i am an idiot... please help!

Hi kzriders,

So I just (kinda) finished my kz550 project. I got my bike together and ready for a ride. I took it for two laps around the block and it was awesome, except the carbs needed to be tuned a little.

When drilling out the caps that cover the air screw on the side of the carb body, I managed to hit the screw on one of the carbs. I was using a reverse drill bit so when the bit caught the screw, it started unscrewing the air screw. This stripped the screw and the threaded hole. The screw's no big deal b/c I can get another in a rebuild kit, but now I've got mangled threads in the carb body... What can I do???

I'm trying to get my hands on a tap to see if I can clean out the threads, but I don't have much faith it'll work. I haven't found an appropriately sized tap yet, but I'm still looking.

Do I have any other options besides getting a new carb rack? Anyone else do this and fix it?

I appreciate any help on this... you can even call me a dumbass.

Thanks fellas.

Not sure but you might try calling SUDCO or going to their website. They carry all parts for your carbs and might be able to suggest someplace to purchase a tap for the pilot air jet hole...It's a long shot but worth a try.
I believe it's www.sudco.com

Good Luck,
Buzz

id get a small extractor for snaped bolts and it would/should undo.

Gin, Far from chastizing, at least you had the foresight to use l/h bit. Taps exist, I've used them, unfortunatly I dont know where. A dear but departed partner had a set I used to borrow. All may not be lost, as I'd guess that as much as 1/2 the threads at bottom are still intact. If unable to find consider..drilling out damaged threads. Cutting shaft off damaged air/fuel screw, & slotting w hacksaw, and using undamaged thread section upside down to clean at least an introducrion for new screw. 'tis fine work, and chancy, but you may be able to salvage that body. Luck. G

I doubt the brass mixture screw thread will clean up the thread in the hole... it is pretty soft. What I would do is remove one of the pilot mix screws... I THINK it will likely be a 5mm but again MEASURE. Then measure the thread pitch using a pitch gauge. Common taps are .8 and .9... these are readily available. Unfortunately, I can't remember ever stripping a Tekei hole and don't know what size or pitch is needed. OK... you ain't got a pitch gauge or tap? You got a Harbour Freight up in Austin? They carry an inexpensive metric tap/die kit that not only contains the pitch gauge but will have both taps I mentioned. If the screw is M6, then the pitch will very likely be .75 or 1.0 and the kit will have both of those as well.

Could also further confirm correct tap size by GENTLY test- screwing the selected tap part way into non-damaged threads on a companion carb.

Don't go too far in with the tap so as to damage the orifice in the air passage where the pilot screw point intersects. Look closely at an undamaged pilot screw and use the thread length as a guide to help determine maximum depth permissible.

After concluding the tapping, would also recommend disassembling the carb far enough to blow out the pilot circuit with compressed air and assure the passages are cleared of any thread remnants.

Good Luck!

Ok cool... looks like I got a some options. Thanks so much for the feedback.

I kinda started down this path when it happened but ran into a wall which is when I posted the question.

When it happened I borrowed a H.F. metric tap/die set from my buddy and the pitch of the screw was .75 (if I remember correctly), but the .75 tap seemed to be too large in diameter... however, I wasn't checking on an unmangled companion carb. Maybe that was the problem. The borrowed tap/die set just moved to Houston, so I'll have to go get my own set.

So let me see if I got the idea straight:

step 1: verify the pitch and size of screw.
-how do I measure the size? is it just the major diameter of threaded section?

step 2: get tap of same size. verify that tap is correct size by lightly threading the tap into a companion carb.

step 3: drill out the upper threads of the mangled hole.

step 4: use tap to create introductory threads and clean up lower threads

step 5: use good air screw as a gage to ensure I don't tap too far into the carb body.


Please let me know if I missed anything here. I can't wait to give this a shot!

Thanks again.

gintree wrote:

...
step 3: drill out the upper threads of the mangled hole.

step 4: use tap to create introductory threads and clean up lower threads

....

If existing damaged threads are totally removed by drilling, there won't be any metal left to tap through for creating introductory threads enroute to the good lower threads.

While no portion of the damaged threads may be salvageable, would strive to minimize removal of metal in the damaged area.

Would exercise great care in drilling and tapping with prime objective of assuring perfect meshing of the screw threads upon approaching and engaging the lower undamaged threads.

This is akin to the problem where a spark plug hole has been "cross-threaded" near the opening and the plug can't be properly oriented and started at initial insertion. There's a special plug tap tool designed to re-thread the plug hole beginning from the deep end where the threads are good and continue threading/chasing from the bottom up. Am thinking it's called a "reverse tap" or something like that. But alas, there's no such tool for the instant problem.

Gonna have to rely on slow delicate tapping to get it right.

Good Luck!

To determine the size of the hole, take a mixture screw and measure its diameter. If it is an M6 size, it will be about 5.9mm if it is an M5 size, it will be about 4.9mm. The pitch gauge lies along the thread and you just match visually. If you had .75 pitch, it is an M6 size.

To do this job, keep in mind that you don't have many thread to work with. The taps in your HF kit are through-bore taps; that is, they have pointy type ends to make them easier to start having taper. The problem with this type end is that it won't allow thread to be cut down to the bottom of the hole. To cut down to the bottom, you need blind bore taps. A blind bore tap is FLAT on the end so it can go down into the hole as far as possible. Since it is tough to find blind bore taps, I generally buy a set of normal through-bore taps and cut off the pointy end and make them blind bore. You may be able to "test" the remaining thread and the hole by taking off your idle screw and seeing if it will screw into the remaining thread. They are mostly M6 with .75 pitch but measure to be sure. Some screws have thread down to the end but some are only threaded in the middle part and won't be useful for this purpose. You won't find any M6 bolts with .75 pitch unfortunately.

Gintree, all good posts. My initial presumed that damage had been done once screw had backed out to ega plug.experiance is that there is usually a gap of roughly 1/2 the depth of treaded shank of fuel/air screw before plug. thus my thought there may be salvagable threads. being unfamilair w/your carb may be wrong. Experiance w/yamaha c/v's with fuel screws overtightened and tips broken off in bodies or enlarging pilot passages are my references. Luck G

Ok cool... I'm gonna give this a shot on Sunday. I'm sure you'll be hearing from me one way or another!

George, Patton, Gane: Thanks for the help!

Well, I'm finally up and running again.

I wasn't able to salvage the original carbs as I wasn't delicate enough to pull off the operation on the threads. Thanks for all the help anyway.

I was able to pick up another set of carbs off ebay for 35 bucks, so I got those and I'm back in business.

I have a quick question. I've got pods and little reverse cone mufflers on my bike and I just upjetted to 96 mains. I'm now trying to tune it. If I'm looking to richen up the mixture some more, which way do I screw the air screws? counter clockwise or clockwise? anyone have any tuning tips for starters?

Thanks!