'81 Evinrude 35 No Power

[MarshMan73]

My friend's 81 Evinrude 35HP is causing problems. It won't plane out now, but idles fine. Starts everytime and idles beautifully until you try to get up on plane. It just makes a loud wah, wah surging noise and stays low rpms. It is using about 5 times the amount of fuel it normally takes to get to his camp. He has checked the float level, primer bulb, fuel hoses and filters, pulled the fuel pump and checked. Has tried adjusting timing settings and nothing works. He does say that if he puts his hand over the front of the carb it picks up and starts running better under load (boat tied to dock in gear). He has pulled the main jet and cleaned and rebuilt the carb, but still has this problem. Is this a carb problem or could it be ignition? We have tried the pull each plug and see if it runs test and it will run on each plug by itself.

 

[petryshyn]

Re: '81 Evinrude 35 No Power

Try running with the filler cap loosened.
Try assisting the fuel system by firming up the primer bulb when acting up. If this helps, it a fuel supply issue.

Could also be a carb issue. Did he use new gaskets when overhauling carb?

 

[MarshMan73]

Re: '81 Evinrude 35 No Power

Yep, he used new gaskets and he has tried pumping the bulb while running and no difference. He even tried cutting a new piece of fuel hose and sticking it straight into a gas can with the hose on the bottom. Has took the carb off and tore it apart many times yesterday at the camp adjusting the float down or up from level where it's supposed to be to no avail.

 

[MarshMan73]

Re: '81 Evinrude 35 No Power

Well now we surely have a carb issue because he broke the tube that goes down to bottom of the bowl. Now have to get new carb for sure. Still can't find out what is the real problem though. Can a powerpack cause this?

 

[petryshyn]

Re: '81 Evinrude 35 No Power

A power pack can cause anything, but its unlikely. Try relocating the plug wires away from any object, bracket, head, block to prevent any leak to ground when under load. This often happens if wires have groves worn in them from rubbing vibration.

 

[tashasdaddy]

Re: '81 Evinrude 35 No Power

Ethanol poisioning. http://forums.iboats.com/showthread.php?t=299680 has he check spark and compression?

 

[MarshMan73]

Re: '81 Evinrude 35 No Power

Just got a call from him. He has 125psi on both cylinders. Motor sounds like it is in good mechanical condition. What else can we test before ordering another carb? Leak down test maybe? How do we do a leak down test?

 

[Ironguts]

Re: '81 Evinrude 35 No Power

I have exectly the same problem with my 81 25 HP. Incidentaly, the 25 and 35 both have the same powerhead. And mine starts and runs perfect at idle. When I pull the choke at WOT it runs great. This seems similar to your situation, when you choke the carb by putting your hand over it, the engine runs better. Because of that I assumed it was the carb. i.e high speed orifice or nozzle blockage. However after hearing that you had already rebuilt the your carb with no change I'm wondering if I'll be faced with the same result. I plan on rebuilding the carb this weekend anyway and I'll post the results. If not that, then I think I'll turn my attention to the fuel pump. According to the OMC service manual, fuel pressure gauge hooked up between carb and pump should read 1 PSI @ 600 RPM. 1.5 @ 2500-3000 and 2.5 @ 4500.

I read somewhere that OMC no longer recommends simply soaking the carb but instead you should clean the passages with a syringe and clear hose using Isopropyl (rubbing) Alcohol. Has anybody heard of this?

 

[kenmyfam]

Re: '81 Evinrude 35 No Power

Clean out entire fuel system. Replace hoses.

 

[Ironguts]

Re: '81 Evinrude 35 No Power

Success!!! I rebuilt the carb and the fuel pump, replaced all the fuel hoses, and even cleaned out the tank. She runs perfect now. Note, don't be an idiot like me and reverse the fuel lines at the fuel pump. Incidentally, you'll still get some fuel into the bowl if you squeeze the bulb hard enough. Not so good for the fuel pump though. She may start but won't run for long. Anyway, once I figured out my goof-up she stated fine. Also, I strongly recommend a complete cleaning of the fuel tank at least once a year or during tune up. I thought my tank was good until I drained it completely. There was a thin layer of water on the bottom. I never saw it cause I always refilled before it got to low. The tank pick-up is close to the bottom as well. Could explain some of the problems I was having. Oh well, now my entire fuel system is cleaned and rebuilt.

 

[MarshMan73]

Re: '81 Evinrude 35 No Power

Well we got a new carb and I'm off to help him sync and lync and set his timing. Does anyone know how to set the WOT timing on this motor without running it? Want to check the timing in the yard this way before we take it out and run it. Thanks again.