stripped carb bolt holes

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Rowbear
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stripped carb bolt holes

Post by Rowbear »

has anyone else stripped the threads in the carb by accidentally putting the longer bolt in the front? Is the only way to fix this to try and make new threads and go to a slightly larger bolt?
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Wheelman-111
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Ace Hardware Carb Mount

Post by Wheelman-111 »

Greetings:

Yes, and your local Hardware Store has just the thing: 1/4 x 20TPI common bolts are just a hair bigger. Run a standard tap through the carb flange mount - you don't even need to pre-drill. Enlarge the manifold holes and the brown carb insulator to 17/64ths. Use a 1.5 for the short one and a 2"-long for the longer side. You may need to trim the bolts a bit so as not to punch a hole in the carb again. Go easy on the Wheaties when you snug up the bolts only enough to flatten the O-rings. A 7/16ths wrench will need to be added to your tool kit, although 11mm seems to work too.

I suggest you fix this before attempting to operate the scooter. Vacuum leaks can get ugly quickly.
Wheelman-111
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"ISO": '03 Vespa ET4 Malossi187 74MPH
Flash 9: 2001 Elite SR Contesta 72 ZX Tran, 9:1 Gears, Stock Airbox/Carb/Pipe 58.8 MPH
Punkin: 2010 Vespa/Malossi S78, 61MPH
Fishman43
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Re: stripped carb bolt holes

Post by Fishman43 »

Easy to do, I have done it as well.

My fix was to get the same size "all thread" (you know the threaded rods with no bolt head) as the bolts. Thread it through the holes and put nyla-lock nuts on the back side. The tricky part is getting the nyla-lock bolts on, I had no problem on one side just holding it against the back of the carb hole and threading the rod through (all this rods and nuts sounds dirty doesn't it), but the other side of the carb the nut hit the carb body a little to much to thread on straight. I sorted that out with a quick bump and grind (might as well stick with the theme) of the dremel on the nyla-lock nut. I had to hold the nut in channel locks to keep the fingers safe, and it only took a very little bit of metal from the nut to clear the carb body. Then thread the all thread "bolts" through the intake, mark them for length and cut to fit (remember to allow length for the nuts on the intake side). I think this write up took longer than the process of making the new carb "bolts".

I would avoid drilling and tapping for larger bolts, then you have to drill the carb and intake STRAIGHT to ensure good seal between the two.

From what I understand (never tried it) Helicoils (sp) work as well.

Good luck.
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Re: stripped carb bolt holes

Post by Fishman43 »

Wheelman's suggestion sounds great also, no tap required.
PimpinSpree
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Re: stripped carb bolt holes

Post by PimpinSpree »

I tapped mine to a larger size just by using a bigger size bolt and carefully threading in and out until it formed threads.
Feels much more solid than the stock bolts.
You have to be really careful threading into aluminum. Very easy to over-tighten
Rowbear
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Re: stripped carb bolt holes

Post by Rowbear »

great info, thanks. I was going to try to use washers from presta valve bicycle tubes, which happen to fit the carb bolts perfectly and are thin enough to go on the back side of the carb. Not sure how I would hold them in place or if the bolt comes out far enough to thread into them.

they look like this

Image
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Wheelman-111
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Re: stripped carb bolt holes

Post by Wheelman-111 »

Greetings:

If'n you're in a hurry to get it running, I solved that issue once by Super-Gluing a nut to the carb flange backside. You'll only be able to take it apart once before needing to re-glue, but it holds the nut for you while you thread the bolt on, at least once. A slightly longer bolt may be necessary, but be careful not to punch a hole in the bowl.
Wheelman-111
Most of my money is spent on scooterparts. The rest is just wasted.
"ISO": '03 Vespa ET4 Malossi187 74MPH
Flash 9: 2001 Elite SR Contesta 72 ZX Tran, 9:1 Gears, Stock Airbox/Carb/Pipe 58.8 MPH
Punkin: 2010 Vespa/Malossi S78, 61MPH
Rowbear
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Re: stripped carb bolt holes

Post by Rowbear »

that seems to have done the trick, although taping it and using the 1/4x20 bolts would have been a more permanent fix, I may still do that in the future.
Rowbear
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Re: stripped carb bolt holes

Post by Rowbear »

the super glue/thread lock and skinny nuts on the back of the carb failed on me today. I guess I hit a bump too hard and then I had to push it home. Sooo, bigger bolts and tapping is in order.
Last edited by Rowbear on Sat May 22, 2010 10:21 am, edited 1 time in total.
skeeter2
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Re: stripped carb bolt holes

Post by skeeter2 »

I just added small nuts on the back of the carb. it seems to work fine, i had no problems
Andrus
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Re: stripped carb bolt holes

Post by Andrus »

skeeter2 wrote:I just added small nuts on the back of the carb. it seems to work fine, i had no problems
I couldn't find nuts that would fit in the small gap on the outer bolt? Can you send me a link where to get the proper nuts?
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Meatball
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Re: stripped carb bolt holes

Post by Meatball »

Its a jamb nut...thin profile
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Andrus
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Re: stripped carb bolt holes

Post by Andrus »

How long of a bolt did you use ?
otto-man
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Re: stripped carb bolt holes

Post by otto-man »

I have used a Tusk m6x1 thread repair kit (like heli coil) on a dozen carbs with great success.
What ever route you take in repairing, be very careful NOT to use a bolt that is too long!!
It will distort the by-starter mount area, then you've got problems.
Andrus
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Re: stripped carb bolt holes

Post by Andrus »

What are the size of the stock carb bolts? I just bought a new carb and the threads are good so I just need the stock diameter and length bolts. Thank you
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