Birken Vogt;52848 wrote:
22kW Evo unit, my first real "hunter" of this series. (But I have seen plenty of other engines hunting or running badly.)
I don't see this much because we are mostly propane up here and I understand this problem usually only manifests on natural.
Gas regulator, meter, piping all good and big.
Started it up in course of regular maintenance and it began to hunt pretty bad. The hunting was due mainly to the throttle linkage getting into the secondary, overspeeding, backing down into the primary, getting a little low, back and forth with a period of about 2-3 cycles per second.
Opening air filter lid stabilized it immediately and interestingly the throttle went back to about 3/4 position on the primary and held steady there.
I found I could get it to start again by pushing the throttle closed quite a ways, then letting it go and it would overcorrect and begin to hunt again. When hunting, it stays at 7/8 throttle plus (into secondary) and my mechanic's ear tells me it sounds like a rough running mixture, over all the hunting noises.
My hypothesis is that there is some sort of mixture issue in the primary mixer happening above about 3/4 throttle causing the throttle to operate a little wider than it normally would to compensate for rough running, banging into the secondaries which leads to the hunt. If you can get it down to 3/4 or less it finds itself in a smooth running mixture and the whole thing works right.
(Frequency stayed well within spec, just a seriously romping engine sound. Not going to cause any power problems but could wear the linkage and could be a little hard on the engine but probably no issue in a standby set.
I blew a 1.20 firmware into it from 1.14 and it did not hunt again but I don't know that FW addresses that, may be a fluke.)