75 Horse Mariner stalls at low rpm

[starkyb]

I have a 75 horse Mariner that stalls out and dies after I put in gear. When I finally get the rpms up to about 1500 the boat runs perfectly. I could raise the idle speed but I don't want to damage my lower unit when I put in gear. Any suggestions out there?

 

[aussieflash]

Re: 75 Horse Mariner stalls at low rpm

How old is motor?Should set idle to around 750rpm in gear,in water.Usually need a second person(incase you fall in).
Id also check compression and make sure spark is good and your running on all cylinders.Dirty carbs a possibility.

 

[carholme]

Re: 75 Horse Mariner stalls at low rpm

If your engine is the '88 (three cylinder) you talk about in previous posts, the idle should be 650-700rpm as seen in this condensed version of the service manual:

http://web.ebscohost.com/serrc/pdf?...c-848b-06e4587d99f2@sessionmgr14&vid=4&hid=21

Let the page load for several seconds and copy to your computer soonest as the link only lasts for a short time.

Gerry

 

[starkyb]

Re: 75 Horse Mariner stalls at low rpm

It is in fact an 88'. The carbs are less than a year old. When the engine gets below 1000 it shuts off. Is there another adjustment In the linkage or the throttle cable that I can make.

 

[CharlieB]

Re: 75 Horse Mariner stalls at low rpm

I suspect that the idle mixture is too lean, either not adjusted correctly, or more likely the carbs are slightly dirty.

The idle passages are very small and easily affected by dirt/mineral accumulation restricting fuel flow.

Idle mixture must be adjusted richer than 'Best' idle speed to provide the additional fuel necessary for crisp acceleration, when the carbs gets dirty the idle fails to flow, acceleration goes away yet once the motor manages to get to RPM and running on the main jet all seems fine.

Order up carb rebuild kits, replace all gaskets during cleaning.

Pay particular attention to the idle mixture screws, before removing, count the # turns IN until LIGHTLY seated, write it down so that you =can return each one to the original setting, this will save you immense time in adjusting afterwards.

 

[starkyb]

Re: 75 Horse Mariner stalls at low rpm

I cleaned and rebuilt the carbs and cleaned all of the jets less than a year ago. I suspect that the idle screws aren't properly set because I have adjusted them several times without the knowledge of doing it the right way trying to get my idle speed right. What is the RIGHT way to do it so that it doesn't idle too high out of gear or shut off when I put it in gear?

 

[aussieflash]

Re: 75 Horse Mariner stalls at low rpm

Did OB run good after cleaning carbs...no idle problems?or is this first run since cleaning?....Im wondering if you reset float height to spec...just a thought.

 

[starkyb]

Re: 75 Horse Mariner stalls at low rpm

Not really because there was moisture in the gas tank and the problem wasn't the carbs but I cleaned everything while I had them apart. I made other adjustments to the motor but I think that it will run perfectly with the right combination of adjustments. I'm just not sure exactly how to do get it there.

 

[CharlieB]

Re: 75 Horse Mariner stalls at low rpm

Idle mixture must be adjusted with a warm engine IN the water to provide the full back pressure on the exhaust and IN gear for the correct load.

Adjust each carb idle mixture screw to 'Best' idle speed, then further open each about 1/8 turn out.

Test holeshot/acceleration, ANY hesitation, cough, lean miss, indicates a need for even more idle fuel. Open each screw just the screwdriver blade width and repeat holeshot test. Adjust to perfection.

A heavier boat will require slightly more idle fuel than a lighter boat. Same with an increased load like pulling a tube or skier.

Finally adjust idle speed using the idle speed adjustment.

 

[starkyb]

Re: 75 Horse Mariner stalls at low rpm

Thanks for the info but I have a couple of questions. Can the boat b tied to a dock or does it actually have to be moving. Also when I get the in gear idle right what should the neutral idle be.