Engine missing and backfiring

[PMDowns]

My 1996 Cub model 2165 with a 16 HPVangard (B&S) engine will crank and run fine at low idle. When you give it gas the engine starts missing badly and backfiring. The problem is particularly bad when you put a load on the engine. It did this identical thing last year and the repair was an easy plug replacement. I went ahead and replaced the plugs again but this did not solve the problem. My thoughts are something in the ignition system. Any thoughts appreciated.

[Matt G.]

Sounds like the carb needs cleaning to me. The main jet is probably at least partially plugged.

[Merk]

Does your engine have Champion sparkplugs in it?
I would replaced the spark plugs with a set of Autolite plugs.
Pull the plugs and look at them. One may be gas fouled.

Another area is the air filter. When was it last change? Is the filter a Briggs and Straton filter? The material Briggs uses in their filters may look ok. They will plug and cause the power loss like you are expenencing. A good way to tell is to run your Van Guard engine without the air filter.

I have a 16 HP Briggs Van Guard that did the same thing. My Briggs will foul a Champion sparkplug out every 10 to 20 hours. Never the same cylinder. My Briggs has a coil for each cylinder.

[PMDowns]

Thanks to both of you for your ideas. I was using Champion spark plugs and as I mentioned I did replace them and that didn't solve the problem. I also ran the engine without the air filter and it had no effect either. I will try cleaning the carburator and see if that helps. It may take me a day or so but as soon as I do I will post the results. Thanks again.

[PMDowns]

I cleaned the carb as well as putting fresh gas in the tank and the missing and backfiring problem seems to have gone away. However after taking off the air cleaner assembly I noticed a hose barb on the rear of the carb with a piece of broken rubber hose attached to it. Despite much searching I cannot determine where this hose is supposed to go. I have attached a picture. You can see the L shaped hose barb on the right side of the carb.
Thanks again for any assistance.

[ol'George]

Originally Posted by PMDowns

I cleaned the carb as well as putting fresh gas in the tank and the missing and backfiring problem seems to have gone away. However after taking off the air cleaner assembly I noticed a hose barb on the rear of the carb with a piece of broken rubber hose attached to it. Despite much searching I cannot determine where this hose is supposed to go. I have attached a picture. You can see the L shaped hose barb on the right side of the carb.
Thanks again for any assistance.

I'm sure others will reply that are familiar with this engine, but to me it appears it is a bowl vent to atmosphere, with newer emission standards I would say it goes to the air cleaner, unless you have a "carbon canister"

[Sam Mac]

That is just the carb vent. I like to run a small fuel filter on just to keep crud out but you can just put a plastic hose on it and run it down uder the frame. Happy mowing

[PMDowns]

The mower ran well for a short period of time (maybe 15 minutes) and now is back to it's old tricks. It runs OK without a load but when you engage the mower deck it starts sputtering, missing and backfiring through the carb. As soon as you disengage the deck it smooths back out. I have also replaced the fuel filter to no avail. Any thoughts?

[Sam Mac]

Still sounds like the carb is dirty. If it was mine I'd pull the top off again and make sure all the small holes are clean. Some guys use twist tie wire to clean them, carb cleaner etc. Make sure the solenoid is clean and moving freely. If the fuel line is old I'd change it all the way from the tank to the carb. I’m seeing a lot of fuel line starting to fail and collapse and the inner liner flaking off; I blame it on the gas but who knows. Make sure the inside of you tank is clean. Wouldn’t hurt to remove the fenders pull the tank flush it out and while you’re in the area give the hydro a good cleaning of all the dirt that gets built up on the cooling fins. Probably not your problem but I have seen the welch plug down in the back near the low speed air screw fall out on one. See attached pic red arrow points to the missing plug. If this is the problem you will have to remove the engine to replace it. The owner of the one in the pic just ran it for about 400 hours with the choke full on; she wondered why it was smoking. Fresh gas with about 2 oz. per gal. of Sea-Foam will sometimes help clean cruddy carbs. Personally I have had good results with it enough so that I use it in all the gas that goes into my small engines including my Harleys along with ethanol free gas. Hope this helps.

[Vince_o]

Main fuel circuit has trash in it, like Sam said