Old Yamaha isn't running right

[Konny]

Hello folks! I recently bought a 1987 Yamaha 30AM, it's a 30hp two stroke, two cylinder outboard and it's in great shape, looks new. Runs good too, on most RPM at least.

It idles perfectly and runs good at wide open throttle, however there is a band between approximatley 800 and 1500 RPM where it only runs on one cylinder. The problem vanishes when you give her some more throttle or go back down to idle.

Anyone got a clue as to what might cause this? My guess is it's the CDI unit but that is an expensive part where I live so if it is something else i stand to save a few bucks.

Any input is much appreciated, thanks in advance!

 

[slimbo3006]

How did you determine that it is only running on one cylinder? Need to verify if both cylinders are getting spark when the issue is occurring.

have you properly cleaned the carbs anytime recently?? could be something as simple as an obstruction in one of the transition ports...

 

[racerone]

A 2 or 3 cylinder motor ?----Model # / picture required.

 

[Konny]

How did you determine that it is only running on one cylinder? Need to verify if both cylinders are getting spark when the issue is occurring.

have you properly cleaned the carbs anytime recently?? could be something as simple as an obstruction in one of the transition ports...

Only the bottom cylinder is getting spark between 800 and 1500 rpm. I'm certain it's an ignition issue.

 

[Konny]

A 2 or 3 cylinder motor ?----Model # / picture required.

As I said it's a two cylinder "Yamaha 30AM". There is little more info on the plaque but i'll attach a pic