bear_au46 Posted February 20, 2009 Share Posted February 20, 2009 hi all have a 15 hp yammy on 12 ft tinny problem - when on plane motor will suddenly rev high with loss of speed like its cavitating or like driving manual car and clutch is depressed go back to idle and take off again and it accelerates ok for a short time then it reoccurs any theories or suggestions appreciated Link to comment Share on other sites More sharing options...
Bruce the Postie Posted February 20, 2009 Share Posted February 20, 2009 G'day Mate, Sounds to me like you've done a prop bush. Easy enough to to get fixed, or treat yourself to a new prop. Cheers, Bruce Link to comment Share on other sites More sharing options...
pelican Posted February 20, 2009 Share Posted February 20, 2009 (edited) Above answer will be it as long as it is a smooth "clutch" feeling not a "bunny hop"which could be a gearbox issue. From this point on use at own risk as once they start slipping you can lose drive quickly so unless you are idling about it is on the fix before using list and warm up those oars. To check it you can sometimes smell the rubber burnt smell when boat is out of water down at the prop or if you pull prop off ypou can see the damaged rubber between hub and prop. Some props you can get rebushed if they are in good nick ( they just press a new bush in) , some have replaceable spline an dbush setups you buy over the counter and others are just buggers. Cal the sponser and ask who he would get to rebush it if you are definate it is a good prop and if not get it done as a spare and buy a new one. If you wern't getting full WOT revs or anyother issues now is the time to tweak the prop while the guys have it. Edited February 20, 2009 by pelican Link to comment Share on other sites More sharing options...
jewgaffer Posted February 21, 2009 Share Posted February 21, 2009 hi all have a 15 hp yammy on 12 ft tinny problem - when on plane motor will suddenly rev high with loss of speed like its cavitating or like driving manual car and clutch is depressed go back to idle and take off again and it accelerates ok for a short time then it reoccurs any theories or suggestions appreciated Hi bear au46 I've got a suggestion for what it's worth I suppose.........If it's not the propellor bush slipping as mentioned, it could be a simple problem similiar to what happened to me last year when I first got my current boat which has a 3 stroke Evinrude on it........ There is a travel rest on the Evinrude that has a lever with a down position for when you put the boat in the water and an up position to support the motor while travelling...... The travel rest and it's lever are hard to find and very confusing in that the motor is meant to sit on the edge of the small support plate while travelling and in the flat position, the motor "down" position, while on the water but it's not quite far enough down when the motor is on the edge of it when you are on the water...... Being hard to find and the preference being for travelling with the motor down, the presence of such a lever was almost impossible to judge on the water. What I decided to do to avoid having to muck around with the lever is to have the motor high enough in the tilt down position for travelling, but rather than using the travel rest, support the motor at the leg by using a standard motor support bracket that fits onto the trailer and leave the travel rest permanantly in the down position to allow the motor to be tilted right down and be able to be trimmed properly under load....For some reason they situated the lever in a hard to find position and also not knowing it was "up all the time", it looked as though the motor was trimmed all the down as it's in a position where the motor looks close enough to being all the way down as far as the down trim is concerned, but the motor would still trim all the way up. Cheers jewgaffer Link to comment Share on other sites More sharing options...
bear_au46 Posted March 6, 2009 Author Share Posted March 6, 2009 thx all for the replies much appreciated Link to comment Share on other sites More sharing options...
seabee113.4 Posted April 11, 2009 Share Posted April 11, 2009 has your prop hit anything when you where driving if that happens it can really screw up your gearchase especailly if it is a stainless steel prop because they dont bend when you hit a snag or log so all the pressure goes on your gears Link to comment Share on other sites More sharing options...
whi7eindustries Posted April 11, 2009 Share Posted April 11, 2009 Mate I'd go with Jewgaffer on this one, it sounds like its cavitating, especially if it only does it on the plane. If it was the clutch it would slip out of the hole, thats were the prob meets with the most resistance. Also you might want to check your water pickups on the leg of your motor, if there is anything stuck to or in it can also cause cavitation, sounds weird I know but had it on a mates brand new Honda 15hp Four. Just my two bobs worth, whatever it is I hope you fix it. Cheers, Tobe Link to comment Share on other sites More sharing options...
rmzbeast Posted April 12, 2009 Share Posted April 12, 2009 hi all have a 15 hp yammy on 12 ft tinny problem - when on plane motor will suddenly rev high with loss of speed like its cavitating or like driving manual car and clutch is depressed go back to idle and take off again and it accelerates ok for a short time then it reoccurs any theories or suggestions appreciated Hi Bear I have had this problem and it was a plastic like bush in the prop i have had this fixed and no more troubles...... Link to comment Share on other sites More sharing options...
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