Dell Orto Slide Springs

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Davo

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Reading the thread on Q/A throttles and finding the twin cable Tomaselli on my new Le Mans 3 pretty darn heavy I did a little research and find that Dell Orto make various weight slide springs. Posts on Guzzi fora lead towards the use of the lightest spring for relieving throttle tension. This is a 0.7kg rated spring, with the heaviest spring at 1kg more than that.

Which springs are used in the dels on the Laverda triples and if it is the heaviest would a drop in spring weight work for reducing tension on the throttle, and therefore be easier on the hand.

All pretty academic for me as I am swapping to Miks, but just wondering, as you do.

Dave
 
Good question Davo.. I have a fairly heavy throttle on the racing Monty, and a Domino quick action throttle has made it a little easier, but I'm keen to see what options there are.. :D
Thoughts lads..??
Ian
 
Dave

According to other posts I've read on this forum triples seem to come standard with the middle of the 3 spring rates. Having said this there's no accounting for vagaries in the Italian supply chain, or for the actions of previous owners, so you could have any or all springs, maybe even mixed. The only way to be reasonably sure to have all 3 the same and as light as possible is to put 3 new ones in.

Having said that, there's been quite a few postings here about simply shortening the original spring to reduce preload. I guess the way to do that is progressively shorten it until the throttle starts to stick wide open, then add a couple of coils back :D

Ken
 
LaverdaIan said:
Good question Davo.. I have a fairly heavy throttle on the racing Monty, and a Domino quick action throttle has made it a little easier, but I'm keen to see what options there are.. :D
Thoughts lads..??
Ian
Click to expand...

Hey Ian,

I have plenty of springs including the so called lightest Dellorto springs you can try. By the way the Domino quick action throttle makes the whole thing heavier hence the complaints from your pilot.  :-*

Cheers Crispin
 
I have the lightest springs in mine but still went back to a standard throttle instead of my tommaselli no hand ache now.Much lighter.

Lemon
 
Snip off about 30mm of the stock springs, bend the ends flat so they don't foul anything and you're good to go.  Have used this set-up almost from the day I got my triple in 1980, transferred it to the RGS as well as many others coming through the workshop.  Never had an issue with sticking throttles.  If the throttle does tend to stick, would most likely to be caused by extreme wear on the slides, which are consumables and need replacing every 100000km or so...

Doesn't shorten the throttle travel any but is so much easier on the wrist!

piet
 
Bevelheaven.com sells these springs in 3 different "weights": .7, 1.1 and 1.4kg. They are about 9 dollars apiece, and since I have had more than a few bikes that used either PHMs or PHFs, I bought a few of each weight. I think it would be difficult to make any generalizations about which springs should be used in any given set up, since there are so many variables determining the force necessary to activate the throttle: bell crank vs. cable "splitter"; wear on slides; whether slides are gummed up; suction of cylinder; type of throttle cable and whether it is lubed..etc. I just insert a set of new springs, make sure everything is lubed up correctly, and test...
 
I wonder how well a PTFE spray would work with a slide, or is it just not worth the risk of possibly getting insoluble particulates inside the fine orifices?
But if it comes to that, what about one of the low friction coatings like titanium nitride or maybe even DLC? I know the metal has to be heated up quite a lot so it might not be worth the risk of warping the slide, but has anybody actually looked at doing this?

Ken
 
Ken,

Chrome plated brass slides were available for quite a few of the Dellorto PHB/PHF/PHM range, guess mainly for moto-x use.  Only ones I can find these days are for PHMs (38-41mm choke diam) at a truely exhorbitant price, ?78/ea.  These will definitely wear better than the stock zink alloy items, may even keep the carb bodies in better shape for longer!

Not much point in lubing the slides, will be washed away by fuel in no time.  A few drops of light oil to see if all is working smoothly is all I use on the slides.  The linkage shafts can do with a liberal smear of grease, but once the bushes are worn, it's best to replace them and shafts if neccessary.

piet
 
I don't know of anyone who oils the slides. If you note, almost all of the wear on the slide is on the portion facing the induction to the cylinder; caused by it getting sucked towards this point. Having a chromed slide would certainly make for better wear, as can readily be seen if you have disassembled a pair of Mikunis vs. a pair of dellortos that have seen similar mileage. I remember when I got my SF2 it would not idle after I had rebuilt the carbs, and until I noticed the play in the slides. I was stumped (I know, should have checked this when I rebuilt, but then I would not have a point to make in this thread). I didn't know there were chrome Dellorto slides available, since I needed a new set for the PHMs on my 900SS when I had it.
 
I had the Delordo slide on my 1992 TE 350 Husky Teflon coated and it worked very well,it had a tendency to work in quick jerks especially in the wet.After the Teflon coating it was as smooth as butter.
So next I did the slides in the Laverda 3C,not so good,they ended up having some reaction and ended up with a blister like finish that even with a lot of fine sanding with 600 would not move freely in the carb,that was with Hot Jet Finishes in Melbourne who apologised and didn't charge me,but I had to buy new slides at $80 each
 
why not taking your old sliders to a workshop that can make sure they are still round (or make the round if they are not...) and chrome them with a thick layer of chrome, get them fine grinded/polished to the right diameter and have nice and easy moving sliders for roughly the same cost of new ones, but some that last?

or - if worn to much, get some new ones and do the above? Might cost 200 ? in total, but well worth it - especially with current gas-prices...  :o
;)
 
I think that the carb body wears at a fast rate also, it is just not as easily visible as on the slide. Ideally the slide should be replaced before it is totally stuffed as they usually are due to the price of them. I never had a slide that lasted anywhere near so long as Piet mentions, but the 36mm have even less support in the carb than the 32mm so that would account for more wear.
I had my slides sticking open in the wet when using K&N filters and it was fixed by changing to Unifilter oiled foam.

 
On my Jota I have a QA throttle by Magura, bought from venhill. the r/h switchgear was replaced by a set from a Firestorm, which that generous old boy Clem had given me a year or 2 previous suitably wired and marked up...it suited because it was nice and thin and looks pretty good too . I never found it heavy going, though did disconnect the accelerator pumps for other reasons, which lightens it up. Now those are back in, courtesy of Keith's insistence(!), I have some lighter  springs now from the dellorto suppliers,Eurocarb. But then I don't find the cable clutch too heavy generally either, unless stuck in a town (Caen a few years ago  was the  worst ever....every bloody light turned red and the old bus got so hot I had to turn it off for fear of seizure...)
Nick7
 
I did what Piet did and shorten the springs by cutting. It made a significant difference, it is a modification I wish I had done years ago. It made it possible for me to continue to ride the Laverda after major surgery to the right wrist/hand. Never a problem with slides hanging up, Cheers Dave.
 
The problem with light springs on a big twin is the slide sticking open from vacuum on overrun at high rpm. My bevel 900 racebike with Malossi carbs would do it in a heartbeat.I can't remember which springs I ended up using but they made the throttle almost as heavy as the clutch.it probably had something to do with the surface area of a big slide and big piston sucking against it.
An old trick a Britbike mechanic told me about is burnishing graphite into the slide to make the slides easier to operate. It seemed to work pretty well on old clapped out Amals.I don't think the pot metal used for the slides will take to chroming or coatings very well. I'm pretty sure the chromed slides are made of brass and that is why they are so expensive.
 
I have 11 Dellorto carbs installed on several bikes currently in my garage (PHM and PHF). Never seen a slide in any of them with an anti-friction coating. They're all bare metal.

Cheers,
Cam
 
The PHF/PHM/PHB slides seem to have something like an anodised finish.  It is a bit harder than the cheddar-like metal underneath, but not hard enough to prevent wear on the slides for long.

piet
 
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