Loss of power in a small engine?

Paulinkansas · Mar 8, 2012

I bought a used skid steer recently. Engine is a 2 cylinder 23 horse Onan engine. It starts easily and goes to full rpm in neutral. When I put it in gear, the rpm's drop about 25%. When I'm in gear and moving, the rpms drop another 25~50%. I can stall it by turning or going up a slope.

It's not using any oil. I've run it for 6 hours since changing the oil/filter, and the level hasn't moved from the full mark. It's not dirty looking either, still looks like honey. The plugs look normal.

I tried to put a compression checking gauge on there, but was not able to make a snug fit.

It has two pancake type mufflers. One of them had a blue glow of fire inside it when I looked at it when running in the dark. The exhaust pipe started to turn red after about 45 seconds at full throttle. It also makes a popping and snapping sound.

Could the exhaust valve or seat be bad in the cylinder that has flames coming out the exhaust?

Greenday · Mar 8, 2012

Make sure its not trying to run to lean

Anonymous-0 · Mar 8, 2012

Most likely running lean, blocked jet or air leak!!
I think if it was a valve problem you would have hard starting and or chuffing from the muffler at idle, however if it is running lean it may burn out a valve!!!! also check valve clearance and plug gaps

t1 · Mar 8, 2012

twin cylinder onan engines can run on 1 cylinder, and still run as smooth as if they are running in two. Until you put a load on them, then the RPM drops due to low power. Check spark on both cylinders. Some models used a single coil with 2 plugs and one side can go bad. Most engines can be converted to run 2 coils, 1 per cylinder cheaper than trying to buy that special 2 cylinder coil.

It might be as simple as a fouled or bad plug or plug wire.

wisbaker · Mar 8, 2012

Sounds like it's running light on one side. I'd test the coil and do plugs and wires and check valve adjustment.

Hendrik · Mar 8, 2012

Ignition too far retarded? Do not know this engine, but could the ignition timing be off on one cylinder only?

Paulinkansas · Mar 8, 2012

I replaced the plug wires a few days ago. Also adjusted the point gap to .020". Those things didn"t seem to make any difference.

Why would I see fire from one muffler and see one exhaust pipe turn red, when the other side stays normal?

If it"s running too lean, wouldn"t the above situation be present in both cylinders?

BushogPapa · Mar 8, 2012

If it is a hard to get to the Points on yours as it is on my Bolens garden tractor..I would double-check the points..!!
Timing may have slipped..I would check it..
The Carb is sort of a Mystery to me...!!
I have been fighting a fuel delivery problem..
The float on mine will seem to stick and it dies, every time I try to move Forward..!!
Put an Electric fuel pump on it but that did not help..I carefully re-shaped the Needle point and it is much better...
I think the rubber point had worn and was sticking in the seat..!
I never did find a rebuild kit for this 17 HP Onan..NAPA does not have a listing for it..
This one has a Big-Bore Block I installed with porting & Polishing and the large Round individual Mufflers, like you would see on 10 HP Brigs or Wisconsin Motors..
Sure has a lot of guts..never even need to open the throttle..!

Ron..

Roger in Iowa · Mar 8, 2012

Any heat coming out of the cylinder not showing fire. It may not be "running", but on one cylinder.

kencombs · Mar 8, 2012

Start with the basics, do a compression test. If it shows that you have issues, a leakdown test will pinpoint the cause.

Post the engine model and we can help more. Certain Onan's have a tendency leaky intakes, others, have been known to drop valve seats.

Paulinkansas · Mar 8, 2012

Yes, there is heat coming from that cooler cylinder. It gets hot enough after running for 30 seconds that I can't place my hand on it.

Paulinkansas · Mar 8, 2012

It's the Onan NHC-MS 3406C, or more commonly called an NHC. It's from a Deere 90 sked steer.

Billy Shafer · Mar 8, 2012

The NH engines did have a problem with valve seats coming loose. Both cylinders should be warm just after starting. Of course the cold one will be your bad one.It can run on one cylinder and carry part of a load. Coils rarely go bad but it can happen. Both plugs fire at the same time.

Do you have any signs of carbon build up. I have seen carbon stick behind a valve.You really need to get a compression reading.Not a lot of problems with air leaks on that engine. Sticking valves were also a problem. There was also a problem with lifters sticking on some Onan engines.

Don't recall any warnings from the factory about loss of power. Except for the normal items.

Onan tech since 1980.

oldtanker · Mar 8, 2012

Last onan I had would do that. PO had let moisture get into the carb and getting it right was a PITA. Seemed like everytime I thought I had all the crud out of it more would come loose. I also rebuilt it. Cheapest source for parts was JD. Cost as much to bore, new pistons, turn crank, valves done, new bearings and gaskets as a small block Chevy would have cost.

It was also critical on plugs. On one brand I would only get about 25 hours out of a set. It would run about how you describe when they started to go. I started using NGK's and got much longer plug life.

Rick

El Toro · Mar 8, 2012

The engine may be running too lean. If the engine carburetor has a main adjustable sc/ew you need to open that. If it has a fuel filter
it may be restricting the fuel flow. An air cooled engine will overheat if the fuel flow is too lean. Hal

olddog · Mar 8, 2012

Check the intake manifold and gasket on the lean side.

barnE · Mar 8, 2012

Are the wires crossed????? Dave

barnE · Mar 8, 2012

Are the wires crossed????? Dave

greygoat · Mar 9, 2012

Our Township has a "Large Article dropoff". I
checked there one day and found an "Almost new"
Simplicity garden tractor, 14 horsepower 42 inch
mower deck. Of course I took it home, found plug
completely fouled, replaced plug and it ran!
Further serviceing found the air cleaner fully
plugged with grass and debris, new air cleaner
and oil change and grease job, and it"s a super machine The RICH person who threw it away,because
it wouldn"t run, probably bought a different
brand! Who can THROW AWAY a one year old $1600 to
$2000 machine?... Anyway..Check fuel and air
filters!

JDseller · Mar 9, 2012

Paul start it and while it is running remove one plug wire and then the other. If it is an ignition issue it maybe running on one cylinder. when you remove the plug wire the RPMS will not drop much on a side if it is missing on that side. Then the running side will die when removed.

I hated those Onan motors in the JD skid steers and lawn tractors. They can be temperamental to get running right. They would last well if they where running right but they are high priced to work on now that Cummins owns them.

Loss of power in a small engine?

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