Mower is lacking in power after I snagged it on a bramble.

Almost impossible to answer without 'year make model'. You may also be talking about a ride on tractor, a mower, a weedwhacker, a power washer, a generator or any item that has an engine. Cars and Trucks is the default category. There are a whole list of reasons in the link.

https://www.google.com/search?q=Engine+is+lacking+power

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could be dirt in the carby , blocked fuel filter or lack of adjustment in the accelerator cable
I will go for a cable adjustment as they slip under the clamp on the carby bracket when the throttle is pull wide open

Sounds like either a compression problem or valve adjustment.
If there is no smoke but just no UMMPH then susspect valve adjustment. Also it may get weaker as it gets warmer or just stop altogether once hot and not restart until cold again. That's Typical Valve clearances.
If it's burning oil or smoking then susspect damaged piston rings or a burnt piston.
If the oil dip stick is a push in one, and it gets blown out of it's seating, then it's definitely piston problem, as compression is getting past the piston into the sump. That pressure has to be relieved somewhere and the dip stick is the obvious place.

• Does deck turn freely? Check and be sure mowing deck is not jammed or bad bearing etc. If nothing is wrong with deck, then check fuel filter, air cleaner element, dirty fuel system, bad gas, water in fuel, restricted fuel flow. Lack of fuel will cause engine to have lack power.

should be a cable connected to the handle, might be reversed or could of been snagged causing it to give you this issue

if it's a 2 cylinder (should be) 1 spark plug is fouled out...rule-o-thumb...replace both...that's step 1...

Have you Contacted Mountfield about a Manual? You can Contact them Using the Options at this Site Addy;
http://www.mountfield-online.co.uk/contact?jssCart=13a24ca4de2a2610f7213de8a0539ffb .
For an Engine Manual you can Contact www.outdoordistributors @ 877-707-2787 or Contact Tecumseh @ 800-558-5402.
Please, Do Not Hesitate, If you Hit a Snag or this Does Not Correct the Problem, I am Here if You Require More Assistance.
Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Be Happy. Thanks.

Good Luck

Respectfully

jbridger (John)

Hello:

You Pull the Handle and it will Pull the Cable that Engages the Transmission.
Please, Do Not Hesitate, If you Hit a Snag or this Does Not Correct the Problem, I am Here if You Require More Assistance.
Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Be Happy. Thanks.

Good Luck

Respectfully

John

Hello

On Some Model Mowers the Engine Pulley Must be Loosened and Lowered in Order to Replace the Top Belt.
Please, Do Not Hesitate, If you Hit a Snag or this Does Not Correct the Problem, I am Here if You Require More Assistance.
Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Be Happy. Thanks.

Good Luck

Respectfully

jbridger (John)

just to let u know CMM1000 mower are on recall for pcboard.
if ur mower is type 1 to 4 then its the subject for recall for convertion to CMM1200.see ur nearest service center right away.