FCRs finally in, specific questions for M900

[hillbillypolack]

Yes, I know it's been a while since I threatened to get the FCRs on the M900.  In a dual install, I've probably complicated things a bit but I also installed the Ignitech at the same time.  Here is a brief rundown of the setup and how it's working.

Baseline is that the engine has high comp std displacement pistons (JE 904cc's), Dyna coils, Arrow slip-ons with standard header.  Now it had FCR 41mms and baselined Ignitech Ignition replacing the Kokusans.  Since I got the FCRs from Chris, he'd recorded the base settings which I doublechecked.

After getting the bike running and idling, it sounds good (haven't ridden it yet, need to replace those old tires).  Exhaust smell is good, horizontal cylinder plug looks darkish / damp but not wet.  When bike is idling, and I snap throttle, engine will bog (say at 2000 rpm), but rolling on throttle doesn't bog bike.  Above 2000 rpm snapping the throttle is crisper (as it kind of should be).

I'd done a search here already on FCRs, though I know my setup may be different than others.  My hypothesis is that the front mixture screw is rich, and that the low speed jet needs leaning out.  If that's the case, where is it and how do I adjust it?

Thanks in advance for any pointers

[Speeddog]

Paging koko64, koko64 to the white courtesy phone please.

[greenmonster]

Here some info & pics:
http://www.ducatitech.com/2v/inside_fcr.html

I have the same setup,
mine responds & accelerates better w Slow air screw 1,5 turns out.

Do you have the default Ducati Kokusan ign map on your Ignitech?

[koko64]

Thanks GM for the photo link.

Try playing with the idle mixture screws first. Go for fastest, strongest idle. If you get a good idle and the motor seems happy, but you get popping on deceleration, say down a hill with closed throttle then consider opening the idle screws another 1/4 to 1/2 a turn. If those settings dont give you cafe' latte' colored plugs, (and good response), then look at the slow jets.

If there are 60 slow jets in it, that could be the problem. With a stock, open airbox, people have gone as low as 50. Try a 52 slow jet, needle position #4, 165 main jets. Slow air screw say 1 1/2 turns out (probably as delivered). These are for "stock", open airbox settings and a good start. If you have a closed, stock airbox, stay with Needle #3 pos-n and the 155 main jets.

I have noticed that despite differences in street fuel the jetting in the higher throttle pos-ns tends to be very close, from people's feedback. However, there may be differences down low with fuel in different parts of the world from feedback I've received. Japanese grey imports often have huge slow jets.
60 slow jets are huge on FCR 41s, but the FCR 39s I have tuned on a 900 worked fine with 60 slow jets. My bike with FCR 41s couldnt get down the street with 60 slow jets without fouling plugs and stalling. If the bike starts easily in the cold with no priming squirts from the accelerator pump, then you know the slow jets are too big! (Probably fine if you live in Alaska).

You gotta pop off the float bowls to change the slow fuel jets. The float bowls are held on with three allen screws. The slow fuel jets are recessed into the carb bottom requiring a tiny screwdriver to get out. I do it with the carbs in place, but you can take the carbs off if its too fiddly. Remember fuel and hot motors! You got a manual tap? The drain plug is 14mm IIRC and a rattle can lid will catch the fuel.

At 1/4 throttle, there is an overlap of slow jet, slow air screw, needle pos-n and needle root diameter, so be patient. The needle should be right and 1 1/2 turns out on the Slow Air Screw is a good all round setting.

I consider Patrick Burns a 7th Dan blackbelt with these carbs. Have a good read of his article linked to Chris Kelleys site, "FCR Tuning procedures".
If you get a good setting and plug color with fuel jets, but find the throttle response down low not to your preference, then you can play with the slow air jet screw. A 1/8th of a turn makes a difference. In the end, how you like the power to come on from a closed throttle at low revs will be a personal preference, and the slow air screw can allow you to tailor this response to suit how you ride.

Let us know how you go.

[koko64]

Here some info & pics:
http://www.ducatitech.com/2v/inside_fcr.html

I have the same setup,
mine responds & accelerates better w Slow air screw 1,5 turns out.

Do you have the default Ducati Kokusan ign map on your Ignitech?

Use premium fuel until you have your ignition map sorted. GM and I have maps you could try as we have similar mods. Many folk knock off 2-3 deg max advance with hi comp. Im at 34 deg max advance from 6000 rpm. If I go 944 i'll go 33. Check out bikeboy.org and Doug Lofgrens MPS site ignition studies.

[hillbillypolack]

Lots of good info here to keep me fiddling for a while.  Thanks, all.

So, just to square things away, it'd be prefareble to fiddle with the carb settings first, and later fiddle with the Ignitech (?)

koko, thanks for the detail in your post.  I've (finally) gotten some time to methodically try to understand the carbs so your suggestion on overlap of settings is timely.  I'll have to try a few things and see what works best.

Working (now) with pods for access to carbs so we'll see how things sort out.

[koko64]

I forgot you are running pods. Are they the angled K&N RU 1750s?

On the dyno from the EGA readings, I noticed the K&N RU 1750 pods wanted smaller main jets and a leaner needle pos-n.

Consider needle Pos-n #3 and 160 mains if you are running the 1750s Chris sells.
I found one notch corresponded to about 0.5 on the A/F ratio. At needle pos-n #5 the thing was running at 11.5:1 and 12:1 A/F at 1/2 and 3/4 throttle. It was leaner with an airbox (tells you something about the relative airflow rates). I think GM was once running 162.5 main jets IIRC but I don't know what pods he's running or if he has velocity stacks in them. Better PM him.

I would sort out the timing by knocking off some advance at peak torque revs just to stop some detonation. At least the canned map is gradual enough compared to the stock timing which maxes out early causing pinging with hi comp (and potentially holed pistons). If you're unsure, maybe keep it at 33-34 degrees from 6000 rpm. Premium fuel is insurance and so is about 34 deg max advance. The JEs have a fair sized crown on 'em! Like I said, with 944 JEs I'd run 33 deg max from 6000.
That Igniteck also has rev limiter and shift light functions among other things. I reckon it's pretty cool.

I just re-pmed that pm to you from awhile ago with the numbers from my map. Maybe go with 33 max advance from 6000 to be sure. Your JEs will be a little taller than mine on the crown as Brad may have machined the crowns on mine when they were in another bike (a buddy gave them to me,..too long a story). You could easily have a good 11:5-1 ratio with your pistons.

[sofadriver]

not trying to hijack this thread but................
i'm considering these for the SS/SP and don't want to get involved with all this tuning.
ca-cycle recommends the 41's but threads like this worry me. if i just want a nice, smooth running bike should i go with the 39's?

[koko64]

39s need tuning too. Everything does. You could leave the SS stock
Get the 41s and leave the airbox stock and ask Chris to give you some 50 slow jets. Put them in and run it with the otherwise stock jetting with stock, closed airbox. Put the K&N filter in there if you don't have one.
OR
Chop the airbox lid
52 slow jets
165 mains
Needle at #4
Should be close enough.
It'll run better and cleaner than stock and won't freeze up on you in winter.

[koko64]

I remember that concept.
If you could check with the ega for each cylinder on a dyno, you could jet each, like mapping seperately. My liquid cooled VFR400s had the rear cylinders leaner by a size with stock jetting. Go figure.
I don't bother. With an air/oil cooled 900, you do well to err on the slightly rich side with main jets for a margin like the jet kits often suggest.
165 mains with open a/b is on the rich side and makes good power. FCRs have a good tolerance for running a little rich compared to the stock carbs.