G'day

I used to have a Surpass 70 but it has been gone for several years. When I bought it it, like yours, was well used. Its low speed needle was tuned too lean and as a result it would not start unless the throttle was wide open. I opened it about a full turn and it would then start. Then I tuned it by the method that I use on all my Saitos (most of my four strokes are Saitos though I also have some OS, Enya and Laser)

1. Start by opening the LSN buy a turn or so. This is not critical but it will make sure it is at least going to start. Too lean and it will simply not start.

2. Tune the HSN for maximum revs. Don't go lean though.

3. Slow the engine to the point where it will idle. This may be quite a fast idle.

4. Adjust the LSN for the best idle you can get but also test the transition. Good transition is more important than the absolute smoothest idle.

5. Repeat steps 2 to 4 until you get the idle you want.

If you can't get a good slow stable idle try some fresher fuel. Nothing mucks up idle better than stale or watery fuel. Also, a fresh glow plug may also help.

You can also try another trick. When the engine is idling, remove the glow plug. If the revs drop, it is probably tuned too rich. When it is tuned correctly, the drop will be minimal if the plug is good and the fuel is good.

You should use an OS F plug or other F type plug. The Enya #3 plug also works well in four strokes. Enya now also make an F type plug.

Hope this helps a bit.

My OS Surpass 70 was never great at idle and I eventually set it up with a single NiCd battery to keep the plug glowing all the time. I have since learned a great deal more about tuning and could probably tune it better these days. I use 10% nitro in all my engines apart from one. It is a Saito 90R3 radial engine and it likes to drop one cylinder on 10% fuel. On 20% fuel it is much happier so that is what I feed it.

Cheers

Mike in Oz