Mark 30 Help

[Team B&H]

The MK-30 likes a heavy oil ratio. Compared to the other 40 and 44 cubic inch Merc 4 cylinder motors which all use similar crankshafts, connecting rods and needle bearings, the MK-30 uses less fuel and oil per revolution to lubricate the same bearings. To get the equivalent amount of oil that the larger engines ingest, keep ration on the rich side 16 or 20-1 is good. Remember, oil is cheaper than parts- a special engine builder's favorite saying. And its a lot easier to add oil than replace parts. Extra oil will not harm your motor at all. How do I know all this? Experience is a great teacher!

[dwhitford]

I'd be quite hesitant to skimp on the oil! When the carbs are correctly adjusted for best performance, the setting is for the FUEL-AIR MIXTURE, regardless whether any oil is in the fuel mix. Additional oil CAN contribute to plug fouling, but the magnetos on 4-cylinder Mercs provide great spark. And the petroleum oils that we mix with gasoline are not nearly so troublesome as the castor oil in alky fuel blends.

[dwhitford]

I'll add to John's comment about starting that the low-speed needle valves need to be set about a turn richer than for best idling in a fishing motor, or about 2-1/2 turns open from fully closed. Opening these needles the extra turn provides the engine the same sort of advantage that the accelerator pump does on your car carburetor: a richer mixture for starting and for accelerating from less than wide-open throttle.

Be aware, though, that when the needles are opened the additional turn, their springs that normally provide a friction lock lose tension from over extension, so it's possible that the needle valves might vibrate loose and fall out, Stock racers in the 1950s & '60s used to drill a little hole in the head of the low speed needle and run a safety wire through it to anchor the needle valve that way. Much more simply, I just put a little daub of silicone seal over the needle valve to seal it into the carburetor . . . easy enough to remove the silicone ''packing'' for general service & maintenance.

OOPS! I just caught myself out! The silicone works on the KA- and KC-series carbs, not the AJs on your Mark 30. You'll either need to stretch the dickens out of your friction spring or safety-wire the needle valve the old way.

[dwhitford]

I think 16:1 was the initial Merc factory recommendation for the fuel-oil mix for the FISHING engine. Oils are better now than they were in 1956, but it never hurts to add more oil for a high-revving racing engine.. Some fellows go as rich on oil as 8:1. Always remember, oil is cheaper than pistons and other moving parts.

[dwhitford]

Puregas.org is a site that lists the availability of ethanol-free gasoline state-by- state. The site gets updates frequently, and local users are encouraged to send in updates to the site's management on a timely basis.


I doubt whether the cork Merc fuel-pump gaskets are much affected by gasoline with ethanol, but it would not surprise even one little bit to learn that the Ruberoid fuel-pump diaphragm itself is an easy victim.

[DeanFHobart]

Maybe I should give up on the Mark 30 and put the Mark 58 on it.....Freaking thing is heavy with the fishing lower unit on it. I have the down housing but will need a lower unit. I am assembling a cornpopper from a padded 20H block that "Quincy" did back in the 70's. Could do that too.

Your Glen-L TNT is 11’ long so the Mark 58 should be just fine... Set it up so the bottom fo the cavitation plate is even with the bottom of the boat. The higher center of gravity will be different, so just be careful until you get used to it.

Your restorations look very nice.

[Fastjeff]

Nice looking rig. Did you get the starting problem resolved?

Jeff

With the 1:1 gears the prop shaft center should be about 3/4 inch below the bottom. A suitable prop would be about 6 1/2" dia and about 9" pitch. The engine needs to get in the 6,500 RPM range to make good power. Looks good on the water!

[cpizze1]

Update!

So I had time to take it to the lake and try a couple of things. First, the was a small air leak in the tank fitting to the fuel pump I fixed. Second, I put a smaller prop on the motor and last adjusted the high speed (slightly) on the carbs. Pulled the first time and ran great! Not the fastest thing around (heavy boat), but ran pretty good!

Thanks "ALL" for the great advise!

Coady

[cpizze1]

Found my test wheel. Next time I get it in the water it will really be helpful. Someone else mentioned timing as well...so I think I will try adjusting the timing too as the throttle opens.

[cpizze1]

Thanks for the info. I also found my test wheel so that will help next time I have it in the water.

[JohnsOldMercurySite]

these vintage 4cly mercury's are known to stall out when put into gear when the idle mixture is too lean, this being a race motor always in gear and if you had the prop on when starting in water would react the same if too lean, easiest test is enrichen the carbs as previously mentioned by others .... nice ride

[squirrelboydeluxe]

The boat is gorgeous. Please tell your neighbor to go pound sand.

[squirrelboydeluxe]

cpizze1
The 1956-1958 Mercury Mark 30 has long been my favorite merc of all time. I've had dozens of them; incl several 30H's.
As far as your motor's provenence, if you bought it from Aeroliner I would give it my blessing. Their stuff is always top notch.
I set my mains (on the bench) at 1 1/8 turns out from lightly seated and the pilots at exactly one turn out from seated. Just make sure you snug up the packing nut on the mains...I can tell in about 1/2 second it one has loosened up on mine.

Test wheels are not too hard to find for a 30H; I would imagine Aeroliner has a few. They have tons on stuff...also check Outboard Paradise.
Joe Poole Jr (Ferguson/Poole Marine) is not far from you; Joe is a Mercury WIZARD and extremely helpful/knowledgeable
Another great resource for old merc's is the John's Old Mercury website- there are some very sharp guys on there and they will fall over backward to help getting an old merc singing
Feel free to call me at 717 919 4726
522-P

[DeanFHobart]

The older motors like yours need 16:1.... Since the rod / crankshaft bearings are individual needle bearings (not caged rollers) so so they need more lubrication. Obviously I don’t know what your motor issues are, but I’m sure it is not your fuel mixture.