Pod Filters and FCR41s...noise?

[TreyRiser]

So today i finally went through with it....i got the FCR 41s for my 1999 900 and i put them in...got her running and went for a ride...and first off i am still smiling , my question is should i hear this chirping noise when i get on it, i can here the whoosh which is sweet, its the metalic chirping noise that i am not sure about? Has anyone heard this before and most importantly should i be frightened? If it isnt a bad thing thats great becuase the bike is running like a dream other wise...2nd gear wheelies no problem...these flat slides are awesome!!

[OT_Ducati]

lotsa miles logged,, sounds wonderfull..
chirpin' the whole time, not to worry.
mechanical symphony, enjoy.

[TreyRiser]

Good thing then... cause i thought it sounded bad ass...now if it wasnt so darn cold i would keep riding.......ah what the hell...one more ride cant hurt right? [moto] If you have a carbed bike by the flat slides!!!!!

[junior varsity]

crickets is normal.

[Autostrada Pilot]

Just out of curiosity (since this is a nice collection of 900 owners), what gas mileage are you guys getting?

I've got a 1999 900 (full airbox, stock carbs, megaphone exhaust, 15/43 sprockets) but I'm only getting low 30's even if I'm pretty easy on the throttle.  Just wondering if I need a jet kit or maybe just need to tweak my current carbs.  The power is fine, but I think I should be getting better gas mileage.

[junior varsity]

My stock carbs are getting the same crap gas mileage.

It, of course, worsens over times as the emulsion tubes and needles wear, along with whatever else can happen to the jets. I've taken mine apart, and I remotely understand how they work, but its still voodoo, imo.

According to Chris Kelley's DucatiTech FCR FAQ, gas mileage is improved with FCRs. Curses! NO reasons not to switch other than money.

[ducpainter]

I get a consistent 40-45 mpg with stock jetted carbs for street riding, but my street riding is more like a back roads tour. Lot's of speed, but very few stops and starts.

I used to get 25 on the track with the same bike.

[Autostrada Pilot]

Sorry for the threadjack (maybe I need to start a new thread).

What do the jet kits do?  How often do needles need to be replaced (I can't imagine that metal that shoots gas would wear very quickly)?

Anyone know of a good carb FAQ?

I'd love some FCR's, but I'm pretty sure $1k to replace something that it working pretty well isn't in the budget.

[junior varsity]

Ok, first some background, the needle goes in and out of the emulsion tube (somebody correct me if i get terminology wrong).

It acts like a tapered plug. As you open up the throttle, the needle is pulled out of the emulsion tube, allowing more gas to flow from the emulsion tube into the intake manifold.

The jets bring gas from the float bowls into the tube. You've got 3 (wait, right?) main, pilot, idle. They are teeny tiny. The floats control how much gas is in the bowl.

A jet kit changes the characteristics of your carburettor by adjusting the size of the jets and how far inward the needle rests to begin with.

I'm not a carb-genius, so others will be able to correct my mistakes and share the rest. Taking them apart to clean is really pretty easy. There are screws on the outside with little spigots - those are the float drains. Anytime you pull the carbs, you want to drain 'em first or you'll be wearing more gas than need be.

[junior varsity]

CV carbs like Mikuni 38's in our bikes are described around 4:50, I believe. Fairly good video for general background:

SI engine carburetor

[junior varsity]

OP (TreyRiser):

Crickets like this: Ducati 900 Superlight, 944 with split keihin

Seems normal to me.

[koko64]

My stock carbs are getting the same crap gas mileage.

It, of course, worsens over times as the emulsion tubes and needles wear, along with whatever else can happen to the jets. I've taken mine apart, and I remotely understand how they work, but its still voodoo, imo.

According to Chris Kelley's DucatiTech FCR FAQ, gas mileage is improved with FCRs. Curses! NO reasons not to switch other than money.

G'day AM/TR/Guys

TR, depending on your bikes mods you may want to get those carbs jetted and checked on a dyno. I nearly forgot to mention that. If it's pretty close to stock the as delivered jetting could be close enough though. Plenty of folk just bolt 'em on and are happy, but if you have significant mods you will want to consider having the carbs set up properly. Chris Kelly's site (Cal Cycleworks) has good information about this.

With the stock Mikunis and a jet kit (DJ kit, stock 40 slow jet, needle pos-n #5 out 6, big 165 mains,and FP stainless needle jets), my fuel warning light came on at about 180-200kms (120 miles).

With 41 FCRs (jetted with needle pos-n #6 out of 7, but 52 slow jets instead of 60 and big 165 mains), the light comes on at about 240-250kms (140 miles).
Hope I got the conversion to mpg right.

I am using 98 Octane fuel.

I mentioned the jetting so you know that neither carb was running stock/as delivered jetting. The FCRs still had better economy with the as delivered 60 slow jets, but I found them too rich for my bikes particular state of tune. I found a greater variance in fuel use with the Stock carbs. Don't know why, but it varied more with how differently I rode than the FCRs.

This is with general commuting and the odd blast through the local hills.

I was quite surprised. I was expecting that the FCRs accelerator pumps would make it use more fuel. Maybe the FCRs probably atomise fuel better, but who knows. What I have noticed is that the bike is so much more responsive at small throttle openings that I am twisting the throttle less to get more acceleration. That's the only clue I have to the better economy. With fuel costing $1-30 - $1-50 a litre (4 to 5 bucks a US gallon) here it makes a big difference.

Another reason to tell my wife that they were a wise purchase.

The chirping is common to flat slide carburetors and they can make a clicking noise at idle. The clicking at idle is the slide being sucked back and forth by the engine pulses. I have had two sets of FCRs and a 40mm Mikuni flatslide carb that clicked at idle and chirped on acceleration, especially with open air boxes or pod filters.
That resonating sound like a bellowing that you hear with an open air box shows a different quality to it between the stock CV carbs and the FCRs. I reckon that the CVs 'bellowed' and the FCRs 'chirped'! The different carbs have an effect on Helmoltz (Helmholtz?) resonance. Some of you more science savvy members could elaborate.

Doug Lofgren's dyno tests show a difference in resonance between stock CV carbs and FCRs. The stock carbs cause a rough or wavy nature to the torque/power curves at certain revs. The FCRs smooth this effect out. It's fascinating stuff.

[brad black]

Ok, first some background, the needle goes in and out of the emulsion tube (somebody correct me if i get terminology wrong).

It acts like a tapered plug. As you open up the throttle, the needle is pulled out of the emulsion tube, allowing more gas to flow from the emulsion tube into the intake manifold.

The jets bring gas from the float bowls into the tube. You've got 3 (wait, right?) main, pilot, idle. They are teeny tiny. The floats control how much gas is in the bowl.

A jet kit changes the characteristics of your carburettor by adjusting the size of the jets and how far inward the needle rests to begin with.

I'm not a carb-genius, so others will be able to correct my mistakes and share the rest. Taking them apart to clean is really pretty easy. There are screws on the outside with little spigots - those are the float drains. Anytime you pull the carbs, you want to drain 'em first or you'll be wearing more gas than need be.

the needle goes in and out of the needle jet.  an emulsion tube has holes in it to allow fuel and air to mix.  the needle jet is high in the carb and just meters the fuel at the needle interface.  i'm sure there's no holes in them apart from the one that goes to the main jet passage in the jet holder

there's two fuel jets in the float bowl, main and pilot.  there's two removeable air jets above that at the carb inlet face, one of which is dedicated to the pilot circuit, and one in the jet holder.  i think that's what i have to press out and replace with a drilled brass tube (a real emulsion tube) in doug's jet kit.  there's no emulsion tube as such in these carbs.

personally i think the issue with them is that to overcome the fact they don't have an accelerator pump the std mikunis are set up rich at low throttle so they don't stumble when cold.  jet kit them with the slides able to move much faster and you exagerate this.  my 750 with the jet kit was either too rich when warm at low throttle or crap when cold.  and the difference in fuel economy (commuting) with a one step pilot jet change could be 30km per tank - 160 to 190 sort of thing.

so if the fcr are jetted well and don't need an inherent richness then there's every reason they could use less fuel. 

personally i'm kind of over mikuni carbs on them, just because of the fact that the more you try to make them responsive the bigger the compromises become.  altho i haven't got to try doug's jet kit yet, it's at the low end of a long list.  and it sounds a bit confusing when i don't have everything out to look at.

i must say that my bike was much nicer going to the wsbk at phillip island with the open mufflers compared to the std mufflers.  especially at low throttle openings.  i think they definitely run richer with the open mufflers.

[junior varsity]

I want to buy beer for Brad Black and Koko64 - your posts are really instructional.

I've found the carbs a bit voodoo-like - guessing which jets, needle settings, and the like are appropriate. The tradeoffs make it quite difficult since its not trivial to disconnect wiring, remove ignition switch, pull off airbox, drain floats, dissassemble and swap a jet, button it all back together just to test. (Perhaps this is why pods are more and more appealing, even if not arguably the most powerful setup). Fuel Injection, though more complicated mechanically/electronically, seems more straightforward for adjustments - plug in and push buttons (+/- till F/A ratio is 14.7 or less)

[Javamoose]

I want to buy beer for Brad Black and Koko64 - your posts are really instructional.

I've found the carbs a bit voodoo-like - guessing which jets, needle settings, and the like are appropriate. The tradeoffs make it quite difficult since its not trivial to disconnect wiring, remove ignition switch, pull off airbox, drain floats, dissassemble and swap a jet, button it all back together just to test. (Perhaps this is why pods are more and more appealing, even if not arguably the most powerful setup). Fuel Injection, though more complicated mechanically/electronically, seems more straightforward for adjustments - plug in and push buttons (+/- till F/A ratio is 14.7 or less)

Has anyone converted a carb'ed monster to a FI model?