1995 90 HP Mercury Outboard - runs for a while then shuts down

[JamieClay]

Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

So after rebuilding the pump, replacing the gasket for the oil tank - things have changed but not necessarily for the better. The motor won't idle (but it didn't before) but now full throttle feels more like 1/5th throttle. The engine is running smoothly but there is no top end, almost like it's a linkage problem. It fires right up and if I throttle up within that start-up time the motor will remain running.

I haven't had a chance to inspect the linkage since docking, hope to later today or tomorrow.

 

[robv1306]

Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

Hi guys,

Ive just read down the whole thread top to bottom. Not got anything to add to be helpful however I am very interested in this issue. We have a 1986 Merc 90hp engine which has some similar symptoms to yours.

When we bought the engine, the oil filler cap clip was (and still is) broken. We first put a zip tie on it and found the engine to run fine. However, when we came to put some more oil in, we did not replace the zip tie... A few days later, whilst towing me on the wakeboard, the engine came to a spluttering halt. The engine seemed to just wind itself down and then stall, and no matter what we did with the throttle it made no difference. It has had high oil consumption all the time we have had it.

It idles VERY roughly and has gotten MUCH worse since its first uncommanded shutdown.

Strangely, after the first we popped in some more oil, left it a little while and it booted right up, only to do the same a short time later...

The engine now will not idle at all (either in gear or neutral), sounds rough as a dog, but still has good (ish) power.

Sounds similar right? Any more thoughts anyone?

Rob

 

[carholme]

Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

Jamie;

Did you get a manual for the engine? If not, what is your engine s/n?

If you send me a PM with an email address, I will forward you a copy of the manual.

Gerry

 

[JamieClay]

Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

Hi guys,
...The engine now will not idle at all (either in gear or neutral), sounds rough as a dog, but still has good (ish) power.

Sounds similar right? Any more thoughts anyone?

Rob

Sounds exactly like my problem. I have a guy coming Wednesday to look at the motor - I'm confident we'll solve this and once we do I'll post the findings here.

 

[CharlieB]

Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

The majority of idle and poor top end problems are simply dirty carbs needing cleaning and correct adjustment.

With that said, troubleshooting outboards should ALWAYS include a simple spark test and compression test.

The spark test makes sure the ignition system generates sufficient voltage to arc across a 7/16 inch gap in free air. Any less and WOT RPM suffers. Any cyl NOT firing of course is a problem and we proceed from there.

The compression test ensures the mechanical integrity of the motor. Al cyls should read very close to each other, and depending on the quality of the gauge used may read up to 120 psi, a poor gauge may read as low as 90. As long as all cyl are close to the same # and the motor starts and runs, then it is acceptable.

Before taking the carbs apart, gently turn the idle mixture screws IN until very lightly seated while counting the # turn so you can reset them to the same exact position once finished. This is important as it will save you a lot of time getting it to start and idle later.

Order carb kits, use the new gaskets. I like wally world super tech carb cleaner, I found it to be the cheapest yet surprisingly one of the best solvents available. Blow it through every passage followed by compressed air. Wear safety glasses as even the smallest droplet in your eye will BURN!!!!!

Be aware of the oil pump linkage, once disconnected it rotates to wide open, note the correct position as it is very easy to install backwards, leaving the oil wide open and reducing oil as the throttle increases.