Yamaha RS100 - Iddles but won't rev up

[NSR_Dan]

My Dad is doing up an Yamaha RS100 (82 model) which ran fine many years ago. The issue is that it ticks over fine but if you try and give it any revs it loses all power and coughs and splutters.

Here is what has been done already to try and solve the problem -

- New crank seals
- carb clean and new jets
- new plug
- decoke exhaust
- new reeds

We don't know what else could be the problem... any ideas?[/list]

[piazza]

Carb rubbers perished? Had similiar on a cb100n they looked fine but flexing them revealed their true state.

[spottedtango]

When you rebuilt the carbs did you set the float heights? Also what’s the fuel mixture screws set to?