1993 90hp johnson sometimes doesn't want to take throttle

[rustybeater]

I have a 1993 90hp Johnson V4. About two weeks ago I just put in the water idled fine away from the ramp, but when I went to give it throttle she started to get on a plane and then died after this she would not take any throttle at all without dying. The motor was even wanting to die out trying to idle back to the ramp I did find out that when she started to die out if i pumped the primer it would stay running. Once I got it back home, I went ahead and rebuilt the carbs (I have been meaning to do this for some time now anyway) and I replaced my fuel filter. I took it back on the water and i noticed that the boat was slower to get on a plane and later on in the day the motor started not wanting to take any throttle again. I was able to pump the primer a couple of times while it was wanting to die at idle then it started to idle fine and i was able to get back on a plane but it was still slower than before. I used to have a top speed of 38 mph and this time I could only get to 35 mph. I went back home and borrowed a compression test set this is my fist time doing this and I did it the next morning when the motor was cold ( I later read on this site that it says to warm it up first I am not sure if it makes a difference) Top Left = 92, Bottom Left=93, Top Right=98, Bottom Right=74. Obviously, I am concerned with the number I am getting from the Bottom Right cylinder. I am not sure if the fuel problem is related to the compression. I am newer to boats and I am trying to figure out what direction I should go with this.

 

[emdsapmgr]

Re: 1993 90hp johnson sometimes doesn't want to take throttle

If you are able to run the engine somewhat normally by constantly priming the fuel hose bulb, you have a fuel delivery issue. That could be a bad hose, bad hose bulb, defective anti-siphon valve, and yes-even a bad fuel pump. The compression is of concern. I'd quit running it till you can evaluate the problem. The compression is considered within "normal" tolerance when it is within 10% of the other cyls. The 74 lbs cyl is not. If you are lucky, you just have a blown head gasket. Pull the low compression head off and inspect the head gasket seal ring around the low cyl. Also inspect the top ring of the low cyl to make sure it is still in one piece. Let us know what you find.

 

[rustybeater]

Re: 1993 90hp johnson sometimes doesn't want to take throttle

That is pretty much what I was thinking, that they are two separate problems. I ended up having to work all this weekend (11 hour shifts) so I was not able to mess with it last night I am going to try to make some time to work on it tonight I am probably going to try to figure out the fuel issue before I pull the head off.

 

[rustybeater]

Re: 1993 90hp johnson sometimes doesn't want to take throttle

Ok so I rebuilt the fuel pump on the motor (everything in side looked good though) changed the fuel filter and rebuilt the carbs. I took the boat out on the water to decarb the motor. I used an external tank with some 93 oct fuel and added a bottle of sea foam to the gallon of gas ran it shut it down and waited five min and ran it again the boat was still real slow to get on a plain and does not have the power that it used to have also I could only get up to 35 instead of the 38 I used to get but it would take me a long time to get up to the 35. I also noticed that the rpms were lower as it would be with the speed. Being how I used an external tank i took the whole boat side out of it on the fuel issue and am still having a problem there. When I got back to the house I redid the compression check while the motor was warm and I got better numbers 3 of them were between 110-115 but the one was still lower at about 96. does anyone have any ideas on the fuel issue? and how are those numbers for compression that one may be a little out of the 10% but it is close to it and i dont know if i should open it up with it being off just a little.

 

[emdsapmgr]

Re: 1993 90hp johnson sometimes doesn't want to take throttle

When you were out and noted the lower top speed, did you try pumping the fuel hose bulb? Did it make a difference on top end? Not unusual to get slightly different readings when taking compression. The low cylinder is about 14 lbs lower than the rest, whereas before it was 19 lbs. lower. Hard to say that's a big improvement, even though it seems like it is. Keep in mind that the low cyl is not contributing as much hp as the other 3 cyls. I'd be inclined to pull the head for a visual inspection. Head gaskets are about $24 and it is worth knowing more about that cyl-even if you find nothing.

 

[rustybeater]

Re: 1993 90hp johnson sometimes doesn't want to take throttle

I had already ordered the head gasket I was just waiting for it to come in I was hoping it would be something simple and I was also worried about pulling the head bolts because they are really rusted this boat has always been in the salt water. I went ahead and pulled the head today and the piston is messed up and there is some scoring on the wall but i dont think that it needs to bored over. I am not really sure why this happened though. If it was an oil issue it would be all cylinders. Does anyone on here know? also do you think the head can be reused and what is your opinion about the scoring on the walls?

 

[emdsapmgr]

Re: 1993 90hp johnson sometimes doesn't want to take throttle

You've overheated the top ring. It broke, got blown into the combustion chamber where it was repeatedly crushed between the piston crown and the head face. Overheated rings can be caused by a number of issues, including: coked rings, lack of oil in the fuel, misplaced water diverters, debris in the carb jets, etc. In your case, I do not see the rubber water divererter in the block. Is it actually missing or is it just not visible in this picture? That's diverter is part of the cooling system. (The block must have 4 of them installed properly.) Attached is a pic of how the diverter (deflector) should be located. As good measure, I'd pull the carb apart that fed that cyl and inspect the high speed jet that feeds that cyl, to make sure it is not restricted with a pc of debris.

 

[rustybeater]

Re: 1993 90hp johnson sometimes doesn't want to take throttle

Emdsapmgr I just got a chance to get on here, I do not remember seeing that and looking at the picture it does not look like it is there. I am new to this what does the diverter do? I will have to get here on the parts break down and look it up. I am at work right now but when I get out I am going to look at it again and I will let you know for sure. thanks for your help

 

[rustybeater]

Re: 1993 90hp johnson sometimes doesn't want to take throttle

There is none of the diverters on either head do they just get placed in there or is there suppose to be a nipple or something that they slide on?