to wrap some stainless wire around it to make a 'sleeve' for it and keep it in check. See below. i thought of some heatshrink and whatnot, but thought it's bullshit.

my thoughts were now it'll simply pass alongside, granted it'll touch/rub, but it's never been an issue in 15+ years of being like this. foreddaboudit. also tidies up the mod somewhat - looks ok?


so off-throttle the coupling sits a little above the throttle-cam and is clear of everything. cushty.


w.o.t the coupling just stops before the idle-screw. see picture below.
adjustments could improve this, i.e. in the picture above, if adjusted so the coupling sat closer to the throttle-cam, but not touching.
then in the picture below the coupling would sit a little further away from the idle-screw, maybe giving more 'comfort' about it?
but to reiterate, in those 15+ years of this mod, it has never given any unpredictable/unstable/scary throttle issues whatsoever.


to conclude this mod has worked flawlessly for well over a decade, maybe closer to two?
i've never found the 'additional' spring on the cv to cause the throttle to feel stiff/hard in anyway, which i thought it might do.

early on i played with trying to adjust that spring to 'relieve' the tension somewhat or removing it altogether.
but without a return spring in the event of a broken/loose/snapped cable. there is possibility for the cv to force itself fully open, not ideal?
so i left it alone and wasn't an issue anyway.

it must be noted that the cv-spring WONT return the twist-grip. but internal-throttle doesn't return anyway and relies 100% on rider doing so.
i've never found that an issue. nice stable, repeatable idle.

in fact it's a plus. kinda like a cruise-control.
i often set it and loosly rest my hand on/around the grip on long rides. allowing a fatige free throttle.
never found it an issue, even under emergency stops/slowing down.
anyone that simply releases a throttle to 'return' it in the event of requiring sudden-shutoff, shouldn't be riding a bike?

anyway, finally i found that at w.o.t, max pos'n on the twist-grip, the cv wasn't fully open, it was like 90+%, which was perfect.
giving confidence that there was no stress on the cables/coupling if you happen to be w.o.t.
saying that, riding around i did some tests and found that the bulk, 95+% riding was less than half throttle. only up the steepest hills maybe you opened it up more or to overtake that sort of thing.

there was some other tweaking: i re-fabricated the outer-cable-grip bracket on the cv to better position/route the throttle-cable. apart from unlcuttering it by chopping off the return-cable-mount . i found that as oem-bracket. the angles weren't ideal for the piano-wire. it fouled somewhat on the rocker-box and also led to stressed cable with undesirable bend-radius. this may have been exacerbated by manifold-setup at the time; push-on adapter, no isolator-block etc? your experiences might be a little different?

so there you have it.
ditch those bulky controls and switchgear.
unclutter your bars and unclutter your mind.
internal-throttles' forever.
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Very nice adaption Julian, the only other thing possibly that could be done is to put a small lead slug in the tapped hole below the clamping screw, some old fashioned nipples used to have the lead slug as standard. But as you say it has been reliable and trouble free so not worth disturbing it now.
on my Pan the piano wire is pushed to open the throttle ,,, not as easy to adapt ,,
but as i am not going to change the Linkert it doesn't matter
one mod i did do was to go for a thiner wire that made the throttle smoother
Rod that looks from covid-SF?


few changes, but pretty much the same.
cool pic, thanks, i've saved it and added it to my misc shovel collection.
This isn't useful but seemed like a good point to mention that our late Fred Warr was quite a fan of the much criticised Tillotson, it appears he had the patience to get the best from them.
(for those unfamiliar with it, it was used from 1967 to 71, it had no float chamber but instead a shallow diaphragm and large adjustment dials. The easy to access dials probably encouraged curious hands to fiddle when they shouldn't have. The diaphragm could stick and needed a prod through the underside vent hole with a matchstick.)
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