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I have 39mm Keihin flatslide carbs on my 1995 900SS CR. I have some questions about these. When I first start the bike I go through a ritual where I turn the throttle 4 times then push start. That's what it seems to like. Then, I have to let the bike run at idle for a while to warm up. Even then, for the first ten minutes after it runs like crap until it's hot. After that it's good to go and runs like a champ. Why is that?

Does it have to do with these carbs dumping too much gas in at first and that causes the surging and popping or is it that they don't put enough gas in when things are cold and not warmed up? My guess is that they dump too much gas in. How does a cold or warm engine impact running condition with aftermarket carbs? These were installed by a Ducati dealer with tons of experience dealing with these carbs so I don't doubt that they were put on incorrectly and I've been told that this is just a characteristic of these carbs, things need to warm up a bit before the bike runs right.

There is no choke when you use these carbs so the bike just has to sit in neutral for a while and heat up. The longer it sits the better it runs when you finally go. If you fired it up and took straight off it would run like crap for ten miles. Why is that?

And keep in mind that I've probably spent more money on my little 900 in mods than just about anyone alive (pending a few even more crazy people - and yes, I know you are out there). It has just about everything you can do to one. Dyna coils, race wires, new plugs, the works. Only thing it doesn't have is a lightened flywheel, a big bore kit, billet wheels, and a front fork swap. Other than that you name it, I've done it.

As always, I appreciate your responses.
 

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I have 39mm Keihin flatslide carbs on my 1995 900SS CR. I have some questions about these. When I first start the bike I go through a ritual where I turn the throttle 4 times then push start. That's what it seems to like. Then, I have to let the bike run at idle for a while to warm up. Even then, for the first ten minutes after it runs like crap until it's hot. After that it's good to go and runs like a champ. Why is that?

Does it have to do with these carbs dumping too much gas in at first and that causes the surging and popping or is it that they don't put enough gas in when things are cold and not warmed up? My guess is that they dump too much gas in. How does a cold or warm engine impact running condition with aftermarket carbs? These were installed by a Ducati dealer with tons of experience dealing with these carbs so I don't doubt that they were put on incorrectly and I've been told that this is just a characteristic of these carbs, things need to warm up a bit before the bike runs right.

There is no choke when you use these carbs so the bike just has to sit in neutral for a while and heat up. The longer it sits the better it runs when you finally go. If you fired it up and took straight off it would run like crap for ten miles. Why is that?

And keep in mind that I've probably spent more money on my little 900 in mods than just about anyone alive (pending a few even more crazy people - and yes, I know you are out there). It has just about everything you can do to one. Dyna coils, race wires, new plugs, the works. Only thing it doesn't have is a lightened flywheel, a big bore kit, billet wheels, and a front fork swap. Other than that you name it, I've done it.

As always, I appreciate your responses.

I have the 41mm FCR's on my '93, and it likes only two pumps of the throttle before starting. If I start it and try to ride straight away it stalls and generally runs crappy for 5-10 minutes. If I let it idle for five minutes before starting it's perfect. My '98 FE likes a few minutes of warmup as well, as have most of my previous bikes with carbs, so I think this is normal. Maybe you should try starting with only a couple of squirts and see how it goes.

Mine is pretty modded out as well; 41mm FCR's, Dynacoils, revalved forks w/ RaceTech gold Valves, Ohlins rear shock, Carbon Fiber front and rear fenders (from the original Ducati supplier in Italy, thanks Motowheels!) Nichols crankcase vent filter, and most significantly a freshly restored set of the beautiful Marvic 2-piece Superlight wheels. I'll post some pics of the bike with the Marvic's as soon as I get it put back together this weekend from the new head stud surgery.
 

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Discussion Starter #3
Thanks for reply

You can see my ride in the 'Superspot Pictures - Let's see em' section of the Supersport Forum. It's the last post made, as of yesterday and today, by "Indy36" - that's me.
 

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Your bike is too lean at 0-1/8 throttle because your slow air screws are too far out (if you have them). The bike should need maybe 1 minute of idling/blipping the throttle, at most, to run well. Remove the air filter and look down at the carbs. there should be two small holes at the front. If one has a slotted screw head, then you have adjustable slow air jets. If not, then you need smaller slow air jets (to richen the 0-1/8 throttle mixture). If you are lucky and do have the adjustable jets, then turn in the screws carefully with the correct size screw driver until they bottom (don't force them!). See how many turns you had to do. They should be from about 3/4 to 1 1/2 turns out from bottomed. Open them up 1/4-1/2 turns less than they were, and try that. Remember, the more you unscrew them, the more air you will get and the leaner the bike will run at 0-1/8 throttle. You might also want to richen the fuel screws a little by unscrewing them 1/4-1/2 turn (they are on the bottom of the carbs). Since they control fuel and not air, as the slow air screws do, unscrewing the fuel screws will richen the mixture (the opposite of the slow air screws). Then it should start with only 1 or 2 twists of the throttle and will idle better when cold. Those carbs have a lot of adjustability. Remember, when the air and/or motor are cold, or at lower elevations, the bike will run leaner. Check out this link:
www.ducatitech.com
go to -FCR FAQ. You will also find a link on that page that shows where the adjustments are located. Good luck :).
Joe
 

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There is no choke when you use these carbs so the bike just has to sit in neutral for a while and heat up. The longer it sits the better it runs when you finally go. If you fired it up and took straight off it would run like crap for ten miles. Why is that?



As always, I appreciate your responses.
seriously?

I mean really? I don't know, maybe ambient temp effects stoichiometric (SP) ratio and your ratio is static? lemme think hard on this one.










just sayin....
 

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Sounds like you have a lean condition but then again, the FCRs do run lean until warmed up. Did you buy these carbs new yourself? If not, you should make sure all the settings, needles, needle position and jets are as delivered and recommended. Also check for air leaks at the intake manifold connections.

If everything checks out, then try to richen up the idle circuit first with fuel and air screws and then with larger slow fuel jets. You don't want to go too far or slow speed throttle response will suffer once warmed up.
 

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Discussion Starter #8
Response

Carbs were purchased brand new through the local Ducati dealership. They were installed by a Level 2 Certified Ducati Mechanic. I believe they got them from California Cycleworks, I think.
 

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Carbs were purchased brand new through the local Ducati dealership. They were installed by a Level 2 Certified Ducati Mechanic. I believe they got them from California Cycleworks, I think.
And your point is...:think:? I bought mine from Ca Cycleworks too, I installed and adjusted them myself, and they work perfectly. Just because a certified Ducati mechanic installed them doesn't mean he knows anything about Keihin carbs, or that they don't need adjustment. You should not have to warm up the bike for 5 minutes before you can ride it (also it's better for the motor to warm up by riding it under a light load, than having to let it idle under no load for 5 minutes).
Joe
 

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Discussion Starter #10
Closure

My point was that I didn't buy them on my own so I do know that I did get everything. Someone else questioned that. Also, I mention that I didn't install them because that was sure to come up. No matter what I do on this forum someone rails on me. I'm either a dumbass for not knowing how to do 100% of the work myself or a dumbass for paying someone that has a wealth of experience to do it. My local Ducati mechanic is very skilled. He's a racer. He spends days with the Ducai techs that come to Indianapolis every year for the MotoGP and those guys go hang with him at the shop. He's certified and tied in. He knows what he is doing. Does that make him 100% perfect, nope. Does it mean that my bike still might be running lean, yep. I did learn about adjustments and I have a little more knowledge so I can better talk to him about what I think the problem is. I guess you take the good with the bad. Many of you offer helpfull suggestions. Some of you don't. I don't wrench on my bikes. I have no desire. I pay people to do that. I can afford it. I know my limits. That doesn't make me a dumbass. I could talk for days about topics many of you don't know crap about but I'd never make a point to jab you or talk down to you. Some people can't resist the urge. For those that helped, thank you, I'll have the settings looked at.
 

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your in brownsburg? nifty. Hang around indy? You should know the name "henley" That's all I'll say about that.


anyway - what we're saying is that you don't understand how carb's work. your mixture ratio is static on a carburetor, and different for the divergent sprectrum of operable ranges.
For street bikes, you try and get it close. For race bikes, you will find yourself adjusting the mixture in the different carb circuits for every degree of temp change or 2% or so in humidity difference.

Sounds like normal for a pumper carb on a bike to me. if you want smoother running in a wider range of conditions, go back to a cv carb with an adjustable choke. of course, you loose your throttle response, but it's your choice.

Your chasing a pipe dream if you think changing settings is going to fix your cold running situation in all temps and humidity points throughout the seasons. Most people only jet for average ambient temps per season. most people live with it running shitty for the first few minutes to have it dialed in when at operating temp (ambient and internal).

If you jet fcr's for cold at start/idle (they have no starter circuit) you will ruin it for 0 - 1/8th at operating temp. that simple.

Now if you didn't know that stuff, sorry. but it's not your mechanics fault for your not knowing it, and not mine. It's yours.
 

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relax

Eh brah.... you no "dumbass" you do need a thick skin around some of these guys however!
We are all here to learn and share....just keep it up you; will be fine.....
Get LT Snyders book from Desmo times that will help you get more confidence

DUCS RULE …Rice grinders drool..

09 Ducati GT1000 Black and Gold; 14/40 with Ohlins F&R, Termis & Rizoma bling
95 Ducati SS 900 CR Red; 15/41 my new project…
81 Yamaha SR 500 total cafe project bike
 

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Sounds like a typical rich idle circuit where the fuel does not atomize correctly and "puddles" or adheres to the walls of the intake tract till everything heats up and the intake charge then will stay in suspension with the air flow. Try leaning it out slightly, there should be a fine balance between warm-up and rideability. Sounds like you are close but remember these carbs are made for airflow (racing) not around town small throttle openings.
 

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Sounds like a typical rich idle circuit where the fuel does not atomize correctly and "puddles" or adheres to the walls of the intake tract till everything heats up and the intake charge then will stay in suspension with the air flow. Try leaning it out slightly, there should be a fine balance between warm-up and rideability. Sounds like you are close but remember these carbs are made for airflow (racing) not around town small throttle openings.
Sorry, I must respectfully ;) disagree. After running Keihin FCRs for 4 years on the street in cool temps (down to the 30s), at elevations from 6000-8000' where I live, to doing track days in Salt Lake City in the 90 degree heat at 4500', and Las Vegas at 1500', I agree with beater. They may be race carbs, but they can be jetted fine for everything from 0-WFO throttle, even puttering around town. Indy36, I think you are being a little sensitive. I don't think your posts indicated that you didn't like to work on your own bike, and I doubt anyone cares anyway. No one accused you of being a dumbass! I do it for fun because I enjoy tinkering and it gives me much satisfaction (and there is no one in Jackson Hole WY. who I would trust to touch my bike anyway!), but that doesn't mean I expect you to work on your own bike. If you prefer to have a mechanic work on the bike, fine! You may just want to tactfully recommend that he richen the slow air jets a little (it's a 5 min. job if your carbs have the screw adjustments) and see how you like it. Mine also runs a little lean when it's cold, but is not too rich when warmed up. However, as was said, carbs are affected by temp., elev. and humidity. We're just trying to give some helpful advice. Did you ask your mechanic if he thought it should take so long to warm up before you could give it throttle? What did he say?
Joe
 

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Okay, fellas. no need to get heated hear. everybody show some brotherly love and chillax. There is no need to rail on anybody, and there is no need to feel getting railed. so, please, let's all be diplomatic.
1,2,5 squirts does no matter... so long as it starts. 1 minute... 5 minute warm up..who bloody cares ???? mine takes 3 minutes ! I don't leave it in idle though, i blip it a few times. and once the throttle response feels crisp... I go.
So now for the question... long warm up time... we then need more gas, right ? so, may I suggest looking at that route first ? let us know.
 

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>>They may be race carbs, but they can be jetted fine for everything from 0-WFO throttle, even puttering around town. <<

+1.
My 900 picks up fr 1700 RPM in 3rd w 15/41 gearing.

A good start to be able to help would be info of jets & screw settings on the
troubled bike.
 

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My point was that I didn't buy them on my own so I do know that I did get everything. Someone else questioned that. Also, I mention that I didn't install them because that was sure to come up. No matter what I do on this forum someone rails on me. I'm either a dumbass for not knowing how to do 100% of the work myself or a dumbass for paying someone that has a wealth of experience to do it. My local Ducati mechanic is very skilled. He's a racer. He spends days with the Ducai techs that come to Indianapolis every year for the MotoGP and those guys go hang with him at the shop. He's certified and tied in. He knows what he is doing. Does that make him 100% perfect, nope. Does it mean that my bike still might be running lean, yep. I did learn about adjustments and I have a little more knowledge so I can better talk to him about what I think the problem is. I guess you take the good with the bad. Many of you offer helpfull suggestions. Some of you don't. I don't wrench on my bikes. I have no desire. I pay people to do that. I can afford it. I know my limits. That doesn't make me a dumbass. I could talk for days about topics many of you don't know crap about but I'd never make a point to jab you or talk down to you. Some people can't resist the urge. For those that helped, thank you, I'll have the settings looked at.
Indy, I'm certainly no expert, but I have raced both Ducati 750SS and Kawasaki EX500 twins with Keihin FCRs and since they do not have chokes but they do have accelerator pumps, I have always, always, always had to pump the throttle several times to prime the carbs, then start the bike, then warm it up by blipping the throttle until the engine is warm enough to idle at normal idle mixture settings.

I'm no expert, but it would seem to me, that in the absence of a choke, if you adjust the idle mixture rich enough for the engine to idle smoothly when stone cold, then it's going to be running really rich at idle when the bike is warmed up. I don't think I would like that in my bike.
 

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Indy, I'm certainly no expert, but I have raced both Ducati 750SS and Kawasaki EX500 twins with Keihin FCRs and since they do not have chokes but they do have accelerator pumps, I have always, always, always had to pump the throttle several times to prime the carbs, then start the bike, then warm it up by blipping the throttle until the engine is warm enough to idle at normal idle mixture settings.

I'm no expert, but it would seem to me, that in the absence of a choke, if you adjust the idle mixture rich enough for the engine to idle smoothly when stone cold, then it's going to be running really rich at idle when the bike is warmed up. I don't think I would like that in my bike.
I don't have them on any of my Ducatis, but I have had a set of FCR41s for 10 years on one of my LeMans. Same here. Also, same with the OEM Webers if I remove the choke circuit (I now have compromised and have a choke on one of the Webers on the second LeMans).

Depending on ambient temperature, they need more or less time to warm up. In winter, I put my gloves over the intakes to act as a choke for a minute or so (I have K&N pods on it).

Also, versions with chokes DO exists. One of the guys at work had a Husqvarna that came with a race kit, and the race-kit carb was a FCR41 WITH a choke! (OEM was a Weber).

Tom
 

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It's easy to get railed at on this forum

Any time you have a forum populated with self-certified experts, you will get this problem.

I, too, have had a nightmare setting up my new FCRs. I am an experienced mechanic and I decided to pay someone else (who has a dyno) to adjust them for me. It's not necessary to be an expert in all things.

My gripe is that I have had the bike back three times for lean condition surging and backfires. It's interesting that, other than FCRs, CarbonTech cans, and Sil-Moto headers, my engine is stock. I fully expected the carb settings from CA-Cycleworks to run straight from the box - no luck!

I don't hold it against you that you don't wrench your own bike. I know how to do it and I frequently pass up the pleasure and pay others. It's not all glamor, you know. Often, it's grease, pinched fingers and frustration.
 

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....Depending on ambient temperature, they need more or less time to warm up. In winter, I put my gloves over the intakes to act as a choke for a minute or so (I have K&N pods on it).
Great idea! Wonder if some sort of retractable cover on the open airbox might work as well. A fast idle cam would be useful too.
 
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