FP and DJ jet kits - 00' M750

[Howie]

Sounds like a good start.

[motoxmann]

So I've been emailing with Marc from Factory Pro all afternoon/evening. He's been a bit dodgey in answering a few simple questions I've had, but generally has been very helpful and fairly quick to reply. I'm most likely going to use a full FP kit with a custom request of which jets to include. He doesnt know off the top of his head which jets are included in the standard kit, but will let me know tomorrow (monday) when he gets to the shop. He did say though generally 1 set of pilots and 3 sets of mains.

When I mentioned I may prefer stock springs over FP or other springs due to what was mentioned earlier, he noted: "As far as springs, there's reasons why we changed the springs. That's why we don't use stock springs." And then: " The dynojet springs don't have enough seat pressure. And that makes it soft at part throttle - If the bike is twitchy, it's usually too lean."

[koko64]

In the end, you can settle on your personal preference with spring/slow jet/needle pos-n combinations to suit yourself, tuning for the way the power comes on so to speak. I used to use the softest spring and a higher needle pos-n, now I would use a stiffer spring and a lower needle pos-n (or buy FCRs with accelerator pump)  .

You have done it with cars, so you will handle this better than most.. It's just a process thing requiring alot of patience. In my mind, it's balancing the jetting requirements influenced by both the butterfly and the slide. There's two things going on at the same time. Flatslide carbs on the other hand have a more (relatively) linear process going on.

You may do some mods that allow you to access the carbs more readily like separating the airbox from the battery box.

Cheers.

[motoxmann]

You have done it with cars, so you will handle this better than most..

haha thanks. yeah, I'm even considering welding an o2 bung to one of the muffler pipes just before the can (on the backside hidden) so I can install my wideband and datalog on the street. that'll at least give me a much better idea of what's going on. and if possible I may try to find a way to datalog rpms simultaneously. might have to buy an HT pickup clamp for a sparkplug wire. all tuning I've done with cars was efi, so I was able to tap right into the ecu for datalogging.

considering I have no clue how long ago the carb parts were last replaced, and the bike has 20k miles on it, I'm dying to see how much difference this all makes. because it does run quite well as it sits right now (besides a pickup coil needing to be replaced, and occasionally glitching causing minor loss of power)

[motoxmann]

I'm buying directly from FP, but in case anyone else is looking for a Factory Pro jet kit for their M750, I found the following ebay listing (they have 2 kits available in their ebay store):

http://www.ebay.com/itm/200775785079?ru=http%3A%2F%2Fwww.ebay.com%2Fsch%2Fi.html%3F_sacat%3D0%26_nkw%3D200775785079%26_rdc%3D1

I contacted the seller inquiring exactly which parts are included in this exact kit he is selling, and I got this reply:
Steve,
This kit includes:
2-PILOT JETS #42.5
2-PILOT JETS #45
2-NEEDLES
2-SLIDE SPRINGS
2-MAIN JET-#135
2-MAIN JET-#137.5
2-MAIN JET-#140
CARB SCREWS
Thanks,
Chris
Starcycle USA
800 990 2453

[ducpainter]

haha thanks. yeah, I'm even considering welding an o2 bung to one of the muffler pipes just before the can (on the backside hidden) so I can install my wideband and datalog on the street. that'll at least give me a much better idea of what's going on. and if possible I may try to find a way to datalog rpms simultaneously. might have to buy an HT pickup clamp for a sparkplug wire. all tuning I've done with cars was efi, so I was able to tap right into the ecu for datalogging.

considering I have no clue how long ago the carb parts were last replaced, and the bike has 20k miles on it, I'm dying to see how much difference this all makes. because it does run quite well as it sits right now (besides a pickup coil needing to be replaced, and occasionally glitching causing minor loss of power)

The new needle jets will make a big difference.

The other stuff doesn't seem to wear too quickly.

Make sure you get some new main jet o-rings.

[motoxmann]

Make sure you get some new main jet o-rings.

Yeah definitely will be, along with any other o-rings I come across while doing a full rebuild/cleaning, like the one between the jet holder and main body and such

[ducpainter]

Yeah definitely will be, along with any other o-rings I come across while doing a full rebuild/cleaning, like the one between the jet holder and main body and such

Yamaha has a model that uses the same carbs. If you do a search it's been posted.

They sell a rebuild kit that might save you time and money over the individual pieces from Ducati.

[motoxmann]

Yamaha has a model that uses the same carbs. If you do a search it's been posted.

They sell a rebuild kit that might save you time and money over the individual pieces from Ducati.

actually I have a hardware store right near my house that has a MASSIVE selection of o-rings, all of which are petroleum and heat safe. so thats covered haha. thank you though

[bigiain]

The new needle jets will make a big difference.

+1. I think FactoryPro suggest replacing them before rejetting if you've got more than 5k miles on them, 'cause that's enough to wear them sufficiently to make getting the rejet dialled in right.

FWIW (this is from decade-old memory), the FP jetkit I put in my 750 came with 135, 137.5, and 140 mains, and 42.5 pilots (and new FP taper needles). After a few rounds of rejet/dyno-runs, I ended up with the original 132.5 mains with the new needles on the second-from-top (leanest) groove and the 42.5 pilots - and a pretty much _perfect_ air/fuel ratio right across the rev range for 100%, 50%, and 10% throttle runs. That was with Staintune slipons on stock headers, and a severely chopped airbox lid (just enough to keep rain out) and a K&N filter. It took a while (and cost a bit), but I was very happy with the outcome.

big

[motoxmann]

good to know, thank you

[marc999]

I read an old post and had had some Duc CV carb spring rate input.
...................

The "stock" CV carb springs are a "thick wire, many coil" spring.

In my experience and opinion,

The stock springs have the same 2 problems as the DJ "thin wire / few coils" spring. Just a bit less in intensity.
...................
The DJ carb springs have less "seat pressure" than stock and that overrichens the part throttle / high rpm operation.
and
I couldn't get the WOT / low rpm to run lean enough to pass my R&D tests - the slides lifted too high and exposed the point of origination of taper on the needle. The DJ and stock spring mid lift "pressure" was too soft.

Those are "my" tests and how I think how a carb should supply fuel to a Duc.
...................
The Factory Pro springs have somewhat more "seat pressure" than stock springs and def more seat pressure than the DJ springs - That's why, with the FP springs, when you are at 5k / neutral throttle  and getting ready to feed the throttle on, the FP springs (because they are not making things overrich) provide crisper power at small throttle openings.
I like that feeling.

The FP springs have a higher midlift pressure and that allows tuneable full throttle / low rpm - getting away from the "too rich" at full throttle / low rpm feature of the DJ and stock.
...................

A feature of the DJ springs is that WOT at low rpm in 1st gear will produce soft power (full throttle) at lower rpm, but then a harder "hit" at higher rpm. I don't care for that as the tradeoff is softer power at lower rpm - both at full and part throttle.

The FP spring pulls harder and cleaner at full throttle / low rpm  but doesn't do the wild wheelie at high rpm in 1st, like the DJ springs.
The FP spring, at 4k / cruise, when snapped from neutral throttle to 1/2 throttle, is likely to pull the front wheel up (controllably). The DJ spring doesn't do that. Very noticeable.

I've resigned myself to the fact that I can't please everybody 

Some people like the DJ spring feel and some people like the FP spring feel.

And then there's slide damping holes.........

[koko64]

Personal preference and "feel" make for interesting tuning for different customers. We're a pernicketty bunch. But seriously personal preference is important, but hard to cater for somtimes. Anyway, they're bloody CV carbs.

I suppose a range of springs available, like a range of jets would just add cost and headaches when making a kit.

I tuned some FCR 41s for a guy on an M900. He chose the jetting option that I thought gave the shittiest power characteristic. Go figure.

Then there's "preloading" slide springs on old Delortos and Amals .

[motoxmann]

I tried both the DJ and the FP springs shortly after this thread was in action, and I must say the DJ springs do pull a little harder up top, but low and mid rpm were pretty crappy and frankly annoyed me quite a bit. then again, the top end may have only FELT more powerful due to the low/mid suffering so much.

the FP springs are MUCH smoother throughout the entire rpm range, and give quite a bit more torque in low and mid.

the issue with the DJ springs I'm sure is simply from the springs being too low of a rate; they open too early, and too far, at all points, which decreases velocity and makes the slides shudder too much, also making fuel delivery inconsistent and "globby"

[koko64]

+1
A pretty fair description imo.
What set up are you going to settle on?