1978 evinrude 55HP cuts in and out at high speeds only

[aejeffor]

i have an interestting problem that maybe someone can help me with. my 1978 2 cyl 55hp rude will crank, idle, and troll fine, but anything over half throttle will sputter and jerk. <br /><br />So far i have had the carbs rebuilt, rewired every wire in the motor to spec. new fuel lines in and out, and new fuel pump. does anyone have any ideas. is this a power pack going bad maybe? or some other ignition problem? my plugs are only about 6 months old but do have a bit of carbon on them. it looks normal though. <br /><br />Any ideas would be appreciated ejeffords@nc.rr.com

 

[Bass Runner]

Re: 1978 evinrude 55HP cuts in and out at high speeds only

I would start with new plugs, then if that dosn't solve the problem get the power pack tested. I have installed new plugs that were bad. Hope you get it running

 

[CorB]

Re: 1978 evinrude 55HP cuts in and out at high speeds only

I know you mentioned you did rebuild the carbs, but are you really sure they are clean? And did the engine had exactly the same behaviour before rebuilding them, or does it behave different now?<br />I had the same problem with my '78 55 HP Johnson.<br />Since the carbs have separate orifices for low-speed and high speed and since the high speed orifices are on the lowest point of the carbs in the float bowls they are easily contaminated with gummed up fuel.

 

[aejeffor]

Re: 1978 evinrude 55HP cuts in and out at high speeds only

i didnt rebuild them. i bought a set off ebay that are in much better shape than mine were and it seemed to run alot better except it still behaved the same way at high speeds. i guess i can take them off and inspect them. <br /><br />any specific recommendations once theyre off?<br /><br />also if it were a spark plug problem wouldnt the problem be at any speeds?

 

[CorB]

Re: 1978 evinrude 55HP cuts in and out at high speeds only

You should buy 2 carb rebuild kits, since you need to tear them apart to thoroughly clean the inside of them. Maybe there is some FAQ or general practice about carb rebuilding found over here, or some posts of other people?<br />It's justr the idea of cleaning them because some contamination might stuff the orifices or old fuel has gummed up and did the same. You can buy carb cleaner to help you removing the gum/contamination. Take care not to damage the orifices with sharp objects and don't try to completely dissassemble the carb like the throttle butterfly etc.. Compressed air will help also a lot when cleaning.<br />Also a service manual would be very handy. I prefer an original OEM manual.

 

[Walker]

Re: 1978 evinrude 55HP cuts in and out at high speeds only

Clean the coil ground straps real good, and check the coils for any cracks. If its possible, give the motor a test run at night without the cowling on and somebody watching for stray sparking from the coils or sparkplug wires.

 

[aejeffor]

Re: 1978 evinrude 55HP cuts in and out at high speeds only

the carbs i bought were rebuilt by the seller. so thats why i havent taken them apart yet. i didnt want to mess anything up. if you gys think this is the no 1 answer ill clean em as good as i can.<br /><br />takeing them apart and cleaning wont hurt any of the adjustments will it...like needles or float settings?

 

[CorB]

Re: 1978 evinrude 55HP cuts in and out at high speeds only

Don't know for sure that the carbs are the problem.<br />But taking them apart & cleaning won't hurt the adjustments, the orifices are fixed as far as I know.<br />If it ran bad on half throttle & above with the previous carbs you could also remove the float bowls of the previous carbs and check if they are clean or not. If they are perfectly clean and the engine didn't run good with those carbs your problem might be elsewhere. It could also be the synchronization of your ignition & carbs (link & sync) but to be honest I can't tell you which syptoms lead to ignition problems and which to fuel problems.<br /><br />You could try some different things though:<br />While you're running and giving half throttle or more, activate the choke a short moment and see if it picks up. If so it's running too lean and getting too little fuel. Another way is spraying some premixed fuel into the air intake side of the carbs (take air silencer off) while giving some throttle (this could be a bit dangerous while boating so be careful or just try it tied to the dock or something. Just pick a safe way and beware of risks for fire while squirting with fuel).<br /><br />Also take care not to run the engine too long in this condition, if it's running lean on fuel it also does on oil, so you could score your cylinders/pistons.<br /><br />I hope for you someone else could jump in with some more & better help.