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Discussion Starter #1 (Edited)
Hey y'all,

First off, a question for racked FCR 41 owners with velocity stacks or pods and stock bore + compression with altitude below 7,000 feet / 2133 meters:

What size is the pilot (slow jet) and how many turns out from bottom is the slow air screw and fuel mixture screws?

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Onto my issue:

Stock motor with Termigs.

155 main jet

EMT needle, third clip from top

60, 65, 68 pilot

200 main air jet

Blue velocity stacks

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I have a recently rebuilt set of racked 41s that function very well on my M900 with W heads. But on my SuperSport's V heads with of course different sized jets and settings I am not able to dial in the idle-to-quarter throttle. I recently did a valve adjustment, compression test, ohm'd out the pickups (a little low at 102.3 or something per pickup) and the CCW coils, replaced the fuel filter, tested the fuel pump for 3.5 PSI, and replaced the fuel with fresh 91. For the record I am testing idle after 10 minutes of hard riding.

Initially the revs would hang sometimes up to 1-2k RPM above idle for 4-5 seconds with a 60 pilot. The motor would also heat up very quickly from being dead cold. In my eyes these two symptoms occurring together pointed toward a lean condition. Even after screwing out the fuel mixture screws until they nearly fell out the revs would still hang. I then installed brand new, larger pilots.

However, 65 was still hanging and so are 68 pilots. have only marginally remedied the hanging or perhaps it didn't even help at all...my head is messed up from inhaling fumes 0:). I have been tinkering with all kinds of combinations of the slow air screw and fuel mixture screws with the 65 and 68 but it still hangs. It won't hang much if I almost completely screw in the slow air screws, but then it will barely idle and eventually shut off. I suppose I could increase the idle speed to maintain proper ideal RPM but I would have it screwed in completely and that seems like a band-aid fix.

To make matters more confusing to me, the sparks plugs are sooty, and I must occasionally burn the carbon off them before using them again. How can they be sooty, which is a symptom of being too rich, if hanging is a symptom of a lean condition? It doesn't make sense to me that the rich condition is coming from the needle position or the main jet, but this wouldn't have been the first time I'm wrong.

I'm waiting for 62 pilots. It's the only size I skipped.

Files attached for anyone who needs them.

Cheers.
 

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Discussion Starter #2
I will post a link to a video of the condition tomorrow morning.
 

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Discussion Starter #4
i'd try 50 or 52 pilots and emr needle.
Hoorah, someone who actually knows something read this long post lol. I just emailed in an order to Sudco.

I might have these by Saturday / PST. I'll update as soon as I install them.

Many thanks!
 

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Hesitating to comment as I lost the paper Chris provided on the specs for the FCR41's he prepped for me years ago but the symptoms you describe on the hanging throttle is how mine acts - but I have noticed one consistent thing.

It is never actually "cold" where I live but I have to turn the idle cable up a 1/4 turn when warming it up. Three minutes or less and I drive off. Within minutes, three stoplights later I dial it back to where it started. For the next 1/2 hour of stop and go with speeds up to 60mph at times, I will get the hanging idle 2krpm. Very annoying, revving it sometimes helps it to drop, it will on its own after about 90 seconds.

Now this is why I am offering any of my experience - if I ride for more than an hour, with some consistent freeway speeds, the hanging idle goes away for pretty much the rest of the day, even with parking it for an hour or so. No more fiddling with the idle cable adjustment. If I drop 200 miles in the desert or the mountains it runs perfectly, idles smoothly at stops, starts instantly. Then the next day its back to same old crap.

I use both the stock airbox lid on K&N filters and one that is cut out across the two snorkle holes - doesn't seem to make much difference other than intake noise. Plugs are always perfect, neither lean nor rich with Remus CF slipons.

*Edit - it has been doing this for 24k miles, I figure it is the nature of the beast, but I'm willing to swap out a jet if it works!
 

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I read those links, some good sources. As I still use the stock airbox battery assembly it is a hassle to pull the carbs out. Having said that I would if I could understand how changing any jet would cure the first hour symptoms without creating problems the rest of the day?
24k miles, track days and lunitic days it runs great after that first hour.
 

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I read those links, some good sources. As I still use the stock airbox battery assembly it is a hassle to pull the carbs out. Having said that I would if I could understand how changing any jet would cure the first hour symptoms without creating problems the rest of the day?
24k miles, track days and lunitic days it runs great after that first hour.
Does any of this stuff get any easier if the stock airbox is replaced with a pair of filters on the carb inlets? Wait .. not ~easier~ (obviously it would be) but rather would it be worth the effort to replace the stock airbox with a pair of filters? After all that I have read about these carbs so far, it seems like using a pair of filters is almost a given, what with the better access to the carbs and so on. Part of the territory. Que no?
 

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I admit I like the look of twin filters instead of the airbox especially when a well made battery holder is installed. I don't like the extra intake noise, and I am not interested in tuning for peak horsepower..
 

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Discussion Starter #10
Hesitating to comment as I lost the paper Chris provided on the specs for the FCR41's he prepped for me years ago but the symptoms you describe on the hanging throttle is how mine acts - but I have noticed one consistent thing...
Based on Salvisberg's Mikuni tuning guide for idling and low RPM a rich condition worsens and a lean condition improves as the bike warms up.

With my carbureted Ducatis they definitely run better when hotter, but I have never had them hang up except for my current issue. I wonder if the pilot is one size too small, or the fuel mixture screws are 1/4 turn away from ideal, or perhaps the slow air screw is every so slightly turned out too much?
 

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Discussion Starter #11
Does any of this stuff get any easier if the stock airbox is replaced with a pair of filters on the carb inlets? Wait .. not ~easier~ (obviously it would be) but rather would it be worth the effort to replace the stock airbox with a pair of filters? After all that I have read about these carbs so far, it seems like using a pair of filters is almost a given, what with the better access to the carbs and so on. Part of the territory. Que no?
I have heard it's more difficult to tune with pods and even more difficult with velocity stacks. But the airbox and I are sworn enemies. I have probably removed the airbox from all my carbureted Ducatis over 150 times combined. There was a lot of tuning occurring per each Ducati, especially as a novice, thus the number. I have been left traumatized by the many times I was cut and bled by that box, and the tedious task of removing it.

I will avoid that spawn of satan even if it costs me the verifiably 5 HP from the top-end. The ease of access to the carbs with pods or velocity stacks makes me very happy. Plus it looks more trick if you have bikini fairings on the SS or an M900.
 

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I have one 900SS with the stock Mikuni carbs, and a great deal of adjustments have been going on with it, but it doesn't have the hanging idle problem. The other 900SS with FCR41's does under the first hour of driving - again, not directly temperature related as I often start the bike "cold" when it is over 100 degrees F outside. Raise the FCR carb idle for about the first three stoplights, then drop it down to keep it from the hanging idle. If I ride for more than an hour I must raise the idle again or it will stall out. Once set back to where it was when "cold" I won't need to touch the adjustment again the rest of the day, no matter how many times I shut it off and restart it unless it sits for more than 6 hours.

How does changing a jet improve this procedure? Which jet? I am willing to listen to any argument explaining a possible sync issue causing this, I have eliminated any possibility of an air leak or imperfect seal on the intakes or filter. I bought the fancy Motion Pro II throttle setup, junked the Sudco provided Motion Pro crap, so it is not my cable routing or binding.

I think after 24k miles this is the nature of the FCR beasts,... prove me wrong and I will attempt to adjust them. It is a little annoying.
 

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RockAZ

Have you had the fcr bike on a dyno / exhaust tester to check jetting?

Your up and down with the idle is not normal but it sounds like you are rich as you get the engine fully up to temp the fuel demands are less with a hot motor . I see rich mains often but I would think you would be a couple sizes off in the jetting to cause it to need the idle raised.
 

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i had one 900 with 41 that was happy with the 60 pilots, which struck me as very odd. then one day it came in and had gone much richer - ended up going down to 50 or so. no idea why, but it was quite a sudden change. stayed that way too.
 

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I would like to have a gas analyzer run on both my bikes, the FCR just out of curiosity - I've had at least 30 pairs of Champion plugs through it and they all looked great except for the couple of times the float bowl stuck and dumped some fuel in while it was shut off.

Come to think of it (until this week I haven't rode it in 8 months), the bike with the FCR does have a hotter cam in it, something out of the 98 Corse catalog most likely but I have not yet opened it up to look. It naturally has a loping idle, very distinctive pattern of "buddadarump, buddadarump" that stands out when right next to the other bike or my buddy's (budda,budda,budda). Maybe that is why I have found fiddling with the idle cable adjustment for the first half hour seems to work?

The stock carb bike is still giving me fits, I need to start trying things again now that I have the other bike running.

I would like to dyno both bikes, just the specs run is relatively inexpensive but I cannot afford a dyno tune - and there is no one left in town that I know of that knows these old carb bikes. I should check around again since I can be without one bike for a while...
 

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It would be worth the hunt for a dyno with air fuel reading, make sure they do not only do a full throttle run. You will be looking at probably as many sets of 3 runs as you can afford and will want to lessen your cost by labeling your throttle in all the settings you want tested. Yes full throttle to warm things up but after 3 full throttle pulls work your way down to 1/2 throttle, 1/4 throttle and then 1/8 throttle. While hooked up check warm idle between runs.

If cost is an issue skip 1/2 and 1/8 and have them cruise at specific gear/speeds you are often at. They can do this while between runs so cost should be little if anything unless they record the run. Ride your bike in the mean time to see what gear and throttle positions you are in and also record the mph. Give them these data points to check and then you can see how close you are and decide if it warrants changes or not. Getting print outs with air fuel and rpm or speed will help you decide what to do next.

If you do the set up and make the dyno time most efficient you can reduce your costs and if the shop see's you as a future steady customer who is capable but not a OCD PIA they will work with you possibly on costs with future runs.
 

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Hanging idle with carbs can be 4 things, 1) a mechanical issue not allowing the slides to close quickly 2) an issue in the enrichener, leaking or not closing 3) a lean condition caused by either a leak in the intake tract between carbs and engine OR a lean condition caused by a clogged pilot circuit within the carb. 4) poor carb synchronization .
My first thought is always 3, a clogged pilot circuit. You must be able to spray carb cleaner from the primary jet and have it come out forcefully in the venturi. A spray, not a dribble, matching on both carbs. Replace the seals on the adjustment screws to rule that out. When adjusting use large adjustments at first. If it’s hanging, go richer one full turn at a time until it stops hanging, then fine tune with smaller adjustments after that. Hanging idle means you’re real lean, not a hair lean. You’ll be there all day turning the adjuster 1/4 turn at a time.
 

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Borrowed carb sticks today - sync is perfect on the FCR's - scratch one item off. Still looking for a gas analyzer, may have to take it to a shop.

Ran a whole tank out yesterday, and again today, not much need to fiddle with the idle cable today - about two notches just during the first half hour but not at all so far today and yesterday four hours of extra legal speeds without a single idle hang.

I love living in this part of Arizona, when the heat goes away at this time of year.
 
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