26hp briggs running rough

Hi, my older 26hp riding mower is running on 1 cyl. I put in new plugs. Any ideas what to check? Ed Will Oliver BC

Well make sure you have spark on both cylinders. IF you do then check compression. These engines are known to have valve and push rod issues.

Take the old plugs and look at them. Choose the one from the cylinder that was firing. If you do not know which is which, or If they look the same, either, and put it near one of the plugs in the engine. Pull off the spark plug wire and put it on the old plug. Use a bit of tape to make sure the threads are touching metal. Crank the engine (trying to start it) while watching for spark across he plug gap. If it starts you now know which cylinder is operating. If that plug sparks, you know the cylinder is getting spark.
If it is not getting spark. the ignition system needs to be inspected. Getting a service manual, or watching youtube can assist in fixing it.
If spark, a compression check is needed, Again Youtube doing a compression check. If the compression is below 75 pounds, that cylinder has problems. If no compression, the engine will need analysis to figure the defect or wear point causing the issue. It could be from a blown head gasket, to a hole in that piston.
At some point a cost benefit analysis will result in either having it rebuilt, or a new engine put in it. Harbor freight might have an imported engine that would fit!!..Jim

Had the same thing with one of those I had. Took the engine cover off and found where the mice had eaten clean through one of the spark plug wires.

Was it using oil? If so I'd bet a valve guide has worked its way out of the head, interfering with valve travel, resulting in a bent pushrod, which now has fallen out. All this because the engines run too hot. BTDT

I also remember reading that there is a diode in the ignition primary wires on one of the coils that goes out making them run on 1 cylinder.

Check that the pushrods are in place in both rocker arms on the non-firing cylinder head.

Typically, a valve is open at hot shutdown, sticks, and then the pushrod either bends or simply falls out of place at startup.

If a vertical shaft engine pushrod may be laying there intact, pushrods in horizontal shaft engines are more prone to getting mangled when they fall down.

In my experience, running a good syn oil like Mobil 1 makes valves sticking much more unlikely.

That happened on a 24hp Briggs I have. I straightened the push rods and found some steel tubing that was an exact fit over the pushrods. I cut the tubing to length and pressed the pieces over the pushrods to strengthen them. Put the pushrods back in, set the tappets, changed the oil to Mobil 1, and so far no more problems.

On the garden tractor forum we have covered this pretty hot and heavy. Check the items the other guys have posted. But, it is very possible you could have a screwed up carb. Very easy to check. Take off the air filter and get a pump can with gas in it. Start the engine and run at a fast idle. Take the squirt can and squirt a couple of shots all of the way to the left. Next shoot some all of the way to the right. If the engine all of a sudden starts runnig correctly you have a messed up NIKI carb. Go on Ebay and buy a new one for around $60.oo. They work fantastic. Carb is NOT worth rebuilding.

I had the diodes short, killed one cylinder.

Easy test, unplug the kill wires from the coils, see if it runs better.

I bought some new diodes, soldered and shrink tubing, lot cheaper than buying the harness.

Move over to "garden tractors" and for more to the story go to tool talk". Starting in the last week of July in garden tractors and the follow up is in tool talk in the first part of August. Look at my questions concerning my 22 hp BS and "Jeffcat's" reply.

My problem was stated there and Jeffcat explained what was happening and I followed his suggestion as I stated and went on farther to include an aluminum intake manifold vs the plastic which came on the engine....you may already have an aluminum intake.

The carburetor and metal intake are listed in the BS parts lists as replacements for the original parts........clue here.....if BS is offering replacements for OEM equipment it verifies the fact that problems were discovered early on and corrections were designed to solve the problems.

Very possibly you will find the answer to your problems there. I did!!!!! Good hunting.