What I haven't thought to be significant before is the engine rpm indications. The engine starts and runs again, without issues, about 1 minute after the previous failure. Today, the selection of this pump to ON when the engine faltered (after about 90 seconds every time) failed to get the engine to pick up. Running engine with the electric fuel pump ON keeps the engine running, but it sounds and feels "lumpy". The tank is full, and if I open the tap with the hose off, fuel runs without restriction. I'm loath to drill carb jets since there wasn't anything wrong with them before, haven't been messed with and they're not blocked. There is a strong and audible vacuum pulse when I turn the prop by hand (vacuum hose off at the pump end). I change all or eliminate (by bypassing) all of the components of the fuel system and the problem persists. Having had the engine run without issues (other than initial tests) for 100 hours with all the same components, I have this problem. So, having changed or by-passed everything in the fuel system I'm still at a loss to understand this. I guess, from the way what came out of the float bowl ate up the yoghurt pot, that it was more fuel than water - if indeed it was water at all - I didn't have time to check before it escaped. Oh well.the work on the carb was promising, but ground runs today show absolutely no change in the symptoms. Given that the vacuum pump seems to be working, there is adequate fuel flow (at least for normal ops) and the selection of electrical (boost) fuel pressure seems to overcome the problem, where do I look next? Is there anything that might cause this in the carb? Static RPM is about 3200 as best that I can judge with the MGL tacho. The fact that the elec pump overcomes the problem suggest that the vacuum pump isn't doing its job well enough at very high revs, although everything seems fine at my normal cruise power (2800-3100 rpm). Since the only time I use full throttle is on takeoff, and the electrical pump is always ON for that, I think the problem has always been there, but gone unnoticed until this week. As I hear the engine lose power, if I switch on the electrical pump the engine picks up and runs OK. Despite all this, the engine would not run for more than 25 seconds at full throttle on the chocks, although at lower rpm it's fine. There is quite a strong vacuum pulse and adequate fuel flow apparent when the engine is off. I also bypassed the electric fuel pump and set up a separate gravity fuel feed from a jerrycan. I replaced all the hoses, fuel filter, spark plugs and vacuum pump, running the engine after each change to test the result. Hi Thomas, a lengthy series of ground runs today suggests a carburettor problem.
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