Opening up the exhaust port

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Posts: 209
Joined: Sun Jun 10, 2012 11:41 am
Main scooter: Early Eibar Jet 200

Sat Jul 01, 2017 4:09 pm

This is a 150 jug bored to 175. I made a mask on the scootrs pipe ubend and transferred to where it attaches to the barrel. So is the process I grind away this material, polish it smooth, and on the inside of the barrel make sure there is no Sharp edge?

And do catch the material coming off, do you leave a shop vacuum on in the barrel?Image

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carpe scooter diem

1974 Rally 200
1965 Li150
1963 TV175
1974 Eibar Jet200

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Posts: 1257
Joined: Thu Sep 16, 2010 9:54 pm
Main scooter: SX 150 running in

Sat Jul 01, 2017 5:25 pm

id say yes that's about it; or you could cut a new flange and weld it onto ya upipe or move the one you have as itll be more central than what you seem to have now might give a better blend when it's finished
C’est la vie

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Location: drax,near selby,north yorkshire

Sat Jul 01, 2017 7:53 pm

are you sure you want to grind the port so wide just because the u bend is that big?you might end up with the rings fluttering over the port and being spit out! better left to the pro's if your uncertain!

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Posts: 1678
Joined: Tue Jan 31, 2012 8:54 pm
Main scooter: Lambretta GP

Sat Jul 01, 2017 8:11 pm

No way that I'd be opening the gasket flange area up like that! All that shows is how badly aligned the ScootRS manifold/u-bend is.

The one side (top of photo) takes the area much narrower than it should be and is likely to encourage the exhaust to blow at this joint. If you do it the other way around and offer up a typical bigbore exhaust gasket (supplied by virtually all dealers for use with clubman exhausts and produced for the standard SIL factory Stg IV GP200) then you'll see that your marked area from the exhaust flange is miles out. Personally, I'd mark-up and match to a decent bigbore gasket and ignore any misalignment of the exhaust. Why open up a good barrel to match a poorly manufactured exhaust? Other exhausts do not have the profile that you've marked-up.

What you do at the gasket face is one thing but what you do at the bore face in the barrel is what will really influence performance. As has already been mentioned, get this wrong and you'll quickly drop/break rings and be pushing the bike home (I'm speaking from experience of doing exactly this on a 150 to 175 iron barrel conversion with standard piston/rings). There is lots of info available on line (including on here) so make sure that you read up on pros and cons before starting to grind/cut the barrel. Hopefully, people will come back with decent info on this thread too.

Best of luck with this. There is plenty to gain but you can easily go very wrong!


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Posts: 1678
Joined: Tue Jan 31, 2012 8:54 pm
Main scooter: Lambretta GP

Sun Jul 02, 2017 6:20 pm



which might help you out too. Just don't widen your exhaust port as the standard rings will not take much width.

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