Surging idle (video) (1992 MK2)

[fallenmikethebike]

Have you sealed the brass oil inlet on the manifold?
Try a larger pilot jet, but carry the old jet with you,and a spare plug , just in case.
Mike

[gregorious77]

running pre-mix will make the bike run slightly leaner as you now have less fuel to air (some of the fuel is oil). I would go up one size on the pilot to see if that stabilises the idle.
Also as Mike says make sure the old oil inlet brass spigot is sealed off.

[sbc]

Brass oil inlet? Okay so I went out to the bike, unscrewed the cover and took the following picture:
https://imgur.com/a/BB2eT

So as you can see, we just left the original tubes all connected. It seems we didn't think it through completely and might explain the lean condition.

I'm not that familiar with this area of the bike. Should I plug both brass things? If so, what would you plug it with? Rag, bluetak? Something more professional?

[gregorious77]

not at the pump but where it goes into the rubber boot between the carb and the reeds.
You could remove the brass tube and replace it with an equally sized solid bar or use a small rubber bung to cover the original brass tube.

[sbc]

A final reply to say that I blocked off the inlet and put a 50 pilot jet in.

It now idles great with half an air screw out rather than all the way in! My dad reckons that because the carb hasn't seen a lot of use that it will clean up in time as I use it. I'm really excited to have this bike working properly!

I also put a 14t sprocket on and that is sooooo much better on the road. The 13t sprocket made the bike sound constantly angry.

Thank you all for your help with this one.

[fallenmikethebike]

Well done for persevering and sorting out the bikes issues, you will be rewarded with it's fine performance.
I used to run 14/45 combo on the sprockets, I found this the best compromise for road/off road use, the engine still has enough grunt on that gearing to lug through most anything, and doesn't spin up the rear wheel as quickly.
Mike

[gregorious77]

I used to run 13/52 but have recently toned it down to 14/48 which is spot on. tried 15/48 but it was a bit too tall for hill climbing in 2nd gear.