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Author Topic: Advanced ignition and petrol "on the rocks"  (Read 1408 times)
Anders Dinsen
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Posts: 2828

« on: February 21, 2009, 03:11:55 pm »

As discussed in the forum, I finally managed to fabricate a tool that would allow me to loosen the bolt that fixes the distributor on the engine, and thus start adjusting the ignition. Much to my surprise, the ignition had retarded no less than 4 degrees since I checked it a few months ago, so static ignition was back to 6 degrees only. That was certainly not enough.

I have now advanced it up to 15 degrees at 1100 rpm idle, which is quite a bit, but not uncommon on a sidedraught equipped engine with a hot cam. With the 98 octane petrol I usually run, it shouldn't be a problem. Max advance should also be within the safe margin.

This has made the engine a bit more rough (not surprising since it was so far back before), but also meant that I had to turn the idle stop back a bit. This is because the increased advance means that each combustion produces more mechanical power than it did before. I actually expect the engine to be quite a bit more fuel efficient with this adjustment, especially with all the local driving I do.

But the idle stop is now so far back that the throttle plates are fully closed. How can the engine breathe at idle, then? you may ask. Well the plates have each been drilled with a small hole allowing a bit of air to pass through the otherwise closed plate. This is not uncommon on the particular DCOE carburettor type which I have, and has to do with the location of the first progression hole, but obviously is not ideal in my case, at least not with the amount of advance I'm currently running. I therefore expect that I have to solder the holes up, but not until I have had the engine on rollers, so I know what the optimum setting is.  It currently idles at 1200 rpm with the throttles fully closed, and there's a small flat spot before the first progression hole is uncovered.

I'm listening carefully for signs of pinking, but haven't heard anything yet. The rough running could hide some though, so I might try backing it off a few degrees to try the difference.

Carburettor ice is a big problem these days with the weather we have. It usually happens if I run the car from cold a few km, then leave it to restart it some 10-15 minutes later. The engine is now not warm enough to radiate heat up on the throttle plates, and the moisture in the air turns to ice in the cold carburettors. It then cannot idle or run properly. It's quite annoying! I haven't fitted the vacuum operated air intake switch, but I really should. For now, I have resorted to the good old solution of using carburettor de-icer in the petrol.

Here's a recent photo of the engine - don't it look good?

« Last Edit: February 21, 2009, 10:09:20 pm by Anders Dinsen » Logged

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