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FCR40 Tuning Woes- XR600R

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It doesnt make any difference what bike the carb came off, the float height should not have needed adustment.  The proper way to set it is to take the float bowl off and tilt the carb so that the float just rests against the check valve but not compressing the spring tip of the check valve.  The float should be parallel with the float bowl mating surface.  If you want to just check the float fuel level with the carb installed, remove the black pipe used to drain the float bowl and replace it with a clear tubing and route it upwards to the top of the carb.  Open the drain screw and the fuel should level off in the tubing indicating where the float is set.  The fuel level should be right at the mating surface of the float bowl to the carb body.  Adjust accordingly.  

 

A #45 Pilot seems large for a nearly stock engine

Yeah, the fact that the float height was so high previously seems strange to me.  I would hold it up to where it was ever so slightly pressing against the spring, and the float seam would create a 15-20 degree angle away from the float bowl surface, and it measured 14-15mm.  After I adjusted it, the seam now lines up with the surface, and blowing through the fuel feed, I can get air through when the float is just past that point (moving downward in the bowl).  

Also, this carb doesn't have a drain screw- it has the hole where a drain screw should be, as well as the drain nipple/tube coming off of it, but on my XRL's CVK there's a flathead screw that will drain the carb.  On the FCR it's just a hole, which is quite annoying when I want to drain it without getting gas all over my hands!!

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What bike did your FCR come from?

I'm also interested in any info on jetting the choke.

The ebay listing said it was a 2003 CRF450R.  I also got the throttle assembly and cables.  

And I have NO idea- the choke has its own jets???  This is well above my pay grade!  Tell me what to look for and I'll find out for ya ;)

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Well I found a quick minute to take carb off. Now I gotta sonic bathe it but I'm busy all day tomorrow and Wednesday. Might finish early tomorrow.

45 on my stock bore 95 is richer cause I just run an oiled Uni pod filter right on carb. No Airbox. And a power core 4 muff. Not sure how rich you need to be for a super trapp.

As for this 88. It's only ran off a 45 with no filter on in the box and starter fluid squirted into intake while full throttle decrompression kicking.

No intake leaks. But gurgled like it's trying to suck in more gas. It didn't run with the 42.

DOT COM, should I pay any mind to the starter jet? What's its role?

Carb was spotless right now by the way.

Plugs got spark for sure.

Choke jets? I pay no mind to the choke. I leave it how it is. I only jet, needle and ap mod these carbs.

Oh and my drain plug is just like that ATu...not like that on my other 2 fcr's. I drain by removing bolt and it slashing onto the motor.

And my floats fine. I do the old school tilt and blow air with my mouth into fuel line. If my air stops blowing when floats level I'm good. Always worked for me. This isn't my issue.

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Just for info: Im running a MJ 158 and PJ42 on my 628cc. Its a tad rich, but have been riding in the winter with colder, denser air. 

a 40 PJ is nice for starting but might be a bit lean. Have to test more. 

 

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Sweet! Well apparently this 88 has a 628 piston, i didnt build the motor.

Stock box, supertrapp muff.

Truthfully I just put in gas and tried to start as carb was not knowing jets or having cleaned carb. Tried to start, and no luck. Pulled carb, tested spark.

Cleaned carb my first time since buying it. It was jetted 42/165.

I figured it didnt start with a 42 and my 95 has 45/160, so I got a brand new 45. Sonic cleaned carb, rebuilt with 45/160 and this is what it ran on. Still trouble starting, neighbor kicked it. And when it ran it sounded thirsty. So thats why I went to 48.

Carb and parts are soaking in cleanser. Carb cleaner and air and guitar strings through every hole. As soon as I get the chance Ill sonic dip it. I gotta sneak and do it cause the sonic cleaner is at my buddies pawn shop for jewlery. I gotta switch out the cleanser so I dont get grease all over someones Rolex! After hours stuff. Going to work now, if I finish early Ill get back to it.

Since it ran on 45 I want to put that back in. But Im tempted to clean carb and clean 42 and retry. I didnt try that jet through a cleaned carb.

Is a Supertrapp enough to go richer? My fmf was. 628 piston and Supertrapp are the only mods here. On and off are a regular for me. Ill try 42 first then 45 and get back to yall.

Atuwitty? Hows it going?

Edited by notoriousE-R-I-C

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The ebay listing said it was a 2003 CRF450R.  I also got the throttle assembly and cables.  

And I have NO idea- the choke has its own jets???  This is well above my pay grade!  Tell me what to look for and I'll find out for ya ;)

I should have phrased it better: I don't have any experience with swapping the starter jet, and am interested in info about doing so.

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I wouldn't worry about the the starter jet, its not really important because with a pumper carb all you have to do is whack the gas a couple times then turn the engine over.  Once its started the choke will act as a fast idle.

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I wouldn't worry about the the starter jet, its not really important because with a pumper carb all you have to do is whack the gas a couple times then turn the engine over.  Once its started the choke will act as a fast idle.

Remember that it not just to push the button, but it involves a leg and and kick on a 600R :-)  

 

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no66 It should start even faster pumping the throttle rather than just using the choke because the fuel it shot right in the engine. I know mine starts right up after giving it a couple WOT and turning the engine over only once. Without the choke though it will start up and die after a few seconds unless you pump the gas to keep it going or use the choke. I use the choke only to make it fast idle to warm up after I've started it.   For the record I have a 75 starter jet in mine.

Edited by D0T-C0M

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No it's not. I just am down to thinking my carbs not clean enough. Next week It's getting another sonic bath with heat. I didn't use heat the first time. I think I rushed it last time and I need to leave it for an hour not twenty minutes.

This mods worth double every penny. Twice the bike it is now trust me.

Jetting anywhere isn't easy

  • Like 1

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So I have a ride coming up, and basically threw in the towel on the FCR for the time being.  Stocker is back in the Pig, and it's running well.  Anyhow, here are some shots of the carb.  Two show the float bowl at just barely touching the spring, another is the cardboard measuring device I made to check the height, another is the stock vs the aftermarket fuel screw for comparison, and the last is how I determined 9mm on the carb float bowl.  Not exact, but precise enough.  Am I doing something incorrectly?

 

 

IMG_1643.JPG

IMG_1644.JPG

IMG_1645.JPG

IMG_1646.JPG

IMG_1647.JPG

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This carb swap seems like a pain in the ass.

i agree.   And I bought the air to carb 3d coupler from a member here, I got the 650L airtake but am waiting to see, how other handle the setup problems.

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So I'll sonic clean my fcr39 and jets tonight.

In the meantime, I took the fcr41 of my 95 600r and tried it on my 88.

The fcr41 is jetted 45/160.

I set the fuel screw to 3 turns out. Bike started but I needed to turn idle all the way up. After it warmed up I took it off choke and turned idle down a bit but the Rpms had a hiccup where I thought it would die so I left idle up a bit. I rode bike. It felt rich in the main. The 95 breathes a little more than the 88. So I think 160 is too rich. I'll put in a 155 into the fcr39. I still had trouble starting, and needing a high idle tells me go richer in pilot. But I'm to understand 45 was already high and 48 is way too rich.

I might stay with 45/155.

I'll update after I clean the 39.

But bike rode okay. First run since a motor rebuild. A few more break in runs and I'll change the oil.

But I can't personally kick the bike over so there's work to do. The neighbor kid did it and he said it was hard for him. He knows the big pig starting procedure.

I was also thinking, I need to turn idle up to get more air cause there's too much gas. So maybe 45 is too rich? I haven't tried the 42 in a clean carb yet. It's what was in there when I got it and I just tried to start it as is. Didn't start with a 42. Put in a 45, it started.

Plug chops today...

Edited by notoriousE-R-I-C

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You should tune your pilot jet by the adjustment position of the idle mixture screw. I don't think the idle speed knob position is generally used as a direct indicator of pilot jetting.

It is normal for the engine to idle at a noticeably lower RPM while cold. That behavior is not necessarily an indication of incorrect jetting. My starting technique is to give the idle speed knob a half twist faster when initially starting, then when the engine warms enough that the idle speed starts creeping higher on its own (after maybe a minute) I readjust the knob back down.

Edited by heart_of_darkness

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