'76 650 Merc wont start - spark good

[hankll]

Motor was running the afternoon before I took it to the lake to go fishing. Next morning, at the ramp, it would not start. I assumed I flooded it. At home later, I have spark, on closed rim spark plugs. I am getting gas, but have checked fuel filter and bypassed fuel quick connector at motor, to make sure of no restrictions from those areas. Primer bulb seems to prime up ok. Choke clicks. I checked idle mixture screws and found them nearly shut off, something like 1/2 turn. I adjusted them out to 1 1/2 turns. The problem is before I did this I was originally trying to improve hole shot, which was a sputtering, nearly dying scenario. Slower throttle advance worked better, until I needed full throttle and still had the sputtering, starving routine. So I was attempting to enrich the idle mix by about 1/8 turn. Now I can't get a sneeze out of it, even when I bring the idle mix back close to shut off. I'm concluding the obvious that the float levels are off, or maybe timing is off somehow. But I don't know what I did to cause a timing problem to pop up. Suggestions?

 

[Jeremy78]

Re: '76 650 Merc wont start - spark good

Do the spark plugs look and smell like they are flooded. I would make sure that i was getting fuel to the plugs before i went any further. I had the same thing happen to me almost word for word and it ended up being the gas tank that I was using.

 

[MacDaddy21]

Re: '76 650 Merc wont start - spark good

Hank, I'm sure you did this but I'm just going to ask, was the gas tank vent open?

If it was open and these things still happened, I would rebuild the carbs and the fuel pump. From my experience with my 79 merc 402 40hp, the carb and fuel pump parts just flat out suck. Seeing as the idle mixture screws were in that far, there is no telling what the carbs and fuel pump look like. If you decide to rebuild the parts, I highly suggest a complete disassemble, followed by a nice long soak in a gallon of Chem-Dip. I always recommend this stuff to anyone doing a fuel related rebuild as it is amazing.

I don't think you did anything to cause a timing issue. Before getting knee deep in a complicated issue like timing, try the simple, cheap rebuilds and see if they make a difference. When you rebuild the carbs, make sure you get new floats and a new needle and seat for each carb.

If you prime your motor with the cowlings off, and see fuel dripping from any carb, you need a rebuild. The fuel pump also could use one. Especially if it hasn't been done in awhile. Those diaphragms can give you hell. A new diaphragm and check valves can make a motor run completely different.

 

[Faztbullet]

Re: '76 650 Merc wont start - spark good

Check spark with a spark gap tester , if it will not jump a 3/8 gap the stator is weak. Plugs against block is not a good test...