Generator Exhaust Noise 1

[itsmoked]

No power since 8am now 3:30pm PoCo thinks they'll have it back on by tomorrow at 3pm. So it's on to the generator for keeping the business running. Never mind we're in the middle of a town of 50k and everyone else has power<sigh>.

It is an obnoxious 5kW Briggs&Stratton thats howling away. Now the noise is bad enough but it is doing this bop.. bop... bopbop..bopbopbop thing with its exhaust note. It is extremely annoying. Does anyone know what causes this? Each bop is accompanied by a power disturbance. These things happen about 20-40times a minute. They completely block every ones ability to "tune out" the generator. They decrease with load.

Is this an engine problem, or a governor hunting problem, or?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[oldfieldguy]

It could be 'missing'. This may be caused by several problems, but on little gas-powered generators, it's often the result of the generator trying to maintain proper RPM at low loads. I've actually added load to generators used for test power in the field, finding that the generator will run more smoothly and with better regulation when loaded around 50%. A resistance space heater or a set of halogen work lights worked well for me in this application.

Those other problems? Bad fuel. dirty carburetor. Old or fouled spark plug. Etc.

Incidentally, Honda generators didn't seem to have this problem.

old field guy

 

[MikeHalloran]

Check the lube oil level. While you've got it shut down, change the spark plug, too.

It's probably time to change them anyway.



Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

Thanks Gents. Will try it all.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rmw]

It just sounds like a Briggs to me. That is why I only use Honda's now.

You might be running just a little too rich or possibly even too lean. Is your muffler all blacked up? Do you see any appreciable smoke? Can you find that little screw on the carbureator with the spring on it? You might try tweaking it, but always ALWAYS count your turns from your starting point. Don't get lost. Check the owners manual (you may have to look at one on line) and see how many turns out the starting place is-might be something like 2-1/2 turns out and then tweaked to sound after that to try to tune out that blasted irregular plopping noise.

Check your inlet air filter before you start screwing with the adjustment. It may be clogged up making the engine run rich.

I've said it in the Mechanical fora, so I might as well say it here, I hate a Briggs. At today's scrap prices if I could have back all those that I have previously sold for scrap, I'd have a tidy sum. Honda's cured me of my woes.

Good luck,

rmw

 

[waross]

I may be incomplete combustion with the excess fuel detonating in the muffler.
Possible causes, choke malfunctioning,
Air filter plugged,
Most probable, carburetor float valve dirty and passing too much fuel.
regards
Bill

 

[rmw]

Is your load swinging at all. The worst problem that I have had with the popping exhaust noise problem with Briggs is when they weren't fully loaded and the load was fluctuating causing the fuel mixture to be constantly changing. The popopopoppping noise you describe sounds like when the load backs off (and when it would then be fuel rich as Bill W mentions). If I could ever solidly load them they seemed to line out and run better.

Someone needs to go the break room and put some lunch to heat in the toaster oven. That will load the dickens out of a small generator.

Did I mention that I am not very happy with Briggs?

rmw

 

[waross]

Hey, rmw, have you ever been close to the tow-boat indusry?
"Line out", or "Lined out" were terms that I heard often on the west coast of Canada when I was young. I understand that the phrases originated in the tow-boat industry. And, the context fits here.
Yours
Bill

 

[danw2]

I, too, think it is running rich and coughing.

1) Try adjusting the high speed fuel needle valve.

On many 8 & 10HP engines the high speed valve is on the lower left of the graphic, extending out at an angle from the bottom of the bowl of the float carbs.

CW closing (tightening) the needle will lean the mixture at load.

Tighten it an 1/8 turn at time, wait and see what sort of change in performance you get. You can always go back to where you started.

2) If the float is sticking because its gummy, then some cleaner might loosen it up. I've always hoped chemical solutions would work, but have never had them do so.

My generator Briggs isn't as bad as the Tecumseh on my snowblower. The driveway descends in elevation to the road and I need one high speed carb adjustment blowing snow 'down' the driveway and another adjustment blowing snow 'up' the drive.

Dan

 

[itsmoked]

Hmmm, exhaust popping/detonation from too rich an exhaust. Interesting. Why would this result in voltage fluctuations?

We have loaded it up to probably 75% load and the popping stops completely.

It seems like the engine is backing off the load and then over shoots then backs off so it's briefly entering decel then back to work. This is taking about 90ms I'd estimate.

The engine only has about 25 hours on it so it has no wear/smoke/rings/valve guide/oil blowing issues at the moment.

Except for this and the crummy choke system that requires removal of the, still new, air cleaner/filter and mechanical manipulation of the choke butterfly it starts with one pull.

So I can't be too harsh on B&S though their corporate environmental concerns are dark ages, as in,("We don't need no stikin environment! Just enough oxygen to run.")

These bops spike the voltage so all the UPSs see it as an impending power loss and each and every bop transitions the UPSs. Clickidy, clickidy, clickidy. I finally had to yank them for fear of destroying them. (Go figure.)

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[danw2]

>Why would this result in voltage fluctuations?

It's missing when it coughs.

When the engine is tuned lean it will 'hunt' and you can see the throttle get pulled open by the governor linkage as it starts to stall, then overshoots, then nearly stalls, then overshoots and the engine oscillates like a PID loop with too much gain.

But when it is rich it will cough: blat, bah-blat, bah-blat, blat. Each blat is a miss and the voltage droop reflects the missed power cycle.

 

[rmw]

If it is the common type of Briggs that I have had to mess with your governor is a mechanical flapper in the cooling air stream inside the engine. If not, it is surely something about as (un)sophisticated.

As the engine misses during these load fluctuations, not only does the power fluctuate, so does the cooling air flow through the engine so that the governor is contstantly chasing that too.

There isn't much way to do any loop tuning (setting PID parameters) on that control loop other than just to load it up so that the governor flap is straining against the air flow stream constantly which lines out (there I go again Bill) the engine. There is a spring in there that you might check along with the entire linkeage system to make sure that trash or cob webs or dirt dobber nests aren't causing some binding of the governor mechanism-suggested since this unit is only used intermittantly.

Other wise, your latest post indicates that my solution is going to solve it-go to the break room and open the door of the toaster oven and load that puppy and enjoy life. If you don't have a toaster oven, go borrow (rob) one from home.

When I have had to run small generators of this size at home for outages for ice storms and/or hurricanes, they would run everything fine (I don't have blap blap blap because I use Honda Generators), but when cooking was necessary on the toaster oven-the only way we could cook, that thing with its dead short circuitry would bring the generator to its knees. We had to turn off every thing else, refrigerators, freezers, unnecessary lights etc to be able to cook so you might have to either use a small one or one that has variable settings so that you have the 75% power left for your other stuff.

rmw

 

[itsmoked]

danw2; I never saw your earlier response,(with pic)! I will certainly try the mixture adjustment. I'll wait until these storms pass as working on wet engines in drizzle isn't one of my favorite tasks.

My question was "how can detonations in the muffler cause engine speed variations". But I see now that the detonations,(as that is what they sound like), are after-the-fact, of the engine missing and hence stoichiometric mix hitting the hot exhaust. I understand now.

That snowblower.. still better than a shovel.


Thanks too rmw. I am very interested in seeing just what the governor mechanism is. I was hoping it was more than the conventional wind-vane.(shudder) I can easily see that being controlled by the spiders, and some nasty stiction.

Overall I was fairly pleased with this Generac's abilities. I ran two refrigerators, multiple computers, forced air heating, and 240v electric heat, with only occasional noticeable voltage sags for 12hrs, using 9 gallons of fuel.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[danw2]

The governor on 8-10 HP single cylinder uprights has traditionally been a mechanical gear driven unit inside the crankcase, not an air vane, something similar to:

The governor spring tends to pull the throttle open. The force of the counterweights, operated by centrifugal force, tends to close the throttle.

Actually, there is a limited, 'gain' adjustment in the placement of the spring on the governor lever (which hole the spring goes into on the governor arm).

The closer the spring is to the axle shaft of the governor arm, the tighter the band, or the smaller the difference between load and no load speeds. Placing the spring too close to the governor axle shaft will cause the engine to hunt (gain's too high).

If the spring is placed too far from the axle shaft, the speed decrease from 'setpoint' before the governor arm response is noticeable is greater (too little gain, sluggish response).

All that said, I don't think it's a governor adjustment, just FYI.

Dan

 

[itsmoked]

Roger that! Thanks. That's looking like my memory of seeing an adjuster at the top of a rod in the past.

I had a 3.5kW Honda based generator that was really nice, just too small. It had what looked like a bolt wrapped with magnet wire that added to the governor with a metal plate next to it. I suspect that it helped in "large hit" responses. Though it could've been for the "eco-throttle" as it could go to idle automatically when unloaded.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com