yamaha 60hp

[boat boy]

Hello all firstly excellent site with heaps of good info and wondering if some one could help me, I have a 4.5m midnight marine aluminium centre console with a 2stroke 60hp yamaha on it with the standard prop. The problem is it reaches max revs at about 3/4 throttle then dies and have to back off and reapply power, do i need to change prop for better prformance or just put up with it. I am happy with speed and power it has heaps:) just thuoght another prop may be better for the outboard any thoughts or help greatly appreciated thankyou.

[Jeremy]

just my thoughts, doesn't sound like a prop issue to me. If it 'dies off', it might be a fuel flow issue. Being starved of fuel at high rpm might cause it to lose power?

Jeremy

[boat boy]

yeah replaced all fuel filters thought the same thing its is as though it is hitting the rev limiter whenit dies ??? im not sure it dies at abot 4800 rpm

[FNQCairns]

Not your rev limiter at 4800, how does it die? lack of fuel will cause all sorts of rough behaviour unless it's a complete lack at the time, have you tried pumping the bulb through the problem RPM?.

How fast are you travelling when this happens? Could the tacho pole setting be incorrect and you are infact hitting the limiter?

cheers fnq

[boat boy]

Not your rev limiter at 4800, how does it die? lack of fuel will cause all sorts of rough behaviour unless it's a complete lack at the time, have you tried pumping the bulb through the problem RPM?.

How fast are you travelling when this happens? Could the tacho pole setting be incorrect and you are infact hitting the limiter?

cheers fnq

it just cuts revs back and you have to back off the throttle and then feed the power on again. i will try pumping the bulb next time i am out, speed is around the 30knts Thankyou

[FNQCairns]

it just cuts revs back and you have to back off the throttle and then feed the power on again. i will try pumping the bulb next time i am out, speed is around the 30knts Thankyou

Ok if 30 knots then a person needs to know the pitch of your prop as it points toward the tacho, I could be wrong on your boat but 30kn at 4800rpm is very good going unless the boat is very light and you are overproped.

On the back of the tacho there is a switch it may be set incorrect but still interested in the pitch.

cheers fnq

[boat boy]

Ok if 30 knots then a person needs to know the pitch of your prop as it points toward the tacho, I could be wrong on your boat but 30kn at 4800rpm is very good going unless the boat is very light and you are overproped.

On the back of the tacho there is a switch it may be set incorrect but still interested in the pitch.

cheers fnq


Yes boat is light and it goese very well on the prop is 13 1/4 x 17-K and on the back of the tacho 1+2 are up and 3 is down thankyou

[FNQCairns]

With the 17p at 4800 and 8% slip you should pull 26.5 knots, would that be the case? At full throttle if not over propped (5500 rpm) you should be seeing 30.5kn.

I do not know at what RPM the limiter cuts in on that engine but if we assume 6.2k you would need to be travelling at 35knots. If I have it right we can discard the limiter properly now and possibly the tacho if you think 26.knots may be closer to the speed you do at 4.8K??.

It could very easily be a fuel supply problem, worth pumping the bulb to see, a bulb can deliver over 150L/h so it's worth a try first.

It might be worth ringing Yamaha to see what pole setting suits your engine as I have forgot.

cheers fnq

[boat boy]

With the 17p at 4800 and 8% slip you should pull 26.5 knots, would that be the case? At full throttle if not over propped (5500 rpm) you should be seeing 30.5kn.

I do not know at what RPM the limiter cuts in on that engine but if we assume 6.2k you would need to be travelling at 35knots. If I have it right we can discard the limiter properly now and possibly the tacho if you think 26.knots may be closer to the speed you do at 4.8K??.

It could very easily be a fuel supply problem, worth pumping the bulb to see, a bulb can deliver over 150L/h so it's worth a try first.

It might be worth ringing Yamaha to see what pole setting suits your engine as I have forgot.

cheers fnq

Ok had to get my facts straight so took the boat for a run on the river 30kn at 5.4 to 5.5k engine dropped in revs back to 4.8 4.9 had to back off throttle and re apply power once up to 5.4 5.5k died off again pumped fuel buld but didnt help could the limiter be set at 5500rpm?

[FNQCairns]

Ok had to get my facts straight so took the boat for a run on the river 30kn at 5.4 to 5.5k engine dropped in revs back to 4.8 4.9 had to back off throttle and re apply power once up to 5.4 5.5k died off again pumped fuel buld but didnt help could the limiter be set at 5500rpm?

Well that's all of the easy stuff out of the way, still it sounds like fuel delivery, your rev limiter should be over 6k, 5.5k is too low for it to be a player.

How does it behave if you keep it at full throttle ...does it hunt/surge or miss as the rpm drops? or is it a fairly smooth engine deceleration until it takes off again? Any warning??

Only other easy one is overheat (popet problem, not thermostat)knocking your revs back but the timing seems too fast.

cheers fnq

[boat boy]

Well that's all of the easy stuff out of the way, still it sounds like fuel delivery, your rev limiter should be over 6k, 5.5k is too low for it to be a player.

How does it behave if you keep it at full throttle ...does it hunt/surge or miss as the rpm drops? or is it a fairly smooth engine deceleration until it takes off again? Any warning??

Only other easy one is overheat (popet problem, not thermostat)knocking your revs back but the timing seems too fast.

cheers fnq

Engine hunts as rpm drops it only has 20 hrs on it so looks like a trip back to the dealer hoping to sort it out and save me the 2.5 hour drive down to the dealer but may have to take it back to him sooner than i thought thankyou FNQCairns for your help.