Repairs Honda HT-R3009 Power loss under load

The mower cuts grass fine going downhill but slows to a crawl when going uphill. This is even a problem when cutter height is maximum, no grass-catcher attached, short dry lawn. This has gradually become worse during this cutting season so not due to something suddenly breaking. Things I have checked:
Blade spins freely when PTO lever is mid-way such that neither cutter brake nor drive belt is engaged.
Drive belt tension correct
Spark Plug clean, correct gap
Carburettor main jet clear
Valve clearances correct.
Is there anything else worth checking before considering to strip down the engine?

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Check air pressure in tires first. If clutch is not slipping or dragging change oil in transmission per manual spec. oil.

Alan_M said:

Is there anything else worth checking before considering to strip down the engine?

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Can it climb the hill with the blade disengaged? Or no difference either way?

Compression test, leak-down test, engine speed check...basic health of the engine should be established. Once that is sorted and solid, look at getting power to blade and rear wheels. Belts, transmission, spindles, drive wheels/axle, etc.

How old is that mower anyway? Original, not-rebuild engine? Any smoke from the engine exhaust?

Check air pressure in tires first. If clutch is not slipping or dragging change oil in transmission per manual spec. oil.[/QUOTE]

Tyre pressures are fine. No evidence of a clutch problem. I'll take a look at the transmission - thanks.

robert@honda said:

Can it climb the hill with the blade disengaged? Or no difference either way?

Compression test, leak-down test, engine speed check...basic health of the engine should be established. Once that is sorted and solid, look at getting power to blade and rear wheels. Belts, transmission, spindles, drive wheels/axle, etc.

How old is that mower anyway? Original, not-rebuild engine? Any smoke from the engine exhaust?

Click to expand...

It climbs the hill fine with the PTO dis-engaged - sorry, should have mentioned that.

I have no idea how old it is - bought it with the house a couple of years ago. House is 15 years old, so could be as old as that. Engine feels/sounds fine. No smoke, certainly not burning oil.