Beautiful spark plugs again

After finding that massive tappet clearance last week, the engine is running again.

Took a few tries, and splutters, and help of Mike Small, thanks Mike !!

But yes running again. Sounding really good. No irregularities, just nice 🙂 One thing I noticed is that without the ring exhaust supplying heat to the carb, the carb is cooling down to a point where it freezes up when running now. Never seen this before with this carb. Ideally that means that its producing max power, but don’t like the freezing temperatures, so would like to introduce some heat again sometime in the future.

So now its just a matter of running in more, but after a little while running between 75% and 100% power I would have thought to have seen some improvement, but I don’t. Still hovering at the 1900 rpm mark.

The good thing is that the spark plugs all look right now. They all have a “nice brown tan”. That must mean that the mixture is sort of right again, this is with my original carb !

After talking with Mike, one of the many people trying to help, all with their own opinion, these are the few things to work on, and its all back to basics. It seems I have done all I can for now with what I have, its just rechecking a few things.

  • It seemed that the carb butterfly valve wasn’t completely open, only needs a little more, so fix that first. Not expecting miracles, but everything needs to be right to get the very last bit out of this machine !
  • Just quickly check the ignition timing again, and the valve clearance.
  • While doing the valve clearance have another look at the valve timing as well.
  • Now I am running with a higher compression, moved from 5.4 to something like 7, I could try a higher octane fuel. Don’t think 7 is high enough to really need it, but worth to try. And all this time I will be running the engine in a bit more…. Who knows 🙂
  • Currently running without an exhaust, and no carb heat. I am going to try to find nuts that fit my exhaust connection on the cylinder and make up 5 exhaust stubs, about a foot long. This will involve getting 5 exhaust bends making 5 rings, making 5 nuts with a washer welded to it…. Not to hard and expensive I think. Plus modify one of them to create carb heat. With the exhaust stubs I will create back pressure again, that could improve the exhaust cycle. Plus also prove one thing that I discussed back in April at the Omaka air show. This was about exhaust gasses being sucked in by one cylinder while another one was exhausting.
  • Then the last thing, is the prop !!!!! I am more and more getting used to the idea, that I have tried everything, and the last thing is modifying the prop a LITTLE !! Making the tip 10 or 20mm shorter. That should make it go faster and hopefully produce more thrust. Making that change is NOT making the prop look any different, so I am comfortable with that. BUT will talk with a prop guy first before I do this 🙂 don’t worry !

1 thought on “Beautiful spark plugs again

  1. Following your ‘excursions’ with great interest Gert. You won’t have overlooked the increase in rpm when the aircraft is ‘mobile’–at a guess, +100rpm or so. What does the ‘manual’ say about static revs? In my limited experience with my VW, timing is critical. No doubt you monitor your settings…… . Good luck! Neville

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