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Discussion Starter #1
I have Keihin FCR41 flatsides on my Superlight that will probably need rejetting. They are currently set up for sea level but will be living at 5-8000'.

Any opinions on where I should start the experiment?

Thanks, in advance.

S:)
 

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Pretty much for sure the mains will be 155. They usually come form Chris or Sudco with 60 slow jets but most go down to 55 or 52. You might get some hanging idle at the lower pilots but it might be an OK trade off for better off idle response. I was surprised how much better it ran when I finally got around to leaning it out on the slow jet side. It idles better, runs better and even starts more easily.

If you are running a 944 and other mods, a richer needle taper might also help. I think it comes with EMRs and mine are now EMT and that's really helped midrange. Most leave the needle clip in the centre position. And don't forget to mechanically sync the FCRs before tinkering.
 

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search by my user name. I have provided a tool. you need a different needle and slightly different main.

I am in denver
 

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similar situation- any harm?..

I recently purchased a '92 SS. Same carbs. Bike came from Seattle and i'm in Albuquerque (5000 feet). I would like to ride the bike some before i deal with re- jetting etc. The bike is running well. Is there any harm riding it a while before readjusting the carbs? Thanks.
 

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When I bought my FCRs from Chris I was living at an altitude of 5700 feet and it ran perfectly with the jetting as it came. It also started very easily and idled perfectly.

We subsequently moved to sea level and the FCRs never performed as well as they did at ilde and small throttle openings since then. I've even removed and opened them to make sure everything was clean and reset all the screws to the "factory" settings Chris provides on his website. I even tried playing with the fuel screw at the bottom of the carb with no real improvement. Then, this past weekend I thought I'll have a look again and tried turinging the slow air screw in the mouth of the carb while it was idling and suddenly after turing the one just a tiny bit the idling picked up and smoothed out beautifully. It's still not perfect, but a lot better than it was.
 

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ok folks, fcr's don't "feel" like cv carbs. you won't really FEEL the slight imperfections in jetting. They are so much more efficient than cv carbs that the sweet spot is razor sharp. HOWEVER, you will notice it when you get it spot on. FCR's are all about full throttle.

plus, every bike is different, and needs to be tuned as such. I have set ups on my two strokes that make the other guys scratch their heads, yet on the dyno, it works.

j
 

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Discussion Starter #8
Beater,

I finally got my SL. Best move I've made in a while. It backfires a bit as I climb in elev on decels. Rich mixture? Do I need to remove the Keihins Flatslides to rejett, or should I bother to rejett?

search by my user name. I have provided a tool. you need a different needle and slightly different main.

I am in denver
 

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I run 58 pilot, an adjustable air screw (instead of air jet), an elt needle and 152 mains in denver.

It runs lean at 40 degrees in the morning, but like a scalded cat at 80 degrees.. I could probably go to a 154 main, but of my hard riding is at an average of 8k feet. Did you use the spreadsheet I gave you?

I don't remove to re-jet, but that's me. you will need to remove the airbox unless you don't have one.
 
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