I am in the middle of rehabbing a KTM620Adv.. The previous owner had replaced the quicksilver carb (it's in a box) with an FCR41 - that has no choke. Apparently it's an older model or something.... Anyway, I am curious to what folk prefer for offroad riding; the FCR or the BST... My 620 will go offroad allot - so while I like the power of the FCR I wonder if it's the best choice (my SXC Motard with the FCR is touchy -power is like a light switch - allot of power on/off). I still have a BST40 from the SXC swap so it won't cost me any $$ to get another carb... I was hoping to elicit some opinions rather than spending a day(s) swapping carbs and trying each out. The other question is does anyone know if it's possible or how difficult to pop in a choke to a (non choke) FCR 41.. It's fairly well dialed in right now (only have to stick a hand over the intake in sub 30 Deg days). However, I am pulling the lower pipes and will be mounting either a later 640 exhaust - or will switch to a single side and bend it up at a 45 deg angle - The routes I take often involve water/stream crossings, so low pipes are NOT ideal.. I am far from a jetting expert - but without a OEM or standard setup I figure it might be better to have a choke to start it. It's why I haven't parted with the BST yet... THoughts, Opinions welcome..... Thanks in Advance -Jason (Note: I don't plan of parting with either the FCR and/or the BST till the bike is back on the road and I am happy with the set up... At that point I will sell which ever one I dont' use. The quicksliver can be had now)
Jason, I don't have any specific information to your application, but a couple of general points about FCRs that I've learned: FCR's don't have chokes. But they do have accelerator pumps. Hard starting? Give it a couple of flicks of the throttle before you start it and it will squirt some gas into the intakes and it does the same thing. As for the ON/OFF characteristic, that's a function of the size of the throttle cylinder where the cables attach to the throttle grip. Larger diameter means more pull for the same rotation. Call Motion Pro and see if they have a smaller diameter throttle. Hope this helps.
I have READ the FCR 41 is too big for the non-Hi-Flow head bikes but I DO NOT have any first hand knowledge. I have an SXC with a BST and have ridden SXC with FCR 41. I have done all the popular update to the BST and I think I have it jetted well. I don't think it has quite the power of the FCR bike but it starts easy, gas milage is not too bad and that is important with the small tank on an SXC and the bike does not overheat since I made the changes. My BST SXC will lift the front tire or turn the rear with out much effort so I would not spend the money to convert MY bike to an FCR. I think you will be happy with the BST depending on how and where you ride.
Thanks for the Throttle Cyclinder info - I didn't even think about that.... I am curious to why you think the FCR's don't come with a choke. The one I got from a fellow ADVRider has one - it's the one that I put on my SXC... I am confused .. I wonder if there aren't some differences between carbs I am unaware of... My SXC with the FCR is a beast - the power is immediate (I will check throttle cyclinders) and rolling off the throttle is like slamming on the brake. I was very happy with the neutral throttle response - it made it easy to ride hard. The ONLY reason I put the FCR on it, is that on the track a bud has a 560SMR and he get about a bike length jump on me when we both get on the trottle at the same time (asap). The ADV620 doesn't have the High Flow - and to be honest - I am leaning toward the BST from past experience. However, if the FCR is doable - It never a bad thing to have some more power on tap, as long as it isn't too twitchy... thanks again
I have the first gen fcr with a choke , is yours perhaps just missing the knob. The fcr 41 works fantastic on my 2000 low flow head, dammm , anyways with basic tuneing the fcr is world class .
My 02 640 adv had an FCR put in soon after purchase by the original owner - the paperwork was passed along over the years. Along with an SXC muffler, I did not notice my buddy's 625 SXC pulling away from me one day when we both hit the throttle coming back from a dirt ride on pavement. Oh, it has a choke, but it sure is fun to operate...
I have the FCR 41 mx. It has a choke and hot start but I have never needed to use either one when dialled in correctly. As stated, just a couple of blips of the throttle is all that is needed to start if cold. After opening up the airbox a little and installing an after market exhaust, the difference is like chalk and cheese. Fuel consumption is higher but a mere pittance compared to performance increase.
If the FCR carb does not have a choke chances are it's a 39 FCR, most of the 41 FCR (that I have seen) come with a choke. 39 are 41, both work vary well on the LC4, I would lean toward the 41 more for street use. The light switch effect is mostly tunning of the FCR carb. BST are FCR, off road it depends on your riding style, and what/where you ride. The BST like any CV carb is more forgiving then an FCR. And if riding mud a CV carb is hard to beat. You won't be squaring off corners and steering with the rear tire like you can with an FCR. If your running a full knobbie rear tire that hooks up...FCR!
