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90 HP Mariner Problems

J

jafo220

New member
I'm new to the forum so bare with me.

Some background: I obtained this boat from my father two years ago. I fished with him in this boat prior to it's hap hazard storage in the backyard where it slowly whithered until I brought it home. It is a 1985 Glasstream fish and ski boat. It's outfitted with a 1985 90 HP Mercury Mariner outboard engine. This boat ran perfect back in the early 90's when we fished frequently. But as we all know, leaving things idle like that takes a tole on mechanical things.

The engine is an inline 6 cylinder triple carb setup.

I brought the boat home, and went to work. I'm some what mechanicaly inclined so working on this was'nt to hard. I had to replace both power packs, and replaced the stator coil also. Rebuilt the carbs, and replaced the fuel pump and water pump assemblies. Boat ran great accept for an annoying problem at full throttle. It would shoot out of the hole great and trim out fine, but after at full throttle and the engine trimmed out to the max, the engine would begin to bog down forcing me to trim back and slow the throttle to half throttle and then it would seem to be fine until your at full throttle again. I was thinking fuel delivery problem, so I replaced the fuel pump again, then the fuel line connectors, then the fuel line and primer bulb and finaly a new fuel tank. All this to no avail. I was out yesterday and it did it again. It ran fine at half throttle or close to full throttle, but it you push the throttle all the way to the max or stopper, that is when it seems to happen. I cannot give an rpm it starts to occur because my gauge was dead. Leading us to today and fixing the rpm gauge. I got the tach working but when I hooked my water up to the engine and started it up, I noticed the tach gauge now works but I also noticed water comming out from around the number six plug.

So this leads me to wonder if this has been the problem all along or this is something new? Blown head gasket, or worse?

Jon.
 
You are going to have to pull the head and take a look - at the very least you have a bad gasket, so nothing to lose by removing the head...
 
There is no head. It is a jug motor. External water leaks are common on these. If the water is entering the cylinder than the exhaust system is failing. Double check the float heights. Because you can see that the carb holds very little gas so if that or fuel pump is not 100% than that will happen. *** Don't keep dogging it like that. Lean at WOT is a death kneel.***
 
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Yes, should have correctly stated "block cover" which looks like a head but is in fact simply a water jacket cover - unlike later models, this one does appear to be a "head"...
 
Thanks for the input.

As far as the carbs go, I've rebuilt these carbs three times thruout the time the boat has been in the family and the float levels checked out everytime and never had any issues like this. Believe me that senerio of the carbs leaning out crossed my mine hence the parts I've put into the fuel system, basicaly the whole system. I have begain to think it may be one of the coil packs breaking down at high rpm or I may have the timing messed up after installing the stator coil. I've read the manual on the timing system of this engine and it has a low idle timing and high idle timing over 5,000 rpm where it advances the timing 6 degrees until the engine drops back below 5,000 or 6,000 rpm. Realy thinking about the symptom it realy explains the dead spot at high rpm. If the engine drops the advance timing before the rpms drop low enough, then it would explain the loss of power and why it picks back up after throttling back theroreticaly. I was going to check the timing system after I repaired the tach gauge and thats when I found the water leak.

Until I fix the water leak on the back cylinder cover, I'm dead in the water so to speak on the engine performance issue.

I waskind of looking for some things to look for after pulling the cylinder cover and it looks to be an invovled process. I have to figure out how to pull the lower cowling off to get to the lower area on the cylinder cover. The lower cowl looks to be held in place by a few screws.

Also, alittle back ground on my mechanical ability, I've spent several years drag racing street cars (legal racing at the strip) and racing vintage MX for several years. I've rebuilt anything from high performance drag engines to simple air cooled and water cooled MX bike engines. Looking at this motor, it reminds me of a sophisticated dirtbike engine, just more elaborate. I am pretty much self taught on all the above applications, but have also had vocational schooling on basic engine overhaul. I learned alot of my techniques from sites like this and it has served me well in all applications above mentioned. So don't think I only read what I want out of the responses, I take them all in no matter how detailed or veg. If you have any inupt, feel free to reply.

Thanks again, Jon.
 
Well, I took it to a dealer a week ago and they found that the plate was warped and they replaced the gasket and plate cover.


Now they tried to diagnose the engine problem of it falling off at full throttle. They finaly got it to duplicate the problem but now they want to replace the fuel pump and rebuild the carbs at a cool 800 bucks......ouch! Problem is I just replaced the fuel pump myself and when I told him that, he still insisted in replacing it. The fuel pumps on these engines are not that technical and now I'm leaning more towards the carbs being rebuilt. I really don't think it's the pump. I've put two of them in in the last year, so to me that kind of eliminates it from the problem.

I'm kind of at odds on what to do. Re-do the carbs myself or have them do them for 600 bucks.

Jon.
 
Rebuild the carbs yourself. They are not that hard, and all you'll be ouut is the cost of the kits. Like time bandit said, it could be the stator, the switch box, or the pick up.
 
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