23.03.11: Well we finally got to thrust test the Egg with the new head and carburettor combo a couple of weekends ago and things didn’t go to plan. As you can see from the video below, we only peaked 38kg thrust which is 2kg less than with the previous cylinder head and stock carb. I wasn’t sure where the problem might have lay and so doing some quick, rough calculations it appeared we were only getting about 4500rpm.
Any way, I took the spark plug out as I suspected it might be running lean with the stock jet fitted (size about 0.88mm) and after I uploaded an image of the plug to a couple of forums the general concensus was that it was quite lean indeed. I had a spare 1.00mm jet lying around and so I fitted it and did a quick rpm test in the garage and I achieved 4900rpm. Yippee!!! If those previous rpm/thrust calculations are correct then that shows that the Egg should now be pushing about 45kg(99lb) thrust.
I then checked the plug again and it still looks a little lean so I contacted Shane at AGK stating the engine specification and asking what would be the best jet size and he reckons about 1.05-1.1mm. So I’ve ordered and now received some suitably sized drill bits and I will be drilling the jet out to probably 1.1mm either tomorrow or the weekend. I might even squeeze a few more rpms and a smidge more thrust too.
So watch this space, the Eggmotor could soon be exceeding 45kg thrust. Lets hope reliability holds up 🙂 New thrust test will be taking place very shortly.