Carb question: need wisdom



11 replies to this topic
  • dezthumper

Posted August 11, 2002 - 02:37 PM

#1

I have need to raise the needle jet clip one position and move to a leaner pilot jet for a race at high altitude.

Other than removing tank, seat, airbox, subframe et al. What is the easiest less timely way to make the above changes. I am going to pre-run the course and will take all necessary tools to make adjustments, however, if it takes an hour or more to make each change - well, that would decrease the fun factor.

Is there a wise one out there that has done this before without damaging anything and without dismantling the mighty beast. Someone that can do this with their eyes closed and one hand tied behind their back. There's gotta be an easier way...

I don't mind details in your decription. If there is a thread covering this, please point me in the right direction.

Please help this ol' Vet... :)

  • Hick

Posted August 11, 2002 - 03:14 PM

#2

Originally posted by dezthumper:
Is there a wise one out there that has done this before without damaging anything and without dismantling the mighty beast. Someone that can do this with their eyes closed and one hand tied behind their back. There's gotta be an easier way...

I don't mind details in your decription. If there is a thread covering this, please point me in the right direction.


You may try a search for “carb removal.”

There are many ways to go about removing the carb, but you don’t need to remove the tank or subframe. I would suggest you split the throttle housing on the bars and remove the two cables and leave them dangling. Then loosen the clamps on both sides of the carb, remove the fuel line, unplug the white TPS connector and take off the lower black factory zip tie (they are reusable, push up on the little tab to pull it out).

Then take your right hand and put a few fingers in front of the air boot and pull it backwards. The boot will come off the carb, or the carb may come out of the inlet, whatever. Grab the two cables you removed and push them towards the back of the bike to create some slack, then you can pull the carb free from the bike. At this point you can remove the cables or just leave the carb dangling by them and do your work. To detach the cables from the carb remove the black plastic cover, it is held on with one allen head bolt and a small tab in the back, then loosen both retaining/adjusting nuts and fish the cable ends out of the pulley.

To get at the needle take the top of the carb off (two bolts), then you will need to remove the allen head retainer on top of the slide. To get at the pilot you will need to remove the bowl. I’ve confused the choke jet w/ the pilot a few times, the latter is the one shielded in the housing and sits lower in the bowl than the former. Both are right next to the main...

I have become very adept at removing the cables from the pulley on the carb with everything still on the bike (but I can’t do it w/ my eyes closed yet), then removing the carb, but if you haven’t messed with this thing before that probably isn’t the way to go.

I ride at 4k ft., and I have done some jetting exercises at 6k, 7k and higher, plus there are several CO riders here, so if you want some jetting tips for your race post the location/altitude.

Hope this helps.

  • Hick

Posted August 11, 2002 - 03:19 PM

#3

Originally posted by Hick:
To get at the pilot you will need to remove the bowl. I’ve confused the choke jet w/ the pilot a few times, the latter is the one shielded in the housing and sits lower in the bowl than the former. Both are right next to the main...


The above applies to the 426, the YZ 400 has a slightly different carb and I believe you may be able to remove the pilot via the large plug in the bowl on that model.

Also, pretty soon someone is going to post that you don't have to take the carb out of the air boot or inlet, you can just rotate it around one way to get at the cover and the other way to get at the bowl but I've never tried this.

[ August 11, 2002: Message edited by: Hick ]

  • skthom2320

Posted August 11, 2002 - 03:27 PM

#4

I don't remove or loosen any cables to get at the needle. I just remove the carb from the airboot/inlet boot and let it dangle. Then it is fairly easy to get at the needle. To change the clip position put the needle inside a clear plastic baggie so that when you fingler-fumble the clip (and you will eventually), it will stay in the bag and be found easily.

If you are changing pilot/main jet, remove the top coil bolt, loosen the lower one, then rotate the coil out of the way. You then have enough room to loosen and rotate the carb float bowl toward the shifter side.

It doesn't take more than 15 minutes to change clip/pilot/main and put it all back together.

  • Hick

Posted August 11, 2002 - 03:47 PM

#5

Originally posted by skthom2320:
To change the clip position put the needle inside a clear plastic baggie so that when you fingler-fumble the clip (and you will eventually), it will stay in the bag and be found easily.


That is a good tip. I use a small pair of vise grips to keep from launching that little clip.

  • James_Dean

Posted August 11, 2002 - 04:33 PM

#6

With all the tools at hand, pulling the needle out can be done in under 5 minutes. Reinstalling it takes a little more time to make sure everything is in place correctly.

I used the same procedure as Hick described on my '00 WR400 many times.
-Cables loose at the grip
-TPS disconnected (hardest part)
-carb clamp screws out
-fuel line off

Pull the carb out on the left and let it hang by the cables.

With the needle out, I place it flat on it's side on a hard surface with the "C" pointing down. Push down on the needle near the clip while holding the clip between your fingers with the other hand. It will stay securely between the fingers.

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  • dezthumper

Posted August 11, 2002 - 05:25 PM

#7

Now we're getting somewhere. This is a super response.

The altitude will be 5300-5500 feet, low humidity (30-40 range) and temp will be about 75.

I am currently considering the first jetting attempt of the following from current stock setting:
MAIN: from 162 to 152
Needle CLIP: from pos 4 up to 3 (1 clip up to lean it out - thus dropping needle into main a little deeper)
PILOT: from 42 to ... uh oh, not experienced here. My calculations say 40 - is there a 40 Pilot Jet?

COLORADO RIDERS or OTHER HIGHER ALTITUDE TTers WITH THE 426 STOCK bike - what works for you?

  • skthom2320

Posted August 11, 2002 - 05:31 PM

#8

Yes there's a 40 pilot. You can buy them from a nearby Honda dealer as well. Best thing is to take in your 42 pilot to match it up. They will usually have a selection of jets under the counter, etc.

You are going the right direction with your jetting. You may even take a 38 pilot with you. As other's have said, once you get used to it, it will be a snap to jet it for your altitude.

  • Hick

Posted August 11, 2002 - 09:44 PM

#9

Originally posted by dezthumper:
The altitude will be 5300-5500 feet, low humidity (30-40 range) and temp will be about 75.


First off, what model do you have? I’ll assume it is a ’01 or ’02 YZ 426...

I don’t think you could go wrong with a 158 or 160 main.
Clip position IMO is the biggest change w/ altitude, if you have time you should try one and then TWO clips leaner. I’m 1.5 clips leaner than stock at 4k+ ft and 85° (needle EKQ #3 vs. stock EJP #4).
A 40 pilot should work well.

Your higher altitude vs. my higher temp.s may be a wash...

As for the pilot jet, if you have a ’00 or newer, the pilot jet will be the same PN as a Keihin PWK or other two-stroke carbs’ pilot jet. This would be the same PN as a two stroke Honda’s pilot jet.

A YZ400 pilot jet would, I think, be the same PN as a CRF’s pilot jet...

  • dezthumper

Posted August 12, 2002 - 01:35 PM

#10

Hick

You mention clip position "IMO." What does IMO stand for?

Some have asked the year - it's an '01 426. This will be her last race/ride as my 450 is due in the next day or very soon thereafter... it was a little wierd buying a bike sight unseen & WITHOUT ANY tests by anyone to read/research first. I believe the reliability of my 98/99/00 and 01 speak for what Yamaha will put out. I pray that Blue didn't take Red's route to lightness w/penalty being reliability - but that's another thread... Thanks guys for all your input. I will print all the responses, buy the necessary jets and will head up to the Pine fresh air to see what works and what doesn't. THANKS AGAIN!!!

[ August 12, 2002: Message edited by: dezthumper ]

  • jaybird67k

Posted August 12, 2002 - 02:33 PM

#11

I hate to be the one to say, but I have removed my carburator many times for cleaning and doing mod's such as the BK mod but I have never removed the carburator for just doing a jet or needle clip change.
The main jet the slow jet and the needle can all be done without removing the carb.
To do the needle all you need to do is remove tank and seat and get a 3mm or 4mm(cant remember which) ball end allen wrench. Loosen the air boot on each side of the carb, rotate the carb slightly toward you and stick the ball end of the allen through the small triangle shape between the frame tube and the main spar of the frame and loosen the bolt, the other bolt is easy to get to.
then take the cap of the carb off and loosen the 4mm allen screw that covers the needle and remove. Then use either a small pair of needle nose pliers that have been ground down on each side or use a small magnet on a stick to remove the needle.
To do the main and slow jet just remove the plug on bottom of the carb and use a mechanics inspection mirror to look up in the carb to see the location of the jets, then use a 6mm socket for the main and remove (Motion pro makes a tool for this) The slow jet is the same but I prefer a small slightly modified flat head screw driver to remove this one.
I like to experiment with jetting, so I'll change them in the winter time between moto's as the air temperature rises from cool to warm.
Any of the three can be done in 10 minutes with practice. All three can be done in 30 min.

Later, Jason
# 67 Over 30 Int.

  • Hick

Posted August 12, 2002 - 02:39 PM

#12

Originally posted by dezthumper:
Hick

You mention clip position "IMO." What does IMO stand for?



IMO = In My Opinion





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