yanicks

Hello all

I have spent a lot of time restoring a used Mac Minarelly 70cc engine and it finally started to crank again. However I am facing severe misfires. The engine is a 2 cylinder 2 stroke boxer engine. So essentially with every rotation every cylinder should be firing. When observing the engine in normal operations I was already suspecting something aint right. I did a slow motion video and it very clearly showed that I am facing like a 90% misfire situation. The video of a run is here:
https://streamable.com/pmcpic

As you can see on average there is one cylinder firing every 3 cycles or so. I was wondering what should I be looking for? Is it fuel starvation? Is it related to the spark plugs? I am using the spark plugs indicated in the manual. Any other ideas?

BR
Yanick

Truckracer

My Feedback: (19)

Have you tuned the engine? Sounds like what any engine would sound like with a very rich mixture.

yanicks

The needles are at factory settings, however I am running the engine inverted and the manual specifically says it could cuase flooding, so it is probably in general running very rich. I am going to give it a try in the non inverted position before drawing any conclusions.

Truckracer

My Feedback: (19)

That engine has a Walbro or Walbro type carb and it should run just fine upright or inverted. It clearly needs to be tuned. So called factory settings are usually just settings where the engine will start and run.

yanicks

That was my line of tought as well, but the manual specifically says:



And considering the valves are at factory setting I think this could be it. However I cannot rule out the tuning, so my next steps are to mount it the correct way and then play around with the screws

yanicks

... well actually before any next step is done I will first properly mount my engine to the wooden plate so it wont wobble around like crazy - like it does in the video

yanicks

I have mounted it the "correct" way and then tuned the needles from factory settings. It is indeed a huge difference, it looks much better now:
https://streamable.com/97gbx3

I am happy with this result