merc 350

[dave36]

Hi all, have merc 350, 1961, 4cyl, 40hp. En No. 1447347.<br />Absolute pig to start and run, when running dies quickly under load. <br />1st Question, carbs - have cleaned them out and adjusted according to manual, no gaskets fitted to covers or manifold - should there be?<br />2nd Question, ignition can someone confirm plug and breaker gap please (Thunderbolt ignition)<br />3rd Question, Mixture - manual states 3/8 pint oil to 2 gallons (my math that is 42:1) is that correct<br />4th Question, Until now motor has not run for 20+ years so is there anything else that should be done to make it more reliable? other than breakers and condenser, which have been replaced<br />tia<br />Dave

 

[WillyBWright]

Re: merc 350

Welcome to iboats.<br /><br />1. Gasket between the carbs and intake manifold are a must.<br /><br />2. Breaker .014"? Sparkplug .030".<br /><br />3. 50:1 with modern 2-stroke oil is fine.<br /><br />4. Rebuild the fuel and water pumps, fresh gearlube. New fuel hoses.<br /><br />Good luck with that classic. Smooth and powerful for the size. The twins were junk. The 4s are nice.

 

[Chinewalker]

Re: merc 350

Breaker points on that motor should be set at approx. .006-.008" with a dwell of 48-degrees. It is a magneto ignition - typically referred to as a Kiekhaefer Mag (almost a part for part copy of a the Fairbanks Morse tractor magnetos they used up to about 1955-56).<br /><br />There should be a gasket between the carburetor flange and the intake manifold.<br /><br />Waterpump impeller can be a bear to replace on that motor - work slow and easy when removing the pump housing cap. Lots of heat and penetrating oil if its stubborn.<br /><br />Get the 1965 and Prior Mercury Service Manual, available through Grubb's Marine (www.oldmercs.com). It's invaluable in getting your classic Merc going again. Best $35.00 you'll spend. They also turn up on eBay from time to time for a bit less... I don't think iboats offers any Merc manuals that go back that far...<br /><br />- Scott

 

[dave36]

Re: merc 350

thanks for all the info. plugs replaced, breaker gap checked and gaskets installed easier but still difficult starting.<br />Once warmed up will idle and providing I throttle up a little does not die when her put in gear - but.....<br />not a lot of power, still struggles under load and not enough poke to do more than feel the stern drop a little at full throttle. I feel that there is just not enough grunt - of course when testing in a barrel you can't throttle up very much - any ideas on what to do next? The engine does run fairly smoothly but I still feel that if I'm not carefull she will die - should I perhaps adjust the mixture screws (I have stripped cleaned and reasembled the carbs, noting the number of turns from fully screwed in)). Another thought is the plug leads, looking at them today I got the feeling that they are probably as old as the engine!?! very discoloured sleeves fitted and very faint 1,2,3 and 4 markings

 

[Chinewalker]

Re: merc 350

Hi Dave,<br /> The idle screws are typically no more than 2 full turns from closed, and no less than 3/4 turn from closed. Work slowly with a careful ear to what each one does to the motor. <br /> For the starting - are you referring to a cold start? Does the choke work properly? Does it cause the choke butterflies to close FULLY? I've found that the old Mercs need all the choke they can get to cold start, and that sometimes the linkages don't give full actuation on the butterflies. As a test, next time you attempt a cold start, stuff a rag in each carb throat and see if it helps. A properly set up 4-banger should start with no more than 2-3 seconds on the key, or 2-4 pulls on the rope.<br /> As for the power issue, are you getting spark on all four cylinders under load? If you spray some fuel mix in one carb at a time, does it pick up? (DO NOT use starting fluid!) That could determine if it's a fuel delivery issue or spark issue...<br />- Scott