1988 Evinrude 48 HP Spl revving and surging at full throttle.

[buddha300]

OK so I just bought a 15' Lund with a 1988 Evinrude 48HP SPL, the guy I bought it from said he had it serviced and looked over. When I put it on the lake it ran good for about 20 minutes then it started to lug down and then rev up, it was like a surging. When I dropped it down to idle or just above idle it runs fine. But when I put it into full throttle it begins the revving thing again. I have replaced the fuel, plugs and fuel pump. All of which I was told could be the issue. I have also heard that the points need adjusted and the timing. This is my first boat and would appreciate some help.

 

[juno pierrat]

48 spl's don't have points, its an electronic ignition with mechanical spark advance, i'd think since it ran well for awhile the mechanical part is good, we need more info, do a compression test and report numbers, an open air spark test should jump 7/16 gap,

also if you've got access to a timing light see if the light stays steady when problem happens

 

[gmanzee]

I have the same motor on my pontoon. Getting the same surging issue. Just took it out for the season. My plan is to clean the carbs and replace the fuel pump. I'll check compression and spark as recommended above. Then I'll cross my fingers when I put it back in in the spring. Any other thoughts. Thanks all