1978 evinrude 55 sputtering at high speeds

[aejeffor]

i know the first thing most of you are thinking is a carb problem. but, i just bought a set of like new carbs and had them rebuilt and tuned to OMC specs. my idle is great and my mid speed is okay, but once i raise the throttle to max power, i get jolts of no power...almost like the whole engine is cutting out and then comes back on ( 1/4 sec spurts) new gas new oil, my gas tank is vented, and my fuel filter is clean.<br /><br />i have ordered a new fuel pump hoping that this will fix the problem, but beyond this what can i do. My plugs are only a season old, so i dont think that would be the problem. BTW does anyone know the proper gap for my spark plugs on this motor>? would that be causeing the problem?<br /><br />Sorry for my ignorance, but i learn with trial and error...just like a monkey.

 

[DJ]

Re: 1978 evinrude 55 sputtering at high speeds

Get a timing light and install it on one of the plug wires, then the other. You may see an intermittant spark on one or both. If that happens, I would suspect ignition coil(s).

 

[sgcheek]

Re: 1978 evinrude 55 sputtering at high speeds

I helped a friend with a similar problem. found a bad power pack. Runs great now.

 

[aejeffor]

Re: 1978 evinrude 55 sputtering at high speeds

so this all sounds electrical to you guys and not a fuel issue>?

 

[DJ]

Re: 1978 evinrude 55 sputtering at high speeds

aejeffor,<br /><br />We're not sure what is the problem.<br /><br />However, I'm thinking of cheap ways to diagnose it, without throwing part$$$ at it.

 

[dperkins4]

Re: 1978 evinrude 55 sputtering at high speeds

What if the drive / prop is slipping for some reason. Knew of 135 Crysler that would jolt on occasion at high throttle ..... Clutch Dog (I think is what they called it) was rounded a litle and would allow it to slip under load.

 

[ob]

Re: 1978 evinrude 55 sputtering at high speeds

aejeffor,If the fuel pump was suspect,you could try pumping the primer bulb when the engine begins to fall at higher rpm and see if it responds.<br /><br />If you are experiencing a warm engine ignition failure ,you can run engine on the hose and add some artificial heat(hair dryer) to the powerpack or each ignition coil and see if the engine reacts.<br /><br />Before doing the heat test I recommend performing a sparktest on all plug leads and insure that each will jump a 1/2" gap to ground with a crisp blue spark .Do this test at starter cranking speed.Insure that you begin this test with a fully charged battery.

 

[aejeffor]

Re: 1978 evinrude 55 sputtering at high speeds

pardon my ignorance. but the spark gap test you mentioned. do i simply pull the plug out and see if i can get it to arc 1/2 to a peice of metal on the motor?<br /><br />also, the sputtering is not a result of the prop slipping its the actual engine misfiring or not getting fuel, etc. im pretty sure its something in the ignition area.<br /><br />please explain what you mean about the hair drier on the power pack and coil. I can replace both coils and the power pack for under 75 dollars. would this not be worth it to go ahead and do anyway?

 

[ob]

Re: 1978 evinrude 55 sputtering at high speeds

You could test them by having the leads(one at a time) jump straight to the engine block but beware if not properly insulated .You're dealing with near 50,000 volts.You can either buy or rig a spark tester .<br /><br />With the engine cover removed and running on the flush muff,if what you are experiencing is in fact a warm engine ignition failure,the hair dryer will add some significant artificial external heat to the ignition components and may help you narrow down your problem.If for example,by holding the dryer heat on the powerpack after several seconds causes the engine to cut out,you may have found your culprit.Intermittent ignition problems,if that is what your problem is,can be a bugger to troubleshoot.<br /><br />I still recommend performing the spark test and then going from there.

 

[aejeffor]

Re: 1978 evinrude 55 sputtering at high speeds

i dont think its a warm engine thing. i can run it on low speeds all day long and it never cuts out. only high speeds. the fuel pump is what im hoping it is because its so easy to replace. it is the original pump...so maybe theres the culprit. i will however try the spark test and the hair dryer test.<br /><br />again pardon my ignorance, but what is the exact mechanical function of the coil and the power pack.

 

[ob]

Re: 1978 evinrude 55 sputtering at high speeds

The power pack distributes stator voltage to each respective ignition coil (in the firing order).The coil then increases the voltage from around 150 to many thousand ,which allows the voltage to jump a gap and create an igniton source for the combustion of fuel mix under compression.<br /><br />I hope that your problem turns out to be the fuel pump as well.If you run your boat up to the speed that it generally cuts out,you can definately get a response by pumping the primer bulb if the fuel pump won't keep up at that speed .This will prevent changing out parts that are not at fault.It can get very expensive,as there are a number of issues that couold cause your problem.If this test resuts in no engine response,then your problem is not likely to be the fuel pump.<br /><br />Trace each plug lead back to its igniton coil and inspect each coil closely for fractures or cracks in their cases.Any cracking is a sure sign of impending failure.

 

[sandollar1978]

Re: 1978 evinrude 55 sputtering at high speeds

Hello, I wanted to know what prop size do you have on your 1978 55hp Evinrude?? I have the same motor but the year is 1979 but is should be the same. I could get my evinrude up to 5000 rpm and wanted to know if I change the prop I could probly get 5500 rpm. Thanks for the help.

 

[aejeffor]

Re: 1978 evinrude 55 sputtering at high speeds

i ahve no idea. it came with the motor and i havent touched it

 

[aejeffor]

Re: 1978 evinrude 55 sputtering at high speeds

anyone know the proper spark gap on this 55hp evinrduie 1978?<br /><br />i have lost my manual after rewiring the whole thing.