Crap, stripped Pilot Mix Screw

Well, first off I wish to thank Mr. RickCoMatic for giving me his phone number and walking me through some parts on my bike, helping me troubleshoot an issue I have. It seems I need to sync my carbs. His walkthrough was absolutely wonderful, and I give many thanks to him for his time on a family Sunday.

Now to the issue. After I got off the phone w/him, I removed the tank and began to look over my carbs. Carb #2-#4, no problems, and I was able to successfully move the screws to their bottom most position. However, Carb #1 was stripped before I did anything to it (thanks to previous owner). I do have easy outs, but I hesitate to use them to remove this. Suggestions on how to fix this problem?

 

A fellow traveller. I've had this problem myself. And after much contemplation (read...indecision) I finally got the courage to fix it myself.

My #1 carb had a stripped head on the pilot screw - it was in tight from years of neglect and I suspect may be a little bit of stripped thread problem.

I shot a lot of WD40 in there hoping to free it up. Finally, after smoothing out the slotted head and having no other option (apart from paying the local Yamaha mechanic) I got an appropriately sized screw extractor (can't remember offhand but 2mm I think).

Gently drilled a hole in the top of the pilot screw, easy does it, not TOO deep, and inserted the extractor. Either with the appropriate tool/handle for the extractor or a small shifter I started a slow and deliberate anti clockwise turning. I could feel the extractor biting into the screw and then finally feel the screw give way and start turning itself.

Not having done that before and with the consequences of failure being potentially expensive and have my daily mount off the road, I was relieved at it being so relatively easy. The only tricky part is drilling the hole in the pilot screw.

Rick, anything to add to this...?

 

Drill it.
Get it out off there.

Make sure you are drilling it -- Dead Center.

Start with a very small drill size and work-up to the size you need for the Easy-Out.

Blow or Vacuum out the hole.
Add a few drops of Vegetable Oil.
Heat. The Oil won't easily fire-up ... but it WILL become very hot.
Use caution. Don't get burned.
Set the Easy-out in there ... good ... with a few taps to get a purchase.
See if it will come out.
** DON'T apply the heat with the Easy-Out IN there**
(Have someone hold the rack steady on-the-bench while you are working)

Go to the next size if the first Easy don't.

Keep going until it comes out.

In severe cases you have to drill until there's hardly any Brass left before you hit Aluminum Threads.

That's when you use a TINY Dremel cutting tool and take a slice out of the thin Inside Diameter of what's left and "Peel-out" all the rest.

 

The carbs are still mounted as of now, can this be done while on the bike? I have a clear overhead shot at this screw with the drill; I will not come at it at an angle.

 

My pilot screw problem was on the #1 carb on the left hand side. I got to it without having to take the carbs off, but then everything went pretty well to plan. If it's the #1 or #4 carb then it should be OK to leave the carbs on the bike to do this job, making sure the drill does not come in at any angle other than vertical.

Might be a little more problematic if it's #2 or #3, in fact I think both the inner ones may be slightly obstructed by the frame.

Apart from that, what Rick said. Slow and methodical and what always helps me is to have a dry run in your head first so you can conceptualise the process. Sounds a bit too intellectual I know but it's a bit like a rehearsal - or as Ansel Adams wrote - pre-visualisation - get the idea in your head forst and then the actual execution of the process should be a little less open to uncertainties.

 

A half of the top of my #3 pilot screw just popped off when I was unscrewing it.

What an awful thing to happen.

I used a dremel and created a new flat head slot deep into the pilot screw. I was able to get it out with a small screwdriver and some vice grips.

Once I got it out, I had to clean the edges a bit on the screw to reuse it. It went back in no problem, and I bottomed her out and pulled her up three turns.


Rick

 

One ought to invest in a set of reverse twist drill bits for this application folks! They are not too expensive and have the tendancy to loosen the bolt/screw you are drilling out. I've had mine remove the screw when it gets just the right bite!

 

i had the same thing happen, made a guide to center the drill
best part is i found it, it's yours if you want it

 

I might be confused, but wouldn't using a reverse twist drill bit leave the screw unusable once it is removed?

With the dremel approach, I tried to save the screw.

 

Can you still purchase new screws to replace the ones you've drilled? I think I'm looking at the problem on two of my carbs.

 

I placed an order for one at my local yamaha shop and they said they could get it. So I guess we will see. If they can, then I will probably get some more just in case.

 

Sadly, you are correct. This effort is a last resort. I agree you would want to salvage the existing equipment (screws are not easy to find nor cheap). I hope your efforts yield fruit, sounds like you have things under control.

 

if the hole is deep enough you can solder a piece of #14 wire in it for a handle

 

I have good used original idle mixture screws available for Hitachi and most Mikuni carbs......inquire with what model/year bike you are working on.

I also have the OEM idle mixture screw set which should be correct for all XJ550 carbs, XJ700-X carbs, and XJ900 carbs (I think---don't have a set of those carbs to match them up against). They're also very similar to the XJ1100 mixture screws, but the needle tip diameter is much smaller....they may work for XJ1100 models, but I'm not sure.

HCP3745 OEM Mikuni Idle Mixture Screw Set....contains the brass idle mixture screw, spring, spring washer, and the o-ring. Each:
$ 16.00

HCP3745SET4 OEM Mikuni Idle Mixture Screw Set, set of 4:
$ 59.00