Newly rebuilt Yamaha 70 has issues

I recently bought a fully rebuilt 02 Yamaha 70hp oil injected 2 stroke. It was rebuilt by a Yamaha dealer and ran fine on land. When I put it under load, it bogged down completely at first and then for a brief moment came alive and I started to get on plane, only to have it bog down again. I checked the spark plug connections, they were good, found 2 of 3 coils were loose so I tightened the bolts that mount the coils to the block, checked connections from coils to CDI(?). Also tested spark by idling and pulling one spark lead at a time. The top cylinder has spark , I could see it and feel it when I started to pull the lead off. 2 and 3, when I pulled the leads, there was no evidence of spark, no change in rpm or sound of the engine. I can pull the boat and take it back to the dealer, but that represents a very long drive with a very wide trailer over a very narrow mountain road, so I would like to avoid it if I can. Is there anything else I can try? Fuel system is clean, new motor more or less. I did mix the fuel in the tank at 50:1 so running 25:1 with the injection. This was the mechanics advice to premix the first tank and run at 25:1 for break in. Could this have caused the issue?

Re: Newly rebuilt Yamaha 70 has issues

According to you it does not have spark but on # one cylinder.
too much or even not enough oil will not stop spark to the plugs.
with the service manual for that motor and proper test equipment you can find out what is wrong with spark, but I would take it back before something happens that you can not prove was not your fault.

by the way pulling the plug wires off without having someplace for the spark to jump to like a spark tester, can and will sometimes do bad things as it jumps someplace internally on the ignition system

Re: Newly rebuilt Yamaha 70 has issues

Take it back to the dealer and let them solve the problem.

If you mess with it, the dealer could point his finger at you. You don't need to accept any blame.

Chances are it's a little simple issue.

Re: Newly rebuilt Yamaha 70 has issues

Thanks for the replies, I have a tow lined up to get it back to the launch. I think it is something simple which is why I wanted to see if I could resolve it myself. The iboats forums have saved me a pile of money and grief in the past on other boats. I found out yesterday that the dealer usually load tests rebuilt engines, but in this case they did not.

Re: Newly rebuilt Yamaha 70 has issues

Each Cyl. has it's own carb. Squirting starting fluid in each carb one at a time while under load may reveal the problem is at the carbs and caused by water and or junk in the fuel and now in the carbs. If so, clean the tank first, remove the water seperating filter, clean out the hoses, fuel pump and dissemble and clean out the enriching gizmo, then remove and clean the carbs. Two spray cans of carb cleaner may do the job.

Re: Newly rebuilt Yamaha 70 has issues

I limped the boat back to the launch and took it back to the dealer. They did find a loose connection under the flywheel. My diagnoses of spark only on 1 cylinder was correct. They fixed it and I relaunched, and the engine runs great. Unfortunately it needs transom shims and a jack plate to achieve the right motor position. Thanks to all that posted suggestions