Subject: Re: Eldo noise.
Author: Patrick Hayes
Date: Jul 7, 2001, 6:19 PM
Post ID: 1707405434
That noise, "when I pull away under load and its very hot", may sound metallic, but it is not. You are hearing a classic pre-ignition or pinging. The cylinder is trying to compress the air fuel mixture, you are sparking it too early, and the whole mixture is exploding instantly instead of as a gently progressing flame in a well tuned motor. Keep it up and you will damage the tender aluminum of your pistons.
You can cure it with better fuel (no longer produced) or with slightly retarded timing, or with some cylinder head work. Old Guzzis are very rough on their valve guides and the guides do NOT have seals like modern engines. When the guide starts to wear, it gets a little bit ovalized. The extra space allows the intake manifold suction to pull a little bit of oil past the intake guide and mix with the air/fuel. It takes only miniscule droplets of oil to effectively and seriously reduce the 'relative octane rating' of the mixture. Remember, I said above to get better gas and you've just made a worse mixture. This amount of contaminant oil is far less than is required to make visual smoke. So the pinging will appear long before the smoking does.
If your Guzzi has more than 30,000 miles since it had serious head work then I suggest you get new guides put in and you may need a valve or two if the stems are worn at all. You'll be amazed that all the pinging will go away with the same engine settings.
Patrick Hayes
Fremont CA