new yamaha 70 hp 4 stroke problem

[BamBam268]

The motor at full throttle will run 4000 rpms and 9 mph. The motor does not do this all the time. I took it back to the dealer and they advised all computer readings were normal. They also did the 20 hour service and changed the fuel filter. The dealer has changed the prop and lowered the motor and the problem is still there. Please can anyone give me any advice? <?>>>{

 

[99yam40]

Re: new yamaha 70 hp 4 stroke problem

Take it back to them and have them test drive it.

What does it do when it is not having the problem? RPM and speed a WOT
Did you buy this from them and they set it up on the boat?

What boat are you running this 70 on?

 

[BamBam268]

Re: new yamaha 70 hp 4 stroke problem

It is on a Carolina Skiff DLV 178. The problem is intermittent otherwise it will run 40 mph with 4 people and gear.

 

[99yam40]

Re: new yamaha 70 hp 4 stroke problem

40 at what RPM?
Is that now or before the new prop and position?
Why did they change the prop and lower motor?
Did they screw up when they mounted and set it up the 1st time?

You have not given much info for someone to give you some help

 

[BamBam268]

Re: new yamaha 70 hp 4 stroke problem

I dont know why they changed the prop or lowered the motor. They told me that is the set up they always used on that boat. If was thought the boat was cavatating. The boat runs very well when it is not having the problem. They hooked it to the computer and sent the readings and a description of the problem to yamaha. The boat ran great both befor they changed prop and lowered the motor and after. The rpms at 40mph is 6000 rpms. Sorry i'm not a mechanic and that is all I know.

 

[99yam40]

Re: new yamaha 70 hp 4 stroke problem

Not much recommendations can be given as you do not give enough info.
Need to find out if you are loosing spark or if it is fuel related when problem is happening.
If you cannot do that yourself then you will have to depend on the Yamaha shop to test run the motor on the water or with the Yamaha test prop in a tank.