Ducati Monster Forum

Because price gouging Pussbucket sucks big black dog's balls.

https://www.flickr.com/photos/150482584@N03/shares/i5hjEs

Pics showing "radiused" bellmouths and transition to the throat and a radius to the slides leading edges to promote airflow and reduce turbulence. 3/4 done and requiring final polishing. For details use the search for carb mods. Title is "Carb mods while you save for FCR's".

Since Pussbucket has wrecked so many threads and tutorials, I have rolled a few of my own into this one. Thanks for everyone's help. I still haven't worked out how to display actual pics, just links to pics despite the helpful advice. I'm doing this here because it's just too much time to go back and fix all the threads those greedy pricks have ruined. Imagine the carnage over the whole Web?!

 [thumbsup]

What tools & machines involved?
How much does this affect jetting?

No luck searching  "Carb mods while you save for FCR's".

http://www.ducatimonsterforum.org/index.php?topic=71115.0

Thanks Nick.
Gert, I used an air grinder and dremel with sand mops of various grades. I also used fine finishing pastes and polishes. The carbs require disassembly of course and thorough cleaning and blowing out with compressed air.

Yes I found low speed jetting requirements changed and I tried smaller pilot jets as low as 35's, but settled for  37.5's like CCW used to recommend. Needle and main jet settings are dependent on air box mods. I use 165 mains in open air boxes with our fuel down here. I recently had to lean low speed jetting off a bit as the 98 RON I was using changed.

sick

Thx dp.
 [bow_down] Tony.

They are nothing compared to FCRs, but better than stock. I just hate how some things are built down to a very minimum standard. I like the choke/enrichening circuit though! They are just so unfinished.

I am going to test a set on my 900 today, but  will have to wrap the manifolds in exhaust heat wrap and cover the oil cooler. I have also fitted a Mikuni quick turn single cable throttle. Jetting for smoothness and economy and accepting that there is no accelerator pump, I'm trying 165 mains (175DJ), DJ 730 needles on notch#4, 37.5 pilot jets, DJ springs and Factory Pro needle jets. I will try this with some open airbox and rubber velocity stack mods.

It will work fine as long as I roll on the throttle for the first half turn rather than crank it in a roll on. The last half turn can be pinned once you are going. For outright acceleration you need the cruise muxture too rich to compensate for no accelerator pump, so as long as you accept the carbs basic design and "ride the carb" they work fine.
The carb mods actually help response and economy with less turbulence, less slide flutter, better atomization and better airflow. I know this by looking at the carbs and spray pattern with the airbox lid off and by the better response. I havent dyno tested or measured flow, but you can concretely see the difference revving the motor with the filter off.

Really enjoying this analogue bike. :D

Tested two sets of CV carbs on the Monster today. First set leaked like a sieve and the slides didn't rise correctly. OK put those aside and pull them apart to transfer the jets to set number two. Set number two required plenty of testing to get the slides to rise and fall together, but no leaks and tight as a drum. Love the choke. Very responsive and I'm quite surprised by that. The quick turn throttle contributes to that, but what must help response is no slide flutter and a nice spray pattern. Even with DJ springs which are very soft there is no slide flutter just snappy response. Thinking about it, I reckon if you just fitted a quick turn throttle to stock carbs it would promote even worse bogging without an accelerator pump and more slide flutter with the square edged slides and steps in the carb throat. I'm theorizing that slide flutter may not just be causing turbulence due to the square edged slide but is evidence of turbulence caused by the steps in the carb throat.  What do you reckon?

 Will do more work tomorrow.

https://www.flickr.com/photos/150482584@N03/shares/SB32U1

(https://farm5.staticflickr.com/4429/35511738514_419acb02b6_k.jpg) (https://flic.kr/p/W73WDG)20170803_162558 (https://flic.kr/p/W73WDG) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr
(http://)

An idea of how the worked carbs sit in the re arranged airbox.

https://www.flickr.com/photos/150482584@N03/shares/qu35z8

What the rubber stacks look like out of the airbox.

https://www.flickr.com/photos/150482584@N03/shares/a4j6Dw


Here is an attempt to maximize airbox volume. This airbox is now on a hi comp M750 with FCR39s.

Filter glued in enlarged box or what?

I used windscreen adhesive/sealant to goop the K&N filter to the airbox lid. The filter is raised and the stacks are dropped, opening up the usable airbox volume in between. I gutted an old oem filter to make a gasket and removed the lethal filter support struts and epoxied them up and under the new filter location. I went into it in great detail in the old thread.

I went to check on my notes and found my pics had been kidnapped. Getting an old Monster again has made me revisit all these mods.

You know you can hotlink pics so they appear on the forum...right?

Im still trying to work that stuff out. :P

(http://[url=https://flic.kr/p/WKc4YE][img]https://farm5.staticflickr.com/4439/35932034410_a6f7c78184_z.jpg)[/url]2013-10-30 21.34.41 (https://flic.kr/p/WKc4YE) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr[/img]

(https://farm5.staticflickr.com/4439/35932034410_a6f7c78184_z.jpg) (https://flic.kr/p/WKc4YE)2013-10-30 21.34.41 (https://flic.kr/p/WKc4YE) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr

(https://farm5.staticflickr.com/4295/35538853483_6b92edcbf2_k.jpg) (https://flic.kr/p/W9rUZa)20170803_163214 (https://flic.kr/p/W9rUZa) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr


So by taking about 20mm off the rubber stacks and "porting" them, and then raising the air filter to the very top of the airbox, there is a large increase in sub filter volume and a larger gap to the 1-2 litres of airbox volume at the front lower section. You effectively unite the airbox volume available to the stacks for each intake stroke.

At present I am testing with stock CV carbs with just a jet kit and have found the power quite ok with this configuration. Not as good as FCRs, but better than with just a stock or open airbox. 165 mains, 37.5 pilots, Factory Pro needles on #5 out of 7 and stock springs.
What's good is you can do this yourself on the cheap.

[/url]2013-10-31 11.30.20 (https://flic.kr/p/X99aWv) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flic(https://farm5.staticflickr.com/4309/36191748541_2055749b20_z.jpg) (https://flic.kr/p/X99aWv)2013-10-31 11.30.20 (https://flic.kr/p/X99aWv) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr

Enlarged airbox on a modded 900 with FCRs before and after with no jet changes on the same dyno (which by the way only get's stingier over time).

Sorry for the Izzidity, but its a pic of the old paper print out from way back.

Im a bit slow on the uptake but I got it in the end. ;)

While working on some oem carbs it really struck me how bad the lip and angle are from the bellmouth to the carb throat. The carb body is cast and then bored from the engine side out to give the venturi size which is advertised at 38mm. However, on most oem carbs I have seen, the bored section stops a mm or so before breaking through to the as cast bellmouth which tapers down closer to 36mm restriction creating a turbulence inducing lip and angle to airflow. It's a built in restrictor caused by cost cut manufacturing imo.
I will post an exaggerated illustration to show this.

https://www.flickr.com/photos/150482584@N03/shares/4X16yB


Series of pics and crude drawings in an attempt to illustrate what I'm trying to describe.

(http://[url=https://flic.kr/p/YxVxMT][img]https://farm5.staticflickr.com/4343/37117238265_584f8846f0_k.jpg)[/url]20170909_174100 (https://flic.kr/p/YxVxMT) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr[/img]

(https://farm5.staticflickr.com/4408/37117194925_867749c29f_k.jpg) (https://flic.kr/p/YxVjUD)20170909_174121 (https://flic.kr/p/YxVjUD) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr

(https://farm5.staticflickr.com/4343/37117238265_584f8846f0_k.jpg) (https://flic.kr/p/YxVxMT)20170909_174100 (https://flic.kr/p/YxVxMT) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr


It's a 1mm lip where the boring bar stopped in the transition area from bellmouth to throat. I believe that and the sharp edged slide face produce flow limiting turbulence and slide flutter. The digital calipers confirmed it. Maybe there were production runs like this and the other batches don't have it. Let me know as I'm curious whether it's a mistake or intentional for some theoretical reason I don't understand. If there was a theoretical reason for this I don't believe it worked in practice.


(https://farm5.staticflickr.com/4380/36928897866_40a519452a_k.jpg) (https://flic.kr/p/YghfKC)20170909_175130 (https://flic.kr/p/YghfKC) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr

(https://farm5.staticflickr.com/4369/37117255885_8fa5f8d0ed_k.jpg) (https://flic.kr/p/YxVD2F)20170909_175100 (https://flic.kr/p/YxVD2F) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr

Clearly answering a question no one is asking in this age of EFI, but for us Luddites with carbed bikes it's what us older members grew up with.

 [thumbsup]

Cheers Gert. It's not interesting to most people, but it is to me [laugh]. While I occasionally play with Power Commanders, it is satisfying to deal with something so concrete, tangible and analogue.

How much were the gains in the chart above? Looks quite impressing!

Know what you mean, promised myself never fiddle w injection or suspension,
lesson learned, leave that to those who know...

The chart above was from airbox mods as covered in that thread. It was a surprisingly good gain (4-5hp). The carbs were FCRs, JE pistons, ported heads and the only change to the bike between dyno runs was a significantly modified and reorganized airbox.

I did some more testing with ported carbs today. They helped smoothness and response,  but I dont expect the power gains or instant response from well tuned flatslide carbs. They are still a 38mm CV carb and surge rather than snap like FCRs, but felt good.

Oh another thing. Initiatially, I thought the modified airbox would only work on ported heads. The owner of one bike tested said the bike wasnt ported and the dyno test showed no improvement. I found out later from the engine builder that the motor was ported but that the dyno also read 10% less due to software/firmware changes.
What this means is that I still dont know if the modified airbox works well with unported heads, but the good news is that me mate's bike (944 hi comp, FCR's) makes 10% more power than he thought. The changes to the dyno I use confused my data (as did incorrect information).

I had an email conversation with Doug Lofgren about this. By the time I did he was doing FI and had no interest in the BDST Mikunis any longer.

He would address the very areas you're noticing Tony. Go for it...

or just let the moths out of your wallet and get some FCR's. ;D

Thanks Nate. Some years ago, I had a similar email conversation with him getting the same response.  I gave up and bought FCRs instead. PM sent. ;)

After more testing with modified carbs and airbox as shown, I have had to adjust jetting by leaning the needles two notches (#5 down to #3 on  DJ730's). In a warmer climate like in our Northern states I would also run 35 pilot jets instead of the 37.5's fitted (as oem 40 pilots were too rich).  Maybe the airbox mods effect wave tuning in a way that reduces the lower end fuel requirement via improved efficiency or maybe there is better fuel atomization from the carb mods assisting this, or both. No matter, the set up is more efficient. I am running 165 Mikuni main jets, stock slide springs, Dynojet 730 needles, Factory Pro needle jets and 37.5 pilot jets. The bike performs well enough with this carb/airbox combination to not miss my FCRs. The "not too bad" performance and the excellent choke allowed me to sell the FCRs for much needed cash. However, avoiding carb icing by wrapping the intake manifolds and running an oil cooler cover in cold weather has been essential.

After plug chops and  playing with the idle mixtures and needle positions, it appears fuel efficiency may have improved (even with Mikuni 165 main jets). With 37.5 pilot jets I have to run the idle mixture screws at 2 1/2 - 3 turns out rather than 3 - 4 turns out with 40's. With the 37.5 pilot jets the idle got blubbery with 3 1/2 - 4 turns out and fouled plugs. I may try 35's again. This is opposite to the normal relationship between pilot jet size and IMS settings so there must be greater efficiency. Needles got dropped two notches from 5 to 3 as I found previously. Fuel range is now about 200 miles out of the early 18 litre tank with highway use.

Dyno time  [popcorn]

Not with my money ;D
With db killers and no FCRs I reckon its down to 80 odd hp from 86. It's fun, but slow. :D

(https://farm5.staticflickr.com/4560/38578895721_b2b09ea607_k.jpg) (https://flic.kr/p/21M5VCv)20170906_100411 (https://flic.kr/p/21M5VCv) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr

A finished item, cleaned up with polished bellmouths. Running this one on the old Monster 900.

(https://farm5.staticflickr.com/4530/37690712915_65b53993a6_k.jpg) (https://flic.kr/p/ZqAKPR)20170906_100450 (https://flic.kr/p/ZqAKPR) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr

(https://farm5.staticflickr.com/4544/37862232154_de461c1a3e_k.jpg) (https://flic.kr/p/ZFKQw7)20170906_100419 (https://flic.kr/p/ZFKQw7) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr

I did that.

Disassembly, cleaning and reassembly with a Dynojet kit.

(https://farm5.staticflickr.com/4566/26369307969_80eb460d97_c.jpg)

(https://farm5.staticflickr.com/4549/24420957048_ca60c77b7a_c.jpg)

(https://farm5.staticflickr.com/4544/24420887968_3afafa3ce0_c.jpg)

(https://farm5.staticflickr.com/4538/38260120782_ca9647fb19_c.jpg)

(https://farm5.staticflickr.com/4582/37580681764_ac233df4d3_c.jpg)

(https://farm5.staticflickr.com/4521/38236984896_e0132d0b4b_c.jpg)

And I'm going to put them on the engine, hoping to gain some responsiveness

(https://farm5.staticflickr.com/4548/24420854488_30f9f14fe6_c.jpg)

(https://farm5.staticflickr.com/4568/37580655274_fa2f3862ec_c.jpg)

(https://farm5.staticflickr.com/4560/38291926401_327912ac0d_c.jpg)

Finally to breathe I'll put it to him

(https://farm5.staticflickr.com/4576/38518802836_d471a85e5d_c.jpg)

Very cool. Modified oem manifolds or Malossi?

Modified oem manifolds  [thumbsup]

Cool [thumbsup]

What is easiest to do:
Big filter  https://www.flickr.com/photos/150482584@N03/35538853483/
or small  https://www.flickr.com/photos/150482584@N03/shares/a4j6Dw  ?

Which do you think works the best?
No need f support under filter, in mid section (filter being sucked in etc)?

I didnt use a support for the smaller one,  it was very rigid. I think maybe a Pani sized filter might be a good size for next time. I would then epoxy in the cross brace up under it for support. It depends how much fiddling you want to do.

I did not do back to back tests between the filters above. I think a slightly smaller filter than the DU0900 like a Pani filter will fit the lid easier.

I'm looking foward to seeing how Pepe's split singles go.

Txh, Tony.
Could you give me the link where you modded the inlet rubbers?

Pepe`...did you lengthen those manifolds?

Hope that helps Gert.
Cheers

Pepe said he used modified oem, so they must be cut n' shut.
They must be angled to avoid the cross braces I guess.

I meant shortened... [bang] [bang]

The reason I asked is because Eric says the real power gains from using FCR's comes from the shorter manifolds. The FCR's on stock manifolds just provide better response.

That is true from dyno charts I've seen when Hord and Lofgren tested short manifolds. The torque curve gets moved up the rev range to make more hp.
I do like the long manifolds on a street motor.

https://www.hordpower.com/gallery3/index.php/Dyno-Charts/album07/manifolds

http://www.lofgrenperformance.com/carbs.htm

How are those split carbs going Pepe'?

I just noticed what he did there.

And I'm totally going to do that when I try this mod.

Angling the manifolds to clear everything is the issue. Easier on a Supersport so I'm waiting to see how Pepe' does it. I gave up on doing this on an M900 even after I seperated the carbs using two donor sets. I slapped em back together
I figure if I was going to all the effort of running split singles, I would use TM38's, TM40's or FCR's. No matter, me cracking the shits is no precedent for others more skilled and motivated like Pepe'. [laugh] I'm glad that Pepe' is having a crack at it. ;D Go Pepe'.

I have a friend who has cut down the piece of frame that hindered the assembly of carburettors in split.Il found no difference in handling of the bike.

http://ducati-mostro-forum.fr/index.php?topic=1383.msg66310#msg66310

Ah, I understand. I thought you had found a way to clear the frame spars with custom, angled manifolds.
Looking forward to your results with the split carbs. [thumbsup]

Just my opinion. I try to mitigate the higher rpm restriction imposed by the long manifolds rather than lose the low rpm grunt by shortening them. I believe the long manifolds are not only too long but actually too narrow in diameter in relation to their length. I open up the inner diameter and port them to taper down to the inlet port to help flow and increase their total volume (and reduce unhelpful high rpm resonance). I also shorten the rubber V stacks and open up the volume of the airbox to counteract the restriction on high rpm torque imposed by the manifold length. It lessens the negative high rpm resonance and terrible eddying in the "right angle"airbox.

I only know this because of what I could extrapolate from others' testing and research who are smarter than me. ;D

Gert
A 33-2060 panel filter fits nicely into the carbed airbox lid and just covers the snorkels at it's widest length while not being too long. I used a K&N filter guide searching via dimensions on their site (Speeddog put me onto it). [thumbsup].

Just a tuning update.
I ended up going for the softest CV slide springs available for that kit. I was using the oem springs with good results in the low rev range but this ported carb will not rise quickly enough in the 1/2-3/4 throttle and rev ranges with oem springs. It is either a change in resonance in the extended air box or the actual porting of the carb that is causing the need for soft springs. Either way, the carb feels great and has picked up a great deal if midrange torque. The response is very good possibly at a slight loss of response right off idle. With the absence of slide flutter with this mod I am very happy with the outcome. 37.5 pilot/slow jets, needle posn #3 with D 730 needles (stage 2 kit), 165 mains and IMS out 4 & 1/2 turns.
I have had to revise my use of stock springs which may still work better with 600 & 750 models in the 38mm carbs for those capacities. I would not bore these carbs even if I was equipped to do so in order to put corner exit response and acceleration as priority One over peak hp numbers. I can run the revs lower now and grunt out of corners on these cams and long manifolds.

These carbs feel really good now. I'm a little surprised how well they work.

Going to try Factory Pro needles and springs. They have a kit for open airboxes. Might just try the springs first on a hunch. Then test needle/spring combinations to set mixture  and slide opening speed over the midrange throttle range.

Anyone old enough to remember the SUs?  Tune rise by changing the weight of the oil.

 ;D yep

Never got to play with one much at all.

I think Tony's old enough.  ;D

(They've been used on Harleys, only reason he's old enough to know... 8) )

I think the slide/spring/damping is the classic stability vs. fast response conundrum.

I have a set of tools for synching twins...as well as a Uni-Syn.

And on an old mates MG.
Harley blokes had issues getting them to clear the 5 gallon tanks. I thought about one for my shovel but ported a Keihin 38mm instead to make a poor man's S&S.

Regarding my ported BDST, it's running rich in the midrange and gives excellent response  with the DJ 730 needle and spring. With the 37.5 pilot jet I can easily get 300+km per 18 litre tank, so it's the needle profile and spring. The needle is on the 3rd notch as per the DJ instructions.

Mine went to the new owner of our 1967 Volvo.

Boxy, but good ;D Na, 1800S? They looked alright, a bit English. I bet you hated the later model styling change.

Yep.  I did like the next generation too.  Used to repair them. 

I'd like to have another B-GT someday. I'll keep them just in case. ;D

Currently testing bigger pilot jets on the rich side for more acceleration from lower rpm's and roll on performance. Testing a bit too rich 42.5 pilot jets with the aggressively tapered DJ 730 needle and soft DJ "stage 2" springs on conservative clip positions (#3). Getting very good throttle response but fuel range per 18 litre tank has dropped 20-25 miles, (185 to 160 miles). I'm thinking that the profiled slide face flows more air acting like a larger cut away. It's definitely power tuning Vs economy and the throttle response is more lively. The fuel must be atomised quite well as the plugs are drag racer rich but not fouled.

Interesting how DJ goes for the stock pilot jet, soft springs and richer needle taper and root diameter while FP goes for richer pilot jets, leaner needle taper and root diameter and heavier springs. People I've talked to like the DJ approach in tuned 900's and the FP approach in tuned 750's, probably due to the 900 needing sufficient air volume while the 750 needs sufficient air velocity running the same 38mm carbs with less capacity.

There are so many possible combinations of jetting, needles, needle positions, spring rate that makes tuning flatslides seem easy in comparison. Flatslide logic is a series of overlapping linear circuits in sequence. The issue with CV carbs is due to the two parallel and concurrent systems that influence each other. The parallel systems are theoretically supposed to work in harmony, but as we know thats not always the case.

Be great if Santa would give me a flow bench for Christmas

https://www.flickr.com/photos/150482584@N03/shares/cZ662B
(https://farm2.staticflickr.com/1723/42638409251_fc47d52d8d_k.jpg) (https://flic.kr/p/27XNZz6)IMG_1099 (https://flic.kr/p/27XNZz6) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr

Same jetting for more response, but different plugs/gaps solves the issue of too much fuel at cruise rpm/load. The Iridium plugs with hi power coils and strong ignition wires burn that fuel with positive results for real world riding. This ignition set up supports the "rough" solution of jetting a non accelerator pump carb for throttle response.

Using iridium plugs with large 1-1.1mm gaps and high voltage coils allows running a rich 42.5 pilot jet
providing more throttle response mitigating not having an accelerator pump. Roll on throttle response and sudden acceleration is improved which is usually a weak point with these carbs. With normal plugs its just too rich, but with large gapped Iridiums the extra fuel is utilized giving the response without fouling. When you jet leaner for smooth cruising and economy the response is weak.
Fuel economy was definitely better with the large gapped iridium plugs compared to regular plugs. The extra combustion effeciency must have had me cruising easier with less throttle and less wasted fuel as economy improved 1/2 a litre per 60 miles. This solution allowed me to "over jet" the pilot jet for throttle response which I couldnt previously get away with. The carb work, airbox/velocity stack mods and "response" jetting supported with strong ignition all assisted performance.
Will be doing some back to back testing against a similarly modded 900SS which has FCR39's to get a measure of how well this all works and whether it's worth the effort. [laugh]
I did a lot of road testing and fuel economy tests to measure this. The thread on Iridium plugs in the tech section covers this "supporting mod".

Good job  [thumbsup]

Thanks mate. [thumbsup] if they made a 41.5 pilot jet Id use it.

You could go old school, solder and re-drill.  Not very accurate since you can't drill a perfect hole.

Yes, back in the day. ;)
I think the 40 pilot is ok with the DJ 730 aggressively tapered needle and it's small root diameter. I would run a 42.5 with a FP needle or 729 DJ needle.
Yesterday I told the GLW that I have enough jetting data on the ported carbs to run different tunes for M750/900 and SS750/900 with pods, stock air boxes, open air boxes and modified air boxes. That testing is thankfully done. I put aside an hour or two each week to probably account for a weeks work, but I learned what I needed to.

Now to test against FCR's.

(http://[url=https://flic.kr/p/22eDPEB][img]https://farm5.staticflickr.com/4519/38879543251_08504400f1_k.jpg)[/url]20171207_080829 (https://flic.kr/p/22eDPEB) by Tony Kokonis (https://www.flickr.com/photos/150482584@N03/), on Flickr[/img]

Buggered why the pic so large on the transfer from Flickr. The link gives a better pic.

Found a before/after pic of the rubber stacks. It helps get the stack mouth further from the air cleaner element. Seems to have a more positive effect on 900's.

Bikeboy found little effect on a 750 on a dyno. One forum member suggested that acceleration/response would be improved even if not peak hp. I have a theory that barrel/pod filters don't negatively impact the 750 motors as badly as the 900's. I believe it's linked to the port/cylinder volume ratio mentioned by Lofgren.

Road tested my ported carbs against FCR41's. Of course I expected the FCR's to be better, but by how much?
The difference in response was in the 1/2 to 3/4 throttle region. Off the bottom to 1/4 throttle and low rpm transitions the ported CV carbs by their nature had the edge, but from 1/2 throttle the FCR's took over. My M900's ported heads really seem to like the bigger FCR's. Accidental 3rd gear wheelies avoiding a carelessly merging car exiting a roundabout can and will occur.
Like others here, I reckon the FCR39's would be a good upgrade on a stock or mildly modified 900. Having ridden and compared a hi comp, extensively airbox modded, light flywheel, mildly ported 750 with FCR39's against my pod filtered, light flywheeled, stock CV carb jetted 750; I have come to the opinion that the BDST38's could be made to work very well on the 750 motors at their 38mm size, or on stock 900 motors. I think the W head 900's would also be a good candidate for a ported CV carb.

 [thumbsup]


Mine had the W heads when I bought it, ok midrange but they just choke at 140 km/h, night and day w V2.

Tony, now it`s time for the ducatigirl100 main jet mod:

http://www.ducatimonsterforum.org/index.php?topic=75075.0

http://www.ducatimonsterforum.org/index.php?topic=74413.30
"The result is a better effeciency from 1/4 to 3/4 .... is nigth and day."

Edited: Lofgren used to do this stuff, but he has rightly moved on to EFI. A partially educated guess has me thinking he may have extended the emulsion tube/needle jet base to the bottom of the float bowl as a main jet holder and redo the top section for more efficient atomization. I'm only guessing because he wouldn't divulge his secrets to the likes of me ;D.
A mate has rightly pointed out that the correct relocation of the main jet is paramount to avoid fuel starvation. Reworking the needle jet for more efficient atomization and effectively adding a power jet adds to the circuits allowing an optimum main jet without an overly rich midrange. Relocating the main jet in line with the needle jet gives a direct route for fuel draw and appears to be best practice for performance carbs. Note the BDST38 takes a less direct route and I believe that this has as much to do with the slow response as anything. All these mods help reduce compromises in jetting and enhances response. This stuff has been done to HD carbs for a long time as there's nothing like a slow bike to drive performance tuning! ;D