Slow Acceleration ?

[charliegiggles]

Hi,
I have a 1973 40HP evinrude on a 16.5ft Starcraft Holiday aluminum boat. I just bought this boat and took it out for a test drive. It seems to idle fine and sound fine "loud" at WOT.

The boat however appears accelerate ver slowly and I'm thinking the prop is finshed. It sounds as if someone is sucking air through a straw when I'm accelerating and the prop does not appear to be engaging properly with the water. I can barely get a fishtail to appear and this only after a minute or so at WOT.

The propeller does appear chipped "not drastically" and I'm wondering if the fact it's chipped could create air pockets and prevent the prop from engaging properly with the water. I checked compression on both cylinders which were about 110 on both and both spark plugs appear to be operating properly from looking at them. IE light carbon build up and proper gap. The boat is rated for an 85HP Max motor. My friend has a similar aluminum boat with a newer 40HP and his flies compared to mine.

Is there something else I may be missing?
Thanks for your help. Much appreciated.

 

[jddenham]

Re: Slow Acceleration ?

First of all, it's a small, old motor for your boat.

The prop is most likely just fine, but might not be the right one for your boat/motor combination.

What RPM are you running at during WOT(and with what load on the boat)? If you don't have a tach, you need to get one to proceed efficiently.

As far as your friends boat goes, your motor is 40HP in strong running condition at the crankshaft. If his is newer it may be 40HP at the prop and is most likely producing 10 - 15% more power.

Good luck.

James

 

[jddenham]

Re: Slow Acceleration ?

One more thought . . . .

Running the motor as it has been run could be building up carbon deposits, further reducing it's performance.

I would search on this forum for de-carb procedures and re-access your performance.

 

[Xcusme]

Re: Slow Acceleration ?

Welcome to iboats!

Try removing the prop and inspect the prop drive pin (shear pin).

 

[charliegiggles]

Re: Slow Acceleration ?

Thanks guys. I checked the sheer pin and it seems fine. I thought that the center of the prop that the driveshaft goes through may be spinning but couldn't turn it at all with a screwdriver. There appears to be wear marks in the center shaft of the prop as if the shaft had spun in it once upon a time.

The prop is the original one and looks like it has been repaired several times over the years. I'll try another prop and the de-carbing tip as mentioned. Thanks again.

 

[mikesea]

Re: Slow Acceleration ?

You can get a good magic marker pen ,one that wont wear off. And mark you prop and the hub with corrosponding marks. Run it and see if the marks still line up. If they dont it slips. As said its a 1973 motor. Different animal then the new ones.That said,the people that you bought it from,did they notice any change at the test run( but would they be honest)the engine runs fine but,isit the right length for the boat? did the previous owner run it WOT ,or elderly just booze cruise it?It almost sounds like it may not be down enough to grab water at WOT.

 

[charliegiggles]

Re: Slow Acceleration ?

That's a great idea. I'll try the magic marker idea as well. The water sits half way up the foot so hopefully it's deep enough in the water. The guy I bought it from was an older gent who had trolling gear on the boat. Don't think he was running it too hard but who know's.

Thx...

 

[mikesea]

Re: Slow Acceleration ?

Ideally,you want the cavitation plate,which is the large plate that runs around the lower unit ,to be even with the bottom of the hull.

 

[mikesea]

Re: Slow Acceleration ?

.double dipped

 

[charliegiggles]

Re: Slow Acceleration ?

Thanks for the tip. I checked with a level and the back of the cavitation plate "furthest away from the boat" is about 1" higher.

One more factor came to mind. The boat was fixed up about 5 years ago and I have a feeling they just laid the new floor over the old which is probably adding a substantial amount of weight to the boat. I'll have to check that out.

That being said I have a 9.9 Johnson on a fiberglass trihaul row boat which is still probably faster than this. The fiberglass boat "having lifted it" weighs a ton......and I doubt this boat is that much heavier as is so still scratching my head as to why a 40HP wouldn't do the job.

The gent I bought it from said the boat did about 25Mph which is what I was expecting not the snails pace I recently experienced. It felt like I was pulling a bunch of tires behind me.....

 

[mikesea]

Re: Slow Acceleration ?

by any chance does it look like the transom has been raised up"any wood across the top that would have the engine lifted .Whats the measurment from the transom top that the eng.sits on and the bottom of the hull?also there should be about the same as where the transom makes contact with the motor and the cavitation plate,Im thinking your eng is 20 inches,which is what the transom hieght should be.Does the bottom of the hull have any objects like transducers,any bottom growth?I'm trying to work with the air pocket description you gave and prop not engaging the water.Do you know anyone that might have a spare prop to try. Sometimes a marina might have one and let you try it for erformance purposes,if it works then you can by it.We often loaned props.How do you have the eng. sitting,assuming it has an adjustable tilt,have you tried it all down,half down,.I had all fiberglass boats with older 1959 40's and we water skiied off them. Why an alum.boat with a 40 would drag is beyond me.Is the throttle opening all the way,INCLUDING the TIMER Base plate under the flywheel.

 

[mikesea]

Re: Slow Acceleration ?

twice today,double dipped,how to delete?or only edite

 

[charliegiggles]

Re: Slow Acceleration ?

The transom does not appear to have been built up at all. I"ll check the mesurements tonight from the top of the transom to bottom of boat as well as top of transom to cavitation plate. 20 inches sounds right but I'll double check. I'm going to get another prop soon and will hopefully have the oportunity to try it out again before the snow flies. I've tried the tilt in different postitions when I took it out and one of settings did help a bit. I verified again last night that the throttle max's out including the Timer base plate which appears to move simultaneously with throttle position. The engine sounded like it was trying real hard however I'm thinking the prop "original" is not getting the power to the water.
Thanks again for your recommendations. This site and the input from individuals is incredibly helpful.

 

[tashasdaddy]

Re: Slow Acceleration ?

if htey put the floor over the old one, the foam could be waterlogged.

 

[charliegiggles]

Re: Slow Acceleration ?

K thanks. Will check that out too.

 

[charliegiggles]

Re: Slow Acceleration ?

Just to follow up in case this happens to anyone else who buys a used boat and is wondering why their boat won't accelerate. Here's my story....

As it turns out the previous owner clipped something and instead of having the prop properly repaired he decided to just shave all the blades equally.

I got a new prop "same size/pitch" and the blades are about 1.5 times larger.

I'm confident the boat will actually accelerate. He either purposely gave me this prop or was simply using the boat to troll. Either way not good....