1974 Mercury 850 won't start when cold

[edyson]

Hi - I have a Mercury 850 that was recently overhauled; Last summer I sent the block off to a shop to have it "redone" (bearings, rings, etc.) and the rest of the engine I overhauled myself last spring. I rebuilt the carbs, fuel pump, and added a new switchbox, wire set, rectifier and installed new plugs. After all of these things were rebuilt/replaced, the engine would start great, cold or warm (using the warm up lever and choke when cold only). However slowly, over this summer, it became much more difficult to start cold (and seemed to flood VERY easily) to a point where now it won't start hardly at all. When this problem first surfaced, it was a problem only when the engine was cold, but recently it has become a problem when the engine is warm, to a point where now it barely starts at all, warm or cold - and to get it to start at all I've been using starter fluid (which I know I'm not to use if I can avoid it). Also, when the problem first surfaced, once I finally got it running it ran fine all day. Now, when/if it does start, it runs for a bit then dies - almost like it is out of fuel (which it is not). I've checked "juice" at the plugs and seem to have good fire. Nothing has been altered on the carbs or cables or anything else over this time. Fuel has remained consistent (standard 87 octane with 50:1 mixture, except during the break-in period). What could cause a problem like this to, over time, seem to get worse to the point where the engine is too unreliable to even take out in the water?

Any help here would be GREATLY appreciated!!

 

[jake505]

Re: 1974 Mercury 850 won't start when cold

I would check the fuelpumps and see if maybe one of the diaphrams got a little rip in it maybe during the year the rip started as a pin hole and got bigger if thats not it go back over the carbs and checkem' out.

you did use silicone sealer on any of the fuel components did you? If you did that could be the problem because silicone likes to melt when fuel touches it and you could have little pieces of it floating around in your carbs clogging them up.

 

[Chris1956]

Re: 1974 Mercury 850 won't start when cold

Those inlines can be hard to start if the compression is low, but they start readily with ether. I know your motor was overhauled, but you might check it just to rule it out. You will want to see 100PSI+ on all cylinders and more importantly, even (within 15%) across all cylinders.

 

[Fuzzytbay]

Re: 1974 Mercury 850 won't start when cold

I'd check the fuel pump, as said, and the float level in the carbs. I wouldn't though use ether to try and start it. Spray pre mixed directly into the carb throats, if you need to try that.