1977 Evinrude 75 hp rough idle and occasional bog on take off

[Wilsonsk1966]

I just picked up a 1977 Evinrude 75 hp motor, it starts pretty good but idles rough, it will idle smooth then occasionally cough and eventually cough and die. I had it out one time so far and after good and warm it didn’t want to take off, it would rev in neutral but just start to rev in gear and then die, I’m not sure if heat is an issue but eventually it started to behave normally. The carbs were recently gone through, I checked the timing pointer position, checked/adjusted throttle pick-up point and pick-up point timing (TDC). It will idle down to 700 smooth until it warms up it seems. I put an inductive tach wire wrapped around number one, when I put my timing light on number one, it gives me intermittent flashing, just misses one here and there but enough are there to check timing. If I clamp on to two or three the strobe is smooth but one is consistently intermittent. This happens regardless of how it is running, smooth or rough. I suspect the PO had this issue because the number one coil looks brand new. I ordered two more new coils and a power pack. Does the coughing and intermittent timing light seem related.

Thoughts?

 

[Wilsonsk1966]

I received my new power pack and one of the coils today, wasn’t expecting them til Monday. I replaced the power pack first, it idled a bit then coughed and died, I replaced the top coil, which looks almost new and it idle for a good 10 minutes or so, I tried my timing light on the new coil and still get hit and miss strobe even when running smooth. It did not cough and die or really seem to miss noticeably. I think I’ve got it but we’ll see, I guess the only other thing could be the stator, but for now I think I’ve got.

thoughts?

 

[racerone]

I am going to be blunt here.----Many good electronic parts are replaced as a guess.----I understand that folks are scared of $100 / hr shops.----Are you prepared to do some real simple trouble shooting ?----Or just try some more parts ?

 

[Wilsonsk1966]

Feel free, I’m open to any suggestions.

I’m not necessarily just throwing parts at it, I’d like to get the electrics replaced with new OEM parts, that being the 3 coils and power pack, then at least during my ownership I know where I started with those, but I’m definitely here looking for help and troubleshooting tips, also looking for specific quirks and things to look for with this particular model.

 

[racerone]

Post your compression test numbers.----And see if spark will jump a gap of 7/16" on a test device.---Report what you find there.

 

[Wilsonsk1966]

120 psi all three, hot.

all three jumped a 7/16” arc, this was with the number 1 coil before I changed it.

i did the compression test hot Monday night, arc test earlier this morning.

 

[Wilsonsk1966]

I did test number one coil with a DMM, it tested good but 95% of the time it ran fine too. It was intermittent missing and seemed to be heat related as well.

 

[Wilsonsk1966]

I took it out on the lake today, it idles better, no coughing, but still bogs on take off, I discovered that a shot of choke along with opening the throttle perks it right up, so I guess I have something in a carb. I don’t see any idle mixture screws, I’ll consult the manual and welcome and troubleshooting tips I can get.

Thanks in advance,

Steve

 

[Wilsonsk1966]

It looks like these have low speed orifice plugs vs. needles, I’ll pull the carbs and give them a look.

 

[Wilsonsk1966]

I pulled the carbs, checked each low speed orifice, 1 and 2 were clean, 3 took 2 or 3 blows to get it clear, not definitive but something. I also shot carb cleaner into the low speed passages an it came out the 3 holes in the top of the bore. I’m going to put new fuel lines on, the barbs on the carbs are super sharp and shave rubber from the i.d. Of the fuel line when you pull them off, the carbs were just done and those fuel lines aren’t new, may have been a chunk of rubber. We’ll see what happens.

 

[oldboat1]

I would buy three CDI coil kits (replace coils and plug wires).

 

[Wilsonsk1966]

Update, I replaced the coils with new OEM and a CDI power pack mostly for peace of mind, the CDI power pack died after a couple of hours, I returned that and went back to the one that was on it. None of that had any impact on the bogging. I linked and sync’d and rechecked a couple of times. I found bulletin number 1429 and checked that, the low speed orifices had been changed to #32 but the calibration holes in the top of the carb had not been drilled. I drilled the calibration holes per the bulletin and ran it, still bogs and needs choke to get past it. I opened up the low speed orifices to .0335 (and bought a set of #32s if I want to go back). It’s pretty good now, fully warmed up it doesn’t bog much at all, cold or partially warmed it needs a little choke still. I’m considering maybe one more drill size bigger on the low speed orifices, there are some later years of these that used #35s. Performance is pretty good but not optimal, WOT with a 13 1/2 x 15 prop on a 1500 lb v hull it’s turning 4900-5100 and going ~28 mph.

Thoughts?