weber what if ?

[higgy]

Just goes to show what could have been if Ducati had spent some time doing their own tuning.A little time and patience and the Weber works very well

[jayh]

And that growling sound Higgy,you forgot to mention that lovely growl that a tuned weber makes , man are those guy's going to be wild they chucked their webers in the bin

[jayh]

If any of you guys with webered 750's have your tanks off at the moment could you please check your pump cams and let me know the number.I'm curious as to if they were all fitted with the 10 cam or not.

There may be an alternative to filing the cam down as mine has a steel plate that fits neatly inside the back of the cam,and slides onto the shaft.It must be to help distribute the load from the plastic cam back to the shaft.It may just be a case of fabricating a new plate with its shaft slot rotated slightly.I'm not sure if the start of the cam is long enough to do this,I can't tell with mine anymore just a thought.

I took the paso to town today,what a difference in traffic and roundabouts,corners etc.No farting or missing,just nice smooth power delivery.I put a cardboard degree wheel on the throttle and tried to get it to miss,so that I could record the throttle position in relation to cam position,I had to actually try to make it miss,it didn't want to do it on it's own.Anyway ,I found that I still could remove a little more of the cam,as there was still a slight miss right where the ramp begins.

There is a problem that I have created now,there is a long way from throttle off (idle stop) to throttle on,that takes a bit of getting used to.You have to get the feel for when the power is going to start,its not an issue in the higher gears but 1st and 2nd can be a bit jerky unless your smooth on the throttle,it could be likened to getting the feel for when a clutch is going to grip.
Don't get me wrong,It's very easy to adjust to,it just isn't 'perfect'.

I still have a few days of holiday left so I'm going to fabricate an aluminium cam,with a slight rise (1-2mm) right at the start,and then a very gradual rise through the next section(maybe 2mm over the next 1/3 of the cam),then a fairly aggressive 5mm rise starting just before the lean hole appears.

This may help bring the power back on less abruptly.we'll see. Jay.

[Turin]

I've got a 10 pump cam.

[jayh]

Thanks Turin,I'm preparing a document for the 750 weber at the moment and every bit of info helps.The 10 cam on mine supplied way to much fuel down low in the rev range which caused sluggish response around 2500-3000 rpm .This translates into a lack of low down torque especially in the taller gears 4th and 5th,and to a lesser degree in 3rd.In first and second gear it caused stumbling. Jay

[scimmione]

jay - I've been following this thread very closely and I appreciate all the painstaking work you've done sorting out the Weber.

Your accelerator cam profile observation is intriguing and as a result I've been searching for any and all info pertaining to Weber accelerator cam profiles and I found the following threads on FerrariChat.

Weber DCNF accel pump function, change and cleaning -Talks about acc pump volume

Weber accel pump cam / Air cleaners yet again / Ansa resonators - Talks about acc cam profiles

I am sure there are plenty of Weber tuners/experts out there but the people at Peirce Manifolds know their stuff. They may specialize in Ferrari, Maserati & Alpha Romeo Webers, but they really know the Weber hardware inside and out. I'm sure Steve would be able to give you lots of insight on design and function of the 44 DCNF. I hope those posts can be of some help: I'll be utilizing your research on my '87 and I'll be sure to post the results here.

Thanks again for sharing that priceless info!

Chris

[jayh]

Thanks Chris,
They are both interesting reading,I've been through the first one before when looking for jetting info,but it was good to go back over it with the pump cam in mind.It would appear that a custom cam is the only way that we will fix the problem,as any fuel at all added in the early stages of acceleration seems to be to much,my pump cam is adding no fuel whatsoever during this phase and I'm getting no miss or hesitation from lack of fuel,even when I snap the throttle.My guess is that ducati tried one of the smaller 3mm cams and it wasn't enough to cover the lean spot further up the rev range,so rather than develop an application specific cam,they went for the fat 10 mm cam,the next size up,even though it was way to rich down low,it covered the lean hole which they considered more important.I will post a rough hand drawn picture of what I have done with mine,but I won't guarantee that it will be the same for yours,because climate altitude etc play a role with the weber.
All I done with mine basically was to file the cam width the same as the width at the start for the first 1/4" or so rather than the cam starting to rise immediately you touch the throttle,then I let it ramp up from that point.I done this in a few seperate goes and tried it out each time,the further it went the better it worked,So in other words the longer it went without getting any additional fuel from the accelerator pump the better the low speed performance got.Obviously there will be a limit to this and my bike is running very nicely so I'm reluctant to file any further without a spare cam to fall back on. I really don't think that it is too important the degree that the cam slopes up at but what I done with mine was use a half round file at this point so that it started to ramp slowly at first and progressively got steeper,you will notice this in the earlier photographs.If I were doing another one from scratch, I would mark where the rod is touching the cam at zero throttle,(this is probably at about the point where the cam starts to ramp,it was on mine),then file it flat for a further 1/8",and smooth the bump so the rod can ride over the start of the ramp without fouling,put it back on,go for a ride.You will probably have to do this several times.I done this three times,the first time months earlier didn't really achieve much,as a matter of fact,I wasn't sure if I had made the problem worse so I went away from the idea for quite some time.If only I'd kept at it I would have saved myself a lot of work.
The end result is I used to have a sports bike,I now have a sports tourer,no change to the top end but much smoother down low ! Jay

[chasaduc]

Just a thought. In my mind this should be posted on the FAQ page. But I would clean it up a bit so that it is not 4 pages long. There is a lot of good info here and a lot of good hands on experiments and trials. I swapped my weber for a mikuni. But if i get really bored and the weather ever cools down maybe I will fix up the weber and put it back on.

i will be honest I did notice there is a bit of difference in the sound between the weber and the mikuni. I dont mean the sound that I usually heard of blump blump thpppbbbbttt when it died. I am gald that i am not proven to be totally insane. I was thinking i was crazy about changing the carb and not the exhaust could make a difference. or am I dumbfounded how well my bike ran with the new carb? Well I am crazy but no one can prove it yet

[jayh]

Just hold the thought Chasaduc,I'm writing a condensed pdf version at the moment and should have it finished soon.As I have posted at various points along the way,some information has become irrelevant,as I have discovered other ways of achieving the same goal,also I havn't got another paso to compare it to,How good is good ? How does it compare to a Mikuni conversion ?,How much difference would just fixing the pump cam make with standard jetting ?,There are still so many things that I havn't tried,but it is time for me to have some fun with my bike,so while it will not be the definitive guide to tuning your weber,I hope that it will provide enough information for those having trouble to inexpensively and easily get their weber to a stage where they can enjoy the bike as much as I am at the moment. Jay.

[Mc tool]

If any of you guys with webered 750's have your tanks off at the moment could you please check your pump cams and let me know the number.I'm curious as to if they were all fitted with the 10 cam or not.

My 906 has #10 also

[jayh]

Thanks from across the ditch, The larger capacity 906 responded better to the weber than the 750 but still wasn't great,according to Falloon,I wonder how much of its problem is pump cam related ?
Wouldn't it be nice if someone had access to a cnc router or lathe and we could just forward an autocad file of a working cam and get 100 copies run off,but more R&D required before that can happen. Better pull my finger out eh! Jay.

[higgy]

would be more cost effective to stamp them out wouldn't it ?

[jayh]

Hey,did you get an early release for good behaviour Higgy ? Seriously though I reckon it would be an expensive exercise getting a die made for such a small run.laser cutting and cnc machining are getting much cheaper as the technology spreads,we get a bit done for us at work,but I'm no expert on the subject though.

[paso750]

lathe is always cheaper than cnc, laser, water cutting or whatever there is.

[Mc tool]

Thanks from across the ditch, The larger capacity 906 responded better to the weber than the 750 but still wasn't great,according to Falloon,I wonder how much of its problem is pump cam related ?

I noticed with mine ( not very scientificaly) that the cam is contact with the ( accelerator pump opperating ) lever at idle and stops moving lever at about 3/4 throttle, I spose if you dicked about with the idle / 1/2 throttle part of the cam profile you may be able to improve things a bit but from what I have read (Weber carburettors by John Passini ) these carbs with a diaphram type pump would seem to me to have relativly poor control over accelerator pump discharge ( amount and duration )compared to some of the better spec'ed piston type pumps, Soooooo I am putting my faith and hopes on ( trumpets and drum roll ) Weberology ( Cheers Higgy and Romus ), just cant find me some of them 4.5 aux venturies .......... nonewheres( the making/ modifying part of my brain is starting to twitch )