Idle but no power

[randyray41]

Took boat out for second time since I purchased. 1st time out had to pump bulb to get it to run. So I replaced entire fuel line from tank to motor. 1978 70 hp evinrude. I also changed props. From 17" to a 19". Same dia. I also changed plugs. Took it out today. Cranked as it should idled well. But when I gave it gas would not come out of hole. I checked plugs and they appeared clean. Honestly the bottom plug looked new. No darkness on it like the top plugs. I checked spark and it would Jump prob 1/2" to block from plug. I checked fuel filter on fuel pump. Was clean. I pumped the bulb and fuel
Came out of hose. Now I did purchase one of those Atwood fuel lines for the evinrude with the quick disconnect on the tank.

After I checked everything took it back to water. It sounds and revs normal
At home.

Back in the water boat fired right up. But still same issue. But I did get it to take off twice. Put it in neutral revved up several times. Back in gear pumped bulb and it took off. But as soon as I idled down started same problem over again. Any ideas on problem?

I didn't have compression gague but 2 weeks ago it was 120x3.

Baffles me about fuel line. Really only thing I did that could have effected it. Shouldn't the bulb stay pumped and firm?

 

[flyingscott]

Since you had to pump the ball to get it to run I would check the fuel pump. The ball does not stay hard while it is running because there is no pressure once the fuel pump starts sucking fuel from the tank. When you pump the ball while it is running you are doing the fuel pumps job. Could be a carb issue also may want to look at those. Your motor is rated at 5500 RPMs what kind of boat 19" seems like a lot of prop for that motor but maybe not.

 

[randyray41]

It's a 13' rapid craft. The one in my avatar.

 

[oldboat1]

carbs cleaned? spraying or seafoam won't do it.

 

[flyingscott]

That thing must fly. Definitely look at the fuel pump and the carbs.

 

[randyray41]

No have not cleaned carbs yet. Boats, especially
Outboards are aggravating things.

 

[emdsapmgr]

When you change to a 19" prop from a 17, the engine will have to make 10% more hp in order to make the 19 run like the 17. Don't think the prop swap is going the right direction......Your engine just did not come across an extra 10% more power. Go back to the 17. You have observed another anomaly with your engine, when you said that the bottom plug was like new. What makes the plug different from the others is that there is something wrong with that plug. Also, you've observed that the plug will spark normally. So the conclusion may be that the bottom plug may not be getting any fuel...I'd be looking at the fuel system and specifically the lower carb.

 

[David Young]

15 to 17 pitch would be your best pick on your 70 hp Evinrude. I went with a 17 pitch on my new prop but i think i'll try a 15 pitch next time.

 

[emdsapmgr]

When you drop from a 17 to a 15, the engine will be able to make 10% more hp. That's a big difference.

 

[interalian]

Clean plug but you're getting spark? No fuel? If no fuel, no oil. If no oil...

 

[randyray41]

I can see fuel spraying into all 3 carbs. Looks even to me.

 

[emdsapmgr]

Time to do a cylinder-drop test. While the engine is running, pull the #1 plugwire off and see what happens. The engine should slow down, as it will be only running on 2 cyls. Put the wire back and pull the #2 wire off-see how the engine runs. Then do #3 plugwire. If you pull one plugwire off and the engine does not slow down, then that cyl is not contributing to running the engine. Could be fuel or spark issue. At least you'll know just which is the faulty cylinder.