Loss of spark under load

[FAJSAM]

Have a 1967 60 hp Seahorse (VXL-13A) that will start and idle but boggs down under load. Was told by a marine mechanic that it was losing voltage and thus spark at open throttle. He replaced the coil and did most of the normal tests to determine it is an ignition problem, however he could not figure it out (or just did not want to). Any Ideas other than sinking it?

 

[FAJSAM]

Re: Loss of spark under load

bump

 

[Joe Reeves]

Re: Loss of spark under load

If you're saying that the engine has a tendency to die out when you apply throttle, that's usually caused by a fouled/clogged carburetor.<br /><br />You'll need to explain more in detail as to exactly what that engine is doing..... "boggs down under load" doesn't really get the problem across to us.

 

[FAJSAM]

Re: Loss of spark under load

O.K. Joe,I will try to explain, It will not go when advancing the throttle. The mechanic said it was not generating the necessary voltage and spark when under load. It was running fine the day we took it out and then started to hesitate then stalled out. He mentioned something about the rectifier (sp?) and possibly bypassing it.

 

[Joe Reeves]

Re: Loss of spark under load

FAJSAM.... It would be a good idea to find another mechanic to obtain a second opinion. The rectifier is simply a component that converts the AC voltage generated by the alternator to DC voltage so that it can be used to charge the battery. It has nothing to do with the ignition system other than keeping the battery charged. Bypassing the rectifier would eliminate the charging system, causing the battery to discharge.<br /><br />From what I gather, the engine starts and runs okay at a slow rpm, even in gear. However, when you attempt to give the engine throttle, you hit a point where the engine simply wants to die out.<br /><br />If this is the case, either the throttle butterfly is opening too soon, the carburetor is fouled, or the timing is set wrong. The usual cause is a fouled carburetor.<br /><br />I assume you've checked the compression and spark? Should be approximately 100+ psi and even on all cylinders (compression)), and the spark (with plugs out) should jump a 1/4" gap with a strong blue lightning like flame on all cylinders. Keep us informed.

 

[FAJSAM]

Re: Loss of spark under load

Joe, when the guy first looked at the motor, he did a compression check and three of the cylinders were in the high 90's and one was pushing 78 psi. He also checked the spark and was getting interminent spark on two of the wires. I believe he replaced the coil and solved that problem. Have not taken the carbs off to clean. Please advice.

 

[Joe Reeves]

Re: Loss of spark under load

You said in your last post "he did a compression check and three of the cylinders were in the high 90's and one was pushing 78 psi"<br /><br />High 90s to me would mean at least 97 or 98. Taking that into consideration, there is a difference between the lowest and highest reading of approximately 20 psi. That spells out major trouble. I'd suggest you remove the cylinder heads to inspect the gaskets, pistons, cylinder walls, and all sealing surfaces.

 

[FAJSAM]

Re: Loss of spark under load

Thanks Joe for your insight. Anyone want to buy a boat?

 

[Hooty]

Re: Loss of spark under load

Before ya call it quits, try doing a decarb on it. Use the search function here to learn about it. It might loosen the rings up and bring the compression back up. Doesn't cost much and could do wonders. I think I'd do what Mr. Reeves suggested and clean and rebuild the carbs first though.<br /><br />c/6<br /><br />Hooty

 

[Crazy Tony]

Re: Loss of spark under load

I had a 1967 80 hp evinrude.<br />Whit the same problem,when I gave it gaz gradually it took it but WOT didn't work and power was missing.<br />I checked everything.Called a good mechanic and he told me on the phone.VOLTAGE RECTIFIER REGULATOR.The ignition coils a getting 6 volt mixed whit ac current, check spark ,spark good.<br />Not good enough.Rectifier or regulator new are 200$ over and hard or impossible to find.BY PASS is the way.Charge your battery after every ride.<br />Unplug the positive from the coil take a new positive lead from the battery pass it trough a switch on off then go to the coil.The breaker points in the distributor will wear a little faster,And be sure to put the switch off as soon as the motor is off to spare the points.

 

[Crazy Tony]

Re: Loss of spark under load

Got 20 hp more instant.<br />My compression was probably very bad to,cause I paid 500$ for the boat whit trailer.And its a 1967 (give it a break).<br />Doesn't matter cause the quick fix costed me 20$ repair and the drove it the whole summer skiing and boating.Till it eventualy died out.<br />520$.... a whole season of fun whit a marvelous bypass on the ignition.