1990 Mariner 75 Stalls When First Launched

[crappie14]

First off, let me apologize for the length of this post but I have an issue that has existed ever since I bought the motor 6 years ago used and I wanted to fully describe the problem as well as what I have tried to this point.

If the motor sits for any length of time without being run, when I launch the boat and give it fuel it will not take fuel and run like it should. Top speed when it is put in the water is 4 - 6 mph. Bulb appears to be fully pumped and firm and has no effect on performance. If I run the boat a few minutes, let it sit a few more minutes, it usually will start taking fuel and run as it should. On a trip where I rent a marina stall and keep it in the water, once it starts taking fuel the after the initial sit, it runs perfect the rest of the trip. I am having to idle in a no wake zone for 5 minutes to reach open water and the motor is never tilted like it is when loaded on a trailer. This idle time make be fixing whatever is wrong but it will run once I get to open water.

When I go on a day trip and just launch I can expect to spend the first few minutes going 4-6 mph, turn the motor off and wait another 15 minutes, then and only then will the motor run correctly.

I completely rebuilt the carbs (not I said I did and not a real mechanic) giving everything a good cleaning, replacing needle valves but keeping the same floats. The floats appeared to be good and were not water logged.

The carb rebuilt didn't hurt but didn't help either. I replaced the electric solenoid choke thinking it was sticking, again with same results.

The engine still has the factory oiler installed and is still working (or appears to be correctly) based on amount of oil used vs fuel used.

I have not touched the fuel pump but yet the engine starts perfect, idles perfect, and runs perfect once it is started, run, then allowed to sit. At the point it starts running you are good for the day. I have even had it fail on the 2nd morning's launch of a two day trip. Again, start, run, sit and wait and it will run.

The boat has an onboard tank, checked the vent, replace fuel filters, lines, bulbs.

Again, this motor will run perfect once it has been run for a few minutes, given a chance to rest, then will run 40 mph the rest of the day.

I have put up with this for several years now and asked a couple of years ago for help to be told to rebuild the carbs, which I did with no change in performance. Prior to the carb rebuild I could smell fuel like it was flooding, now it simply acts like there is a fuel flow restriction.

My thinking is it has got to be somehow air related in the fuel system and sitting after running allows it to work out.

Any thoughts or suggestions appreciated via a reply or PM.

Thanks in advance.

 

[Lone Duck]

Re: 1990 Mariner 75 Stalls When First Launched

Interesting ! I suspect sitting after running at idle for awhile allows the engine to heat up more because there is no cooling water running through it. (1) correct spark plugs ? (2) On 1st warm up if you bump the choke will it rev up while giving throttle ? (3) After shutting down for 15 min and restarting, does it take right off or bog a bit 1st. (4) If you shut down for a few hrs. Will it start up and go or do you have to shut down again and restart? (5) Start it up cold and try to go, when it stalls check your plugs, are they wet or dry ? I am leaning towards lync and sync. Maybe your butterflies are opening before your advance system engages. Or vice versa. but it will operate when engine and fuel in crank case is hot or at least warm.

 

[sschefer]

Re: 1990 Mariner 75 Stalls When First Launched

It's difficult to nail this problem down exactly but I believe what you are experincing is over oiling.

This is caused when one or both of the crankshaft bearing oil transfer check valves fail. When the motor sits, oil drains back out and puddles in the crankcase. When you first try to start it the incomming fuel mixes with the puddled oil creating and extremely lean fuel but oil rich mixture. During a normal day of starting and stopping it won't have much effect but overnight it will.

These check valves are connected via a 7/64(i.d.) tube that runs from the bottom of the block up to the top and is most often on the port side of the engine just behind the carbs/crankcase cover. The two check valves are different so when ordering make sure you get the right ones. Do not remove the old ones until you get the new ones in hand. If you have trouble removing them PM me and I'll walk your through it.

You can also try to test them with a syringe. They should allow flow in only one direction. You have to be sensitive enough to feel zero flow and unrestricted flow. I've tested and then left them as good only to find out later that they were bad. Just change them, they're cheap.

 

[Lone Duck]

Re: 1990 Mariner 75 Stalls When First Launched

It's difficult to nail this problem down exactly but I believe what you are experincing is over oiling.

This is caused when one or both of the crankshaft bearing oil transfer check valves fail. When the motor sits, oil drains back out and puddles in the crankcase. When you first try to start it the incomming fuel mixes with the puddled oil creating and extremely lean fuel but oil rich mixture. During a normal day of starting and stopping it won't have much effect but overnight it will.

These check valves are connected via a 7/64(i.d.) tube that runs from the bottom of the block up to the top and is most often on the port side of the engine just behind the carbs/crankcase cover. The two check valves are different so when ordering make sure you get the right ones. Do not remove the old ones until you get the new ones in hand. If you have trouble removing them PM me and I'll walk your through it.

You can also try to test them with a syringe. They should allow flow in only one direction. You have to be sensitive enough to feel zero flow and unrestricted flow. I've tested and then left them as good only to find out later that they were bad. Just change them, they're cheap.

Hey! nice call ! I learn something every day. Hope you are right.