Generator surging

[Russ from MN]

My friend near Duluth had to use his generator last week for a power outage during the big snow storm. it
started and ran ok, but continued to surge somewhat. What is the most common solution when an engine surges?
I suggested opening up the main jet a little, but it's a replacement carb and may not be adjustable. Another
thing I suggested is to put some load on it before trying to start the furnace, or another sensitive
appliance. I use electric heaters to put load on generators when calibrating the governors.

 

[J.Wondergem]

I found with the neighbor's that it had a little junk in the main jet.

 

[M-MAN]

Pour some Mechanic In A Bottle in the tank and let it run. TSC and Lowes both carry it.

 

[Janicholson]

Ethanol gasoline needs to be run richer than non-ethanol fuel. It often requires the micro drilling of the main jet in those carbs with no adjustment screw. There if you use a propane torch with the air mixing tip taken off to add fuel to the intake, and do it incrementally, a little at first, then tiny bits more, it should straighten out the surge. If it does, and there is crud in the carb, it might just need cleaning. if it is clean using a number drill set, increasing the drill size one step at a time will work. do not over drill. Jim

 

[Phil Tibbetts]

As others have said the ethanol gas will plug the main jet if left setting for any length of time. I will put nothing but ethanol free in my small engines now and have no trouble.

 

[John T]

In the MANY gensets of different brands I used for years, surging was often due to a LACK OF ADEQUATE FUEL

Perhaps the power/load jet (if adjustable many are not) needs set richer

Perhaps theres a bit of crud/gum/varnish which Gumout or Sea Foam may cure or else disassemble and clean

Perhaps the float bowl level is too low

Perhaps theres inadequate fuel pressure from an elec fuel pump or regulator

Perhaps the fuel filter needs changed

Perhaps there are some mechanical governor adjustments needed


John T

 

[RM-MN]

Generators are governed to try to run at a constant speed. When the speed goes beyond its set point it closes the throttle and the engine runs on the idle mixture, not the main jet mixture. If the idle jet is set too lean or is plugged the engine can't get enough fuel to run at the reduced throttle so the governor does what a governor is supposed to do, it opens the throttle to speed up the engine. Now the engine is running on the main jet again and the engine gets going too fast and the process starts again, surge after surge.

 

[Steve@Advance]

Replacement carbs are not always properly jetted.

If it used to run good on that carb, it probably needs the main jet cleaned, especially if it sat for a season with gas in the bowl. The jet needs to be scraped out with a stiff wire or torch tip cleaner. Carb cleaner alone will not get it clean as the ethanol residue adheres to the surface just enough to slightly restrict the flow.

If it never ran right on the new carb, and you still have the old one, compare jet sizes. Use the old jet to experiment with drilling it out. You will need a jet drill set to make very precise increases until it runs best, talking .001 at a time!

BUT, before making jet changes, be sure everything else is right, like valve lash, compression, clean oil, spark quality, and no vacuum leaks.

 

[JF in MI]

I used to have a generator that was built way before E15 was in use and it used to surge (lean roll) when E15 came out. A slight increase on the main mixture screw fixed it. Also still have a 1990 golf cart that did about the same thing. Drilled out the main jet for 10% more area (3.14 x original hole diameter x 1.1) and it has run perfect since.

 

[MarkB_MI]

Surging, particularly under light load, is usually caused by a plugged idle circuit. If the main jet is blocked, either it won't run at all or it will die as soon as you put a load on the generator.

I suppose sometime, somewhere, somebody was able to fix a surging motor with a dose of Sea Foam or other snake oil treatment. It's never worked for me. I take the carb apart and clear out all the jets and passages with a fine wire. (I use monel fishing leader, but anything fine enough to go into the smallest orifices will do the job.)

Folks have suggested changing or enlarging the main jet. This is seldom necessary. Small engines are jetted to operate at sea level, so unless you live at sea level the mixture is probably already on the rich side. I have three jets for my Honda RV generator: The stock jet is good from sea level to 4000 feet, another jet is good from 4000-8000 feet and the third jet (which I bought by accident and have never used) is for elevations above 8000 feet.

 

[Russ from MN]

Thanks for all the ideas, if it's still a problem when we get back to MN in the spring I will try to help him fix it.

 

[cwtech]

I did small engine repairs for 35+ years and have never believed in additives.

I have witnessed Seafoam fuel additive do some amazing things and I am now a believer.

I have used it several times to eliminate surging after prolonged storage of engines.

For $10 it is worth a try !!!

 

[buickanddeere]

Surge ? Or lug down when starting a load ?
On occasion idle and main adjustment screws exist but are hidden under metal plugs or covers .

 

[Hobo,NC]

Lets don't forget they need air to run its not a given.

Remove the air filter and see how it runs.

Fuel additives may clear it up if it does I would not leave the additive in it as it may decay the fuel lines. BTDT but I use the good stuff 100% Techron.

This post was edited by Hobo,NC on 12/19/2022 at 04:04 am.

 

[Geo-TH,In]

A surging engine is caused by a blocked idle jet.
You can buy a voltmeter/frequency meter to add to a generator.
I have 2 honda clones, champion 3500 watt RV's.
One came with a voltmeter/frequency meter.
The other one I bought a volt/frequency meter off Amazon or Ebay.
One champion was surging. I looked at carb model# and ordered the same one off Amazon for under $20.
To my surprise, new carbs from china don't have to be California compliant. The new carb had a fuel adjustment screw.

Buy a new Chinese carb. Buy a frequency meter too.

 

[UncleTom]

Check main jet first. I have fixed so many mowers and small engines by cleaning the main jet. Then check your fuel tank for junk, then check your gas can for junk. It gets in there, i promise.

 

[miangus]

This is the correct answer. There are a couple of solutions, keep a light load on the generator at all times, just enough to keep it running on the main jet. Clean/enlarge the idle jet. There are several U-Tube videos on how to do this. The idle jet is very small and often obscurely located. Sea Foam might work but the problem for Sea Foam to work it actually needs to pass through the jet and the best you can hope for is to clean the jet which will not enlarge a jet which is too small.

 

[T.R.K.]

All are good replies. The problem is usually in the jets.

I do recall a Jing Dong generator. (That was the name. No kidding.) that I worked on once that had a restriction in the needle seat. The needle seat on the (supposedly correct) replacement carburetor was bored for a fuel pump and that particular generator needed a gravity feed carburetor. The hole in the needle seat the fuel goes through in a carburetor set up for a fuel pump is smaller than the same hole will be in a gravity feed carburetor. The fuel is under pressure, (I know. only 2 psi.) So they use a smaller hole in the needle seat to reduce the surface area of the fuel the needle has to hold back.

The fix in that case was to use the body of the original carburetor with the bowl from the replacement.

 

[Mike(NEOhio)]

I've been following this for a while. I'm not familiar with gens but maybe the governor rod needs to be adjusted.

 

[Den N Ms]

Russ from MN ,The cause of surging is not getting enough fuel through the main jet and has nothing to do with the idle jet.As cwtech said Seafoam has also made a believer out of me as it has worked for me on many small engines surging many many times.Other things may be something stuck in the main jet,float level set to low,restriction in the fuel inlet,filter or needle and seat.Check and open up the main jet one size at a time to enrich-en up fuel mixture.

 

[IaLeo]

My Briggs powered wood splitter always surges just before it runs out of gas! Leo

 

[MarkB_MI]

Well, Russ, there you have it!

It's the main jet. Or the idle jet. Or something else.

It's caused by ethanol deposits, which is that stuff you see anytime you wipe something down with alcohol. You can remove the ethanol deposits with Sea Foam. Or not.

You can adjust the carb, unless it can't be adjusted.

Anytime you want a straight answer, just ask a bunch of old pharts! They'll never lead you astray.