99 WR400 with 01 WR426 Carb (FCR gen2) Help!


20 replies to this topic
  • fadingfastsd

Posted February 17, 2008 - 02:19 PM

#1

Hey guys, I'm having a problem I just cannot figure out.
Please help me get to the bottom of this. I've searched all over TT and have not found an answer.

I have a 99WR400, YZ timed, all free mods, stock exhaust head/mid pipe with FMF PowerCore IV can.

The bike has run very well and been very reliable. The stock carb started leaking from the overflow regularly due to a damaged needle valve/seat in the float bowl. Rather than replacing those parts, I came across a carb off a 01 WR426 for very cheap ($65 for carb & 01 WR426 head pipe to replace my crappy stock 99WR400 head pipe that blocks the oil filter cover).

So...I pulled the 426 carb & my 400 carb apart. The 426 carb is the newer generation Keihin FCR flat slide with the integrated hot start & the internal accel pump. I had my old carb jetted correctly and dialed in w/ a ZipTY fuel screw, so I wanted to swap my old jets into the newer carb. Here are my initial jet settings:

-main: 172
-Pilot: 45
-Pilot air jet: 65 (i hope i'm not confusing the Pilot & PAJ here)
-needle on 4th clip down from top (was set like that when i got it)

So I clean the carb, everything looks good, and I put it on the bike.
I give it a couple kicks, and notice I had to plug the vacuum line on the head, since the new carb has internal hotstart. I do that.

Kick it again, the bike won't start. I pull the hotstart on the carb to see what happens. 1 kick and it fires right away. As soon as I push the hotstart back in, the bike dies. So I figure its running way to rich. I adjust the fuel screw pretty much all the way in to compensate, kick it without the hotstart, still won't start. So I pull the hotstart out again, bike starts immediately. The fuel screw seems irrelevant.

So now I figure the bike is set way to rich, since it will only run with the hotstart leaning it out. I pull the carb to check the needle, and it was on the 4th clip down from top. I move it up to the 2nd clip down from top to lean it out. Put the carb back on the bike, fuel screw at standard ~2 turns out.

Bike still not start, not even pop without the hotstart on. So now I'm very confused. I pulled the hotstart plunger off the bike and clean it out. Put it back in, same thing.

What the hell is going on!!!?? I figure my jetting should be pretty close, as the bike ran excellent with these jet settings on the old carb. Why will the bike only start with the hotstart on (plunger out), and dies as soon as I turn hotstart off (plunger in). Why does the fuel screw make no difference!?

Please help!!!!!

Evan
If theres any pictures or more explanation I can provide to help let me know!

  • fadingfastsd

Posted February 17, 2008 - 10:37 PM

#2

Any ideas you guys? I'm really frustrated here.
One thing I forgot to add, having the TPS plugged in or not doesn't make any difference. One of my buddies suggested it's almost like a kill switch when I shut the hot start off, and to pull the plug and check for spark with it on/off. I don't see any possible way the hot start could interface with the electric system other than some extremely remote possibility through the TPS, but I guess I'll check. I feel that the jetting and setup is in a range general enough that the bike should start and run, although maybe not well.

Please help!

Evan

  • evilinsano

Posted February 18, 2008 - 11:04 AM

#3

What is the deal with the internal hotstart? I have a 99 WR400 so it sounds like there is a difference on the 426? What is choke status do you have it one or off when trying to start? did you check those connections?

  • SXP

Posted February 18, 2008 - 12:11 PM

#4

Are you sure you are not confusing the hot start knob with the choke knob? If it is indeed the choke you are pulling to get the bike to run, then you have a clogged pilot jet or pilot jet circuit. If I remember correctly, the red knob is the hot start and the black knob the choke.

  • byggd

Posted February 18, 2008 - 12:53 PM

#5

The hotstart knob it larger and sticks out further. The choke is just up and to the left.

  • Rich_in_Orlando

Posted February 18, 2008 - 01:15 PM

#6

I think the choke/hot start colors are the other way around- black is choke and red is hot start.

I am wondering about the needle. Is it the same as your other carb? As in, did you move it from the old carb or is it just what came with it? When I put a carb off an '04 WR450 on my bike, the jetting was totally different than the original. (The jetting on the original carb was basically stock.) I was expecting to have to rejet but I left it alone, figuring that it worked on the bike it came off of and I would adjust from there. I didn't have to touch it at all. The bike runs way better now than it ever did with the new carb and jets. If I knew the jetting numbers, I would post here what they are but since I never had to mess with them, I don't know them by heart. I do know that it was a different needle. Stock is a DTM needle. The new one starts with an "E", I'm pretty sure of that.

  • 426boy

Posted February 18, 2008 - 06:23 PM

#7

red is the hot start, black, and up and to the left is the choke.

  • fadingfastsd

Posted February 18, 2008 - 08:27 PM

#8

Hey guys thanks for all the replies, its much appreciated. I'm definitely not confusing the hot start with the choke. The choke is a black knob, the hot start is red. The bike is a 99 WR, which originally had an external hotstart, that was just a valve between the airbox and a fitting at the intake. The 426 carb has a hotstart knob integrated into the carb.

So I guess I'll swap all the jets back the way they were when I got the 426 carb, and give that a shot. I was thinking it would jet the same way as my old carb, but maybe not.

I'll try and do that tomorrow night and give you guys an update.

Thanks,
Evan

  • dirtysouth

Posted February 22, 2008 - 10:05 AM

#9

Hey guys thanks for all the replies, its much appreciated. I'm definitely not confusing the hot start with the choke. The choke is a black knob, the hot start is red. The bike is a 99 WR, which originally had an external hotstart, that was just a valve between the airbox and a fitting at the intake. The 426 carb has a hotstart knob integrated into the carb.

So I guess I'll swap all the jets back the way they were when I got the 426 carb, and give that a shot. I was thinking it would jet the same way as my old carb, but maybe not.

I'll try and do that tomorrow night and give you guys an update.

Thanks,
Evan


have you figured it out?

  • dugabrams

Posted February 22, 2008 - 02:00 PM

#10

What effect does using the choke have, if any?

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  • fadingfastsd

Posted February 24, 2008 - 01:02 AM

#11

Sorry for the long delay, I haven't had a chance to work on the bike until today. I took you guys advice, swapped all the original 426carb jets back in. 170main, 45pilot, 60pilot air jet, air screw ~2 turns out, needle on the 3rd clip down from top.

Same exact problem. Bike will not so much as backfire without having the hotstart on. 1 kick with the hotstart, the bike fires up, but dies immediately after turning hotstart off. TPS on or off makes no difference. Bike will not start with choke either, only with hotstart.

Just out of curiosity I pulled the plug out and checked for spark with the hotstart on and off. (it seems almost like a kill switch!). Strong spark either way.

What the hell is going on here? I cannot figure this out. Please help!

  • tweav

Posted February 24, 2008 - 02:00 AM

#12

do you have the idle speed screw opened up at all? it sounds like it is way rich at idle . is your fuel/air screw in right? may be an extra washer or o-ring up in the hole.

  • fadingfastsd

Posted February 24, 2008 - 11:37 AM

#13

Tweav thanks for the help. The fuel/air screw is in correctly, and set right. I am using a ZipTy fuel screw. I pulled it out yesterday and double checked. It is installed correctly, with correct spring, washer, and o-ring. I could go back and try the stock fuel/air screw, but the ZipTy one worked flawlessly on my old carb.

I will check the idle speed screw, I never though to check that. I'm sure it's open enough to idle though. And that shouldn't affect the fact that if I rev it up the bike will still die when i turn off the hotstart.

Thanks for the help!

  • fadingfastsd

Posted February 25, 2008 - 07:18 PM

#14

Ok heres some updates.

I realized I was still using the intake boot from the old gen1 carb, which had a notch that did not line up with the new one. Looks like I was getting an air leak there. I replaced it with the correct boot from the gen2 carb. The bike would then start when using the choke (!?) but run like crap, popping and backfiring, and wouldn't idle. I went through the carb again and everything is fine.

Bottomline, I'm selling both carbs and getting and Edelbrock, which I should've done in the first place.

Both are up for sale on here and locally, although I've already had local calls.

  • ncampion

Posted February 25, 2008 - 07:39 PM

#15

You'll love the Edelbrock!!!!!

  • fadingfastsd

Posted February 25, 2008 - 08:04 PM

#16

thats what I hear! I'm looking forward to it. These FCR's are good carbs, but I'm just sick of the hassle. I've been contemplating moving to the Edelbrock for a while, and this is just the motivation I need.

  • krust36

Posted May 20, 2008 - 02:52 PM

#17

Sorry I didn't read this sooner, but just an FYI for anyone else searching the archives. You can't use the fuel screw from a Gen 1 FCR on a Gen 2 FCR. They are different. Probably why this didn't work.

  • SXP

Posted May 20, 2008 - 04:09 PM

#18

Sorry I didn't read this sooner, but just an FYI for anyone else searching the archives. You can't use the fuel screw from a Gen 1 FCR on a Gen 2 FCR. They are different. Probably why this didn't work.


Not exactly true. The stock fuel screws will interchange quite happily with either carb. It's when you go to an aftermarket extended screw that you will have to be careful what you buy. The design of the float bowl is different on the 426 carbs, allowing the use of an extended fuel screw with a knob on the end to turn it. This same screw will not have enough clearance to fit on the 400 carb. For the 400 carbs, the knurled end of the extended fuel screws are pretty much the same diameter as the shaft, or they are made with a "T" end.

  • maxtherat

Posted May 20, 2008 - 07:49 PM

#19

I think the stock size pj for that carb is a 42. Running a 45 with the fuel screw at two turns out may be too rich to idle. Try a 42 at 1 3/4 turns and see if it will idle. I also thought the zip ty was specific to the different generations of carbs.

  • pdrides

Posted May 22, 2008 - 05:01 AM

#20

The previous post is correct, the aftermarket fuel screws are different from one generation FCR to the next.




 
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