Hey everyone,
I could really use some input from the carb experts. I have a 98 M900 with fresh FCR 41s and pod filters. Install went fine, but its not running as it should with FCRs. I havent mae any adjustments to the settings, and I'm fairly confident all my settings are in line with how CA Cycleworks sets them up (though I bought from another one of the forum vendors). Only change was I bumped up to 165 mains.
I've gone through this thread to confirm:
http://www.ducatitech.com/2v/fcr_faq.html (http://www.ducatitech.com/2v/fcr_faq.html)
So here's my problem: Coming off idle (around 1/8th to 1/4th throttle) it runs absolutely terrible. It coughs, spits, bogs, dies, etc. I pretty much have to grab the clutch and slowly blip the throttle to get the rpms up before I release the clutch. At 1/2 to WOT it seems to run as it should.
I started adjusting the slow air jet screw (started at 1 1/2 turns out). 1/4 turn change in either direction doesnt seem to have a noticeable difference.
Has anyone had experience with the FCRs? I dont know if I need to change the slow jets (considering I'm set up nearly the same as ducatitech has it). I was hoping they'd be great out of the box...biggest reason why I got rid of the Mikunis (could never get them tuned right).
Thanks for the help!
What, specifically, are the settings on your carbs?
Pilot jet size, slow speed fuel screw setting, needle and clip, etc......
The settings that ducatitech has are a basic guideline, at best.
Likely they worked better when our fuel didn't have ethanol in it.
On that note, what fuel are you using, and it's fresh, yes?
If you're still using the OEM vacuum-operated fuel shutoff, *and* it still works, carry on.
If not, install an in-line fuel shutoff.
Keihins are a bit prone to hanging a float, and if you don't have a fuel shutoff, they'll fill your crankcase with gas.
Have the valve clearances been set properly, and how long ago?
What colour are your plugs?
+1.
I'm no expert, but I'm always suspicious of a hanging float or way too large pilot jets with those symptoms. I have run as low as 50 size pilots in FCR41s, commonly using 52s for open airbox lids and pods. A manual early model tap is great if you get flooding on the run. Shut the tap, let it run down then switch it back on to slam the float needle shut with the 3psi vacuum pump. All on the go.
If you get fuel pissing on the ground at stoplights from the overflow hose you know its flooding. If not, and everything speeddog mentioned checks out, then consider 52 pilot jets as a starting point.
You can change them easily running pods by removing the float bowls with the tank up.
A search will reveal much detail on this. [thumbsup]
Thanks for the help everyone! Here's my set up:
Mains 165
Slow jets 60
Needle clip at 3rd position
Needle size (need to pull them to verify)
Fuel screw (3/4 turn, but need to verify)
Air screw (started at 1 1/5 turns, but now at 3/4)
I spent the afternoon (65 degrees in DC!) adjusting the slow speed air screws, and I think Ive solved the problem. So I was definitely running very lean at idle -1/4 throttle. Once I started tightening the air screw the mixture enriched and now its running like a bat out of hell. I'd like to fine tune it further however.
Next question: Since I'm now at 3/4 turns on the air screw (tested and found that 1/2 was too rich, or simply not enough air as the bike would die), can I gain power by increasing the slow jet to 65? This is assuming I would back the air screws out at the same time.
Additional details
Im running the original vacuum fuel pump but I added an inline valve (although maybe you guys are referencing a different type of setup).
@koko I've searched this board, the "other" board, and several others ;D Ive been dealing with this since last fall. Finally making progress though.
If I want to enrich the mixture at 1/8 and 1/4 throttle, do I need to go up a size or down a size on the slow speed jets?
Your new question is all about experimentation. You might find a smaller pilot and a richer needle position yields better performance.
With not a ton of FCR experience I'd tend to go with a leaner pilot so you have some adjustment range and play with needle position/taper to get through the next transition.
It's all smoke and mirrors and black art these carburetors... ;D
What do your plugs say? What colour are they? Have a look and report back.
The symptoms you have could also mean very rich in the 1/8-1/4 range which is the pilot jets being too big, so check your plugs. If you have made more than one adjustment you could be masking one circuit with another. For some reason, these 41s run well at 1 1/2 turns on the slow air screw and playing with that often is compensating for a problem with the fuel jet or needle, as DP suggested. The overlaps with jetting circuits can cause confusion. That's what DP was referring to.
If your size 60 pilot jets are too small, then this would be the first time I have ever heard of this. Of course there is always a first time, but I take it your motor is stock bar the pods?
A hanging float will give you over rich symptoms, a jammed up float or choked vacuum tap will give you lean symptoms (as will an inlet manifold leak). Some vacuum taps leak open into the manifold with one cylinder rich, and on it goes... ;)
Your tests need to be with the bike well warmed up. Without a choke, things should seem on the lean side until the motor is warmed up, then once warm, running well. If the troublesome range gets worse as the bike warms up, then its too rich, or improves, then it was too lean.
Here is a test to try, please do this and report back: With the bike warmed up, turn the idle mixture screw in all the way, does the bike run or die at idle?
Quote from: Preppyr6 on February 28, 2016, 05:13:13 PM
Additional details
Im running the original vacuum fuel pump but I added an inline valve (although maybe you guys are referencing a different type of setup).
@koko I've searched this board, the "other" board, and several others ;D Ive been dealing with this since last fall. Finally making progress though.
If I want to enrich the mixture at 1/8 and 1/4 throttle, do I need to go up a size or down a size on the slow speed jets?
The slow speed fuel jets are richer, the higher the number. I have usually heard of your symptoms with an over rich slow jet and size 60 has clagged most of the bikes running 41s in the idle to 1/8-1/4 range. My experience on the one 900 with 39s was different as it liked the big slow jets running 60s and then 58s.
My experience with these motors was 900s with V heads, so if your motor has W heads with the milder cams and smaller valves then that could be a different matter. For example, efficient head and manifold porting on one V headed 900 required only 50 size slow jets.
The fuel pump is that large hexagon pump on the rhs under the airbox. The vacuum tap that can choke up is a tap at the back of the underside fuel tank. I forgot, if you have an in line tap you can remove the vacuum tap, as it will be a potential problem.
Quote from: koko64 on February 28, 2016, 11:46:10 PM
What do your plugs say? What colour are they? Have a look and report back.
The symptoms you have could also mean very rich in the 1/8-1/4 range which is the pilot jets being too big, so check your plugs. If you have made more than one adjustment you could be masking one circuit with another. For some reason, these 41s run well at 1 1/2 turns on the slow air screw and playing with that often is compensating for a problem with the fuel jet or needle, as DP suggested. The overlaps with jetting circuits can cause confusion. That's what DP was referring to.
If your size 60 pilot jets are too small, then this would be the first time I have ever heard of this. Of course there is always a first time, but I take it your motor is stock bar the pods?
A hanging float will give you over rich symptoms, a jammed up float or choked vacuum tap will give you lean symptoms (as will an inlet manifold leak). Some vacuum taps leak open into the manifold with one cylinder rich, and on it goes... ;)
Your tests need to be with the bike well warmed up. Without a choke, things should seem on the lean side until the motor is warmed up, then once warm, running well. If the troublesome range gets worse as the bike warms up, then its too rich, or improves, then it was too lean.
Here is a test to try, please do this and report back: With the bike warmed up, turn the idle mixture screw in all the way, does the bike run or die at idle?
Koko, thanks for this, this is really helpful. I'll start gathering more information as soon as I can. Unfortunately, bike is stored in DC while I'm working in NYC so I wont have another chance to pull the carbs until next month.
One thing of interest to me is your comment on the air screw adjustment compensating for another issue. Next time I'll pull the fuel jets and needle to confirm the sizes. One question, assuming Im running EMT needles (to be confirmed), what tends to be a popular needle to move to? EMS? I'll keep searching the forums for answers/experiences. The only significant upside to all of this is that the FCRs are so much easier to pull than the Mikunis.
This forum is GREAT! Next issue is to figure out why my Rizoma signals have gone all haywire...
You may find EMTs work fine but you may need to play with needle position. I have gone as rich as EMR needles with an enlarged modified airbox. EMTs are as delivered and have every chance of working with pods.
I would focus on the pilot jets. Set the slow air screws at 1 1/2, remove that vacuum tap, (remembering to seal all vacuum openings), and do the tests. Plug colour and that idle mixture screw test will tell us a great deal about the pilot jet size, then you can set idle mixture once you have selected your pilot jets. [thumbsup]
I was able to grab a few pics of the plugs. Looks like I'm running pretty rich. (http://uploads.tapatalk-cdn.com/20160302/f2bde66f5bae6ed5609c703b1bfb5d26.jpg)(http://uploads.tapatalk-cdn.com/20160302/74694bdd3c9c3fc5176558a908be1d26.jpg)
Yep, certainly is. If it's not flooding from a hanging float (thanks Speeddog for that term, I'm gonna use it from now on), then try 52 slow jets. Hanging floats :D, will flood the carbs and you will usually see overflow out the hose. Make sure you use an overflow hose and route it away from the hot motor or rear tyre. It usually goes to the lhs or rhs to the elongated hose guides (wire brackets off the engine bolts).
Slow jets are cheap as chips, so order 2 x 52s, 2 x 55s and even some 58s and throw them in your jet box (I use fishing tackle boxes). With pods, its easy to access the float bowls with the tank up. It's good to have a few spares as you never know what future mods you might do. If you cant find the jets any place then they are the same as old Harley 38mm Keihin butterfly carb slow jets.
With the correct slow fuel jets you should be able to stall or at least make the motor miss badly at idle when turning the idle mixture screw in all the way (gently seated) or out 1 1/2 to 2 turns. A turn is 360 deg btw. You know you have a good, responsive setting when you can turn the idle mixture screw 1/2 a turn each way from the sweet spot and notice the motor falter at idle.
Some fuels do affect this and our premium fuels down under let my old M900 idle with the IMS fully closed, but a bit ragged. E fuels can have other effects.
Koko, this is fantastic. Thank you so much. I'll go ahead and check the floats and start experimenting with the slow jets. Probably won't get to it until late March, but I'll report back my findings.
Cheers [beer]
Quote from: Preppyr6 on March 03, 2016, 11:59:11 AM
Koko, this is fantastic. Thank you so much. I'll go ahead and check the floats and start experimenting with the slow jets. Probably won't get to it until late March, but I'll report back my findings.
If you don't get fuel leaking out the overflow which is a sure sign of flooding, I would guess that you just need to change the slow jets. That could be a first change to test. Put in fresh plugs and see how they are after some riding.
Haven't seen any flooding to date. I just placed an order for 50, 52, 55, 58 slow jets. Fingers crossed...