Vacuum Throttle Binding

[pehayes]

I'm helping an Irish friend to diagnose and resolve a sticky throttle.
Cali-III with round slide carbs.
Throttle system works smoothly.
Riding at 90kph he backs off to slow for a curve.  As he tries to accelerate out of the curve, the throttle feels very heavy and sticky.  Under more twist force it eventually jumps free and delivers and uncomfortable jerk of power.

Certainly sounds like carb slider binding under vacuum to me.  I've asked him to inspect slides and bores and polish anything that feels like a burr or rough surface.

Any further recommendations or suggestions?  Lubrication?  Any source for replacement slides?

Patrick Hayes
Fremont CA

[ccoli]

My SPIII has been like that for years and 100,000 miles. Tried replacement slides, no better. Changed cables, no better. I may have even changed carbs completely.  I just have gotten used to it.

[Antietam Classic Cycle]

Any source for replacement slides?

http://www.herdan.com/dellorto/slides/

[John A]

Two things come to mind first is accelerator pump links on phf carbs not correctly in place and sticking ignition advance

[dguzzi]

Maybe that's why Dellorto is know for strong springs?  I found that out w/ Alazzura owners.

[flangeman_70]

I'm running my return springs in PHF36 at approx. 25 mm shorter due to the heft they required and have NEVER had binding issues.
If in Ireland  two best bets for parts are http://www.gutsibits.co.uk/pr/Home/index.php and http://www.stein-dinse.biz
I agree with your advice to your friend and add to check the bar end weight isn't binding on the grip as the Tomaselli roll-off is not limited and he might be over doing it and the bar weight is grating the grip.
Check carb slider and be sure the Idle speed screw is not slipping off the adjustment ramp and grabbing the side of the slide. If this is the case you can just swap the left and right slides as the ramps will wear out over time.

Good luck!

Adam

[mtiberio]

remove the accel pump lever from the top cap of the carb and try again...

[Antietam Classic Cycle]

If in Ireland  two best bets for parts are http://www.gutsibits.co.uk/pr/Home/index.php and http://www.stein-dinse.biz

Why not Eurocarb Ltd. for Dellorto parts in the UK?
http://www.dellorto.co.uk/product-category/dellorto-motorcycle-carburettors-parts/carburettor-parts/phf-parts/

[bmc5733946]

Shortening a coil spring does not decrease spring rate it may decrease seat pressure depending on installation height.  Making the spring with more windings and or smaller wire all other things being equal will!  Spring science is weird, talk to a spring engineer some time for a list of the variables.  My knowledge comes from experience with trial and error and minimal research.  Hope someone with real knowledge chimes in here!

https://www.eatondetroitspring.com/cutting-coil-springs-calculations/

Brian

edited to add link

[flangeman_70]

Hope someone with real knowledge chimes in here!

https://www.eatondetroitspring.com/cutting-coil-springs-calculations/

Brian

edited to add link

Hi Brian,

You are absolutely correct in your statement BUT when the spring is installed it is under pre-load and by shortening the spring we are reducing the Pre-Load and by doing that we are reducing the work to compress spring.

Check out Hooke's Law https://en.wikipedia.org/wiki/Hooke%27s_law

Adam