Good day fellow member’s, I hope someone can give me some advice with a problem I’m having with the new (second hand) outboards motors I recently fitted to my duck. The detail of the boat taken off manufacturer website are as follows: Predator duck Model: 4.9M, Length 5M, Beam 2.060m, Mass 290KG, recommended HP 1x90HP or 2x40HP. When I bought the duck it had a single 85HP Yamaha year ’95 fitted to it, the motor had a hard life but was still running well, it got on a plane fairly quick and the maxed out top speed was 55KMH with a 15 pitch prop. I recently decided to get the boat ready for CAT C so the whole boat was restored and fitted two Yamaha motors 2006 40VEO with 11 3/8 12pitch props which are in pristine condition with only 80 hour on them and a full service history done by a Yamaha dealer ship. I took the boat out on Sunday for the first time with the new motors and they run very quietly and got on a plane much quicker than the old 85 but they do not rev higher than 4000RPM on WOT while the boat was carring two people and 4 x 25L cans of fuel. We played around with the tilt of the motors toe-in and toe-out and all the throttle cable are set right so the carburettor flaps open fully. I started doing some resursh on RPM’s and most of the research seems to point to the props. What I understand is for every pitch I go down I’ll increase the RPM by roughly 200RPM so from a 12 pitch down to the smallest pitch prop I can find which is a 9 Pitch I will only get the revs up by approximately 600RPM which is still far below Yamaha’s recommended RPM range for the outboard which is 5500RPM. Any suggestions on what else can I do to get my outboards RPM up would be greatly appreciated.
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Outboard RPM issue
- Thread starter RocheH
- Start date
The 12"pitch props that you have should be the correct props for that rig and if the boat gets up on the plane quickly, then this suggests all is good. It is possible that your tach is reading incorrectly. if you can see speeds of around 47kph then you will be at about 5500rpm with those props. This is exactly the rpm's you want to be seeing.
If your tach is correct and you are only seeing 4000rpm, then your speed will be about 33-34kph at those rpm's. If this is the case, then there is a problem. But on that rig the 12"props should be correct.
If your tach is correct and you are only seeing 4000rpm, then your speed will be about 33-34kph at those rpm's. If this is the case, then there is a problem. But on that rig the 12"props should be correct.
also thought tachs are not set right.
you will also hear your motors revving above 4000 rpm.
4000 rpm is low ear wise
you will also hear your motors revving above 4000 rpm.
4000 rpm is low ear wise