1968 18hp Evinrude stuttering/losing power

[BassAckwards80]

Runs fine at idle. It idles great! Once you give it throttle it stutters/pops and after a little while loses power. It still runs but won't go get 7 mph or so. I can't seem to ever get it to run over 14 mph.

It has new plugs, condensers and points. The fuel pump is relatively new and the carb was rebuilt last year. The fuel hose and primer bulb are new. The compression is 112 on both cylinders. All wiring is good. I've rebuilt this motor and restored it so I'm befuddled as to this problem.

I paid to have a mechanic look at it and said everything is great and should run fine. They even put it in a tank and ran it, they adjusted the fuel air and called it fine.

But, I get on the open water and it does what I said.

 

[BatDaddy1887]

....sounds much like a timing issue.....

http://forums.iboats.com/forum/engi...ds/364885-1968-18-hp-evinrude-ignition-timing

http://forums.iboats.com/forum/engi...-1968-evinrude-18-hp-throttle-timing-question

http://www.marineengine.com/boat-forum/showthread.php?294277-1968-18-HP-Evinrude-ignition-timing

 

[racerone]

Follow these steps.---Hook up a timing light to top cylinder and does it fire between the 2 vertical marks on the magneto plate , yes or no ?---Repeat that with the bottom cylinder.--Now hook up the timing light to the top cylinder and run it up to full throttle on the boat , do you get steady spark , yes or no ?-----Repeat with the bottom cylinder.---Did this motor have 2 new coils ?--Did you replace the coils ?---Did you inspect the bottom of the coils for a " burn through " condition.

 

[BassAckwards80]

The answers to all questions are yes. The coils and points are brand new. The timing was checked at the mechanics, and the timing is good.

I've disassembled the carb and its immaculate looking. The fuel filter screen is clean.

The compression on cold is 110 on both. Someone told me that maybe it's losing compression once it's heated up. Is that possible?

 

[racerone]

Well, don't believe " someone " in this case.---Hook up a timing light and wind the motor up on the boat to see if spark is steady up to full throttle.----This should be easy to find where the problem is !!!

 

[BassAckwards80]

I hooked up a timing light and I had a coil going in and out. So I replaced both coils with two new ones. It only did it when it had been ran for awhile, so I kept missing that. So the stuttering and popping is now completely gone. However now there's no power what so ever! With the throttle completely open there's very little power coming out.

So to recap. There's 2 new coils, points, condensers, carb rebuilt, fuel pump replaced, new plugs. I'm getting a very nice blue spark (noticeable difference) timing is firing nicely.

But still only about 6 mph of power coming out.

 

[BassAckwards80]

Now the nice blue spark is gone. Something is causing me to burn through coils.

 

[AlTn]

did you replace the plug wires, terminal ends, and plug boots?...doubtful your coils burned out that quickly....as a test, pull the terminal ends out of the boots, remove the terminal, clip 1/4" or so off the plug wires, reinstall ends and boots...has your spark returned?

 

[BassAckwards80]

i pulled the wire out and cut off a 1/4 inch or so and the wiring itself is a little black and put some ash in my hands. It wasn't a whole lot of ash, but the wire itself is pretty brittle.

I'll try replacing all this.

ty

 

[F_R]

I think you are on the right track now. I'll bet one of those wires is pin-holed through where it is clamped to the plate. Just an experienced guess though;

 

[BassAckwards80]

All new plug wires and boots and it still has the loss of power. It's not a wiring issue, as all wires have been replaced throughout the whole motor. It's not timing....

What else do you guys got?

 

[AlTn]

at wot...what is the position of the carb roller on the timing cam and what is the position of the throttle plate in the carb throat?

 

[BassAckwards80]

Well I can't tell you know as I removed the carb. But normally the roller is centered between to marks on the throttle cam and the throttle plate (Choke Valve?) is completely horizontal. I've had several knowledgeable people look at that and say that it's aligned and set right (that was before I pulled the carb off)

I pulled the high speed nozzle out of the carb thinking maybe it was clogged. But the hole going through it is pretty large and doesn't look like anything is clogged. Not really sure what to look for in that anyway. I'm not knowledgeable when it comes to carbs

 

[racerone]

What about the high speed jet / orifice plug.---It is found in the carburetor BOWL.

 

[BassAckwards80]

I toke some solder wire since its a soft material and pushed it through that small orifice. It went through just fine and no debris came out. The seals to everything look great and there isn't a spec of varnish anywhere.

 

[BassAckwards80]

I talked to that mechanic again this past weekend and he said the carb runs lean. He said that normally it shouldn't be that way but on my motor it is.

 

[BassAckwards80]

I talked to that mechanic again this past weekend and he said the carb runs lean. He said that normally it shouldn't be that way but on my motor it is.