Year & accleration

[tlucci]

What year is my 90hp Mariner ser#OD252549 and why does it acclerate on its own at random when running at almos top speed?

 

[carholme]

Re: Year & accleration

Comes up as:

MARINER - ( 90 H.P. (1993 ))
Serial No: 0D252549 Model No: 7090412BD

Parts Listing:

Mercury Parts, 75/90 HP (3 CYLINDER)

Service Manual P/N: 90-136452

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

Are you saying that at WOT throttle the engine still accelerates or are you talking about boat speed? Do you have a tach on your boat and if so, can you say what engine speed this is happening at?

Gerry

 

[tlucci]

Re: Year & accleration

I guess I mean the boat speed. With the stick almost all the way forward the boat will suddenly take
off (and runs like I think it's supposed to) for about 3-4 secs then speed backs down. Tach works sometimes so it's not a good indacator.

 

[Texasmark]

Re: Year & accleration

Not much to go on. I have a later model of the engine. I would say that you are ventilating due to your prop being too near the surface when running at WOT.

My current boat has a steep slope to my transom and I can't trim out until I push the prop out of the water and start doing what you said you are doing. But my last boat could and it was caused by trim too far out.

So, to start with, tuck her in a tad till it stops. Or get a cupped SS wheel that will resist "blow out" better than an alum non-cupped.

HTH,
Mark

 

[tlucci]

Re: Year & accleration

Not much to go on. I have a later model of the engine. I would say that you are ventilating due to your prop being too near the surface when running at WOT.

My current boat has a steep slope to my transom and I can't trim out until I push the prop out of the water and start doing what you said you are doing. But my last boat could and it was caused by trim too far out.

So, to start with, tuck her in a tad till it stops. Or get a cupped SS wheel that will resist "blow out" better than an alum non-cupped.

HTH,
Mark

Not sure it's the trim as I have run it in all positions. Never had this problem before. Same prop. Could it br fuel or carb?

 

[carholme]

Re: Year & accleration

What is the engine doing at full throttle? Does it seem to be surging or does the rpm drop a bit and remain there? How is it at idle and lower rpms.

Do you want the manual or not?

Gerry

 

[tlucci]

Re: Year & accleration

What is the engine doing at full throttle? Does it seem to be surging or does the rpm drop a bit and remain there? How is it at idle and lower rpms.

Do you want the manual or not?

Gerry

Yes on the Manual. Thanks. At full throttle engine runs smooth then once in awhile it surges and gains speed for about 4-5 seconds. Idle is good and lower rpms are good.

 

[tlucci]

Re: Year & accleration

Yes on the Manual. Thanks. At full throttle engine runs smooth then once in awhile it surges and gains speed for about 4-5 seconds. Idle is good and lower rpms are good.

 

[carholme]

Re: Year & accleration

You have to send me an email address by PM.

Gerry

 

[tlucci]

Re: Year & accleration

I'm not eal smart. Whats PM

 

[tlucci]

Re: Year & accleration

I'm not real smart. Whats PM

 

[Texasmark]

Re: Year & accleration

PM is the abbreviation for Private Message. You talk directly to him and bypass all of us. It's where you do things in them that you don't want the world to see. You should be able to double click on his "handle", upper left corner of any thread he is involved in and pull up his profile wherein you will find a PM route.

One question I have now is your rpms. What are they when running normal and when revving? What's the history of your prop? Reason for the prop question is that it could be starting to slip the hub in the prop casting....like slip, catch, slip, catch. Course if it is doing that, if you have a heavy rig to get out of the hole it surely would do it there too.

Mark

 

[quicktach]

Re: Year & accleration

Check the gray wire from the tach and make sure it's fastened at both ends. A regulator acting up can affect the tach too. Your problem could be one of several causes...as readers have noted. Did it just start acting up? You may have to take the prop to a dealer to check it to see if bushing is starting to slip. Could be a fuel problem or a timing/advance related problem too. Speed up, slow down cycle sounds more like a fuel starvation problem ....erratic fuel getting through carbs. Water filter on board ..plugged up or full of water ? Other filters ?

 

[roscoe]

Re: Year & accleration

Engine surge may actually be a bad coil, cutting in and out.

 

[Maxz695]

Re: Year & accleration

Mark the prop and take it out for a spin and when you return check to see the line is matched up past the hub from prop to spline Nut, If they are off then time for a rehub or new prop. Find the max RP of your engine. See if you are hitting the Maximum or recent known top RPM and it loses power but not RPM then the prop may be slipping. If you have the same RPM (TOP) and lose power momentarilly then it comes back it may be a carb or electrical related issue such as a bad plug plug wire trigger coil etc. My guess Yes I said guess is it,s time for new plugs