Penta 9hp speed problem....weird!

[Flyingdragon_uk]

Hi,<br /><br /> I have a strange problem with my engine, recently updgraded from a 5hp to a penta 9hp, and the boat goes slower with the 9hp on! (the boats a 16ft microplus). when setting off it all goes ok but when throttle is increased the revs just build up with no boat speed, it tries to go faster but wont, and its feels like the props not grapping as the engine will rev right out!!, it feels like theres no load on the prop (but there is if u know what i mean!!) checked/changed the prop and its not spinning on the hub, drive shaft has been checking and the engine is working 100%. I have tried adjusting the angle at the transom but its made no difference, any ideas anyone?<br /><br />Also once u throttle up to half power it becomes almost impossible to steer it on the tiller as it gets very stiff untill u throttle down, is this normal??<br /><br /> Thanks,<br /><br /> Graham.

 

[steelespike]

Re: Penta 9hp speed problem....weird!

If the prop hub is OK it is probably prop ventilation. Check the antiventilation plate.<br />It should be about even with the bottom of the boat.If it is higher you will need to lower it till the ventilation stops.

 

[Flyingdragon_uk]

Re: Penta 9hp speed problem....weird!

Hi,<br /><br /> can u please educate me? I've never heard of prop ventilation?? what am i looking for??<br /><br /> Thanks,<br /><br /> Graham.

 

[Spidybot]

Re: Penta 9hp speed problem....weird!

Hello Graham,<br /><br />The plate just above the prop is called the 'anticavitaion' or 'antiventilation' plate. Among others it serves to keep water around the prop when the prop is spinning. This plate is supposed to be at approx. bottom level. If too high the prop will run on an air/water mix and not produce sufficient thrust. If too low it will work but suffer from a big drag.<br /><br />The prop shaft should be parallel to the bottom line, as a starting point for trim.<br /><br />Provided your prop pitch is about right, the motor should run a reasonable amount of rpm at wot.<br /><br />If you want to know more about props look here

 

[Flyingdragon_uk]

Re: Penta 9hp speed problem....weird!

Hi,<br /><br /> I thing its too high as its a std shaft all my other engines have been long shaft, never thought about if it was long enough (DOH!!) will check on boat tonight, many thanks.<br /><br />suppose the stiff steering at high rpm could be caused by the centrifugul force created by the prop spinning way too fast?<br /><br />Graham.

 

[Spidybot]

Re: Penta 9hp speed problem....weird!

Can't say about the steering. I'd solve that later.<br /><br />If your lower unit is 5" short, you've got yourself a windmill

 

[Flyingdragon_uk]

Re: Penta 9hp speed problem....weird!

God i'm so stupid, damn things too short!!!<br /><br />

 

[Spidybot]

Re: Penta 9hp speed problem....weird!

Before cutting the transom to make it fit, consider another motor. The Penta, if running OK, could be worth something to help the price of another. Your Microplus is rated for more than 9hp so you may have a wide choise, depending on your budget.<br /><br />Check www.ebay.co.uk to get an idea.

 

[Flyingdragon_uk]

Re: Penta 9hp speed problem....weird!

Thanks, its already on ebay!!! looking for a long shaft, it'll be a lot easier than hacking the transom to bits!!!<br /><br /> Graham.

 

[jasper2447]

Re: Penta 9hp speed problem....weird!

Originally posted by Flyingdragon_uk:<br /> Hi,<br /><br /> I have a strange problem with my engine, recently updgraded from a 5hp to a penta 9hp, and the boat goes slower with the 9hp on! (the boats a 16ft microplus). when setting off it all goes ok but when throttle is increased the revs just build up with no boat speed, it tries to go faster but wont, and its feels like the props not grapping as the engine will rev right out!!, it feels like theres no load on the prop (but there is if u know what i mean!!) checked/changed the prop and its not spinning on the hub, drive shaft has been checking and the engine is working 100%. I have tried adjusting the angle at the transom but its made no difference, any ideas anyone?<br /><br />Also once u throttle up to half power it becomes almost impossible to steer it on the tiller as it gets very stiff untill u throttle down, is this normal??<br /><br /> Thanks,<br /><br /> Graham.

 

[jasper2447]

Re: Penta 9hp speed problem....weird!

Graham<br />Do you still have the Microplus 16 ??<br /><br />I have just bought a new hull (new to me anyway) and I know nothing about its history exce john@foodhygiene.com pt that it has Microplus plates on the side of the cabin.<br />Can you e-mail me a couple of photos perhaps, as the Shetland Owners Club think mine's a MIcroplus 16 from the late 80's<br />Regards<br />John Barrow