78 merc 115 having problems with WOT

[Jeffs62]

I have a pretty well maintained 78 merc 115 6cyl. I recently replaced the fuel lines all the way from tank to carbs and replaced the cover for the cracked fuel I'm not sure the exact term but fuel diaphragm mounted on the engine next to the carbs. The carbs have been rebuilt and synced the only problem is up to about 35 mph it runs pretty good but if I push it above that it starts pulsing and dying like lack of fuel. I had a crack on the engine side in the gas line that caused some problems with the ball sucking and not wanting to start but since the new lines it fires right up. by ideas what I can look for

 

[Maxz695]

Re: 78 merc 115 having problems with WOT

see if there are any filters that may be clogged or on backwards if theres a screen it may need to be cleaned. also check your airmixture setting on the carb. look for linkage problems etc. who rebuilt the carbs?

 

[Chris1956]

Re: 78 merc 115 having problems with WOT

Jeff, the fuel pump is marginal on that motor. it must be in tip top shape to work properly When she starts dying at high speed pump primer to see if she will run better If it does, rebuild fuel pump and replace pluse lines from fuel pump to thansfer cover on crankcase.