1984 35HP ROUGH START AND IDLE

[me2longnwide]

Hi guys, new to the site and the boating world. Hoping I can get some help here. Recently purchased a pontoon that came with a 1984 35HP MERCURY motor. They told me they had it regularly serviced, and carb rebuilt last year. Took it out to the lake last week and had one hell of a time starting it. After taking it in and out of the water several times, i found a pair of older used spark plugs and replaced the non-fouler plugs that were in it (they were getting spark). I have since bought new plugs for it, but, it seems to idle really rough (wants to die), and will only start with the throttle pushed about half way. Seems to run decent at speed. Could it be something as simple as just got a bad plug? Apparently these are very good running motors Ive been told by local boat shop.

 

[me2longnwide]

Also having a very hard time finding any technicals on this motor. Guessing due to it being so old, Not sure what the spark gap is supposed to be

 

[afsvanderveen]

Even the manual does not seem very helpful in terms of plug gap. I just looked. It only says "set" Try the gapless plugs then you at least know thats not the problem. This is just my two cents as Im still learning myself. A hard start could be fuel delivery related also in the carbs. Once shes pulling fuel through the high speed jets it clears.... just a thought.

 

[Dekker500]

Post the serial number of the engine. Someone could verify the plugs required for that engine. I'm leaving for a week so I might not be the one who could respond though...

 

[Dekker500]

Actually, it appears the 1984 and later 35hp model is actually the 40hp model of old, but due to changes on how HP is measured (from crankshaft on old, to propeller shaft on new), it was re-designated to 35hp.

Anyway, looks like you need Champion L76V or L77V, or their direct alternatives. These do NOT have a gap, as they are surface gap type.

Could be just the idle adjustment on the carb is off (too lean).