1978 70 Hp Evinrude reoccuring issue

[randyray41]

Yes

 

[F_R]

No Title

I don't know if you are getting water intrusion or not. But it deserves to be considered because it is such a common problem on those motors. The exhaust cover baffle plate is such a poor design. There is no support along the exhaust ports, thus it warps and leaks, squirting water into the cylinders. The water causes a running problem at first, but if allowed to continue will totally destroy the powerhead. And that, my friend, is why you must consider it.

 

[oldboat1]

Check to see if plugs are washed or grey residue in cylinder, similar to the water/fuel mix you normally find in the leg or leaking out of vents. Normal running temp (not running hot)? and could be prop issue (slipping hub).

 

[fireman57]

If the prop was spun it would rev very high and go nowhere. This is not the case. Next time out bump the "choke" and see if it picks up. If it does then it is a fuel delivery problem and we'll go from there.

 

[oldboat1]

^^agree (hub). Not revving in gear.

 

[jakedaawg]

Why are we chaseing down all these other paths? OP clearly states that when he cleans carbs it runs well for a bit. He is, at least to me, got a contamination problem or a collapsing fuel line some where.

Yes, I agree that these can have water issues. no evidence so far leads to that.

Yes I agree there are many things that can cause this but when he cleans the carbs it runs good for a bit.

Clean the carbs. Figure out where the contamination is coming from and be done with it.

Just my humble opinion.

 

[fireman57]

Pretty much what I said earlier. Thanks for seconding my opinion.

 

[oldboat1]

Except he's running it up to 2K in gear (steady running, sounds like), and has a fresh tank and assembly, and (maybe) clean carbs. ("maybe" because the sequence isn't altogether clear -- not completely sure the carbs are fresh and running on a fresh tank, although seems to say that.) If the carbs are professionally cleaned/rebuilt, and only a fresh tank has been used since the rebuild, I would say fuel contamination or carb issues are pretty well eliminated.

 

[randyray41]

taking it out tomorrow. Thanks for all the hints of info. if it don't run, choke is first thing i will hit to eliminate that issue.
Unfortunately, the guy who fixes my boat is in hospital and not doing well. Had another guy look at it and he said tank was not venting. But I'm thinking a tank that won't vent will suck bulb flat and my bulb get real hard. Honestly I think it gets to hard.
Looks like its going to be me and the great iboats forum members to help solve this problem. Thanks for all the responses. Boat mechanics in my area are very very limited!

 

[jakedaawg]

Check to make sure arriw on bulb points to engine.it should nit be hard while running with throttle

 

[randyray41]

I agree. But arrow is pointing in correct path.

 

[randyray41]

Ok. Took boat out this morning. Took it a few seconds to spool up. But it did run. I replaced vent cap on motor. The brand new tank would not vent! I am taking it out later. Will see the results. Had to choke it to get it going. But once it went. It flew. My new 19" prop is not enough. Was turning almost 6 k full throttle.

 

[fireman57]

Good to hear. Yes, the tank has to vent.

 

[David Young]

Ok. Took boat out this morning. Took it a few seconds to spool up. But it did run. I replaced vent cap on motor. The brand new tank would not vent! I am taking it out later. Will see the results. Had to choke it to get it going. But once it went. It flew. My new 19" prop is not enough. Was turning almost 6 k full throttle.

I think your tach is off or you have a prop hub slipping. I have a 17" pitch prop and might have to go to a 15" pitch for my next prop to get a few hundred more rpm's closer to the 5,500 rpm redline