Boat is very slow

[Wayne R]

I have an 1970 boat with a Chrysler 273 V8 in it the motor runs like a champ, however the boat at top speed will only go about 15 miles per hour. My question is how do I get it to go faster and whats the best prop for the Volvo Penta 270 outdrive thats on there?

 

[steelespike]

Re: Boat is very slow

More than likely you are missing at least one cylinder perhaps more.
What size/style boat?present prop size?To select a prop we need a properly running boat,the max rpm and speed and present prop size.This will serve as a base line.
Is throttle opening all the way.Is it properly tuned and timing correct.
How's the compression?

 

[Wayne R]

Re: Boat is very slow

It has great compression and was recently tuned up. The issue is it just wont plane and there is no speed, I currently have 17pitch 3 blade prop. The boat is a 1970 19 foot Seaflite.

 

[Chris Hyde]

Re: Boat is very slow

Sounds like prop slip. Does the prop have a rubber center section?

 

[Wayne R]

Re: Boat is very slow

No it doesn't have a rubber section in it is it supposed to? The stern of the boat feels like it has some what hard vibration when I throttle up and try get the boat plane.

 

[redfury]

Re: Boat is very slow

Check to make sure you are getting spark at all cylinders. I ran an outboard that did the same thing, but only 2 cylinders were actually firing. Fixed the problem and the boat did 35mph.

 

[Wayne R]

Re: Boat is very slow

How do I check to see if all cylinders are getting a spark?

 

[Wayne R]

Re: Boat is very slow

I was told that boat may be going so slow because I may have a bent drive shaft or bad u-joints, could this be true?

 

[steelespike]

Re: Boat is very slow

If it has bad Ujoints it will make noise rattle when you steer.What is the rpm drop when you put it in gear?What is the idle speed.Is the idle smooth?Loosen the wires in the distributor cap then while idling remove one at a time.There will be no change when you pull the dead cylinders wire.doing it at the cap lessens likelyhood of getting zapped.use insulated pliers.You could pull the plugs and note their condition.Look at the engine at idle should be smooth no bob or shake.What is the present max rpm?
What style boat?Cuddy cabin,bow rider,closed bow,center console,etc.?
any unusual gear? Is the prop in good shape?Unless the boat is really heavy that boat/motor/prop combo would probably run over 40 and 5,000+ rpm.

 

[Wayne R]

Re: Boat is very slow

How do I check to see if the throttle is opening all the way and if it not how do I get it to open all the way?

 

[Wayne R]

Re: Boat is very slow

What does a thrust ring do on a volvo penta 270 outdrive.

 

[JoLin]

Re: Boat is very slow

Wayne,

You have some choices:

You can start replacing stuff willy-nilly. You MIGHT solve your problem(s), but it's gonna get expensive.

OR

You can take the boat to a marine mechanic for diagnostics and repair. You'll probably solve your problem(s). Certainly nothing wrong with that but again, it gets expensive.

OR

You can start answering the questions you're being asked, and you might be able to solve your own problems with help from some of the very knowledgable people who hang out here. You're not paying attention to the folks who are trying to help you. Steelespike and redfury asked you some basic questions about the boat and motor. Why not start there?

 

[haskindm]

Re: Boat is very slow

Also check for waterlogged foam causing the boat to be very heavy and sluggish.