1984 Evinrude 90hp V4 Piston Blow By

[Mudball_3]

My motor had been running really rough at idle and would die if it idled for to long. It would also die when trying to engage the gear. So I took it into a repair shop and just got a call back. There is a lot of blow by on the pistons. He states that this is causing the fuel pump to not draw the fuel that is needed and that is what was causing my problems. Blow by is as follows.

75% on one, 30% on two more and 5% on the other.

Just wondering what my options at this point are.

Thanks.

 

[Bosunsmate]

not quite sure what he means, low compression of the pistons can cause the fuel pump not too work (as piston compression in turn relates to crankcase compression). Loss of crankcase compression reduces fuelpump performance- lower seals, bad bypass gaskets etc,
Bad reeds can cause that too.
If the engine ran ok at high rpm but not idle, id suggest just reeds.
Id ask him to clarify what he means by blow by and ask him what his suggested fix is and then tell him you will consider it and then repost it here.
If it sounds like crap you can then whip in and rescue your motor before he sabotages it

 

[Mudball_3]

I called them back and had him explain it a bit more to me.

They tested the compression. They said that it came up to about 125 psi on each cylinder. They then added 100 psi of air to each cylinder. Then depending on how much psi (out of the initial 100 psi) the cylinder lost is how they test for blow by. Said the cause of this is scorched cylinder walls and it wouldn't be worth rebuilding the engine based on its age.

 

[Bosunsmate]

125psi on each cylinder is a very good result, i dont think you could get that with scorched walls that were so bad the fuelpump wouldnt work.
Id go grab it back by surprise so he has no chance to take parts off of it.
What you can do is have someone sit in the back and prime the fuel bulb by hand to act as a manual fuel pump.
If that fixes it then i reckon you just had a bad fuel pump, if it doesnt fix it then his theory of a bad fuel pump caused by "blow by" is definitely wrong and its just something else like some dirt in the low speed jets

 

[Bosunsmate]

i rebuilt one of these for my mate last year, compression was about 110 after rebuild so 125 is very good, especially all being even

 

[Mudball_3]

I will pick it up. Is it hard to pull the cylinder head to take a look inside? Also which carb rebuild kit would I need for this engine? I am no seeing the 84 model year listed on iBoats website.

 

[Bosunsmate]

I will pick it up. Is it hard to pull the cylinder head to take a look inside? Also which carb rebuild kit would I need for this engine? I am no seeing the 84 model year listed on iBoats website.

Pulling the heads easy, apart from if the bolts are seized. My mates was a salty that had sat for years and they came out fine so long as you loosen then tighten while undoing them to make sure the gunk doesnt jam up the threads. But i wouldnt bother doing that at this stage, no point adding more potential issues.
Not sure what carb rebuild kit, you might need to ring them, i wouldnt order one now, need to get it properly nailed down whats going on.

You could also pull off the pump from the side of the motor and hold your finger over the pressure port that feeds the pumps, then while someone turns the starter/or you short the solenoid you can feel for the air pulses.

 

[racerone]

Pull the 4 small by pass covers to inspect pistons and rings.---Very easy and a MUST do for yourself !----These motors are certainly worth rebuilding if you can find a " small shop " mechanic or do it yourself.

 

[emdsapmgr]

Agree with all the guys, 125 compression is pretty high for that year crossflow. With that compression, you should have a good runner. If you do have any blow-by it could be resolved by running a can of Bombardier Engine Tuner through it. See instructions on the can.

 

[Mudball_3]

Thanks guys. I am going to get the boat home at take a look at the engine myself. I just ordered a manual for the engine and should have it on Thursday. I do think the carb is suspect on the engine though. When i prime the ball it will not get hard only firm. if i pump it to many times gas will start to drip out of the cowling and it wont start. I also plan take off the VRO at some point. Just have to get the engine sorted first.

 

[racerone]

Removing the bypass covers will reveal condition of pistons and rings.---Perhaps you are not familiar with them.---Easy to do and just 6 small screws on each cover.

 

[Mudball_3]

I have never worked on an outboard before. I have build SBC eingines and worked on small einges. Hopefully that will help out some. Where are the bypass covers located?

 

[Bosunsmate]

Thanks guys. I am going to get the boat home at take a look at the engine myself. I just ordered a manual for the engine and should have it on Thursday. I do think the carb is suspect on the engine though. When i prime the ball it will not get hard only firm. if i pump it to many times gas will start to drip out of the cowling and it wont start. I also plan take off the VRO at some point. Just have to get the engine sorted first.

Hard to explain how hard it should get but it should be very firm and no gas should leak out ever, unless you are squeezing almightily. Id have a look to see where thats leaking from, it could well be your problem (ie sucking air in while running). Also a leaking carb valve would make the primer bulb not go firm.

You mention that the problem was at idle, is it running ok at fast speeds (if you can get to that speed)?
Ps dont try and rev it up in neutral as that tests nothing and just threatens its bearings etc

 

[Mudball_3]

She runs like a scalded cat wide open on the lake. It runs just fine in the midrange as well. It's just Idle and transition in to drive when it wants to die. Can't even get it trailered without it dying a few times.

 

[V153]

Sounds to me a lot like blockage in the carb idle circuit?

 

[Bosunsmate]

She runs like a scalded cat wide open on the lake. It runs just fine in the midrange as well. It's just Idle and transition in to drive when it wants to die. Can't even get it trailered without it dying a few times.

Says it all really, an engine having bad "blow by" or whatever causing a bad fuel pump would never be able to summon up enough fuel to meet the heavy fuel demands at wide open throttle when the butterfly plates are wide open. When you are idling its only the small idle circuits that are delivering fuel and even as you advance the throttle most of the increase in rpm is by advancing the timing, so its not until you get to much more open throttle does the use of fuel increase dramatically and as you say she runs super then, which a bad fuel pump never does.
Get her back before that mechanic can even feast his eyes on her again.
Carb or reeds is what i suspect. Both are easy to narrow down

 

[Mudball_3]

I ordered 2 carb rebuild kits and a couple of floats. I am going to rebuild the carbs a soon as those parts show up. After completely tearing down a carb is there any rubber pieces left in it? The reason I ask is when I would clean the aluminum engines of my R/C airplanes I would fill a crock pot with straight antifreeze and put it on medium heat and let the engine blocks soak for a couple of hours. This strips away all of the burnt on oil and varnish and leave a perfectly clean engine block. Only catch is here cant be any rubber or it would get eaten up.

 

[Bosunsmate]

I ordered 2 carb rebuild kits and a couple of floats. I am going to rebuild the carbs a soon as those parts show up. After completely tearing down a carb is there any rubber pieces left in it? The reason I ask is when I would clean the aluminum engines of my R/C airplanes I would fill a crock pot with straight antifreeze and put it on medium heat and let the engine blocks soak for a couple of hours. This strips away all of the burnt on oil and varnish and leave a perfectly clean engine block. Only catch is here cant be any rubber or it would get eaten up.

nothing in the carbs but you wouldnt want any getting near the engine seals. You really want to blow some compressed fluid down all the tiny passages, both on the front, the little one in the middle top and the little ones under the cover on top, its them that block up easy.
Have a look at the reed block while you have them off

 

[Mudball_3]

No Title

Took the carbs off and cleaned them. Will be putting them back together tomorrow. I was spraying seafoam into the spark plug holes to loosen up the rings and the red straw shot off in to the cylinder. I pulled the head to get the straw and look at the walls. The rings are not stuck and there are no visible scratches. There is however brown discoloration on the walls. Does this mean anything?

 

[Bosunsmate]

a bad additive used during break in, bad oil left in cylinder