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08 CRF450R FCR Mods and suggestions upon rebuild...???

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Hey guys!

Just picked up a low hour 08 CRF450R,.. from what I can tell and what the PO told me, it's all stock on the inside and he's never messed with the Carb. (?) It does have a full Yoshi exhaust system on it but I haven't even checked to see if the air filter screen has been removed or anything like that yet.

The bike fires right up cold - first kick with one twist of the throttle prior to kicking - runs great and strong,... but if I stall it,.. she no starty :(  .... did a quick search and there were like 50 million threads on this so I gathered up all the hi points and I'll be going over the bike with a fine tooth comb this coming weekend. (Adjusting valves,.. rebuilding carb,.. .. )

I do have a couple of questions though ... :D

Since it does have the full exhaust and I'll be doing the air box screen removal and box mod, will I need to richen it up a bit? From what I keep reading, the carb is pretty spot on for the most part when the motor is stock.. but... ?

FCR Carb Mods - I'm no stranger to the FCR Carb ... just went down a miserable road combining two 39mm FCR's off of an 06 YFZ450 to make one good carb and then retro-fitting it to my 03 KFX400 ... super long story :(  .... anyway, I know about the Oring mod,.. but it seems tuning the Leak jet is maybe a better option? Any other mods or adjustments I should be looking for my bike while the carbs off and on the bench?

Also what about Air Filters?... There's a UNI or Twin air on there now,.. but what about K&N or Green Filter?... I'm doing mostly woods riding.

Thanks!
Rick

 

 

 

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The 2008 FCR used on your bike cannot accept any of the traditional 'mods' because Keihin did them all, already.

Your carb was only found on that bike, that model, that year, and no other. It is the best FCR ever made.

  The hot start is the only issue left on the carb....it's still a terrible design prone to corrosion of the cable and the plunger and cavity. Service all, especially the surface of the cavity.  

Set your fuel screw with a HOT motor, like this:

Lower the idle as low as it will go. With the fuel screw at 1 turn out, turn it more to raise the idle. As so as it stops raising, stop turning. This should be approx 1.5 turns.

If it is more or less than that by a signifgant amount, the pilot jet is too large/small. 

You can further fine tune it by listening to the speed of the idle drop after a blip. Faster is better, but it might promote a slight decel pop.

The stock jetting is typically spot on for up to 7000 ft too, so if it's not running well, check the pilot jet passage for partial corrosion, replace the needle jet (emulsion tube) as they wear, as well as the slide plate seal.

 

 

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Ok thanks for the info! I'm pretty up to speed on dialing these carbs in for the most part,..

One other question in regards to rebuilding it is: I have an ultrasonic cleaner which uses water based chemicals, so I usually don't have to completely disassemble the units before running them through the process - 

Is there anything I need to be aware of or take note of before I pull say the TPS stuff off or anything like that? ... never had to do one with that stuff on it before (?)

Also, from what I take the Pilot jet should be spot on from the factory for the most part... or is it typically a tad rich?

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There is no reason to sonically clean that carb unless you see corrosion or contamination.

The only passages that are really an issue is the one above the pilot jet. It has a very sharp bend you have to ream with copper wire.

All the rest are easy to clean out with fine wire or 100+psi compressed air.

The most common issues are corrosion of the hot start cavity, broken hot start nut, clogged pilot passage, and worng out emulsion tube and slide plate seal.

The carb body is split, and the seal inside has a shelf life. If you use the solvents or strong chemicals, it can melt and block passages.

A replacement is available from JD Jetting.

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Thanks again,..

I just split a 39mm FCR recently,.. wasn't as bad as most folks tried to make it out to be,.. I needed the clearance to drill & tap the throttle cavity for a flexible idle control,... fun stuff.

I'll be going through the carb this weekend if all goes well.

 

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Forgot to mention I also ordered a Slavens Racing 4T Keihin/FCR Fuel Screw - it has the brass tip like the OEM one,.. but has the extended shaft with a knob'ish type end on it so you can turn it by hand - 14 bucks shipped (Red) ... I guess for about 15 bucks more I could have opted for the flexible fuel screw.,.. but oh well :) 

I also have plenty of new Keihin jets on hand from my other projects so I should be loaded for bear when I go to dial things in ;)

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