2000 70 johnson motor breaking up under throttle

I have a 2000 johnson 70 2 stroke with a vro system. The motor had old fuel and bad plugs and caused it to smoke like crazy..so I drained the fuel in the tank and fuel line, and put plugs in the motor. Fires up right away and seems to idle pretty well but when you give the motor throttle you can tell the motor is breaking up. I'm not sure about the timing because theres two sets of numbers. Theres markings on the flywheel and at idle, the timing light is spot on with one of the marks....but as I understand it, theres a WOT timing mark that the motor needs to be on as well.

Mainly my question is what/how should I check to see whats causing the motor to break up to go about fixing it.

Thanks for any replys.

Re: 2000 70 johnson motor breaking up under throttle

Have you checked the spark with an air gap tester, what is the compression like?

Re: 2000 70 johnson motor breaking up under throttle

You say it idles well, is that under load or on muffs? If you can get it to start, get it on the water and verify it will run through its full throttle range.

On my '76 70 HP Johnson, the timing settings are TDC at idle, 17 degrees at WOT. Look up the Joe Reeves WOT timing procedure to verify your WOT timing. Engine doesn't have to run for that, just crank and have spark.

If you ran old fuel through the motor there is a good chance you may have sucked some gunk into the high-speed circuits. A carb cleaning at the least is probably in order to make sure you haven't fouled up the high-speed jets.

Rgds

Re: 2000 70 johnson motor breaking up under throttle

im unfamiliar with an air gap tester...what exactly is it, and where can i get one? Compression is 110-120 on all 3cylinders.

It idles well on muffs. It just breaks up when you give it throttle. I just got the registration for the boat today, so I'll try dropping it in the water and tie it to the dock and see how it runs in the water but my guess is either the same or worse.

The timing is at -4 at idle, and theres a white mark at -4 where someone has marked it. Theres other marks as well so I'm not sure if any of them are correct.