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Mercruiser 305 Wont plane little power

T

tmullins23

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"Hey Guys... I recently purcha

"Hey Guys... I recently purchased a 81 Sea Ray 19 1/2 foot with a 305 merc. The motor was rebuild, including the carb.

After replacing some floor boards, new carpet and adding some new vinyl. I decided to take her for a spin, and well.. it seemed like all she was doing was spinning her wheels with the nose in the air.

No plane, and very little power to get over 15mph. (if that).

Any ideas?"
 
What pitch prop do you have on

What pitch prop do you have on it?
Is it the original engine size and drive unit with the original gear ratio?
Try a prop with 4 inches less pitch just to see how it does. If no difference there is something else causing a problem. Is the drive trimmed all the way down? Need more info.
 
"The prop that came on the boa

"The prop that came on the boat was a 15 x 15p. (ugh). I tried changing the prop out. Tried a 21p and a 19p.

Under load I could only get around 2000-2500 rpm at wot.

It seems to only do this under load. I checked the fuel filter, no water.

I was taking apart some of the sides vinyl to be recovered. I noticed on the throttle there are two cables coming off, and a wire with a plug / clip. This was not connected to anything. Could this be the problem? Any idea where it goes?"
 
"I'm thinking that would b

"I'm thinking that would be the neutral safety switch wiring, so that you can't start it in gear, Depending on the type of shifter/throttle control, could also be for the Safety Lanyard again if equipped."
 
"Thanks Brian...

I checked

"Thanks Brian...

I checked the carb, plugs, wires, all cylinders are firing,

I only have the issue when under load. (in water). I can't get above 2500 rpms. I tried changing out the prop.

The boat doesnt seem heavy, so I don't think the fiberglass is water-logged, even though I did replace old floor boards.

My only thought, maybe water in the tank. I checked the filter but there was no water."
 
Check to see if the ignition t

Check to see if the ignition timing advances with RPM.

Any idea how "old" the fuel in the tank is?
 
"4 bbl carb. I had a mechanic

"4 bbl carb. I had a mechanic check timing, carb, and all cylinders are firing. His only recommendation was to change the prop. Which I did, and yet I still have the same issue.

The fuel was in the tank when I bought the boat. It is a 40 gal tank. I put 15 gallons of 93 in it when I bought it.

Should I drain the tank? New fuel?

Guy... sorry i'm not sure what you mean by what ignition, points or electronic."
 
"Tom:

Guy's asking what

"Tom:

Guy's asking what is inside the distributor.

Did the mechanic check the timing at idle, at 3000 rpm, or both?

If you don't have any idea how old the fuel is, removed it all and start with a fresh load - may not solve this problem but will help prevent others in the near-term."
 
"Old fuel or having water in t

"Old fuel or having water in the fuel will cause the same symptoms, and with the problems boaters are having with fuel, i would have it all removed, at the very least get a sample into a glass jar, if it doesn't look and smell like fresh wonderful gasoline, well.. you know what you need to do. Especially if you've exhausted the typical issues.

So, we had a aged and knowledgeable mechanic work on a engine, ran it and tuned it on our fuel, then the customer took the boat, plugged in his tanks and complained the engine ran terrible and couldn't get on plain. Again our mech worked on it with our fresh fuel.. cleaned carbs for a second time, again cust took the boat, ran crappy again.. we did this one more time before realizing the customer was using old gas that was almost half filled with water ( 2 small 6 gal tanks for a 115 Mercury outboard)

This was a customer that owned a landscaping company and should've had a clue to check and make sure the tanks had fresh gas. He bought the boat from an old employee of his, he never checked it and we never checked it other than noting the tanks were full, he blamed the shop i "previously" worked for, for not checking the fuel.

It only takes 5 mins to check a customers fuel but do 12 a week, that's an hour lost, but could be 1-2 + lost customers, but isn't it the customers responsibility to make sure they have good fuel in their boat? This was no luxury liner, this was a very not pretty 18'."
 
Low compression; it will allow

Low compression; it will allow the engine to run but not produce sufficient torque.
 
"Tom,
Going back to your orig

"Tom,
Going back to your original post - is the bottom clean? My boat will kick up to 4800rpm but still get only 17mph if the bottom is 'nasty' but 40mph if she's clean.

Trying to help. I just know that some things are really 'simple' but finding the answer is a bitch."
 
"incorrect outdrive gear ratio

"incorrect outdrive gear ratio
compression test
leakdown test
full tune-up
verify correct plug wiring order
1,8,4,3,6,5,7,2
fuel filter/fuel system"
 
"Go back to the prop. It came

"Go back to the prop. It came with a 15" pitch, this was probably about right. If it has a spun hub it will act as you have described. You tried a 21" pitch and got the same results, this is normal, it's like trying to start in your car in 4th gear. You then tried the 19", again too much prop, expected result. You need to try a known good 15" pitch prop and go from there. I would think a 19' deep V with a 235hp engine would be turning a 17" pitch prop. With a good 15" prop you should easily reach the recommended wot so be careful. 3500rpm's should get you in the mid to upper 20's with a 15" prop."
 
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