Loss of speed

[campion90]

I have a 1992 90hp Mercury on a 16ft Campion (fibreglass) - last year I had a top speed of about 42 mph. For some reason I can only get about 36 mph...the RPMs are at about 5000 - 5200. Not too mechanically inclined.<br /><br />Any suggestions?<br /><br />PS not too mechanically inclined.

 

[LubeDude]

Re: Loss of speed

Well, are these speeds from the boats speedometer, or GPS, Does it feel the same or noticably slower? May just be some trash in the speedometer pick up.<br /><br />Fresh gas or old gas?<br /><br />When did you last change your plugs?<br /><br />Is the RPM the same this year or lower?<br /><br />Have you hit anything with your prop latly?

 

[campion90]

Re: Loss of speed

The speeds are from the boat speedo but I know it is slower this year relative to my friend's boat (I was always able to beat him).<br /><br />Fresh gas, nothing wrong with the prop and the RPM level is about the same (maybe a couple hundred lower but not sure).<br /><br />I bought some new plugs over the weekend and when I get back to the lake in a few days I will replace (plugs are 1.5 yrs old with minimal hours).

 

[LubeDude]

Re: Loss of speed

Is your primer bulb staying hard, you might try pumping it while at WOT just to see if you gain the extra RPM back, if you do see an improvement, you might need a new diaphram in your fuel pump.

 

[campion90]

Re: Loss of speed

Primer bulb stays hard but I haven't checked it while at WOT but will give this a try.<br /><br />Maybe its just me but it also seems to be burning a lot of fuel but can't really confirm from fuel efficiency over last year. Could be my mind playing tricks. (burning about 5 gallons in 30 - 45 minutes at 3500 - 4000 rpms).<br /><br />thanks

 

[Max7]

Re: Loss of speed

may be one of your cylinders is not working you should check for spark may be you have a bad power pack also know as switch box

 

[campion90]

Re: Loss of speed

Silly question but how do you check for spark? <br /><br />I remember reading a detailed way of doing this but I can't find that posting.<br /><br />Like I said...not too mechanically inclined.

 

[campion90]

Re: Loss of speed

I changed my spark plugs with no real difference in perfomance. I couldn't squeeze my primer bulb while WOT (I was with myself) but right after going WOT and stopped the bulb was hard.<br /><br />If I only had two cylinders working would I even be able to get to 36mph and 5200 rpms?