70hp Evinrude Fuel Problem?

[Bryant Davis]

Hello all...<br /><br />I have a 1977 70hp Evinrude that is driving me crazy. I bought the motor about a week and a half ago. Tested compression (140, 135, 135 cold, 130, 130, 125 when warm) and the engine is spotless as far as overall condition.<br /><br />First thing I did was replace the impeller. Took the boat to the lake and it started right up, idled fine but when I tried to take off it bogged and wouldn't accelerate. You could play around and once it got on plane / moving it ran perfectly. My first thought was carbs. I tore down all three carbs, cleaned and put in kits. Went to lake, same problem. Tore down carbs again this time soaking all parts in cleaner for about 15 hours (vs. about 30 minutes 1st time). Also set float levels this time, as I overlooked that in the book first time around. I replaced spark plugs (gapped .40) made sure of fresh fuel, clean fuel pump screen, etc. Went back to the lake, same prob. I did notice this time that while idling, if I put it in gear and immediately run the throttle up, it acts somewhat fine. If I go just into gear, let it idle in gear then try to run it up, it dies. (Also just as a note, it doesn't cough and sputter just acts like it slowly runs out of fuel)<br /><br />I'm about out of ideas. When the boat is idling in neutral, should the timing be exactly TDC on the flywheel? Also when you first put it in gear (idle speed) should the timing remain TDC and then start to advance when throttle is applied? I have tried sync & link, but not sure if I did it correctly. I am almost positive carbs are clean..all orifices and jets clear, etc. The one thing I have not checked is the fuel pump..could the pump cause these symptoms that seem to be just at slow speeds?<br /><br />Any help is GREATLY appreciated.<br /><br />Frustrated for now...<br />Bryant

 

[rickdb1boat]

Re: 70hp Evinrude Fuel Problem?

I would look at the lync and sync again. This simply means that all the throttle plates are all opening at the same time and the same amount in relation to the cam on the throttle. Disconnect the remote cable and operate the throttle by hand and peer into the carbs to make sure they are all open the same amount. Same when you let off, they should all close the same amount. You can also check of the linkage roller to throttle cam and insure the center of roller is aligned on center with scribe mark on fiber cam and just touching when throttle is in nuetral position at idle setting.You can also experiment with fuel mixture settings. Too lean of a mixture will cause the same problem. Back out the adjustment screws evenly 1/8 of a turn and try it again. 2 turns out from a lightly seated position is a good starting point. If you feel like it's the fuel pump, have someone squeeze the primer bulb while you attempt to accelerate and see if this helps. Most of all, find yourself a Manual for reference. When you have the throttle cable disconnected, it would be a good time to visually check to see if the timer base is advancing as you give it more throttle.

 

[jim dozier]

Re: 70hp Evinrude Fuel Problem?

Sometimes a leaking fuel pump diaphragm can inject fuel into the intake port of the associated cylinder. This causes that cylinder to run rich particularly at idle and off idle speeds. If you can get it revved up it may run better at higher rpms where the engine demand overcomes the leak. Orrr... a leaking fuel pump may just not pump enough and the engine will lean out at higher speeds it depends on where the leak is. Might be worth a check since you've covered the carbs.

 

[Bryant Davis]

Re: 70hp Evinrude Fuel Problem?

Thanks for the suggestions so far...the carbs don't have any adjustments so that is out.<br /><br />I will take another look at the carb plates. I assumed the sync and link was to do with the timing advancing at a certain time in relation to applying the throttle.<br /><br />Bryant