Which carb is best on LC4 640

[meat popsicle]

Originally Posted by outfront

Can someone direct me to that thread? Ive hunted this site for a step by step, no luck. Maybe I need a step by step, using the search feature.

...

not sure if it:

http://www.advrider.com/forums/showthread.php?t=206427

has the info you need, but it can't hurt.

[MODNROD]

....off a 2008 YZ250, 168 main, 42 pilot, std air jets, OBEKN needle on 4 fm top, and a home-made slip-on, with pocket-ported head and 5-angle seats to give 12:1 comp ....... === ....... power-only front rises in second, with 17/38 gearing, smooth surge of power from 2300rpm, high-12's, somewhere over 175kph top end. Wired up TPS, 2 colours are the same (on a 2006 KTM SM anyway), so easy to do, only 50Ohm difference between resistance values on FCR and BST TPS switches (negligible), haven't noticed much difference with or without TPS though to be honest.

Just thought I'd mention it for anyone who wasn't sure if it was worth it, or having difficulty trawling thru conflicting opinions for a set-up that MIGHT be a place to start. I live 300m above sea-level in a very dry (under 15% humidity) environment.

[outfront]

Originally Posted by meat popsicle

not sure if it:

http://www.advrider.com/forums/showthread.php?t=206427

has the info you need, but it can't hurt.

THANKS.

After reading the pros and cons; I think I'll mod the BST and sell the FCR.

Im riding the TAT this summer and I don't want carb issues at 11k ft.

[mstenkil]

Hi there,

Just wanted to share my 2cents. I had to replace my 40 BST because I had the time and wanted to get some low in snap that I have on my 450 but lacked on my 03 LC4 ADV. I manged to snap off the corner off top and bottom of the lower bowl. I was tempted to just do Creepers mod and JB weld it permanently and pray I never had to mess with the jets...not likely so i went shopping.

Ended up with a lightly used 2008 EXC FSR-MX 39mm with throttle cables for $180 delivered from ebay. I then purchased JD Jetting Kit with Needle screw. Here is what I have in it for elevation set for: 1500-3000ft.
#42 pilot jet
2 turns out on the fuel screw
Red marked needle in the #5 from top clip position
#172 man jet
Thicker O-ring for the accelerator pump linkage modification as described in the kit

So far i have been lucky with the boots and its aligned pretty good. I have taken it for some small spins and it hasn't moved. I must say Creeps post saved me I have some sort of issue going on with my estart so i have to kick it. It used to take numerous kicks with the choke on. Now, its one-two kicks with the choke on for a few moments. It has significantly helped out starting it and its more responsive. Super happy right now

[rruugger]

I had a fcr 39 carb and a leo vance pipe installed on my 07 640 adv ....man it runs much stronger! But I do have issues in the miles of endless woops we ride out here in california desert. It floods-out and dies in that type of terrain. Had it back to the shop a few times and they change the needle valve and some other adjustments, but to no avail. IS THERE A CURE FOR THIS????????????? Just ran a 1300 mile rally, bike ran flawless with this only issue. Any help from the ones that are wise in the ways of 640 carburation would be appreciated.
Or direct me to where to ask this question.

[dirty_sanchez]

Sir-

Check the float height.

You can do a rough check with the carb still in the bike by holding the free end float bowl overflow tube (which normally hangs down by the swing arm) even with the seam where the float bowl mates to the bottom of the carb. You're making a horseshoe shape with the tube with the open end at the top.

While holding end of the tube next to the carb body but above the top of the float bowl open the drain a bit with a phillps head and make note where gas begins to drain out of the overflow line by slowly moving the end of the tube up and down. Once you slowly begin to move the end of the tube up and down while being held next to the carb, you'll notice where the gas begins to drain out of the tube. From what I understand gas should begin to drain out of the overflow tube at the seam. If the float is too high, gas will drain out of the tube above the seam, too low-below the seam.

The fuel should just begin to show right at seam level.

Dirty

[rruugger]

Thank you will give it a try.

[1Pots]

dellorto

[dzrtracin]

Here's the deal, i just bought back my sxc 400 from a buddy i sold it to 5 years ago. Back then i was going to get rid of the BST but never did. Now that its back in my possesion i plan to. I have been through all these carbs threads & have found nothing for the lc400, just the 640's. Question #1 will the TM40 be a direct fit front boot & rear boot? Cables, do they need to be changed, or use the existing one's? Basic jetting for 2500' elevation.

RIDE ON!!!!!!

[hammmerboy]

I have a '95 620 with the Dellorto PHM 40 carb. It needs to be rebuilt- any thoughts on this? Any words of wisdom?

[Tseta]

Katumo's "Rebuilding a Dell'Orto PHM SD Carburator"-thread will answer most, if not all, of your questions...

-T

[Young-gun-640]

I have myself an old '98 640 LC4 with the BST and thinking on the FCR-39. Does anyone know if all FCR-39 carbs are the same or were the same models tweaked in different ways to suit other bike makes and ages?