Starter cord hard to pull on 1975 Mercury 200 - help me get this motor started - Thx!

[CigarXO]

Members -
Need continued advice on bringing a new-to-me, 1975 Mercury Thunderbolt 200 (20hp - 1200225) to life. I had a thread going "advice on starter assembly" but after a week of tinkering and replacing the many tiny wave springs, friction springs and a missing part - I have the starter assembly operating (it will engage flywheel). Now to next issue...

Though the starter pawls now engage the flywheel, it is almost impossible to pull the pull cord. With both plugs in, I cannot get the engine to turnover via the pull cord. With the plugs out, the cord, flywheel and pistons seem to cycle perfectly. I believe the engine ran less than a month ago and has had regular service. I sprayed a little carb cleaner and lube in the spark plug holes and worked the cord some more, but the effort remains difficult/impossible with plugs in.
What should be my next steps???

I've already:
1. ordered a shop manual,
2. crawled these forums,
3. hit the gym 4-5 days a week so, don't infer that my physical strength is an issue.

I was told the motor has new plugs, carb rebuilt, head gasket replaced, water pump and lower unit refurbed.

I am new to 2 cylinder repair, so don't assume. Thanks in advance!

CigarXO

 

[CigarXO]

Bump - Anyone?

Timing?
I've seen mention of an exhaust chamber hole for allowing crank pressure reduction on some models, but cannot identify?

 

[undone]

Pull the recoil start mechanism of the top of the motor and put a wrench on the flywheel nut, spin it and see if it turns over with the correct amount of effort.

 

[Chinewalker]

What plugs do you have in it? You said it turns over with the plugs out, but not with them in. I had a motor given to me once that was thought to be stuck. Turned out it had the wrong plugs in it - they were long reach plugs and were hitting the pistons.