[Billboard]

I just changed out my cylinder head and rods. I cut grass for about 1 hr and now it seems like I'm only getting half the power. I took off valve covers on both sides and all looks ok. 1 spark plug was dry and jet black with soot the other was damp and gray looking. I have a Briggs & Stratton 24 hp els725 ohm engine. Muffler sounds a little muffled too. Engine sounds weak not like when running good. Any ideas.

 

[Greybeard09]

Are you sure it's running on both cylinders? Remove and ground one spark plug wire, and start the motor. If it runs try again with the other side.

 

[Billboard]

Ok ill try. It did have a big backfire while starting

 

[3v0]

By rods do you mean push rods? If so maybe one one the cylinder with the wet/damp plug has a problem with the push rods.

Why did you change out the heads ?

 

[Billboard]

The rods were bent and the seal on the spring was out. Yes the push rods. The spark plug works just checked that. I'm seeing light black exhaust coming out too.

 

[3v0]

Check to see if the rocker arm stud(s) have come loose.

 

[rayjay]

After having a big backfire I would check the flywheel key. Remove the nut on the end of the crank and make sure the keyways in the crank and flywheel are lined up.

 

[38racing]

The rods were bent and the seal on the spring was out. Yes the push rods. The spark plug works just checked that. I'm seeing light black exhaust coming out too.

are you saying here that it will run on each cylinder when other is grounded out?
I just put a used tec vtwin on a friend's mower and I got some backfire and miss . I used my laser temp gauge on the exhaust pipes and found one was not hot so i knew that cylinder was not working.

 

[Billboard]

What im saying is the plug sparked good when grounded. So the plug is good.

 

[Greybeard09]

Maybe it's the way I said it... The concept I was trying to get across is to run the engine on one cylinder at a time. Even with spark one cylinder may not be working.

 

[wwxx]

Muffler sounds funny, I would start looking there for blockage...after you have checked your flywheel key as others have mentioned.

If your spark plugs aren't new, I can't imagine installing new heads without new sparks, but hey, I can't blame a guy for saving $10 whenever possible.

Holding a spark plug against the ground is 'good', but it really doesn't tell you much as compared to a spark plug working under pressure, that is why professionals use 'spark testers' and other equipment. Occasionally even a new spark plug turns out to be a dud.

wwxx

 

[tomw0]

I would be re-checking valve clearance as the 'gray' plug side is not likely firing. It would not hurt to remove both spark plugs, and the rocker covers, and watch the valves work on both sides. It is possible the cam may have a bad lobe that won't open the valves properly, and a visual check of operation could rule that out.
Given that the cylinder heads were just replaced, that is the area that is most likely causing the problem. There could also be an intake manifold leak or mis-placed gasket causing lean conditions preventing one cylinder from firing.
tom

 

[3v0]

Check to see if the rocker arm stud(s) have come loose.

... because when the studs start to back out the rods can get bent. Putting in new rods without tightening the studs will not fix the problem at least not for long.

If the studs are loose you need to take them out and use the red thread locker.

 

[markusedma]

Sounds like you may have a valve guide backing out of the head....