Bored out carb difficulties.

So tonight I finally drilled out my 12mm BING to a 15.8mm. This was for my Maxi with a 65cc Metra and an estoril techno pipe.

The bigger hole made it so my throttle slide doesn’t move down far enough and my moped idles at a quarter throttle. Its really high. It wont go down any further because the shape of it to the hole.

Also, for some reason I have to keep my choke on until I get to about 32 to 35 I’m guessing or it boggs down. Once I get going 35, I pop the choke off (which I have to do by hand) and go flyin really fast.

So in the end I think I go faster, but I idle ridiculously high and I have to play with the choke as I ride.

Anyone else run into these problems when boring out carbs?

Re: Bored out carb difficulties.

Get a small round file or a sanding drum on a dremmel and work out the rough spots on the slide housing. When you drill through there it tweaks the material up and gets in the way. File it down, but make sure to not sand off the nub that orients the slide, it is about half way down on the side of the carb.

Re: Bored out carb difficulties.

I did that... it just won't go down any further.

Re: Bored out carb difficulties.

Then do it some more.

Re: Bored out carb difficulties.

Last time I peered into a 12mm Bing it didn't look possible to bore because of the slide set-up. I have drilled 14s but someone correct me if you can drill 12s out to 15

Re: Bored out carb difficulties.

Buy a different carb before you blow up your kit dude.

Re: Bored out carb difficulties.

make the slide longer with quicksteel

Re: Bored out carb difficulties.

Thats not a bad idea, the quick steel and all.

Dude its not that I have to file it down, trust me. I'd have to draw a picture for it to make sense.

When the hole got bigger, the slide could not go down past normal still, leaving a bigger hole when idling.

Re: Bored out carb difficulties.

Did you re-jet after you bored out this carb?

Re: Bored out carb difficulties.

yeah seriously...reason why possibly you are running fast because you are mad lean with all this air coming in....

Re: Bored out carb difficulties.

No dude I know for a fact its because the throttle slide wont go down all the way. you can see it when you look in the carb.

Theres a huge opening instead of a small one that used to be there when it was normal.

Re: Bored out carb difficulties.

Ben Van Zoest /

So what is holding the slide up I wonder if it still rest on the idle screw like before enlarging the intake, sure you get a larger 2mm extra gap driving up the idle air feed. Logical I think. I bet you bored too deep all the way into the slide house instead of stopping short and than dremmel the upper side. The aim is for a flat bottom hole about 3/16 gap.

Re: Bored out carb difficulties.

i've bored at least 10-15 12 mm bings out to 5/8 and 41/64 (16.2mm) with no problems whatsoever. It helps to use the emulsion tube and needle out of a 14 or 15 tho.

you need to pull up your needle a lot, probbly all the way to the top, and you should be running around a 74-78 jet.

Re: Bored out carb difficulties.

Thank You

Re: Bored out carb difficulties.

As far as I can tell Steve Bing uses the same carb body for there 12,14 & 15mm models, just different diameter venturi.

Re: Bored out carb difficulties.

Yea I guess the issue being the slide slots aren't as deep on the 12s

Re: Bored out carb difficulties.

I ran into the same problem , you have to grind the slide off on the bottom so it goes down all the way look and see where it is hitting in the slide tube and remove that matterial on the slide

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