Flywheel not spinning fast enough

[jack.watts]

Hi all, need some advice

Trying to get the engine started, it's a 2-stroke 75hp Mariner (The older style) and the flywheel isn't spinning anywhere near fast enough to get it started and sounds like it is struggling. Without compression (Spark plugs out) it spins at full speed perfectly fine, this was after we took the starter motor off, cleaned it all up and put it back on however as soon as there is compression it just struggles again, could this be a battery issue, even though it's still measuring at 12v?

Any advice would be greatly appreciated.
Jack

[A1an]

A duff battery can read 12v. Don't trust that.

If the starter was working before you tinkered with it I'd be looking at the battery or a loose cable/bad earth.

[ShinyShoe]

A good battery shouldn't be reading 12V

A good battery should actually be reading at the very minimum 12.7V and hopefully 13.2-13.4V if its freshly been charged.

[matt h]

Drop test the cells in the Battery.one cell down can cause your issue, check battery cables and connections.. also check for damaged battery cables etc. lastly starter condition

[jack.watts]

Okay, thanks for the advice, i'll inspect the wires now as it is quite an old engine but havn't noticed any wiring problems yet, looks like i'll have to go get a battery charger now haha!

[beerbelly]

its probably the battery or the starter motor drop check the battery if that's ok the starter

[paintman]

Take the battery off, fully recharge it with a battery charger & try again.
Putting a multimeter across the terminals & getting 12v or thereabouts is meaningless.
As an example I recently had an issue with the petrol pump in the car - 1986 RRC 3.5EFi. Multimeter assured me there was just over 12v at the pump. Battery was fully charged. A 12v headlight bulb connected from the pump feed to earth wouldn't light. Turned out to be corroded wiring in the vehicle connector being incapable of providing the current required.