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Old 08-13-2009, 02:23 PM   #1
einfahrt
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Default Improved Fuel Screw Extension

Let's try this again, this time message composed off line so no chance of getting booted out. I also used Preview Post instead of Submit then Edit, as suggest by Glenn, to also reduce getting booted out.

Enjoy!

Zerebrel (Engineering Services)
Chris Johnson (Einfahrt)

Low Budget Fuel Screw Extension

BACKGROUND

The Keihin CVK carburetor is a great carburetor design. As a result of emissions mandates, however, the mixture on some bikes is a little too lean, and the fuel screw being capped with a 1mm-thick plug pressed into a shallow counterbore, prevents access. A typical modification is to drill a hole in and pop out the cap, which allows access to the screw so the low-speed mixture can be adjusted, but then the location of the starter blocks direct access to the screw head. Only the very squat screwdriver tip will fit in the space, and has to be turned by feel, which is not accurate.

One available solution for this problem is an extended screw with a small knurled head, but while into my KLR650 carburetor recently, I discovered a very simple way to extend the screw that is also easier to adjust than the knurled head solution.

FUEL Versus AIR SCREWS

Motorcycle carburetors typically employ a low-speed mixture adjustment via a ‘fuel screw’ or an ‘air screw.’ Opening a fuel screw enriches the low-speed mixture and opening an air screw leans the mixture. How to know which one you have? Air screws are always on the airbox side of the carburetor body, and fuel screws are on the engine side. The KLR screw is on the engine side, thus it is a fuel screw – meaning if you turn it out further, it will richen the mixture.

PROCEDURE

This procedure assumes a high level of experience (every step is not described) and adequate tools. For those less experienced, get help, or approach the work very patiently.

The following photos picture a 2003 model carburetor, but the fuel screw is essentially the same across all the model years.

- Wash the bike to clean all around the carburetor

I suggest cleaning with a pressure washer, with the tank off, so you can get the work area very clean. Plug the fuel and vacuum petcock hoses before washing.

- Remove the carb from the bike carefully

This is not fun on the 650, as the airbox boot is very stiff! Undo the choke cable from the handlebar control so the whole cable assembly stays with the carb! Do not push or pull on the elbow of the choke cable at the carburetor or the plastic part it mates to can snap.

- Mount the carb upside down in a vise. I like to hold it in a vice, squeezed gently but firmly between a rag.

- Liberate the fuel screw from being capped

Use a center drill if you have one. A drill bit can plunge through the 1mm plate and touch the fuel screw and rotate it, losing the factory setting.

- Blow out any chips and put a drop of oil in the threaded bore of the fuel screw

- Count the turns to seat the fuel screw (clockwise) and record the factory setting

My 2003 was 1-3/4 turns out from bottomed.

- Remove the fuel screw

Make sure no chips drop into the hole! You can keep the spring, washer, and o-ring in the hole. Losing the o-ring is very bad because the low speed circuit can suck air through the fuel screw threads.

- Put the fuel screw in a lathe, center drill, then drill .15" deep to diameter .096 (#41 drill), or use a 3/32" drill with some side pressure to get the slightly larger diameter

- With some 3/32" brass rod from a welding supply, make an L-bend part like this:



Note the photo shows all the parts associated with the fuel screw in the correct order of assembly.

- Clock to bent brass rod

Mark the fuel screw head when fully seated (be gentle when bottoming it). I put a scratch in the upper part. You don't have to do this, but it's handy to know your fuel screw setting by position, because you took the time to clock it to, say, the float bowl center, before soldering it.

This is what mine looked like with the fuel screw seated:



- Solder the rod to the fuel screw

Use a liquid flux and lead-based electrical wire solder. You can use a Bernz-type torch, but an electric wire soldering iron works fine. It only takes a very tiny amount of solder! Don’t let solder run onto the threads! If you do, heat the part and blast the melted solder with a quick pulse of compressed air.

Here's the end result on the carburetor:



OTHER DETAILS

When you liberate the fuel screw, you can adjust the low-speed mixture. The KLR650 also tends to run lean in the mid range. One low-cost fix for this is to remove the slide, pull out the needle, and shim under the head of the needle with from .030” to .050” of shims. I typically start with .050”. I try to retain a balance of good fuel economy while getting rid of too-lean carburetion. So far I have not had to spend money on jets or kits, or drill slides or modify slide springs to get a favorable result on the KLR650 and KLR250.

While working on the carburetor, I truncated the idle adjust screw and machined a slot into the new head. The porky knurled head has bugged me for years, so I cut it off. The idle is very stable on the 650, so frequent thumb screw idle adjustments aren’t often needed unless there are major elevation changes in your area. Even then you can compromise with an average idle adjustment and adjust less frequently.
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Old 08-13-2009, 05:29 PM   #2
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Default Re: Improved Fuel Screw Extension

Great idea was wondering how i could fine tune mine without twisting the carb back and forth a zillion times Thanks for the post.
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Old 08-15-2009, 10:23 PM   #3
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Default Re: Improved Fuel Screw Extension

Great idea.Thanks for posting it.

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Old 09-09-2009, 01:12 PM   #4
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Default Re: Improved Fuel Screw Extension

u really should sticky thisª

i was looking for it near the 22cent mod

in how to and procedures!!
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Old 01-24-2010, 03:48 PM   #5
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Default Re: Improved Fuel Screw Extension

Hi I was wondering if you could help me, a friend of mine was doing the dynojet mod and accidently drilled out the wrong plug, he drilled out the brass plug behind the pilot plug. I managed to get it out for him but [IMG]file:///C:/Documents%20and%20Settings/Shelley%20and%20Dave/My%20Documents/Dave%27s/float.jpg[/IMG]https://s837.photobucket.com/albums/z...rent=float.jpgI can't seem to find a replacement part number. Any help would be greatly appreciated. Thanks in advance.
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Old 03-04-2010, 01:27 PM   #6
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Default Re: Improved Fuel Screw Extension

Could you make me one of these?
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Old 03-04-2010, 01:40 PM   #7
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Default Re: Improved Fuel Screw Extension

VERY NICE procedure...

thread is now a sticky...
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Old 03-04-2010, 01:53 PM   #8
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Default Re: Improved Fuel Screw Extension

EXCELLENT write-up Chris (two thumbs up)

Definitely Worthy of being a Sticky and I am sure a lot of guys will appreciate your design / efforts.

Thanks for the contribution !!!!
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Old 03-04-2010, 04:27 PM   #9
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Default Re: Improved Fuel Screw Extension

Quote:
Originally Posted by pub27 View Post
I can't seem to find a replacement part number. Any help would be greatly appreciated. Thanks in advance.
Don't think Mr. Kawasaki considers that particular plug a replacement part; rather, integral to the carburetor body (found no separate illustration in the exploded parts diagram, nor any mention in the accompanying parts list).

I'd look to J-B Welding the plug (if perforated) and reinserting it; don't know if the fuel ("air mixture") screw plug could substitute or not.

Let us know how things work out!
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Old 07-19-2010, 12:14 PM   #10
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Default Re: Improved Fuel Screw Extension

I appreciate the effort put into sharing this well laid out solution...

For those w/ limited time (or less tools), they can pick up the "Extended Fuel Screw for KLR 650 all years (by KoubaLink)" from Happy-Trail for $20... It was a quick install...

Turned the carb, drilled plug w/ hand drill, replaced screw w/ new one.

I even called Happy-Trail and they offered reduced shipping for me since that was the only thing I was purchasing.
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Old 07-30-2010, 12:30 AM   #11
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Default Re: Improved Fuel Screw Extension

FYI

https://www.johnsmotorcycleparts.com/...roducts_id=152
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Old 07-30-2010, 04:19 AM   #12
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Default Re: Improved Fuel Screw Extension



Glad that HT and John's sells them already made, my lathe is in the shop (keeping my flux-capacitor and plazma cutter company)
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Last edited by thevanrat; 07-30-2010 at 04:21 AM.
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Old 07-30-2010, 09:54 AM   #13
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Default Re: Improved Fuel Screw Extension

I kinda like the OP's screw looks like one finger will do all the adjusting you need,kinda push the screw to turn.
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Old 07-30-2010, 10:03 AM   #14
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Default Re: Improved Fuel Screw Extension

Someone should make em and sell em that way. It is a great design. I grew up with access to a full machine shop, and miss being able to do stuff like that. He found a happy medium there by chucking up that little brass fitting and not damaging the threads- I would have ruined it for sure.

I could only picture a three jawed chuck on that right onto the threads.
Brass machines very nice, indeed, but sometimes it can be a bit soft and fragile, if you are chucking on it.

Good job, I'm just sayin. I really miss access to a shop. I farm my projects out now, and find the youngsters in the game have some real talent too, better welders and such than myself!

Find a machinist with a dirt bike, atv and or a snowmobile, and you are in good shape, cause he is no doubt making parts that exceed factory specs for his own toys.
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Old 08-05-2010, 11:20 PM   #15
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Default Re: Improved Fuel Screw Extension

Excellent idea. I'm doing mine next weekend. Thanks for posting this.

Are there any other ingenious mod's you've come up with?

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Old 08-14-2010, 10:06 PM   #16
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Default Re: Improved Fuel Screw Extension

great idea!...did mine today...quick and easy mod...took me bout 10 minutes to do...thanks for the idea!!
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Old 04-03-2011, 06:28 PM   #17
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Default Re: Improved Fuel Screw Extension

I bought a small flathead screwdriver bit for one of those crappy multi-tools... You know the kind.

Ground down the flathead bit to make it fit the fuel screw, shortened the whole thing so it would fit in right... now I have a tool to adjust it as I please. :-)

I have one of the thumbscrews, but the damn thing seems to just rattle all the way out. Don't understand!
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Old 04-23-2011, 10:04 AM   #18
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Default Re: Improved Fuel Screw Extension

Did mine today, following your procedure - turned out great! Thanks for the idea and for posting it. I drilled the hole slightly deeper - .20" for more surface area for the solder to adhere to. Good job!
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Old 04-23-2011, 12:14 PM   #19
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Unhappy Re: Improved Fuel Screw Extension

Drop that little thing and if the pointy end strikes first - bent !! Ask how I know.
Well that project went South !! -- Happy Trails to the rescue.

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Old 04-23-2011, 01:12 PM   #20
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Default Re: Improved Fuel Screw Extension

Quote:
Originally Posted by richarddacat View Post
that would be too easy!!
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