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Anyone managed to fix a stripped mixture screw thread?

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huw s

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I have one carb in a set which has been drilled to remove the mixture screw. The problem is the machinist? Took out the thread in the body.
Anyone fixed this?
 

Fire-medic

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I suppose you could fill the hole w/JB Weld, then drill & tap it. Use another carb body to get the depth and size. I used a left-hand drill bit, and was able to successfully back-out the screw when the drill 'bit.'
 

OEM2004RIGHT!

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I would make the machinist fix it. HE should have known better. Like FIRE-MEDIC said about using a left hand drill bit. You can get a lot of stuck or broke bolts etc. out with them. As far as your carb goes you cannot tap it out larger so i would have the machinist turn down a peace of aluminum just about one thousand larger than where he cut out and press the pin in and there you have a fresh start for him to center it up and make things wright where he made a mess. something to think about.
 

dragonhlm

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Not sure if they make a Time-sert the correct size. I have used them to fix stripped threads in carb float bowls. If you haven't tried them you should. They are awsome way better than helicoils.
 

huw s

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I would make the machinist fix it. HE should have known better. Like FIRE-MEDIC said about using a left hand drill bit. You can get a lot of stuck or broke bolts etc. out with them. As far as your carb goes you cannot tap it out larger so i would have the machinist turn down a peace of aluminum just about one thousand larger than where he cut out and press the pin in and there you have a fresh start for him to center it up and make things wright where he made a mess. something to think about.
Can't, bought them like this, knew about it...
 
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Screwloose

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Doubt whoever done the drilling could do a repair. Also would you be able to align a new thread with the existing screw tip area. I’ve had many problems with these carbs and new (second hand) carb bodies sounds like a good easy option to me.
 

02GF74

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I've just had a quick search for mixture screw and it has a very pointy end. The replacement thread needs to be very precise for the screw to fit properly.

I'm sure the hole can be opened out for a brass insert to be threaded and pressed in and then drilled precisely before being tapped.

The matching would need having the carb body clamped so everything is lined up.

The threads on these types of screw are fine so it may be fun finding the right tap.

You'd be looking at £200-300 for a set of s/h carbs, set of 4, I've not seen them sold separately.

Else search carb repair, quite a few companies pop up, worth contacting them for a quote.

It must be really annoying that such a small thing has rendered the bike unusable and gonna cost a fair bit to fix.
 
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Fire-medic

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I've re-tapped, chased, really, a mix screw. I wrote-up my removal, a left-handed drill bit unscrewed the brass needle, then I used the tap to clean it up. I didn't really feel the chase-tap doing any removal. I carefully measured the depth I need to get-to, and when the tap reached that, I stopped. It also was the OEM stop-point, so all-good.
 

huw s

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That's what should have been done - but someone drilled the screw and the threads out...
Got the taps today, will spend an hour or two tonight seeing if I can jig it all up to drill out for an insert.
If it all goes wrong I could always make a new insert taking the whole lot out , then drill the plug out of the end and replug. Bit of a faff, but these are a spare set I bought because I have the exact same issue on the ones on the bike - but I haven't drilled that one out yet.
 

huw s

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I've just had a quick search for mixture screw and it has a very pointy end. The replacement thread needs to be very precise for the screw to fit properly.

I'm sure the hole can be opened out for a brass insert to be threaded and pressed in and then drilled precisely before being tapped.

The matching would need having the carb body clamped so everything is lined up.

The threads on these types of screw are fine so it may be fun finding the right tap.

You'd be looking at £200-300 for a set of s/h carbs, set of 4, I've not seen them sold separately.

Else search carb repair, quite a few companies pop up, worth contacting them for a quote.

It must be really annoying that such a small thing has rendered the bike unusable and gonna cost a fair bit to fix.
Not annoying - as stated above these are a spare set. I was faced with the same issue with the vmax at the start of the summer, but I left it alone for fear of cocking it up, then waiting for a fix...
So when these are done the ones on the bike are coming off, and judjing by the screws holding them together a certain vmax expert in the UK has had a field day on them...
 

huw s

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That's what should have been done - but someone drilled the screw and the threads out...
Got the taps today, will spend an hour or two tonight seeing if I can jig it all up to drill out for an insert.
If it all goes wrong I could always make a new insert taking the whole lot out , then drill the plug out of the end and replug. Bit of a faff, but these are a spare set I bought because I have the exact same issue on the ones on the bike - but I haven't drilled that one out yet.
Update since yesterday - semi successful, I drilled the carb, made an insert, just it was not tight enough in the carb. So will make another 3 thou bigger, should do it.IMG_2604.JPG
 
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huw s

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today I can reveal that the new, larger diameter (by 4 thou) was indeed a success. I parted it off at 9.8 mm long, put a skim of loctite on it and tapped it home. Testing with a used oring, washer and spring showed it came out into the carb throat, held tension to 5 turns out, so I hope it will have been a success. Won't be certain until I get to set the carbs up. I need to rebuild plus set float heights before I get to refit them.
Now that I've done one, got the drills and taps, I think it could be done in a morning, so not a huge job really.
 

huw s

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Fitted the odd set (bought on ebay as a set, but the seller had replaced two), with the repaired mixture screw thread today. Had bench synced well enough to run and idle. So I set about with a set of gauges to balance and adjust mixture. I got what I thought was a reasonable idle, but thought they were all a little insensitive to the mixture screw setting. Anyway, it got dark and I put it away. That's when I noticed I hadn't fully pulled the richener lever closed..
Bugger.
 

huw s

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Fitted the odd set (bought on ebay as a set, but the seller had replaced two), with the repaired mixture screw thread today. Had bench synced well enough to run and idle. So I set about with a set of gauges to balance and adjust mixture. I got what I thought was a reasonable idle, but thought they were all a little insensitive to the mixture screw setting. Anyway, it got dark and I put it away. That's when I noticed I hadn't fully pulled the richener lever closed..
Bugger.
A couple of things this proves:
You can swap carbs between (at least) Some sets - that's not to say there aren't distinct differences - maybe in the progression holes?
You can repair a messed up mixture screw thread, ideally by drilling and unscrewing, or ultimately drilling completely down to the bottom,of the thread, pushing the taper/parallel bit out and making a new insert. Much care and patients required...
 

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