jmendoza
Petty Officer 1st Class
- Joined
- Jun 9, 2008
- Messages
- 314
Re: 15hp lacking power
Hey, that's great you were able to confirm the issue and rectify it. Glad to see that worked for you too, as it was a hard won piece of knowledge for me. I took what I had learned about timing 2-stoke Yamaha twins (RDs and RZS) and applied it to outboards, as they are essentially similar.
That .020" point gap setting only insures the engine will start and run, but the timing can be off by as much as 15 degrees or more, it's just a rough setting. On our McCulloch vintage kart engines, they too call for 0.020" points gap, in fact that spec is almost universally called out for small engines using points. We have found to get max performance, you have to set the timing dead on with the flywheel timing marks. This is especially true with twins because if their ignition timing is not exactly syncronized, the two cylinders fight each other instead of working together, and you loose power.
Not to fault any of the excellent mechanics out there, but this seems to be a neglected area that can benefit significantly from some closer attention to detail beyond using a simple .020" feeler gauge. The problem is we have become so used to relying on CDI ignition that the nuances of doing points has become arcane. But I'll take points over CDI any day, as they can be fixed, whereas CDIs cannot, and they are notoriouse for failing.
I am very fortunate that the local marina lends me their OMC timing arm special tool, which is also for the earlier 9.5 models. This enables you to set the timing with the flywheel off, making things much easier. But I still check the timing with a strobe timing light with the engine running as this will show you where the timing is when running, which can change if the points are sticky, the mag plate bushing is worn, or the crankshaft upper bearing is worn, and it will also reveal any weak or intermittant sparks, as caused by a intermittant condensor or coil.
The very last part of the chapter on the ignition shows how to use a strobe light to check the timing, and I have found it well worth the extra effort to do this, as it allows you to fine tune and dial in the ignition timing of both cylinders for premium performance. There is nothing quite as smooth as a 2-stroke twin that has the timing perfectly syncronized. The main thing to look for is a steady mark that does not jump around, and that both cylinders are firing within 1/32" of each other as referanced to the static mark on the stator.
Hey, that's great you were able to confirm the issue and rectify it. Glad to see that worked for you too, as it was a hard won piece of knowledge for me. I took what I had learned about timing 2-stoke Yamaha twins (RDs and RZS) and applied it to outboards, as they are essentially similar.
That .020" point gap setting only insures the engine will start and run, but the timing can be off by as much as 15 degrees or more, it's just a rough setting. On our McCulloch vintage kart engines, they too call for 0.020" points gap, in fact that spec is almost universally called out for small engines using points. We have found to get max performance, you have to set the timing dead on with the flywheel timing marks. This is especially true with twins because if their ignition timing is not exactly syncronized, the two cylinders fight each other instead of working together, and you loose power.
Not to fault any of the excellent mechanics out there, but this seems to be a neglected area that can benefit significantly from some closer attention to detail beyond using a simple .020" feeler gauge. The problem is we have become so used to relying on CDI ignition that the nuances of doing points has become arcane. But I'll take points over CDI any day, as they can be fixed, whereas CDIs cannot, and they are notoriouse for failing.
I am very fortunate that the local marina lends me their OMC timing arm special tool, which is also for the earlier 9.5 models. This enables you to set the timing with the flywheel off, making things much easier. But I still check the timing with a strobe timing light with the engine running as this will show you where the timing is when running, which can change if the points are sticky, the mag plate bushing is worn, or the crankshaft upper bearing is worn, and it will also reveal any weak or intermittant sparks, as caused by a intermittant condensor or coil.
The very last part of the chapter on the ignition shows how to use a strobe light to check the timing, and I have found it well worth the extra effort to do this, as it allows you to fine tune and dial in the ignition timing of both cylinders for premium performance. There is nothing quite as smooth as a 2-stroke twin that has the timing perfectly syncronized. The main thing to look for is a steady mark that does not jump around, and that both cylinders are firing within 1/32" of each other as referanced to the static mark on the stator.
