weber what if ?

romus · Post by **romus** » Tue Jun 07, 2011 1:00 pm

Hi,

I worked with Higgy on that Weber mod doc he gave a link to. Glad you have the Air fuel indicator plugged in.

You talk about that lean spot. Yep, typical on the DCNF, so it's a DCNF quirk to tweak out.

The other typical issue with all carbs it seems is the factory setting jet them rich for low end and lean for high end. So then that makes it too rich at low end, which can bog it, and too much fuel dumped in on acceleration/fuel pump injection. Okay, so you fix part of that issue with smaller idle jets, but then that opens up that DCNF lean spot more.

For sure the taller aux ventui made a noticeable difference. Really, you should try that. it increases the vacuum pull through the carb making it more effective. On its own it almost totally takes away the lean spot.

the lean spot is occurring when it is transitioning between the idle circuit and the main circuit.

I too tried blocking the top holes in the ET, but that also does not help that lean spot, because the top holes help efficiency at low speed/idle/cruise and that is where the lean spot is. So, I ended up making holes in the bottom of the ET so it enriched higher end running. That way the Air Fuel mix was evened out across the rev and speed range - that finally fixed the DCNF lean spot. Then I could drop the idle jet down a little to perfect it and I also dropped the accelerator pump jet down a little.

The Grose jet that Higgy likes added response, because the fuel gets in more instantaneously and with the tall aux venturi it is getting sucked through more efficiently, as I said. This matters because the DCNF lean spot hits on cruise on very light acceleration, aye. So, on light acceleration it's normally not sucking the fuel in quick enough through the main circuit when it first transitions to it. That's why if you hammer the acceleration there is no lean spot - because the acceleration pump injects extra fuel covering the lean spot.

You are doing a lot of testing. It's worth it. that is what the Webers are. they are high performance carbs that need tuning. Okay, maybe the pushed it a bit by putting Webers (better on Ferraris) on bikes, but with some adjustment your Paso will sound like a Ferrari/like a Paso. Once you sort it, then its fantastic - my thoughts anyway. Hope it helps.

jayh · Post by **jayh** » Thu Jun 09, 2011 9:44 am

Start two weeks holidays next monday,then I'm back into it,the break has been good,it's given me a chance to think things over and formulate a couple of new plans of attack .Thanks for the encouragement Warwick ,I think that the 906 and the 750 are a little different in the way they react to the weber,less capacity seems to really amplify the problem.Aren't the taller aux venturies a larger size ?.The information I have says that for more vacuum signal you require a smaller diameter aux vent.? gee the weber information is always conflicting isn't it,some say that a larger air corrector will push the transition down the rev range,some say up.The only information that I trust now is from my own research. Jay

higgy · Post by **higgy** » Thu Jun 09, 2011 10:48 am

Yes Jay, What works well on the 906 will not necessarily work on the 750.

Also there are small variations among all the DCNF's. What is perfect on one can be troublesome on another, it is a transition thing related to the progression holes in your DCNF and choke size

You are correct the Tall 4.5 aux are significantly different than the 3.5 aux.
If in the end you are stuck without a solution that works...try a different choke size first, if you can find them

jayh · Post by **jayh** » Sun Jun 12, 2011 7:39 am

An update on my lastest test which is basically the same as the previous (54,170,160) with a larger air corrector to stop it running rich at high rpm.That is 54 idles,170 mains and 185 air correctors...NICE !!!...I should mention a couple of other points,the float level has been raised from 46 mm (stock) to 45 mm.in an effort to bring the main circuit in earlier.Also my emulsion tubes have had all of the top holes blanked and a step machined from the top to just below fuel level,with the first holes positioned just above this step.(approximately at fuel level).This is a rich setup and is very similar to the weber f7 tube setup.designed to start the mains rich initially to cover the lean hole.

A run with the air fuel meter showed that the afr drops no lower than about 11 at low throttle and 2000-4500 rpm where the rich stumble can be a problem and sits nicely between 12.5 and 14.5 at steady throttle depending on gear selection.Hard acceleration drops to high 9's briefly before settling around 10 - 10.5 ,this is perhaps a little rich so perhaps 200 air correctors could be used to increase upper rev responsiveness a little.It certainly wouldn't hurt anything if the air fuel ratios went a little higher than they are at all load situations.I can see a lean spike on the meter at the transition to mains,but can't feel any performance drop at this point while riding.

I will be fitting iridium plugs during the next week or so and expect these to just about finish my 'rough tuning' of the weber.I'm sure that much more fine tuning can be done to tweak the performance of my setup,and I still have a tiny stumble just after taking off in first gear,but maybe the plugs will fix this.I don't find this to be an issue because I spend very little time at this rpm/gear selection but it may be a problem for those that spend much time in heavy traffic or have a lot of stop signs/traffic lights.

Just about there Jay.

Post by **paso750** » Sun Jun 12, 2011 8:23 am

I`m curious how the iridium plugs will do. They ran terribly on my bike but that may have been before the coil wiring mod and swapping the coils. I can`t remember.

jayh · Post by **jayh** » Sun Jun 12, 2011 9:13 am

Anyone else have negative results with iridium plugs ? I was going to ask the question before I purchased them but thought what the hell can't make it any worse,maybe I can ?

Jay

higgy · Post by **higgy** » Sun Jun 12, 2011 12:29 pm

Hey guys, on the 906 with the Dyna green 3ohm coils I had to open up the gap a bit to get rid of a stumble on accel . Last time I had it out the stumble had returned but I also had put a tank of premium in, The weber on the 906 always runs best on a mid level octane especially in the hot weather. Might be time to put a regulator back on,I do now have a decent adjustable on the fly model to try.
Hey Jay How about a picture or drawing of that ET..
A thought on that stumble, There is apparently a cam for the accel pump with a steeper ramp .Also on all the weber I have I have had to play around with the linkage to get the slop out

Nice to see someone is finally fixing the 750 Weber, Sounds Like you are well on the way to solving it at last

Many have tried and given up. Won't shut up the nay sayers, but for sure it will add value to one of the most undervalued Ducati there has ever been

And that my Aussie friend is a good thing for all of us

romus · Post by **romus** » Sun Jun 12, 2011 9:12 pm

jayh wrote:...Aren't the taller aux venturies a larger size ?.The information I have says that for more vacuum signal you require a smaller diameter aux vent.? gee the weber information is always conflicting isn't it,

The 4.5 aux is the same diameter, just taller. But since it increased performance on mine it must be it gets air through in better streamlined way resulting in a better vacuum signal.

jayh wrote:some say that a larger air corrector will push the transition down the rev range,some say up.

Don't know - worth testing. From memory I didn't find it a significant factor for the lean spot. I did find even though they say a larger AC affects the higher rev range, that it still also affects the lower (just not as much), which could worsen the lean spot. My guess is increasing AC from what you have won't improve the lean spot - but of course check it out - I could easily be wrong.

But, you said no noticeable driving issue. Yes it will be in your reading, but the whole point is to take it out of the driving. Maybe you have already done that. I found the way to check I totally got rid of it is when cruising on the motorway and just very lightly accelerate. If no hesitation there then the lean spot is fixed.

Still the grose jet is good because it gets the fuel through for the transition faster. I too had the float level up a bit, 1mm more than you, but after I put in the grose I changed it back to spec as didn't need that. Instead of grose jet you could increase float level 1 more mm and that might help the lean spot. My guess is better than a bigger AC. Your top end reading is already fine, so I don't think you need that leaner.

Wow, you basically have got it sorted though.

jayh · Post by **jayh** » Sun Jun 12, 2011 11:46 pm

Where can you purchase the fuel pump cams higgy,any ideas ?.Some silly bastard attacked mine with a file in an effort to relieve a rich take off,and now I'm not sure if this is part of my 1st gear take off issue or not!.(IT WASN'T ME I SWEAR)

I read somewhere about making a plaster mould and casting your own so I was thinking I might try a few different profiles as well as building up the little bit that silly bastard filed off the original.

I am going for a decent ride today as soon as it warms up a bit,and then I will pull the tank off for a decent measurement of everything that has been done.(I have that many notes that I'm a little confused as to which ones are correct).Once I have the details I will post my full setup. Jay

jayh · Post by **jayh** » Thu Jun 16, 2011 12:18 pm

Here's a plot of the 54 idle 170 main 185 air corrector setup.
Air fuel on left 10 rich 14 stoich 18 lean
revs across bottom

1) shows the idle mixture (a bit lean,I've since adjusted it back down via the idle mixture screws)
2)shows that troublesome rich stumble area (now well clear of the 10 stumble zone)
3) shows the trend under acceleration,all good here,the harder the acceleration the richer the mixture,not lean at all.
4) all of these lean readings are on the over-run back off the throttle the revs drop off and the mixture leans right off (perfectly normal).
5) yeah I know there ain't no 5) but if you look between the tail and the point of the no 4) arrow you will see quite a few spots,most of these are low load cruise readings which are quite acceptable in the 14-15 afr range ,this is good for fuel economy.Some are as a result of a lean spike between the mains and idles,but it is no longer an issue as I can't feel the spike when riding.

A couple of notes from my last test ride.

I have to choke the bike now to start it,same procedure as before though first set the choke to 2nd or 3rd click then 3 or 4 pumps of throttle,fires right up then quickly adjust choke so that it doesn't scream its head off.switch choke off after 30 seconds or so.

iridium plugs helped alot in smoothing out any rough spots,a much smoother ride now,still a bit hesitant when cold in the lean zone 4000-5000 rpm,but disappears once warm.Hope these guys last for a while,time will tell.

still has the niggly miss in first gear just on initial take off ,I'm almost positive its a rich miss,It is much less of a problem if I turn the choke all of the way off.

also will chug a bit if I labour it below 3000 in 4th or 5th accelerating out of corners,but this is just me being lazy,if I had chucked it down a gear and been more aggressive,it would have come out of the same corners right on the sweet spot,ready to unleash its fury.It all comes down to riding style and adapting to the jetting changes I think.

more soon Jay.

jayh · Post by **jayh** » Sat Jun 18, 2011 5:29 am

Ok, some good news guys,the niggly little miss,just after take off, that has been pissing me off for quite some time,well I got a bit bored today and had a play.
I've long suspected that it was the accelerator pump shot,delivering too much fuel too early,and I even got the file out at one stage and took a bit off the start of the ramp on the cam to see if it helped,but at that time there were a lot of tuning issues and some were masking others.Anyway to cut a long story short,I grew a set of balls today and decided I was either going to fuck it or fix it,so out with the file and off with a substantial part of the cam.

What I figured was that I would keep the same profile but just move it further around the cam so that it wasn't dosing an already rich idle circuit with extra fuel at low revs when it couldn't handle it.

As I was madly filing my cam away to nothing,another idea struck me,'what if I was lucky enough to position the ramp over the lean hole rpms'.This may enable me to go a size bigger in idle jet and cover the lean hole all in one operation.

Well I just took the bike for a spin and the niggly miss is all but gone,Iwould have to run the lambda meter to see if I have covered the lean spike,this was the one area that was still bugging me with the setup.I think that I can safely take a bit more off the cam as I can still make it miss a tiny bit by labouring the engine in 4th or 5th at 2700 rpm but over all I think that this is the breakthrough that we've been waiting for.

If anyone can find a source for the pump cams please let me know as I would have to be extremely lucky to get this right first time up,this may even work with the standard jetting too.If we can find a source anyone can have a play without risking their 'good cam'

getting there now Jay

higgy · Post by **higgy** » Sat Jun 18, 2011 10:07 am

I also had pump cam issues that took a lot of time to sort out. Mine was basically too sloppy.

I think Pierce has them,Thornbury down under as well

Post by **paso750** » Sat Jun 18, 2011 10:32 am

a few pics would be good for those incl. me who don`t know what the pump cam is you`re referring to.

G.

jayh · Post by **jayh** » Sat Jun 18, 2011 12:29 pm

I'm battling to take a decent digital picture at the moment,took the dog fishing and he got the camera case strap caught around his leg and took the whole lot swimming in the river,took a few minutes to realise,and now the camera is a bit average,but I'll give it a go in the morning,and try to get some pics of the emulsion tubes as well as the pump cam and the rest of the setup.

I'm also going to do a ride with the air fuel meter plugged in and double check plug conditions etc. before I get too carried away.

I havn't tried to start the bike cold with the current setup so that could be interesting as the pump cam doesn't start operating until nearly half throttle now.

The pump cam is the plastic disc on the left hand side of the throttle shaft of the weber (viewed as if sitting on the bike).

Mine was a number 10 cam which started operating almost as soon as the throttle was turned,and continued squirting fuel quite quickly for another 1/3 turn of the throttle,where it stopped being of any use (right about where the lean period starts on the paso) .

So during the initial low revs the engine was already running quite rich and was also getting a big dose of fuel right when it didn't need it,(just as you started to accelerate in first gear)and then as the idle progression circuit started to lean out and before the mains had fully kicked in the cam had already finished pumping additional fuel right when it should have been starting it's main dose to cover the lean hole.
These cams are probably perfect on a big heavy vehicle,but no doubt this was the closest ducati could find to a workable solution,if only they had spent the dollars on developing their own cam.

the cam may need some work to get perfect,for example it may need a small step right at the start to help accelerate off the line ,but it will then go nearly flat most of the way to half throttle(won't pump much if any fuel) or where the lean hole starts,where it will start to ramp up to the point where the lean hole finishes,thus depositing the majority of its fuel right where its needed,not right where it isn't.

I only went for a short ride after modifying the cam,the bike was already warm,but I could tell it had made a BIG difference to the low speed operation of the carby,hopefully there won't be to many issues when its cold,and it needs to be rich,but after all thats why they put a choke on carbys isnt it ? Jay..

jayh · Post by **jayh** » Sun Jun 19, 2011 2:56 am

Here is a picture of the pump cam as I currently have it.

and another showing very roughly what I have filed away.
the blue bit is what I have removed.
the top 12mm section was much shorter probably 5mm long.
the bottom 11 mm section was much longer probably 18mm long.
I have basically rotated the cam away from the pump actuator rod 20-30 degrees.The pump is not functioning at all for the first part of throttle operation - no problems.

My poor paso has spent far too long like this,and every time I remove the bodywork,more damage to my new paint work,I've given up trying to protect it now and am resigned to the fact that it will have to be re painted,but I'll ride it until my 600 is back on the road,then do the engine up as well.

If your paso behaves like a pig up till about 3000 rpm this is the root of your problems.One way to check would be to simply remove the cam and see how your bike behaves.I think you'll be surprised. Jay.

Just got back from a test ride with 55 idles fitted,No problems with cold starting,a slight lean miss on hard acceleration until warm,I don't think that I have owned a bike that doesn't do this.
Once warmed up,it's a completely different bike to ride,without a doubt the single biggest improvement I have made to my paso,and this was my first shot at it.Either I got really lucky or theres still some improvement to come ! Jay.

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