Mercruiser 3.0l not firing?

[RTiffner]

Hello all, first post after reading these forums for years now. Having an issue w 3.0L Mercruiser that will crank but not start. Boat started and ran great several weeks ago, slowly though it has gotten harder and harder to start and began not wanting to idle. At first I was able to crank, start and immediately throw it into gear to get it warmed up, then all would be fine all day. Slowly it began cranking and cranking longer and longer before it would run. Now it wont start. Initially, I rebuilt carb, changed plugs, wires, cap, and rotor. Starter did test bad several weeks ago and I replaced that as well. Engine cranks strong and when throttle only is engaged I hear a good stream of fuel squirt into carb and plugs are wet after trying to start. Disconnect safety at the throttle is in correct position. Not real familiar with troubleshooting ignition systems. Is there a good way to test the firing system? Any help or direction would be great.

 

[Scott Danforth]

welcome aboard.

there have been dozens of design families of the 3.0 from the 60s on.

so WTH are you working on?

post year and serial number to help us help you.

most likely you have two issues, if not three

first issue is a fuel system issue. when was the last time you serviced the carb? most likely you have a plugged idle circuit in your carb. go back to your carb.

second problem is probably fuel itself. have you checked to make sure you have pure fuel and no water in the system?

if you have points, did you service them?

 

[RTiffner]

Hello, Im working on a 2000 3.0 Mercruiser, Engine tag reads M085887 for serial number.

Apparently I was getting fire, it was just never trying to turnover whether with gas or with starter fluid. I actually just went through last night and did a carb rebuild with new needle, made sure float was set to spec. My issue was my ignorance with carbs. The idle speed screw appears to have vibrated out and was not holding any throttle whatsoever. Adjusted that in, fired it up, was idling at 1500 rpm, unscrewed some and now have it at roughly 850-900. I think it could probably idle smoother, maybe when warmed up completely? I'm guessing I need to put it on the water for back pressure on exhaust for optimum adjustment? At what point do i need to adjust/verify the idle mix screw?

Upon first cranking however, it gives a huge whistly puff with white smoke and then will fire up and idle. Any idea what this may be?

As for fuel, I saw a little crud, not much, when I pulled the filter in the f/w seperator, hoping that blowing out the lines and cleaning carb may help with that matter. I have filled it from, according to Glastron fuel tank spec, within 2-3 gal of empty to full recently with ethanol free fuel. No water appeared in the f/w separator when drained into clear glass jar.

Not really sure about points, what they are, where they are etc...

 

[Scott Danforth]

being a 2000 you dont have points

the whisp of fuel vapor and cough when starting would lead me to think timing is off

did you replace the filter? they are not reusable