Poulan V-Twin Mower backfires when load is applied from the blade

bricha2 · Aug 6, 2017

I have a Poulan V-Twin 42in Mower. The mower run fine when in idle no moving. Once a load is applied with the blade engaged or start riding it start back firing out of the right exhaust. I have removed and cleaned the Carb several times. Nevertheless, I can not fine where the cause of the back fire is coming from. Can you all help?

JRobyn · Aug 6, 2017

Look under the hood and tell us who made the ENGINE. Backfiring is often a symptom of running too "rich" (too much fuel). Are you sure that the choke is all the way open and the air filter is clean?

bricha2 · Aug 7, 2017

The Engine is a Briggs and Stratton Model 40777, Type 0167 E1, - Poulan PPR20H42STA - Yes, The choke is all the way pushed in and the air filter is clean and new.. Again, while running in idle the mower runs perfect, no surging or sputting, just runs fine.. But as soon, as I apply the blade, it start to backfire thru the right-side exhaust... I have cleaned the Carb several times, replaced any gaskets or O-rings that look worn....

DaveOmak · Aug 7, 2017

Look down the throat of the carb and check the choke to make sure it is not partially closing... That the cable is adjusted properly....

JRobyn · Aug 7, 2017

If not running real rich due to a choke or air filter issue, the next place I would look (particularly if this seems to be in just the right side) is that the valve adjustment is too tight and the exhaust valve of the right cylinder is not closing fully. I have also heard of situations with the B&S engines of the valve stems becoming carboned up and sticking with the valve partially open. If this is happening, a strong dose of Marvel Mystery oil in the fuel tank MIGHT help. Maybe even pull the right side plug and squirt a teaspoon or so directly in the cylinder. If you have or have access to a compression tester, that would also confirm that there is a problem with valve sealing.

TimberHole · Aug 7, 2017

I would start with compression, intake leak and valves on that side. What makes you think it's the carb when it is only affecting one side?

tomplum · Aug 8, 2017

These Briggs twins are creatures of habit and those of you discussing valve issues could be in the right area. What tends to happen is that valve guides can migrate in the head- preventing full valve travel, rocker studs come loose, cam lobes wear etc. So when you remove the valve covers, note if the amount of lift both valves have are similar and that the valve guides protrude from the head also relatively equal. With that being said it could be one of several issues. Does choking happen to improve the situation? Does the engine seem to be low on power under load? Have you at least tried a set of spark plugs?

Spanner · Aug 8, 2017

First: Switch the existing spark-plugs from L - R. Then you can verify or eliminate them as a cause of the issue. i.e. If the backfire moves with the spark-plug or stays on the same side regardless of which plug is in-situ.

Second. Tell us what brand of Spark-plug you have and the type number pls.

Walt 2002 · Aug 8, 2017

First thing to do is see if it is actually running on both cylinders when "running great" at idle.

Walt Conner

bricha2 · Aug 8, 2017

Thanks Guys for all your comments.... Here's what I find from the Spark Plugs... I switched them from L-R. The Left side (non-backfiring side) spark plug is a Champion RC12YC. This SP appeared to be dry and good. The Ride Side (backfiring side) SP is a Champion RC14YC. It appeared a little wet from oil. When I switched them, the backfiring was not as constants as before, but still backfired a little. I don't think the mismatch plugs are the problem, though....

I then went to the 2nd option of removing the valve cover. Now, I don't know much about valve, but willing to learn. The rockers on the Left side (Backfiring side) appear to be level but the top rocker was a little loose. The (non backfiring side) the bottom rocker was a little loose as well but not backfiring. The top rocker was not even or level like the left side. See my picks of the valves. Another note, the bottom side underneath the Valve, muffle connection was wet with oil. I have also provided a picture of that as well.