Just a question for all of you who have FCR 41s on a M900.
What slow fuel jets do you run?
The kit comes with size 60 slow jets from Cal Cycleworks. Mine is quite rich and I have tried size 58s but still rich at idle even at 1/8th turn out on the Idle Mixture Screws. Slow air jet is set at 1 1/2 turns out as supplied. I have been advised to maybe try 52s from a good source. I don't want to go perfect for summer but too lean for winter as I am happy to stay on the slightly rich side for easy starting/warm up.
My bike has porting and cleaned up manifolds which I think makes it efficient at low throttle positions. It wanted less fuel than stock on the CVs with the porting also. Bloody flows more air up top though needing to be jetted up on the main and the needle.
It otherwise has Termi slip-ons, JE pistons, open air box, Dyna coils and dialled cams. I am happy with the needle posn and main jets (smooth and good power, no actually awesome). It's just right down low that its stinky rich! [puke]
Cheers [drink]
Have you checked the float height / fuel level?
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What heads do you have, which cams, and what cam timing?
I think it's primarily the cam timing that's influencing your slow jet issue.
But that's just a suspicion, and no help really, as I don't think you want to change that.
Quote from: Speeddog on February 13, 2010, 08:52:56 PM
Have you checked the float height / fuel level?
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What heads do you have, which cams, and what cam timing?
I think it's primarily the cam timing that's influencing your slow jet issue.
But that's just a suspicion, and no help really, as I don't think you want to change that.
Float height/fuel level is 9mm (spot on), I have ported "V" heads with stock valves (nice 3 angle valve job) and stock cams 7deg advanced as per Brad Black's specs.
I may try the 52s or 55s but they cost $15-00 each, so I was hoping to see what most people ran with a similar engine set up before I buy more.
Cheers [drink]
I dropped mine down to 58's to help with idle issues, and had to turn in the slow air screw in the throat of the carb 1/4 turn Look up Chris's ducati tech website for locations.
Quote from: printman on February 14, 2010, 04:52:01 PM
I dropped mine down to 58's to help with idle issues, and had to turn in the slow air screw in the throat of the carb 1/4 turn Look up Chris's ducati tech website for locations.
Yeah, the adjustable slow air jets are excellent allowing tuning without buying new jets each time. You can have the bike idling at about 1600-2000 rpm and adjust them for highest and strongest RPM. If they are set wrong you feel a pause as you roll on from off idle at lower rpm.
I first tried to lean them off to try and compensate for the overly rich slow fuel jets, but this negatively affected off idle throttle. I put them back to 1 1/2 turns and will fiddle with them once I have settled on my slow fuel jets and IMS. I'm going to settle on the slightly rich side of things to make winters easier.
Compared to the stock CV carbs, the FCRs are so linear and straightforward to tune. I love the direct connection to the throttle that they give. Even set up 'just ok', they crap on the CVs.
That's a great website as is Patrick Burns' site which is linked to it.
I am using Patrick Burns' test to check for the correct slow fuel jets; they will be correct when the fastest idle/strongest vacuum is obtained between 1 to 2 turns out from lightly seated and the engine rests back to the same idle speed when lightly blipped.
By the way, the slow fuel jets are the same as those on older Harley Keihin butterfly carbs. I'm gonna check out my local harley dealer to see if they are cheaper there.
Cheers [drink]
QuoteBy the way, the slow fuel jets are the same as those on older Harley Keihin butterfly carbs.
Nice find, thx f sharing!
Not so so easy finding jets where I live but Harley dealers there is quie a few. [thumbsup]
Quote from: greenmonster on February 16, 2010, 06:06:17 AM
Nice find, thx f sharing!
Not so so esay finding jets here I live but Harley dealers there is quie a few. [thumbsup]
Nice bike Greenmonster.
I found a set of 52s at my Harley dealer for half the price and no shipping compared to the Keihin importer. They only had one 55 jet! I was advised to try 52s or even 50s. I'll try to stay on the slightly rich side for cold weather starting.
Cheers [drink]
i might be needing some too.
Quote from: brad black on February 17, 2010, 12:11:12 AM
i might be needing some too.
Have you got 'em yet (39FCRs)? It'll be interesting to see what they come with for a 750 and what it will need. Will catch up soon.
Quote from: brad black on February 17, 2010, 12:11:12 AM
i might be needing some too.
We can get you them for a fair price. I buy japanese made alternatives to Keihin jets. Or we can get you Keihin branded ones from Sudco.
Quote from: brad black on February 17, 2010, 12:11:12 AM
i might be needing some too.
Hey Brad. If you order jets from Chris I'll go halves in a full range of spares. I couldn't beleive how cheap. Include a set of 55 slow jets ;D.
They are $6-00 at the Harley shop here and $15-00 a piece from the importer (plus shipping $8-00).
Jets and petrol (gas), our American friends have it better.
Look Here (http://www.denniskirk.com/jsp/product_catalog/Product.jsp;jsessionid=053PY4SBQRRQHLA0WTVSM4VMDK0NCIV0?store=&skuId=H17216&mmy=)
Quote from: Some Dude on February 17, 2010, 06:31:35 PM
Look Here (http://www.denniskirk.com/jsp/product_catalog/Product.jsp;jsessionid=053PY4SBQRRQHLA0WTVSM4VMDK0NCIV0?store=&skuId=H17216&mmy=)
Thanks SD
Your bike sounds great, like mine but with a few extra ingredients for more oomph.
Heres to carbed Monsters [beer]
Well I tried 52 slow jets and it runs smooth as silk. I still have the fastest idle at about 1/2 a turn out which may well mean they are a little rich which is fine by me. There is still winter after all and only an accelerator pump for a choke.
There was no fuel smell pulling up to stop lights from the carbs loading up on small throttle openings around town. A slight rich dip in response is gone rolling on from small openings. My garage is not stinking of fuel with the bike at idle (doors open of course).
I noted that I could achieve higher rpm on very small throttle positions than before with the bike a little more eager to rev. Even more linear in low speed response.
The spark plugs had a nice tan ring around the porcelin and the raised, fluffy soot on the circumference of the plug is gone. (Idle and 1/8 and 1/4 throttle plug chops). Instead it is dark but dry and flat.
These carbs are so good they operate well with less than optimum settings that's for sure.
Please don't go and put 52 slow jets in your FCRs based on this thread unless you have the symptoms of extreme richness, I don't want anyone holing a piston. My bike has very good inlet porting from someone who knows what they're doing (not me). It also has dialed cams which has shown a mixture change on the dyno.
If you are DIY'er I think it is best to test jetting a step at a time and just spend the money on jets as needed to see what your particular bike requires. You can't just use another persons settings without accepting them as a base setting only. Bottom line is that the base settings are there for a reason. Who knows, I may have to put those 60 slow jets back in when winter comes?
I found it hard to accept that I had to jet down so much. My Superlight had similar mods (pistons, pipes, open air box, dialed cams), but only mild porting and the manifolds weren't cleaned up. It liked 60 slow jets, but ran the same needle posn and main jets and I tested it extensively. The carbs were FCR 39s however. This motor seems more efficient and I may drop the needle back to posn #3 after a dyno test. My presumptions about base settings from past experience are only that.
Overall these carbs are bloody responsive and much easier to work on. The logic to tuning them is simpler.
I still have the slow air jets/screw at 1 1/2 turns out and I will test half a turn each way.
I will add more after the dyno test. I want to thank Brad Black, Chris and Candice, Patrick Burns and you DMFers who contributed their thoughts.
Cheers [drink]
Thx f sharing! [thumbsup]
Think I`ll go to the HD shop n get some smaller jets to try.