Suzuki DF 90 Throttle\Gear linkage

[Grasshopper]

I have a Suzuki DF 90 which is jumping out of gear when you reverse at low speed. If you increase the speed it is OK but that just brings water over the transom. I am sure what is happening is that the engine is increasing speed before reverse is fully engaged, so how do I adjust the linkage I have the Suzuki manual but there is nowt about adjusting the linkage.
Any help or ideas would be greatly appreciated.

[Erin]

Pretty much the same on all engines. Unhook the gear cable where it mounts on to the gear selecting lever under the engine cowl. Make sure the lever is in neutral both at the helm and the engine (usually has a detent to help it settle in neutral) and then adjust the length of the gear cable until it matches the position of the gear lever on the engine. You will need to undo the locknut and then unscrew or screw in the plastic end until it is the right length.

[Grasshopper]

I thought that might be the answer, but when I undid the lock nut the plastic end felt really tight and I did not want to force it.
Thanks