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LC4 Carb
Hello all, was wondering if any overlanders have tried the Keihin FCR41MX carb in the 640 adv yet? I know there are a lot of fire road riders who have made the change with excellent results and much improvement in power delivery and fuel consumption over the stock Mikuni BST40. I have found the BST40 a real pain in the ass on rough rocky roads and fast dunes where if any sort of negative G is exerted on the carb, it just shuts up shop for a second resulting in very nasty surprises when you need the power most only to find its all on vacation until the carb gets over its hissy fit a second or two later...I note the new 625's have the FCR and the 660 has always had it so it must be good. Anyway, I am thinking of changing to the FCR and was hoping someone has some long distance miles using it who could comment, especially regarding the claims of better consumption. Cheers A |
Hello,
Im riding a 03'Adv and like you said, the BST carb is not doing well on bumpy roads... From what ive read, steady mpg is doing better... BUT, and there is a big BUT, Ive you (full) throttle it a lot -you know these bumps, bit of throttle and ur flying?- the accelerator pump will kickin and increase fuel consumption a lot. Its true, ive noticed this when riding two 450EXC on the same track, 9l tank, i used 1l more than my mate...!! Got a FCR39 some time ago, but still need to find some time to complete the job... on the 41 vs 39 subject, I was told that the 41 is more geared to top HP -which i dont need- and the 39 is towards torque which sort of makes sense since the EXC have 39's and the SX 41's... Anyway, hopefully i have this thing sorted out soon... [This message has been edited by gozell (edited 10 January 2005).] |
Cheers Gozell, thanks for the info.
I also have the 03 and the reason I'm going for the 41MX version is that it comes with the TPS unit. Has your 39mm got a TPS already or will you make a modification? Re the acc pump, you can set it to kick in at a certain throttle position (stock is 50%) so I will try say about 25% for cruising / overlanding and change it if I need more power in deep sand etc. I can then make a mark on the grip to show when the acc pump comes in...emergency power, like a WW2 fighter eh! I ordered one last night and it will be here tomorrow so this weekend I will fit it and let you all know how it goes. I will have to modify the choke cable and a few other things. I am worried about the size and if the carb will hit the header pipe, might need to be offset a little bit. Anything to solve the problems on bumpy roads, especially with a loaded bike! Salaams A |
TPS? Is that the hot start thingy? Havent got that one, its an older type FCR but still should be better than the BST... Do you have a link for the mod?
Thanks for the tip on the acc. pump, im not a star on these carb jobs but got someone who can help me out... I noticed some pic with 03's on the australian safari, not u is it? |
TPS = throttle position sensor The 03 adventure has a throttle position sensor, its a small black plastic plug looking thing with an electric wire and connector on the right hand side of the carb. Your BST will have one, take a look. The bikes electronics incl variable timing etc uses the TPS to determine the position of the throttle, you will also see some electric cables going into the throttle itself on the bar which is also related. If your FCR39 does not have the TPS sensor, then you have to do a mod. Its been done before but I'm not sure of the how to etc. I have heard it is not easy. Perhaps you should look at exchanging the FCR39 you have now for the MX model with the TPS. The stock electro plug snaps strait into the FCR's TPS. I had a look and I see they now also make a 39mm MX version with the TPS. N/less don't worry too much about it, there is always a way to make it work. Re australian safari, nope not me mate, I gave up enduro / rally riding a long time ago. Too much time, expense and pain involved... |
Yep, got the TPS... So my FCR is not stoneage after all....
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Gozell, Finished putting in the FCR on the weekend. One word...F'INGEL!!! It is a different bike, smoother, less vibration, huge amount of power available all thru the range. Low end so much better and cruising very very smooth. The carb makes a distinct whistling sound when the acc pump kicks in, pretty cool. Have some work left to do on jetting though to fine tune. Get your FCR on there as soon as you can mate. BST40 is dead, long live king FCR! |
Be interested to see some fuel consumption figures for the FCR. Thinking about one for my 02 LC4-E, but since the bike gets non-racing desert use the fuel consumption's important.
Also 39 or 41? I believe some of the 660 Rallye LC4s have the 39, hence the 39 may be more use to me. Opinions welcome. Re: Throttle position sensor - wasn't that introduced in the 03 models? Finally, presumably the choke cable needs changing at least. Is a new choke lever/LHS switchgear needed? Is a different throttle cable and/or throttle needed? Is it all just a matter of fitting the parts from, say, the 625SXC? Cheers, Ian. [This message has been edited by Ian (edited 22 January 2005).] |
G'day Ian,
Re fuel consumption, too early to tell yet, I finished tuning the machine on the weekend so haven't had time yet to put on some miles. Overall, a flat side carb will always do better than a CV carb. On the FCR in particular however, fuel consumption is all about the acc pump, which is adjustable for different throttle positions. What I've done is back the tab for the acc pump control off so that the pump comes in at about 60%. I then marked the throttle but I din't actually have to do this as you can hear the acc pump, its an unmistakable whistling sound, sounds a bit like a turbo charger. Anything under 60% throttle position should be fine for cruising (although I have yet to test it on a longer distance, I may even be able to back it off some more) plus you have a serious reserve of HP if you need it, perfect for the desert. I'll let you know re fuel consumption as I get some more miles under me belt. The TPS was introduced in 03. Yours should not have one which means you don't need the FCR with the TPS so that will save you some money. Re 39 vs 41, its an ongoing debate. Most folks reckon that the 41 tends to get more HP at higher rpm and the 39 more Torque at lower rpm, (one of reasons KTM went with 40mm carb to try and find a happy medium) however, more "go" regardless whether its HP or torgue, means more juice and I'm guessing the 39 would have to have the acc pump set to come in very early in order to get the additional torque on the low end. For me I would prefer my "gas guzzling stage" to be at the top end of the range where I don't need to use it and can avoid it if I'm in the poo gas wise. Besides, the LC4 properly tuned even with the BST40 is hardly in need of more torque IMHO. The main reason I went with the flat side carb was to kill the cut out problem on bumps / rocky roads. I have to say that particular problem now resides with troy in myth. Re cables, the choke cable screws strait in, you may have to cut / file the little nib off the carb end of the stock cable. If you remove the standard choke unit from the FCR, and compare it to the carb end of your existing cable you will see what I mean. Its too easy, 2 minute job. The throttle cables are a different story, the geometry of the standard cables is not quite right being designed for the left hand side. However, I got mine to work and they would do as an emergency pair but I have ordered some 04 625 SXC cables for the long term. The problem is more with the lower (open) cable than with the top (close) cable. In fact you could probably get away with the top cable and just order the SXC bottom cable. You will need the SXC airbox boot, it has a folded coupling in it so it is heaps easier to work with the stock solid unit. These are cheap, AUD 17.00 here, worth every cent. Again, you can get the stock boot to work but its a pain in the butt. You will also need the airbox adapter (which connects the boot to the carb) and the o-ring for same. KTM are cheaper than Keihin for these smaller parts. Cheers AD |
AD,
Slowly im getting closer to mounting the FCR.... I did notice that the position sensor on the FCR has a different type of connector than the BST but matching colors... What did u do on this one? Just cut off the connectors and solder 'the colors' together? Thx I just read "The stock electro plug snaps strait into the FCR's TPS... u sure? u mean the plug that was plugged into the side of the BST or another one? [This message has been edited by gozell (edited 14 March 2005).] |
Yes, can confirm that the '03 FCR39 has TPS as picked up unused from a 525EXC apparently. Still waiting to fit so am interested in what jetting settings etc people use on the LC4 and the 39 combination.
Re economy, believe that the pumper part of the carb operates whilst opening the throttle to pick up speed - that is it is transient in nature and will only only operate for a few seconds. If someone knows different pls post it!! The 39mm FCR used on the Rallye bikes can get away with a marginally smaller choke diameter due to the much better breathing characteristics of the engine - Twin Exhaust being the main factor here. No hot start feature on mine though but gather it is not really needed! And don't forget, the larger choke diameter of the 41mm (over the 39mm) will only be noticed when at WO or fully open throttle position. Anybody got a before/after set of economy figures for similar useage of BST vs. 39?? [This message has been edited by overlandr (edited 25 March 2005).] [This message has been edited by overlandr (edited 25 March 2005).] |
Hi I am new to this forum, well done . The FCR/TPS idea has been on my mind for some time as a way to improve my '99 adv. (I just bought an '03 to see what it's like...much smoother.)
I am thinking of the FCR for either/both bikes. It looks to me that the TPS on the CV/BST 40 monitors the butterfly not the slide? This would be different to an FCR/TPS where the slide must move 1:1 with the twistgrip. Maybe the difference doesn't matter much and the std '03 3D ignition map will do OK. (Any pinging with rapid acc'n?) However, as I need a switchable CDI anyway on the'99 to cope with occasional low octane fuel, I was wondering about how a programmable system like the Vortex might work? Obviously this would need setting up/development as they don't have a cdi "of the shelf" for the LC4. And, Having 10 different ignition maps available could keep one busy mucking around for some time! ?Too hard? Has anyone used an aftermarket ignition at all or with the FCR +/- TPS? also.., what is the best source for the FCR carb ? thanks. Mike |
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OK, I am not in favor of changing the carb. If it is not running right fix it. The bike should run with the stock carb in every condition. An accelerator pump carb is to give more gas and so more horsepower when the throttle is opened. Good for racing but not necessary for the traveler, in fact it could cause problems. The BST carb has a flat slide. It is a daiphram carb. It should work fine otherwise why would KTM have chosen it? I think it is better to get the most out of the stock carb and easier to get spare parts.
Bill. |
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