Issue with Speed

[Matthewt]

1998 skeeter zx185 Yamaha VMAX TRP with low hours did 74 mph on the speedo when I first bought it one month ago. Since then I changed the spark plugs, and changed the lower unit oil and took the props off to see if there was fishing line around the shaft. Now Im only able to get it up to 70mph until it chine walks. My water pressure is at 25 WOT and RPMs are about 5900. Im running stock 25m props. I have been running 91 octane and I just read i should only put 87 in. Any suggestions? Raising or lowering motor? Thanks

[PSM207]

Warmer weather conditions will cause a drop in performance. Speedo readings are not very accurate, that is why most folks depend on a gps.

[kk4iz]

Check your plugs the 91 could have fouled your plugs. We had that happen to me. But sounds if you do need to raise the motor some to stop the chine walking.

[EJP]

With only taking readings off of the speedo, you could actually be going faster. You might just have something in the Pitot tube, or not? Check there first. Second it is a speedo, so who knows, unless you have lavorsi or yammie digital guages they are not even close to accurate, so don't pay them any mind.....

[kk4iz]

As PMS207 said the warmer weather will have a lot to do with lost of speed and HP also.