OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Popping noise from exhaust every so often

Hi, A friend asked me to look at his mower after some relatives had borrowed it-say no more. It had a broken shear pin and I repaired that. Now it starts easily but every few moments it will make a "popping" noise from the exhaust. I think it might be an exhaust valve in need of some service. I have tried another carby, cleaned out the old one and replaced diaphragm and gasket without improvement. The problem is not a major one and I tested the mower on a patch of my own lawn and it seems to go alright but to my "professional" pride it just isn't right. It is a Briggs and stratton sprinter engine on a Victa Vantage mower. Do you think the exhaust valve is the likely culprit. Any other ideas? I've attached a photo of the carby and the broken shear pin.

Hi Sparker,

Ask your friend if the relative has a wife and if so borrow her and send her back the same way as the mower you have to look at.

Anyway you could check the spark plug to see if it has a whisker on it, as it could be the issues( always take the easy/cheapest one first). I would say that they put the mower through some rough work causing the damage.

It would probably be worth checking the valve clearances and that the exhaust valve seat is not loose just to be sure.

I have an almost new victa tornado here that has also hit something hard, repaired flywheel key, crankshaft output is nice and straight, shakes violently.

There are 4 things I never lend out, my car, my wife, my tools or my f**cking lawnmower.

Can we just clarify one thing, please? Have you replaced the flywheel key? The symptoms are consistent with incorrect ignition timing, which depends on the flywheel key being intact. You said "shear pin", and I'm not sure what you meant by that. The Briggs flywheel key is made out of zinc, not steel - be sure you replace it with another zinc one, or the next time he hits a water pipe he'll turn the crankshaft into a pretzel.

If the ignition timing is correct (that is, the zinc key is intact) I agree with Joe - the next most likely cause is a tight exhaust tappet, sticking or burned exhaust valve, or a loose exhaust valve seat. However mixture problems should not be discounted.

Joe I have just recently had the same problem ,a near new victa but vibration was very bad , it end up being the blade boss itself ,it was broken off uneven each side of the boss. Had another blade boss and swapped it over ,it went as it should ,nicely balanced again, it ran smooth.

I love the way you guys regard your mowers. Like here where mower=wife. heh,heh. Hi Grumpy, yes I replaced the key but it was hard to get it in the slot. A very tight fit.

If the key is OK, and the spark plug is OK (you need to clean it, inspect it, and test it) I think it is time to check the tappet clearances. If the exhaust clearance is much larger than it should be, you've probably found the problem, but if it is correct, it still doesn't mean the valve is OK. It could still be sticking or have a loose seat.

The other thing you should do is remove the cooling air shroud and check that the cooling fins are clear. Obstructed air flow will cause overheating, and your symptoms are somewhat consistent with that. Overheating is also a leading cause of valve seats coming loose.

Incidentally and more or less off topic, I recently tried giving a spark plug a burst of carb cleaner after I'd scraped it and gapped it. Made the insulator look like a new one, all the way down the cone to the base. Runs nicely too.