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I have a 2005 Husqvarna YTH2448. It has a Briggs & Stratton 24 HP ELS V-twin engine. The engine runs but it runs rough (lopes, rpms going up and down and almost sounds like it is backfiring especially at high idle, low idle it doesnt run as bad). I've taken the carb off and cleaned it but did not rebuild it yet. If I pull the plug off of either cylinder it runs like a new mower, as soon as I plug one of the plug wires back onto the plug it starts running rough and missing, both plugs have great spark (grounded the plug and wire to the block), I've put new plugs on it, drained the fuel tank and used higher octane fuel, new fuel filter, new air filter, changed the oil, cleaned all electrical connectors, re-gapped the Magnetos, and still have the same problem. It's starting to get expensive replacing parts. Can anyone give me some direction as to what I may try next? Thank you in advance for your help..

Check the valve clearance, you could also give it a compression test before doing so, do the valve's and then come back.

EngineMan said:

Check the valve clearance, you could also give it a compression test before doing so, do the valve's and then come back.

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Thanks I will give that a try.

ybugster said:

Thanks I will give that a try.

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I strongly suggest you NOT run your mower until you have identified the rough running. I speak from owning a 24 HP Intek which self destructed twice . Both times the symptom was similar to yours. Want more worry? Use "search" this forum and find my lengthy tale and overheat warning.

What color are the plugs? When it is running rough, is black smoke coming out the muffler? Does it act the same when either plug wire is pulled?

The plugs are grayish white.. I checked the valve clearance and they are within range .005-.007.. I think I may have found the problem. When I turn the flywheel by hand I can hear compression leak off on the right cylinder bank, I'm pretty sure I have a blown head gasket..Motoman it sometimes has white smoke (puffs) and it started backfiring yesterday. When I pull the plug wire off of either side it runs perfect until I put the plug wire back on, then it starts to run rough and missing.

You will have less compression if one take's away the spark to the said cylinder.
You're next step would be to take off the head.

I would advise you to take a compression test on both sides and compare, before pulling the heads. White smoke is normally a sign of moisture in the fuel, but that is not cosistant with your problem.

But he know's that there is a compression leak on one of them so doing a compression test so there will be a difference between the two, and if you havn't got a tester would it not be better to take off the top and have a look..?
head gasket not that much.....tester much more, unless you have that is.

The guys are right who suggest not to plunge in dismantling without more diagnosis. If you don't have a comp guage try to borrow one or see how much they are. H-Frt may may have a cheapie which will support non pro use. Short of that have you taken both plugs out and tried the "thumb or finger "plug" method? Reach in and cover the spark plug holes while turning the flywheel by hand onto TDC. It's not the best but should lift your finger or thumb off with similar force. You really need the guage.

I never said that Rivets was wrong, what I said was that the (lad) know's of a leak.

The only reason I suggested it, was to make sure that both sides are not bad. I understand what EngineMan is saying and agree with him.