Mercury 900 starting issues

[79camaro]

My mercury 900 died last night and I can't figure out why. She's been running like a champ. I've replaced the entire electrical systems, cleaned carbs, etc.. and it's been running great all season. Last night after a few hours on the lake we docked for at a restaurant for an hour or so then I got back in and she wouldn't start. It feels like it isn't getting spark but I connected a timing light (yes it's an old motor so we carry one on board) and it has spark. I eliminated a fuel issue as I even tried to use some starting fluid and nothing. I went through both batteries trying to get her to start before getting a tow from the cops. Any ideas on where to start finding the problem. I guess it could be timing but the belt is there and I can't imagine how I could just loose timing like that?

 

[pktzygt]

Re: Mercury 900 starting issues

Sounds familiar. When you prime the bulb does it get firm? If this is the case, pull the cover off the carbs and pump the bulb a bunch of times. Does fuel come out of the carb throat?

I have a 850 and it was acting like that. I went through the carbs only to discover that they were very recently rebuilt by the previous owner. Turned out to be a hole in the fuel pump diaphragm. What did you do to eliminate the issue?

 

[Chris1956]

Re: Mercury 900 starting issues

It would be unusual for it to jump timing, but after reading your troubleshooting procedure, it seems a possible candidate. Set the #1 cylinder to top dead center using a screwdriver. Now read the timing pointer or timing marks and see if it shows TDC. It would be real unusual if it didn't. Next remove the distributor pulley cover and see if cast arrow is pointing at dot(s) on flywheel. If not, the motor has jumped time. Inspect the timing belt and replace it. Check the distributor pulley for smooth operation or seized bearing.

You might tell us the year. I am guessing it is early-mid seventies with battery powered distributor CDI ignition.

 

[79camaro]

Re: Mercury 900 starting issues

It's a 78. It was dark when we got back in the boat so I couldn't check much. The timing belt is brand new too. The primer bulb was hard and I assumed the carbs were full. The odd thing is that it didn't even turn over a little with ether which made me assume it wasn't getting spark. I am going to look at it closer today in the light but needed a place to start.