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Old 04-03-2013, 10:24 AM   #181
davesupreme
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Joined: May 2011
Location: palm harbor, fla
Oddometer: 1,177
Quote:
Originally Posted by gunnerbuck View Post
Nope, it's a fuel screw, so more turns = more fuel...
+1

i believe there are some carbs that the screw is air, but not this one...
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Old 04-30-2013, 06:10 AM   #182
Lortdadu
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Joined: Aug 2010
Location: Finland
Oddometer: 207
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?
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Old 06-27-2014, 05:08 PM   #183
MacMan
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Joined: Jun 2007
Location: Outer NW Melbourne
Oddometer: 696
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.

Jetting was:
178 main jet
85 starter jet
40 pilot
100 pilot air jet
200 main air jet
OBDTR needle on leanest clip

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!
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