I have a problem on my RT1 with the carb flange being a concave.
It came to me with the o-ring in groove which I believe was not standard at that time.
Putting my straight edge across the face I'd say it's about 1mm of curve and the problem is when I tighten the carb it distorts enough to pinch the slide.
I am going to attempt to draw file the surface flat and wondered if anyone else had had the same problem and how did you rectify it.
I'm trying to get to the bottom of a running issue (and starting) where the revs when coming off throttle hang a about 3,000 rpm for between 3 and 5 seconds then return to 1,500, so I want to rule out an air leak on the inlet.
I will also replace the jet setter o-ring.
Pete

The concave is a result of over tightening.
A gasket may help that situation?
The o ring may not be required DT1 / RT1?
The jet setter / yes.
Check for throttle cable slack.

Hi asco.
I've tried it with just the gasket but as the flange is already curved it still pinches the slide when I tighten it.
I'm hoping that by filing the surface flat I will be able to do away with the o-ring and just use the gasket.
Throttle cable has slack so I don't think it's causing a problem.
Thanks for your help.

Mount the carb with the nuts loose and check the movement of the slide up and down with the throttle cable attached and rotate the throttle grip.

Yes, file it flat. And it should have the o ring, no gasket.

I have a big piece of flat glass with sand paper taped on it I use for situation like yours.

My RT2 carb flange was the same. I used a good clean flat file to get it back flat. Also make sure you have the correct size (thickness) o-ring. I don't think the correct o-ring should fit snug in the groove. There needs to be clearance for the o-ring to expand as it's compressed when tightened. I still had a problem with the throttle slide sticking if I really tightened the carb mounting nuts so I use nylock nuts and tight enough to make sure the o-ring is compressed, I have a good seal and the carburator is secure.

Thanks Kenny, I knew someone here would have had the same issue.
I need it right so that I can see if it's that causing the revs/running problem or a least eliminate it as a possibility.

I'm following this Pete as I just fired mine up for the first time a couple weeks ago and does same thing. I didn't think to check my flange but have a new correct o-ring and gasket. Both are required on the RT-1. I also have a new o-ring in carb bowl. I set mine up as all stock which shows needle clip on 4th slot (pretty rich). I moved it to 3rd slot and I went for a 20 mile ride today. Absolute pleasure to ride...only issue is that slight hangup before returning to idle at 1400 RPMs.

Actually both Partzilla and Babbits Online show both the o-ring and gasket. The o-ring is included on carb listing and the gaskets (each side of the intake) are shown on the intake listing.