Birken Vogt
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.)
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78buckshot
I had one last week on natural gas, plumbing and meter all correct, air filter cover made no difference. I adjusted the fuel pin ever so slightly and it took care of the hunting at idle and loaded.
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Birken Vogt
Was the hunting bad enough you would consider it a real problem or just more of a nuisance?
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Cobranut
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.)


Sounds like you already answered your question. A restrictive intake, usually one designed to reduce noise, is a common problem on automobiles, but other than the loss of power, the EFI corrects the mixture, masking the problem.
Carbureted engines can't correct the mixture, resulting in reduced fuel economy or rough running.

I'd drill some holes in a place where cool air can enter, but still protected from water.
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78buckshot
It never had any alarms and it ran several short outages without issues, I didn't check freq. and volts while it was hunting but I'm sure it wasn't too good as it had quite a lope to it. Home owner did question the sound of it before I straightened it out.
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Birken Vogt
This one hits the secondary pretty hard, but only to make it bark, not to increase speed appreciably. So I doubt the frequency is increasing more than a few tenths. It would probably play with cheap LED lights but nothing else. Since the mother ship has told us not to worry I decided not to go on a goose chase. I informed the customer and we will see what happens from here.
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