Wrong Prop?

[motoking_1990]

So I have a 1988 Mercury Mariner 3cyl. 75hp outboard. I have had this take off problem I cant pin point maybe someone here can help. When I give it throttle it wants to fall on its face and die. Most of the time to take off I have to floor it and then it either a 50/50 chance it will go. It only does it in water and in gear. If I have a hose and muffs hooked up revs up no problem. So im thinking the guy before me put the wrong prop on causing these issues. Its a stainless turbo prop says M13 1/4 x 18 on the back. Can some confirm this would cause my motor to bog down?


Also I have done everything else I can think ofthat it could be including timing and fuel pump rebuild. Only thing I have yet to try is prop which makes sense to me to be the culprit. Any Help is appreciated if you need any other information let me know and I can get it.
Thanks,
Greg

 

[Scott Danforth]

you probably have a fuel system issue. I would start by getting the carbs cleaned and re sync'd.

if your problem was all the time, it may be something else, however with it being a 50/50 shot, it more likely a fuel system issue.

 

[Bondo]

and then it either a 50/50 chance it will go.

Ayuh,.... Welcome Aboard,...... I agree with Scott, if it works right 1/2 the time, it's probably the carbs,....

If it were the prop, it wouldn't work 100% of the time,.....

 

[Frank Acampora]

It is definitely a fuel problem. Remove both carbs and clean them. Disassemble them and replace the inlet needles and seats.
Rebuild the fuel pump. Check the complete fuel system from tank strainer to carbs.

DO NOT run the engine in this condition because you stand a good chance of doing major internal damage.

 

[steelespike]

Classic symptoms of a motor that is a little bit lean.Rev freely on muffs but stumbles in the water.
By the way don't rev too high on the muffs sometimes you may get a runaway when revving on muffs or in neutral.
After you get the carb problem solved ; if you read the stickys at the top of the prop forum and get us as much info as possible
we can help you tell if your prop is right.

 

[motoking_1990]

I cleaned the carbs but I have not replaced the needles and seats. It has three carbs.

I shouldnt say 50/50. I open up the throttle
from a stand still and it tries to die then takes off. If I give it throttle too fast it dies. I tried adjusting the timing with no success. Once I put it in gear it dies most of the time unless the rpms are high enough.

Greg

 

[racerone]

Always start with a compression test.--Running on a hose even when it is in gear , it is still in neutral.--The prop has no work to do !!!

 

[motoking_1990]

I did a compression test last year and it was perfect. I dont remember what psi they were, I just knew they were where they needed to be and I didnt need to worry about it. They were within spec.

 

[Frank Acampora]

Start from scratch! If an engine dies when put in gear it is one of two causes. 1. Idle speed set too low. Idle speed should be around 700-750 RPM in forward gear in the water.

2.Carbs set too lean. If there is a low speed adjustment needle, it usually needs to be set about 1 turn out from lightly seated--CAUTION--this varies from engine to engine. get a manual or ask the dealer service dept. Check that the float level is not set too low and check that the floats are not binding. Be certain the inlet needles are not binding. I have seen where they will stick closed until engine vibration frees them. VERY frustrating to diagnose.

You might have better luck asking this question at the Mercury Forum because this is definitely not a propeller problem

 

[Texasmark]

I cleaned the carbs but I have not replaced the needles and seats. It has three carbs.

I shouldnt say 50/50. I open up the throttle
from a stand still and it tries to die then takes off. If I give it throttle too fast it dies. I tried adjusting the timing with no success. Once I put it in gear it dies most of the time unless the rpms are high enough.

Greg

Get a manual and look up the linkage setup for the carb-spark advance control. Just diddling it won't get it. Spark advance is on the order of 0 BTDC at idle to around 20 at WOT so synchronization with the carb butterfly opening is important. The idle speed screw sets the idle (per the manual 675 +/- 50 rpm, in F gear in the water) by changing the timing, not fuel flow from the carb. Once you get that set, open your low speed jets per the manual and take it out on the water and test it. If that isn't enough, crack all 3 low speed screws simultaneously about a screw driver blade width at a time for up to another 1/4 turn or so. If that doesn't get it look elsewhere.

When you did your carbs did you blow them out good with compressed air especially in the area of the high speed jet located in the bottom of the bowl? and use a carb cleaner like Berryman's Chem Tool? Did you find any crud or black specks of rubber.....from decaying fuel lines? Did you remove the bowl and the top cap and clean out? Wonder why I am mentioning black specks of rubber clogging things up? Other thing is your fuel line from your tank. Is it the Quicksilver/Merc OEM gray silicon hose? If so, is it the original for that engine? If so, you need to inspect it for degredation which manifests itself by tan pieces of crud in the fuel line. These can work their way to your fuel filter and clog it. How'd I know that? When was the last time you changed that? The things I mentioned happened to my 2002 90 triple and your's being an '88 you surely could have hose degrdation helping to make your current problem.

Not discounting what others said about low speed setting is too lean, but it could be more than that as I experienced and mentioned.

Edit: On your thread heading of "Wrong Prop", that engine has a 2:1 gear box and unless you have a big, heavy boat, your current prop numbers look good to me based on my experience with your engine's big brother.

​Mark

 

[motoking_1990]

Get a manual and look up the linkage setup for the carb-spark advance control. Just diddling it won't get it. Spark advance is on the order of 0 BTDC at idle to around 20 at WOT so synchronization with the carb butterfly opening is important. The idle speed screw sets the idle (per the manual 675 +/- 50 rpm, in F gear in the water) by changing the timing, not fuel flow from the carb. Once you get that set, open your low speed jets per the manual and take it out on the water and test it. If that isn't enough, crack all 3 low speed screws simultaneously about a screw driver blade width at a time for up to another 1/4 turn or so. If that doesn't get it look elsewhere.

When you did your carbs did you blow them out good with compressed air especially in the area of the high speed jet located in the bottom of the bowl? and use a carb cleaner like Berryman's Chem Tool? Did you find any crud or black specks of rubber.....from decaying fuel lines? Did you remove the bowl and the top cap and clean out? Wonder why I am mentioning black specks of rubber clogging things up? Other thing is your fuel line from your tank. Is it the Quicksilver/Merc OEM gray silicon hose? If so, is it the original for that engine? If so, you need to inspect it for degredation which manifests itself by tan pieces of crud in the fuel line. These can work their way to your fuel filter and clog it. How'd I know that? When was the last time you changed that? The things I mentioned happened to my 2002 90 triple and your's being an '88 you surely could have hose degrdation helping to make your current problem.

Not discounting what others said about low speed setting is too lean, but it could be more than that as I experienced and mentioned.

Edit: On your thread heading of "Wrong Prop", that engine has a 2:1 gear box and unless you have a big, heavy boat, your current prop numbers look good to me based on my experience with your engine's big brother.

​Mark

I haven't had any time to work on the boat until this past weekend due to moving into our new home. When I bought the motor I didn't notice but it didn't have the timing cover that goes over the flywheel. I ordered one that came yesterday so hopefully I get this thing straightened out. All the lines and filter are/where brand new last year. I will check everything everyone here has mentioned and report back. Also I have a manual and a local boat tech said the prop is good for the size boat. It's a 1860 aluminum welded polar craft.
Thanks again,
Greg

 

[steelespike]

Get us a lightly loaded wot rpm and gps speed.Remind us of the prop size.
If the idle mixture screws are set too lean it may cause a stumble on hard acceleration.
Initial idle mixture setting is 1 1/4 turns out from gentley bottomed
Idle speed should be 700 with the motor warm in gear and free to move.If it requires more speed to stay running when put in gear
another indication it is lean.
Operating at higher idle rpm may cause premature shift dog wear.

 

[motoking_1990]

I think it was timing. I put the timing 2 degrees btdc like the book said. And the 1 1/2 turns out on the low speed screw. It runs perfect on bottom end now. But at wot it doesnt seem to open all the way up. The linkage is pulling it all the way open. Any ideas guys?
Thanks,
Greg

 

[motoking_1990]

Bump

 

[motoking_1990]

Should I start a new thread since its not a prop issue? What is maximum timing and how do I adjust it?
I fixed the low speed issue now when I give it full throttle it seems to cut back and doesnt go as fast as it used to. This is what makes me think its timing.
When I hooked up the timing light the first time it was 12 degrees btdc now its at 2 like its supposed to be.

Greg

 

[Bondo]

Should I start a new thread since its not a prop issue? What is maximum timing and how do I adjust it?
I fixed the low speed issue now when I give it full throttle it seems to cut back and doesnt go as fast as it used to. This is what makes me think its timing.
When I hooked up the timing light the first time it was 12 degrees btdc now its at 2 like its supposed to be.

Greg

Ayuh,.... Sounds like yer still ignorin' the Carbs,.... Rebuild 'em,... All signs say they ain't providin' enough gas,...

No need for a new thread,....

 

[motoking_1990]

Went through carbs Saturday everything is clean floats are good and adjusted perfect. Dont have any cracks either. All jets are clear. None were clogged. Havent taken the boat out yet to see if there is any change which I dont think there will be. They are also synced. Checked compression again and they were all within 5 psi of each other. Fuel filter is new and so are the lines once again.
Only thing im unsure about is when I bought the stator the did away with the red stator or something and they had a replacement one. One was 9 amp and the other was 16 or something could I have put the wrong one in? Not sure which one I bought but I could go out and look if need be.
Im getting wet plugs also. They are not tan.
Greg

 

[motoking_1990]

MARINER - ( 75 H.P. (1988 ))
Serial No: 0B329769 Model No: 7075412ND


174-8778k1 is the stator i put on it.

 

[motoking_1990]

Stator is right. Still have the cut out on top end. Traded bottom end problem for top end problem.

 

[motoking_1990]

Took it out this weekend running way too rich now.Its going to local marine shop i am done with it.