V50 II Slide Return Springs

[DoubleGuzzi]

I generally struggle to hold a throttle open at a set speed for any length of time (not much more than just a few miles) - not very good in these speed limit obsessed days. Ride by wire has helped a little though the 900 Street Twin had a crazily over-sprung throttle; the V7III ain't so bad.

My V50 as some of you will know is back to old skool Dell'Orto carbs with the associated heavily sprung 2Kg slide springs. I've seen plenty of mention of lighter springs for the PHB carbs but next to nothing about ones for VHB(Z). There's an old thread on here that mentions V65 ones can be used but I can't fathom out how the straight springs can replace the "tapered" ones on the V50. Before reading about the consequences, I snipped a little length off the originals, to no avail, so if you guys have suggestions/ideas then I'm listening.

In the garage, I've tried an el cheapo click&set cruise control but it's too flimsy and not very suited to the V50 brake lever arrangement. I've just added an equally cheap heel rest gadget to the end of the grip, though untested as yet. It sure looks clumsy at rest.
   

[moto]

Clipping off the end of a spring makes it more resistant, not less. Imagine clipping the end off a diving board to see why.

I believe Guzziology addresses remedies and whether or not they are dangerous. You could just get used to it, or maybe build up your twistus maximus. I have.

[DoubleGuzzi]

Clipping off the end of a spring makes it more resistant, not less. .. You could just get used to it, or maybe build up your twistus maximus. I have.

a. Yes, I did say that I had snipped before I read that - though stretching the spring to the original length means less metal to compress but spring angle is altered.
b. Not an option for some: I have RSI (4+ decades of computing) and carpal tunnel syndrome/tendonitis. Extended typing (like this explanation, takes time.) 

[n3303j]

I had issues with VHB air leaks at slide running the lighter springs on my T3. Might have been the worn slides and carb body. I finally got disgusted and went with new slides and original spring and all is fine.

I did buy that fugly Cramp Buster then went for a 2,400 mile ride to Labrador. It did make a whole world of difference in right hand comfort. No more need to squeeze that grip at all to maintain speed. Just relax the hand and ride in comfort. For the relief it provides I'll live with fugly.

[DoubleGuzzi]

I did buy that fugly Cramp Buster ..

Yeah, the cheap heel rest gadget that I mentioned is a copy of that, from guess where.

[DoubleGuzzi]

Just purchased Guzziology v9 Kindle edition - this ain't gonna be fun finding info in it. 

[bmc5733946]

These, while not particularly attractive, are very useful and can be made to fit. Beware imitations as they are flimsy and don't work well.

https://soundoffrecreational.com/products/7-8-universal-vista-cruise

The stay arms on mine are all mounted to the brake clamp using a small spacer and a longer bolt. I have them on three bikes. Here's how it looks on one of my Breva 750's




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Click image to embiggen.
Brian

[n3303j]

Just purchased Guzziology v9 Kindle edition - this ain't gonna be fun finding info in it. 

You are supposed to read the whole thing & remember it. Otherwise your Kindle gets awfully greasy. 

[DoubleGuzzi]

Being big block focused means there's little information on the VHBZ24 
Would be a shame to have to sell the '50 just 'cos the throttle springs are too strong!
My original plan was for the '50 to be my last bike, when the V7III became too heavy to handle.

[Paradoxically, the Breva is easier to push around the garage - likely due to the higher headstock. I've got the clutch working a little bit lighter, though not quite as light as the '50. The throttle is substantially lighter but still room for improvement. Maybe I should pull it from sale - has been up for sale since the '50 arrived!]

[moto]

I was out today on my T3, which also has a VHB carb, and was reflecting on why I it has always seemed so easy to maintain speed with the throttle. It must be because the throttle tensioner incorporated in the twistgrip housing is always kept fairly firmly screwed in. This might help you too, though not with the action needed to open the throttle. 

Sorry about your incapacitations that I didn't consider before.

[DoubleGuzzi]

I've re-routed the throttle cables to be in front of the headlamp holder/fork shroud, rather than behind. Seems like a smoother path and now the cables don't touch the tank on the steering at full right lock. I've still to check that there's sufficient slack to not alter the carb idle, when moving the 'bars.
A little bit of clarity on the two adjusters at the twistgrip would be useful - the manuals aren't clear. I figured one was for cable free play and the other for frictional rotation but I've fiddled a few times but not nailed it down, so to speak. I assume the larger of the two is the friction control - C & D in the poor quality pic.

[Dukedesmo]

Check out;   https://www.dellorto.co.uk/product-category/dellorto-motorcycle-carburettors-parts/carburettor-parts/vhsb34qd-rotax-max-parts/


They list both medium and weak slide return springs for VHSB, are these correct?


A word of warning though; I wanted to reduce the pull on my LM2 throttle (PHF carbs) and so bought both the medium and light springs first I tried the lighter springs which felt good but, when the engine was running the throttle hung open when releasing the twistgrip - can only assume the 'suction' prevented them from returning so I fitted the medium which work fine.


Throttle is still heavy but less so than the originals.

[DoubleGuzzi]

Rather than exerting spring force straight down the slide, the (weird though I understand the reasoning) VHBZ setup has the spring mounted at an angle and has a taper.
https://www.dellorto.co.uk/shop/dellorto-motorcycle-carburettors-parts/dellorto-vintage-carburettors-and-parts/vhb-vhbz-vhbt-parts/slide-return-spring-2kg35mm/



70mm long: 35mm outer diameter?

Your 0.6Kg option is particularly light, and can only be suitable for a few cases, I suspect. I would hope for a 1.4/1.6Kg or thereabouts; a 50% spring rate reduction could make a big difference.

[n3303j]

The amgular spring position applies pressure at a vector that moves the slide to the closed position and influences it toward the sealing face of the carb body.

[Frenchfrog]

And that interface between slide and body is worth having a look at...after decades it's likely to be scoured and worn thus causing more stifness

[DoubleGuzzi]

The angled spring, I suspect, is more to do with a not very convincing effort to counteract the inlet stroke vacuum, rather than an air tight seal. When was the last time you saw a carb slide with an air-tight seal on it? How many years did that idea last? Other bikes that have followed suit? (All rhetorical!)

Friction (stiffness) either from the slide action or twistgrip modifier, is not the real issue. It is the spring pressure closing the slide; less friction increases the problem, rather than improve the situation.

I know that you're just trying to help but...

 

[DoubleGuzzi]

In other news:
My missus tried the cheapo heel rest on the Speed 400 - it lasted less than 3 miles. Far too awkward for urban travel before hitting more rural roads. I think I'll chop my one down to about a 3/4" stub and try that. I got two of these for <$1.50 

[Frenchfrog]

Ah well....

[n3303j]

The angled spring, I suspect, is more to do with a not very convincing effort to counteract the inlet stroke vacuum, rather than an air tight seal. When was the last time you saw a carb slide with an air-tight seal on it? How many years did that idea last? Other bikes that have followed suit? (All rhetorical!)
<SNIP>
 

Struggled with a "slow return to idle" on my T3. Once I lapped the slides flat and touched up the mating carb body surface all the problems disappeared. Of course the setup isn't airtight because the slide stop screw is set to not allow a complete closure. But the designer's goal is to make the juncture as airtight as possible. This allows the slide stop screw full authority over airflow with minimum random interference.

As far as the angled return spring goes, it does influence the slide to mate with a specific face in the carb body. There is a certain amount of play between the slide and the body. Left without the influencing spring pressure the slide would rattle in the bore as pressures changed. It's effect on airflow would be less uniform. Certainly.dont need that. Repeatability is a goal all engineers strive to attain.

[Frenchfrog]

Precisly .