Johnson 70 HP - No power when under load

[RJDAWSON]

Re: Johnson 70 HP - No power when under load

Go back to the top of this forum and look at "Sticky: Top Secret File " for more info on timing, its the best for what your looking for.

 

[chucko]

Re: Johnson 70 HP - No power when under load

I got a 74 looper that set ten years. When checking it out prior to running, found all the electrical stuff except the timing pickup was bad, decayed, cracked or had leaked. Problems like you have are rarely nechanical, but are fuel or electric related. The ignition is the frankenstien result of the trend toward electronic ignition, and is a nightmare considering the early magneto jobs. This is partly due to the interest of designers in "staying ahead" as well as creating a monster that will depend on factory trained service to keep going. Reading the manual, and buying a meter, and testing the items one by one was a great learning experience for me. Ive never messed with such a new motor. been boating since 1960 but this motor was on a vintage boat I recently bought. back to the problem, I sure got a lesson that the electric stuff when new may be reliable, but its very failure prone with AGE. Wireing was cracked, coils were all cracked and arched and blew the power pack on one cylinder. I replaced everything with new parts, which I searched for and got cheap on ebay. Now its doing just fine. The carbs are just fine. they were okay when it was put away, and are ok now. Dont go throwing money at everything, but check things one at a time. Then blow your money! I sure got a lesson. I enjoy the forums, and have learned a lot in the short time Ive been visiting. These forums are the best!

 

[Silvertip]

Re: Johnson 70 HP - No power when under load

There is nothing "hi-tech" about those motors. They need fuel, spark, air, good compression and everything needs to happen at the right time and it will run. People tend to jump to conclusions about timing when an engine doesn't run right when it is more often carburetion. Until you've determined if it is or is not a fuel related condition, keep your fingers off the timing adjustments as you will likely screw it up worse -- especially if you don't have a factory service manual. Timing is part of a process called "Link & Sync" which synchronizes timing advance with throttle opening. It is a long process that must be followed to the letter from start to finish and involves lots of linkages. Do just one part of the process and you mess up the rest. Your a mechanic. Read the plugs. Check spark. Squeeze the primer bulb when the engine is bogging down. If it picks up momentarily you've discovered the issue (fuel pump or carbs). When you clean the carbs make darned sure every passage and jet is squeaky clean. A lean running cylinder on a two stroke will burn down (too little fuel means too little oil which destroys that cylinder). And don't overlook a fuel restriction in the pickup in the fuel tank.
Lastly -- you learned a boat buying lesson that applies to cars as well. "It ran fine when last used" means it runs like crap or it would still be used.