Mtd model 673 no power

[Magee16749]

Just got a older mtd model 673 lawn mower to be used instead of push mower. I believe it has 18 horse briggs twin cylinder engine on it. With throttle all the way up and shifter on right fender in 1st gear I constantly have to stop and let blades get back up to speed. Yesterday i had enough and parked it and used push mower and it mowed it without a struggle. And I was pushing it pretty dam fast. So grass height shouldn't be a issue sharpen checked the pulleys all spin freely I have Sharpen the blades but gonna give them a 2nd look again before I reinstall deck. Besides that the motor starts right up easy and don't smoke. Don't have any other problems until you use to mow. Please help

Thank you

 

[bertsmobile1]

Your symptoms correspond to a twin cylinder engine running on one cylinder .
Check the exhausts to see if one is substantially hotter then the other
To be of more assistance we need the make & model numbers of the twin cylinder engine and the full numbers off the mower ID tag also helps .