Stripped threads in carb idle mixture screw hole. Ideas?

[CruiserInProgress]

Due to a long running manifold gasket leak, that I am now fixing, I've messed with the idle mixture screw more than I should have, finally stripping threads in the casting. So, I'm looking for suggestions on how to repair it.

The carb is a non-US Fuji carb from City Racer that I bought a couple years ago and it's worked very well, so I'd like to continue using it.

About the stripped threads, using a helicoil seemed logical, but due to the size and fine thread pitch, I couldn't find anything in a search to do the job. Without measuring, it seems like it might be a M5x0.5mm? A proper machine shop may be able to install an insert and re-tap, but nobody local comes to mind.

Using JB Weld to form new threads in place with the idle mixture screw inserted seemed like it might work initially, but probably wouldn't hold up for long.

Fyi, I tried wrapping the idle mixture screw with Teflon tape, which sort of worked without the spring, but I wouldn't trust it to hold. I lost my original idle mixture screw when it popped out on the highway. Took me a while to figure out why it was hard to start and wouldn't idle. Not fun on a main highway over 4th of July weekend. Don't want to risk that again!

My third option is to salvage the butterfly section from a cheap aftermarket carb I have for parts. It appears compatible, but I kinda wanted to preserve the complete Fuji setup, because it's worked well for me.

Any suggestions before I do the butterfly swap?

 

[charliemeyer007]

1st figure out the thread size. 2nd Look at the taper on the screw - if you see a ring - that's bad. 3rd look at the seat good chance if there a ring on the screw taper then you ruined the seat too. Adjustment will be mind blowing sensitive from nothing to wide open in a few degrees of a rotation.

If the seat is good, you could drill out the carb fitting 2 sizes up and tap the hole with a plug. Then drill and tap the plug to the screw size. Could be done with hand tools but you will need to be careful. Much easier with a drill press and a small lathe such as a Unimat.

 

[CruiserInProgress]

Update:

After checking in with City Racer for advice about stripped threads in the throttle body for the idle mixture screw, they really came through, and then some! Excellent support.

My 79 project FJ40 is now back in action, running and idling as it should.

 

[Mark Jennings]

Update:

After checking in with City Racer for advice about stripped threads in the throttle body for the idle mixture screw, they really came through, and then some! Excellent support.

My 79 project FJ40 is now back in action, running and idling as it should.

OK, City Racer came through? What did they do? How did you repair?

 

[CruiserInProgress]

OK, City Racer came through? What did they do? How did you repair?

Ok, here's the story. After a couple of emails discussing the issue, I purchased a replacement idle mixture screw and a couple of gaskets, thinking City Racer was also going to include a used throttle body housing for my carb repairs.

I was very pleasantly surprised to find a complete customer return Fuji carb in the package received. The back story on the replacement carb was unknown, so I went through it, cleaning, adjusting to FSM specs and replacing gaskets. In the process, the only issue I found was a bent fast idle screw tab/stop, which was an easy fix. So, I thought, let's try it. It fired right up and seems to work in all respects!

So as not to let my original Fuji carb with stripped idle mixture threads go to waste, I salvaged a throttle body housing from a lower quality Chinese aftermarket carb I had on the shelf for parts. It took a bit of swapping, fitting, cleaning and adjusting to FSM, but it also fired up, and idles. Nice to have a working spare on the shelf if needed in a pinch.

Anyway, City Racer really helped me out. And, I learned a lot in the process.

Nice to be back on the road with my FJ40!

 

[samatulich]

City Racer LLC has come through for me. Replaced a brake booster that failed after several thousand miles. No questions, just sent a replacement.

 

[JohnnyC]

As for the original issue about being stripped … you COULD have used a Helicoil on it … however I don’t know if a drill would go in enough for the kit to work and that is a pretty small and fine thread it looks like

I’ve used helicoil on cylinder block… but … it’s usually much bigger and it’s a through hole

Glad cityracer came through for you … he’s a good guy and cruiserhead … everything I’ve got has been great

 

[CruiserInProgress]

As for the original issue about being stripped … you COULD have used a Helicoil on it … however I don’t know if a drill would go in enough for the kit to work and that is a pretty small and fine thread it looks like

I’ve used helicoil on cylinder block… but … it’s usually much bigger and it’s a through hole

Glad cityracer came through for you … he’s a good guy and cruiserhead … everything I’ve got has been great

Yeah, I've used helicoils before; a very handy fix. But, I couldn't find any in that size with such a very fine thread. A precision machine shop may have been able to figure something out, but none in my area. Just glad it worked out the way it did.