Keihin Carburetor Re-Jetting for Dummies (like me)

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Keihin Carburetor Re-Jetting for Dummies (like me)

Postby JohnBG » Thu Aug 16, 2007 11:18 pm

This is a re-print of a write-up I did a while back on RIMC. It is archived here to avoid being purged in the future.

Today I had the time and parts to re-jet the Keihins on the Raven. She had been kinda lugging on acceleration and while starting, the right side cylinder wanted to burp, fart, and sputter for a few minutes until it got warm.

Here's the parts you'll need:
- New CVK main jets - I went with 130's (the stock carbs come with 125's)
- New CVK pilot jets - I went with 45's (the stock carbs come with 38's)
- 3/16" and 1/8" flat blade screwdrivers (if you have them about 12" long it works better)
- Phillips screwdriver
- 3mm Allen (hex) wrench
- pan to catch a small amount of gasoline
- dish to hold carb screws (I have one of them little magnetic parts dishes which is handy)

You can get the jets from a variety of sources: Sudco (http://www.sudco.com), carbparts.com or perhaps your local Kawasaki dealer. I think they use the same Kehin carbs as the Urals on the Kawasaki Concours. I bought mine form Holopaw Gene - http://www.uralfla.com.

Before undertaking this project, I had studied Dwight Rahl's CVK carb re-jet website and it was extremely helpful! Link: http://www.dwightrahl.com/carb-jetting.html

Dwight removed the carbs from the heads to re-jet them. There's nothing wrong with doing it that way, but there's more than one way to skin a cat.

I didn't want to go thru the hassle of removing and remounting the carbs, so I chose to do it with the carbs still fastened to the bike. It's a little bit trickier, you have to lay on the garage floor while doing it. If you have a 2WD, it makes it a little easier to shimmy under the sidecar to do the right side carb. If ya gotta 1WD model, you might need to jack up the sidecar a bit. The shift lever and the rear brake lever might be in the way slightly but I was able to work around them.

Step 1. If you have a vacuum operated petcock, remove the vacuum line from the left side carb that goes to the fuel tank petcock valve.

Step 2: Put a catch pan under the left side carb and disconnect the fuel line from the carb. This will drain all of the gas out of the fuel lines and filters.

Step 3: use a 3mm Allen wrench to open the drain screw on the right side of the bottom of the float bowl. Once the gas has completely drained, tighten it back up snugly so you don't forget to do it later.

Step 4: Use a Phillips screwdriver to remove the 4 screws underneath the carb that hold the float bowl to the carb body. I find that you need a fat Phillips screwdriver with a sharp point, so as not to booger up the screw heads (they booger easily). As you remove the screws put them in your dish so you don't lose them. One day I should prolly swap out those Phillips-head screws for some nice little Allen head bolts.

Once you have the float bowl removed, take a look, there are three jets inside: The main jet, the pilot jet, and the starter jet. I attached a pic showing where they all are located.

I replaced the main jet and the pilot jet on both carbs. The starter jet is for the enrichener (choke) circuit and is only used when the enrichener know is pulled. I left that one alone.

The main jet is right in the middle, and the pilot jet is recessed in a cavity near the other two jets.

Step 5: using the 3/16" flat blade screwdriver, remove the existing main jet and install the new one. The main jets have numbers stamped into the side of them. My existing ones were 125 and I switched them to 130.

Step 6: Using the 1/8" flat blade screwdriver, remove the existing pilot jet and install the new one. You'll have to shimmy under the bike so you can see the slot so you can position the screwdriver. Test you screwdriver with one of the new jets first to make sure it fits. You don't want to booger up the the slot. The pilot jets are stamped with a number in the bottom face. My existing ones were 38's, I switched them to 45's

Step 7: Look at the float bowl, clean any crud outta there. I found just a little crud in there. Put the float bowl back on the carb and tighten the four Phillips head screws.

Step 8: Repeat Steps #4 through #7 for right side carb.

Step 9: Reconnect the vacuum line to the petcock and the fuel line on the left side carb

Step 10: If you have a vacuum operated petcock, turn the lever to the "PRI" (prime) position for about 30 seconds to fill the carbs with gas then place it in the "ON" position.

Step 11: Start the bike!

I found that the bike was easier to start. It still sputtered just a little on the right side for the first 15 seconds, but nowhere near as bad as before. I took it for a little spin around the block a few times. She accelerates easier and is more responsive while coming off idle.

The whole process took about 25 minutes. I hope this helps.

Here's a few pictures
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Last edited by JohnBG on Wed Feb 13, 2008 2:14 pm, edited 1 time in total.
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Postby Ragman » Thu Aug 16, 2007 11:35 pm

I will do it... yes, it looks simple, I will do it.. :? I will get the jets, and then take the plunge... :? Thank you John.. I want to get into the carbs and look, just to see what jets are in there. I have no clue if the dealer rejetted it when he put the Dunstalls on.

The only problem with doing something, is I will mess with something else later too.. :wink:
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Postby cubituscubitus » Fri Aug 17, 2007 5:19 am

Howdy John,
It looks simple. I will do it one day, but as for now, I 'm using some improved carb needles. They seem thinner than the stock ones and I get more torque and power @ low and mid' RPM. Mr. Cob has a pair of them too. He seems to be pleased with.
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Postby Hoot Owl Pete » Fri Aug 17, 2007 9:03 am

John:
On another site I read about shimming the jets.Could someone explain how is it done,what it does and the purpose and outcome?Thanks ..Hoot
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Postby Dan » Fri Aug 17, 2007 10:17 am

Thanks for the info. I should rejet mine, as it farts and sputters till it gets warm. Better acceleration would be a plus. I always thought rejetting was one of the great mystries of the universe, looks simple enough.
How tight do you go when screwing in the new jets-or do you feel them as you bring out the old ones and tighten accordingly.
Any downsides to rejetting?? Just a dumb question I am sure.
Thanks
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Postby DaveO » Fri Aug 17, 2007 11:25 am

Hoot Owl Pete wrote:John:
On another site I read about shimming the jets.Could someone explain how is it done,what it does and the purpose and outcome?Thanks ..Hoot


You actually shim the jet needle, not the jet, by placing a washer under the needle retaining clip,...This allows the needle to raise out of the jet earlier in the application of throttle, it richens the mixture earlier...
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Postby JohnBG » Fri Aug 17, 2007 2:51 pm

Hoot Owl Pete wrote:John:
On another site I read about shimming the jets.Could someone explain how is it done,what it does and the purpose and outcome?Thanks ..Hoot


I assume you mean shimming the needles.

I haven't tried that.

Basically, it involves removing the tops off of the carbs and removing the needle and diaphragm and putting small washers unfer the top of the needle to raise it a tad.

The old Mikunis and the K-68 slide carbs had needles with grroved and circlips wehre you could manully raise and lower the needles.

I assume that the Keihins do not. I have never opened up the tops of the carbs to look.
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Postby catfish » Fri Aug 17, 2007 8:43 pm

I don't know about the Keheins as far as the grooves for adjusting the needles I would imagine they have groves but on the Mikunis even with the circlips in the lowest groove the needles would not raise up enough so you would put the circlip in the last groove then pull the needle out of the slide and place 1 or 2 or 3 tiny washers under the needle and then place it back in the slide.This raised the needle even more than the grooves could making the mixture richer in the upper ranges.A cheap and fast thing you could try and if you didn't like the results you could put it back where it was and only lose maybe 60 cents instead of $25.00 on jets.

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Postby Dwight » Sat Aug 18, 2007 8:00 am

Dan wrote:Thanks for the info. I should rejet mine, as it farts and sputters till it gets warm. Better acceleration would be a plus. I always thought rejetting was one of the great mystries of the universe, looks simple enough.
How tight do you go when screwing in the new jets-or do you feel them as you bring out the old ones and tighten accordingly.
Any downsides to rejetting?? Just a dumb question I am sure.
Thanks

Hi Dan,

I just snugged up the new jets when I put them in - no need to really "lean" on them. Especially since they are made of brass...

You'll get a feel for how tight to go when you remove the old ones.

The new jets made a real difference in my bike. I found that starting up in cool weather was much easier, the warm-up time was cut in half, and I got smoother throttle response. Nothing that would be a make-or-break difference; but significant none the less.

Good luck,

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Postby Flagman » Fri Oct 24, 2008 12:00 am

Howdy all

Any one have some guidlines for our carbs at difference elevations?

I have a 06 GU, live at 7,000feet with out any modifications. It runs fairly well but of course I have nothing to compare it to, in other words, how good can it run? I have the stock jets in the carb. Can anyone give me some recommendations for jets and idle mixture (number of turns out)?

Also thoughts in regards to advance. I should be able to advance some at my elevation. Anyone ever driven at or above 7,000 feet?

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shimming the needles on the Keihin CVs -

Postby TheWildOne » Fri Oct 24, 2008 1:10 am

Actually, <b>this</b> year (last week) I discovered that you don't even have to remove the slide to shim the main needles. (Prob'ly will have to when I take out the 'shims' next spring, though.)

This is on my '07 Tourist, by the way...

If you have a pair of fairly long-nose hemostats ("roach clip" to those of us of a certain age...), or maybe even super-long-nosed needle nose pliers, all you need to do is take out the four tiny Phillips-head screws that hold the top on the carbs - that's the <b>tiniest</b> ones, in case there are others up there. And I believe someone (in FL? Can't remember for sure if it's Gene @ Holopaw or Heindel) sells allen-head replacements for these, too.

Got 'em off? Gently pull that top off & look down. You'll see the top of the needle. Snatch that sucker up with the 'stats (it's not held in by anything but gravity), poke it through a lil' #6 hardware-store washer, and poke it back down through the hole in the carb slide/piston, <i>keeping the washer on it</i>, which can be a little tricky, unless you re-grab the needle by that washer/shim, once you have it installed on the needle.

(all my #6 washers measure right about .04" thick, which is 1/25", which is close enough to 1/32" for me - besides, it works ! - what else could you want?)

Voila.

This avoids the hassle (which I've personally never run into, BTW) of getting that rubber diaphragm back in the groove in the top of the carb.


Like I said, removing the 'shim' next spring w/o pulling out that slide/piston/diaphragm will be a little trickier. But come to think of it, the slide & carb body ain't ferrous, like the washer/shim. So a slender magnet should fish it out once I've pulled the needle up. Wait - maybe the slide <i>is</i> steel, come to think of it. Ah well. I'll find out either way when the warm weather returns.

BTW, again, I early-on (spring of '07) re-jetted to #44 pilot / #130 mains already, and that works just swell <b>w/o</b> the washer/shims 'til it gets chilly enough around here that the engine rarely gets a chance to get really, thoroughly, deeply warmed up (trips under 10 miles, in other words). Then the fartin' und poppin' reappears, 'til I put in the shim/washers. This takes care of that, and hopefully I'm carbureted as lean as I can be w/o wasting a whole lotta gas &/or fouling plugs right and left.

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