175 power loss

[trigg29]

have a 1995 175 blackmax on a model 2002 trophy, one day the boat does 50mph and 5300rpm and the next it will only reach 42mph and 4700rpm. changed the prop...no diff!? I thought it must be the carbs so I had a mechanic come for a run on the lake and he says he doubts it's the carbs because the engine purrs like a kitten and has decent power up to 3500rpm. From 3500 rpm you punch it and there is almost no jump in the boat, just a light nudge. Changed the plugs..no diff in top speed but now seeing 4900rpm at WOT. There is no " lean pop" or roughness to the engine and even at WOT it runs smooth..just no go!! Mech thought the exhaust might be restricted so off came the power head...exhaust is clean with no evidence of a rich or lean condition. Compression is 120 across the board. Any ideas where to look next? thanks....trigg29

 

[KCLOST]

Re: 175 power loss

Is your loading of the boat consistant?

 

[trigg29]

Re: 175 power loss

Originally posted by KCLOST:<br /> Is your loading of the boat consistant?

yes the loading of the boat is consistant.The puzzle here is the fact that besides the power loss, the motot runs great..maybe a little louder but no miss or other indicators. Could it be electrical? or internal? I read that if there is excessive crankcase pressure then there could be a power loss but that this is usually accompanied by a lean pop or miss and rough running.Also, at WOT I did notice a small amount of fuel spitting out of the carbs...cause??? thanks for your help.

 

[trigg29]

Re: 175 power loss

If this is an electrical problem...where might I look? If it was in my Z28, I would say that the motor seems to be running out of advance at around 3500rpm. Is this possible in an outboard? Could it be a weak spark from the coils at higher rpm?(is this possible from all the coils at the same time?) And what about carbs? I've been told that the secondaries on a 175 are the size of your finger and they are never the problem..it's always the primaries..but if the secondaries were not functioning as they were designed, say only flowing a fraction of the fuel they should, could the engine lose power and still run smoothly?

 

[AndyL]

Re: 175 power loss

Probably obvious but have you checked the fuel bulb when this condition exists, ie is it firm. Does pumping the fuel bulb change the rpm. If so your problem could be the fuel pump which is readily servicable/replaceable.