SOMETHING BETTER THAN THE DELLORTO

The Dellorto PHF which is standard fitment on most Laverda twins and triples dates back to the beginning of the 1970's. In the intervening years many advances have been made in the field of fuelling, firstly with much better performing carburettors, and more recently with electronic fuel injection. After the addition of a modern digital ignition system, fitting more modern carburettors is the next way to reap a vast improvement in the performance of your Laverda. There are a few options available, all will require some work on the part of the owner.

Adapt carbs from a more recent production bike: This is the path that I took some years ago, with details shown below. It is not the path to take for optimum performance, but the CV type of carb offers many advantages for the street rider. They generally have a semi-flat slide but do not confuse this type of carb with real "flatslides". Probably the best source of these carbs for the Laverda rider is from the first series of "big block" Hinkley Triumphs, which are already in a bank of three, though they need to be re-spaced.

Aftermarket performance carburettor: The best carburettor ever made is generally agreed to be the Keihin FCR flat slide, and with the prevalence of fuel injection in recent years no-one is likely to make a better one.
Here is a current link showing FCR's and why they are the best, they even list a kit for Triumph triples in 39mm which would make an excellent starting point for installation on a Laverda triple. Twin riders of all persuasions have many options, usually from late model Ducatis- 900SS etc.
Another option, and one that is slightly simpler, is the Mikuni RS. The good news is that a company in Germany will sell a partial kit to suit the Laverda triple. There will still be some fitting problems for the owner to sort out, but at least the carbs come at the right spacing and ready to go. Supposedly the jetting is even at a decent starting point. Check it out here.

Electronic Fuel Injection / Engine Management: This is the next logical step, especially given that an ignition system is already required if upgrading a Laverda triple. I have yet to see anyone who has actually done an EFI system as yet, I guess it is questionable whether the return would be worth the effort. One problem of course is the load on the electrical system, especially on the pre-ND alternator bikes, but it is nothing that cannot be overcome. Even if not utilising an IIS ignition box, the ND-180 alternator and pickup system made by IIS would be almost certainly necessary as a starting point for such a conversion.

MIKUNI CV CARBS FOR THE TRIPLE

Updated 20th January 2001 (see bottom)

The venerable old Dellortos, though they were fine in their day, are showing their age now. There are a number of newer carbs that will improve the performance of your Laverda depending on what you desire. If you really want to get serious the best carb available is the Keihin FCR flatslide, these are a truly wonderful piece of gear but are very race-focussed with no chokes, a very heavy throttle action and a v-e-r-y high price.

JULY 2000- I wanted something better than the Del'ortos for my RGA so armed with the knowlege that modern bikes all seem to use CV's and have little trouble making bulk hp I wandered down to my local wrecker and came home with a set of 36mm Mikuni CV Flatslides sourced from a 1989 GSXR1100 for the happy sum of au$150. Putting CV's on a Laverda is nothing new with a fellow here in Canberra running a set of Suzuki Kettle (GT750 2-stroke) carbs way back in the early 80's and a Canadian fellow by the name of Gerry Nagy having used a set similar to these on his RGS. Many thanks must go to Wolfgang Haerter for putting me onto Gerry who was a great help in the initial stages of the project.

The first step was to pull them apart and see how they worked, what strikes you after the Dellortos is how small and light they are and when you take them apart you see why- there's nothing to them! The first thing to do was decide which carb to ditch from the original rack of four and I elected to remove the left side one as it seemed to make the linkages easiest to set up. Second job was to respace the carbs to the correct centre distance for the Laverda, with a new pair of spacer plates fabricated for the job.

September 2000- As the spacing had changed radically from the original Suzuki setup (whose cylinders are much closer together), the butterfly actuators had to be linked together again. This was achieved with a little welding onto the original tab and a small extension shaft for the other. Fuel manifolds were now also incorrect so a tee was made to fit between #2 and #3 and an elbow type connection for #1 which will require a clip to retain it at some later date. Plain sailing so far...

Next on the list is the chokes which are opened by a flat shaft running across the top of the bank. After trying to cut and reweld the original I threw the resulting mess away and made a new one from scratch- a flat shaft with welded-on tags to actuate the chokes.. All that remains to do is make a tab onto which the cable nipple can attach.

November 2000- And so it was time to fit them to the bike, after fruitlessly scrounging the wreckers for inlet rubbers I had noticed that modern Triumphs run the same carbs and have a nice female-female inlet rubber with a slight downward kink. This is important as I was already realising how tight the clearance under the RGS tank would be- even though these carbs are much smaller they are a bit wider especially at the top. A call to the Triumph dealer had them on my doorstep a few days later and by pure luck the engine side connection is very close to that of a Laverda and only minor modifiactions were required for a satisfactory fit, although ideally the stubs should be a little bigger- a job for later perhaps...

As I already had '90 Kawasaki ZZR switches on my bike I needed the moulded ends to fit the switchblocks so once again I hit the wrecker and found that a ZZR600 throttle cable was spot-on once I'd trimmed about 20mm from the inner and resoldered the nipple. Likewise for the choke I got a ZZR one but this didn't really fit but I needed the moulded end anyhow so I'll strip it and make a new cable from scratch.

From the outset I wanted to make an airbox but needed some nice connection onto the inlet side of the carb, once again the wrecker had the answer in the form of a nice inlet rubber which fitted the oval carb throat beautifully and also had a nice velocity stack-type profile and a nice looking ridge that would push into a sheetmetal airbox to form a seal.

With the carbs on the bike, the needles set to the middle clip (of 5) and nothing more than the rubber stacks as an airbox I was most suprised to press the button and have the bike fire up immediately and settle into some kind of rough idle. I had assumed the vacuum balance port on the Suzuki was in the inlet stub as there is no provision on the carb body but it soon became obvious (from the sucking sound) that the port on the top of the cap was used for this purpose- only trouble was that three of my four were broken. I plugged them with duct tape for the moment and the idle immediately improved enough so I could roughly balance them by ear. The bike sounded great and revved up well but a ride around the block showed bad stumbling once 4000rpm was reached.

I raised the needles (richened) to the bottom notch which made a slight but not major improvement so just to be sure I dropped them to the top notch and this was much worse so I knew it was running lean. Rather than try to jet it any more for the lack of airbox I am pressing on with gettting a good box and filter setup then dial in the jetting. Clearance around the right hand carb is extremely tight (about2mm) under the tank so it will be a fiddle but I'll see what I can do.

Oh, and I fixed the inlet vacuum stubs on the by machining up some tubes in black plastic and stucking them on with epoxy glue (5min Araldite).

December 2000- Airbox Development:

My God what a job this turned out to be, twice as difficult as getting the carbs onto the bike! I was adamant that going along with modern principles and having a proper airbox was the way to go from the start. The RGS airbox has a very small volume after the filter and a turbulent path into the carb via the removable rubber snorkels. Shown above is the first step in the airbox construction- making the front plate to fit the rubber velocity stacks into the box and onto the carb. You'll note the edge of the front plate very close to the right hand stack- this is dictated by the underneath of the fuel tank being *very* close to the carb due to the assymetrical engine / frame layout. There is no such problem on the left hand side. My only objectives were to make as big a volume as practically possible, have a large filter area and a smooth progression into the carb throat. The RGS replacement filters made by UNI FILTER on behalf of Club Laverda NSW seemed to have ample flow so the rest of the job concentrated on making a box that would fit into the required space. The result is shown here with quite a complex shape on the right hand side to clear the tank, the filter in the bottom plate and the rubber stacks inserted into the airbox. I had entertained thoughts of running cool air ducts into it but thought I'd keep it relatively simple untill I'd proven the project was worth pursuing.

I started off assuming the box would need to be in two halves to be able to insert it into the bike- quite a headache, but fortunately once I had it mocked up I realised there was *just* enough room to slip it in in one piece which changed how I went about construction. At this point in time the front plate is not yet welded onto the box (just in case there was a clearance problem) and is sealed with duct tape but as the whole thing has gone together very nicely I will trim up the edges and weld the front plate on too, leaving only the bottom plate removable to enable filter location.

So tonight (22/12/00) I slapped it on the bike and with the needles still at the leanest setting (where the bike would not pull more than 2000rpm sans airbox) took it out for a ride and the difference was staggering! It still felt a little hesitant in the midrange but pulled through it to redline no problems though the top end felt a little weak- hopefully just too rich but a plug chop tomorrow will tell me. I changed the needles to the middle position (all jets and needles are accessible in situ so it's a 5 minute job) and it was even stronger in the middle with just a slight hiccup in the 2-3k rpm range at some throttle openings. The thing is so tractable you would not believe it, the combination of 1130 JE pistons, Axtell cams, IIS ignition and the carbs are a killer! I can't wait to get it a bit more sorted and visit the dyno.

January 2001- Well it's nearly another month down the track and not too much has been achieved aside from a couple of thousand km of testing (it's a hard job but somoeone's got to do it!). After a little more fiddling with the jetting I had a quick run on a local dyno to check the jetting wasn't too radiacally lean to allow me a run to Syndey and back. It showed up generally a little lean throughout and richening the needle helped in the midrange but the top end required a larger mainjet which I didn't have available, there was also a bit of a rich patch when the slides first opened that I'll need to look into. Best of all though was the torque curve which was as flat as can be, between 55 and 60 ft-lb from 1800-6000rpm, where it started leaning out- very promising indeed. Those disapointed by the ultimate hp of just 62 will note that this is an eddy current dyno which tend to be more pesimistic (and accurate) than the dynojet inertia dynos that seem to have become the norm. The operator suggested that this output would be around 70-80hp on a Dynojet dyno, something I will test once I've set it up properly on this one. There should also be an extra 5-10hp coming along with correct top end jetting which will also hopefully iron out the whoop-de-doos at peak hp.

The trip to Sydney went well and the bike ran great aside from an occasional stumble when severly provoked at low rpm, which I put down to leaning out at the slightly lower altitude- it never did it in Canberra (~650m). The ride was extremely pleasant (though hot at 38degC), the bike was a pleasure and my fuel economy improved by around 20%. Any doubt I had vanished when I swapped back onto Marty's 3C with it's stock carbs- the heavy and long throttle pull along with the lack of throttle response reinforced the fact this was the right way to go.

Cheers
Steve

All content copyright of breganzane.com 1996-2005.