Separate names with a comma.
Discussion in 'Thumpers' started by creeper, Feb 20, 2007.
i believe there are some carbs that the screw is air, but not this one...
Okay, so I made a dent in the pipe to make it fit... If I had the proper tools, I'd route the exhaust from that point a bit differently. But anyways, that can be done later.
I've now got it running, somewhat. Idle Jet is 42, fuel screw is 2 turns out, main jet is 170, Blue needle from JD Jet kit and clip on 3rd grove from top.
Runs well on higher throttles, but the low throttle area is a bit gunky. Now it idles crazy high when warmed up, and sometimes falls down to normal idle speeds. It seems like an air leak to me, but it could due to the idle jet being too small, i.e. getting too little fuel?
Thought I should chime in here. I have a relatively new to me 1999 640 LC4 Enduro currently with just over 53,400 km on it. It had the standard BST carb and original header and old style head, fed into round Staintune exhaust. The bike runs superbly for something with significant mileage, but curiosity got the better of me.
I'd spoken to someone with the identical bike but even higher mileage and he had good things to say about the 39mm FCR-MX he had fitted. Thanks to the brains trust here I knew which carb would fit and what was involved. I nearly bought a low mileage High Flow motor from a wrecked motard just to take away in case of mechanical troubles down the track, but missed out after hesitating for too long. What I did end up buying from that seller was the newer header and matching oval shaped Staintune.
Not long after that I located an FCR-MX 39mm from a 2005 KTM 525 and snapped it up. It turned up in good but grubby condition.
178 main jet
85 starter jet
100 pilot air jet
200 main air jet
OBDTR needle on leanest clip :eek1
It also has a non-standard AP cap - a bulky red anodised alloy job.
During the evenings in the last couple of weeks I started the swap between the headers, knowing it was going to be too tight especially with the AP cap. That went smoothly but the stock exhaust springs don't fit the new header (spring tabs are in different places on the headers). Strange because across the models the OEM fiche diagrams indicate the same part number for the springs. It gave me the opportunity to change out some plastics too with the back end of the bike in bits. I ran the bike a few times with that header and realised the jetting was now way off. The ID of the newer header is larger and the bottom end to mid range power was softer and fluffy.
Rather than mucking about jetting that carb I decided to jump and fit the FCR. I left the jetting as found other than setting the needle clip to the middle - I thought it was most unusual to have it set on the leanest clip. The standard BST cables worked with a bit of a fiddle once the routing was changed. I already have very tall bars so this was a surprise. The original carb boots and clamps remain, but fitting the boot between the airbox and carb was a major pain because the plastic intake bell on the carb is larger. In the end I had to swing the subframe up to get it in there. It was still a very tight fit and couldn't be managed without removing the TPS (which I had to refit to seal it all up even though it's not used).
The moment of truth was interesting. The bike started without hesitation and idled smoothly. I took it for a short ride and was immediately impressed by the additional response off idle. I ran it at varying speeds and all in all it was at least as good in most places but a little flat after the AP squirt (measured at 2.5 seconds) petered out. WOT power was good but fluffy. A nice surprise is the reduction in vibration. It really only has a very narrow band of havy vibes now, whereas it was pretty rugged at anything other than 90+ kph in the top two gears. When I checked the exhaust baffle (my own design, less restrictive than the standard Staintune) it was blackened slightly.
I picked up a 170 main and 45 pilot yesterday and fitted them last night. A quick blat this morning shows substantial improvement for doing so. I didn't really feel like picking up a ticket for a flat out top gear run so will save that for another time and place. Bottom end response is now very strong and the front comes up in second on throttle alone. I love the immediate response in all gears at pretty much all speeds. Roll on response in 3rd is brilliant. The bike was never low on power but is now much more lively. I can't wait to take it bush and have a play. The only problem I can see will be staying ticket free with the motard wheels and taller gearing fitted.
So, in summary I am a convert. Smoother, more response and more grunt. I could manage 5.5L/100km before with gear and mixed riding so I'm most interested to see what the change means for range out of my big tank.
I'll update my findings as I find them!
Not sure this is right place to post this question, but I'll give it a shot on the off chance that some of you in the know are still subscribed to this relic.
I just installed an FCR MX-39 on my 1999 640 Enduro. Gotta work on jetting, etc., but can anyone tell me what the hose barb on the intake bell of the carb is for? Bike ran fine with just a filter on the end of it, but I'm thinking maybe I should plug it off?
Maybe it's a spot where the exhaust gas circulation for cutting emissions connects to? Sort of like the SLS system with the BST, where exhaust gases are brought back to the carb. Mine is plugged and was when I got it.
That's what I was thinking, but wasn't sure. . . If yours is plugged, I'm gonna plug mine and see what happens. Makes no sense to have it vented to atmosphere but pumper carbs are new to me.
hey, maybe 6 years late, but...
just bought a 2006 640adv with fcr 39 carb.
i have many issues with its functioning.
at low rpm the engine stops, arround 4K rpm there is a "hole" - when i twist the throtle it stucks on 4k until it brakethrough to 5-6K rpm, and thats the only range that the engine works fine.
checking the history of the bike in 4 different workshops, turns out that the "4k rpm" problem was since the beginning, and nobody succeed solving it.
does someone met this problem before?
I bought a new 2006 640 and put a FCR39 from a 525 and it ran perfect at any and all rpm ranges, lugged or light load.
Got better mpg then the POS bst. Make sure the fuel mixture screw didn't fall out, If not I would take the carb apart and be sure all jets and passages are clean and the float set properly. If still not running correct I would look for some other problem. I loved the whistle the FCR39 makes.
If it's time for a rebuild on the FCR, get the JD jetting kit for the 640 while you are at it.
Hey, retroone.............nice Super Rat! I have a Wombat!
Does anyone know if FCR clears Akrapovic headers? I have a lead on cheap carbs. One is 39 from a 2004 525EXCR and 41 from a unknown KTM. Which one would be best for off-road/adventure/rally application? I found some information that a 2003 660 Rally used a 39, so that could be the one to go for?
Thanks for your help!
The 41, 39 and 37 share the same body, so flip a coin.... They are a bulky carb that just barely work to fit in the 640s space... They do get pretty close to the stock headers, haven't tried with a bigger pipe.. You will also need the sxc fcr carb/ air box boots to get a proper fit..
there are also 3 different types of FCR's. Generation 1- 3. Depending upon what year your bike is, that will determine which will fit easily, and which you will have to squeeze. The 2003 rally bikes i bet still had the older gen1 FCR with the exposed accel pump. in '03 the headers were changed on production bikes to allow room for the newer gen carbs. these carbs were only put on the european versions of the LC4 except on the 625sxc and smc which came with the 41mm. i have a 43mm Gen1 FCR that i use on my 640 w/ akrapovic headers. i have no fitment issues at all.
I knew I can count on the wast knowledge of the inmates here. Thanks! Now I only need to decide which one to get. If my research is correct, FCR39 should give more bottom end torque compared to the high strung FCR41. I am correct on this? So for a adventure/rally riding the 39 would be the better, and 41 for a sumo configuration.
Macman great to see you are having success with the FCR39, I am about to fit and FCR39 from a DRZ400E to my 2001 Adventure and your jetting will be a huge help.
Just to clarify, are you running the jetting below?
170 main jet
85 starter jet
100 pilot air jet
200 main air jet
OBDTR needle on leanest clip
If so, I will order the correct jets for mine.
Im running on my 03 640ADV
39 FCR- 45 Pilot, 185 main, OBETP needle on 4th clip & 1-3/4 turns
At sea level Perth WA
Cheers Jabba600, great to know what works with these, the more I read about the BST, the more I want to throw it into the nearest large body of water!
Is the '03 the low flow head or the high flow number?
Its a high flow head mate
It transformed the bike the old BST felt asthmatic
Best mod u can ever do other than suspension
I wonder if the jetting would differ since mine would be a low flow head?
I dont reckon it will be much different
Jam the carb in and go for a ride see how it runs
I'll give it a try but it should have a 165 main at the moment, I should order a 170-175 at least before trying it. I have another electrical issue to sort first with the BST in place so that I'm not introducing too many variables. Thanks for your help!