Mark 30 Help

[cpizze1]

Guys, I have a Mark 30 that I'm trying to run on a home-made runabout. The motor runs strong out of the water, but won't start in the water. I have check high speed jets and seem to be set properly. Gear case is 1:1. Next is timing.....I'm a 2 cylinder guy so the 4 cylinder is unfamiliar to me. Any thoughts on what I should try next would be appreciated.

[Art K]

What about the idle jets? has powerhead been gone thru reeds rings etc. Just looking at the prop It looks pretty stout for 1;1 gears. The boat is beautiful. But I think your going to have difficult time with this setup even getting on plane. Most probably would perform better with a pleasure boat lower unit.

[cpizze1]

Thanks Art....haven't check the idle jets yet. I will do that. Motor was bought thru Aeroliner. Has not been gone thru. Changed to a smaller prop. Ran it about 40 years ago with a 55H. Thought this Mark 30 would have been fine. I'll try a little more tinkering.

[ZUL8TR]

Nice looking setup might be to much for a 30H compared to a 55H? Do you know the weight of the boat ? From the pic that engine looks to high on the transom for that rig, have you measured where the rear of prop shaft center is relative to the bottom? I agree with Art K that looks like a big pitch prop for that 1:1 30H. Starting some of these race engines with the prop on in water is sometimes a problem. As suggested the carb idle jets need to be checked and timing as you note. Check all the fuel line connections for any air leaks esp from the tank to the fuel pump. Might also need a float adjustment.

[cpizze1]

Prop shaft is 1 1/2 inches below the bottom of the boat. Recommendations? Also, you may have something on the fuel.....I do have an air leak from the tank fitting to the fuel pump! I only hope it can be that easy! Thanks!

[mercguy]

What about the idle jets? has powerhead been gone thru reeds rings etc. Just looking at the prop It looks pretty stout for 1;1 gears. The boat is beautiful. But I think your going to have difficult time with this setup even getting on plane. Most probably would perform better with a pleasure boat lower unit.

and a 30H came with a 16/21 lower unit, propping with a 1/1 unit might be challenging...……….it will be a really small prop...…….

[Charlie Pater]

Mark 30 H came with 1:1 lower units. I believe the 16/21 is legal only for mod.

[T Chance]

back when I was running a 30H, my first set up was a full Quincy alcohol burner with 1:1's. Then I went to a pure bone stock Mark 30 powerhead (except for pipes) and switched to 16:21's for C-Mod. I'm guessing the prop shaft was around 1/2" below the bottom of the boat. Boat was a 13' DeSilva. 1-1/2" deep sounds way to deep and I can understand why it won't pull itself up on plane. Propellers I used back then were 2 blade, a little 6" Smith prop on the Alky and a 10" pitch Seebold on the Mod with gear reduction. And I had to have 3 people help me even way back then in the 60's and 70's to launch it.

[Larry M]

Thanks Art....haven't check the idle jets yet. I will do that. Motor was bought thru Aeroliner. Has not been gone thru. Changed to a smaller prop. Ran it about 40 years ago with a 55H. Thought this Mark 30 would have been fine. I'll try a little more tinkering.

The Mark 30 should run this boat all right after you get the motor right. The block on the 30H is the same as the Mark 30 pleasure boat motor and they would run on a boat this size. I had a Feather Craft at least this size with a 30 Merc that I had raced with and it planed off the boat fine with the racing unit. the 1 1/2 might be a little deep. Take the prop off and start it in the water and see what happens. Sometimes a motor will run fine on the bank but will not run right because of a water leak. Motor right and the right prop you should be good to go.

[DeanFHobart]

cpizze1,

Very nice looking outfit. What is the design or make of the boat and who built it?

Thanks, Dean Hobart......

[cpizze1]

This is called the TNT. I believe it is a Glen-L design. A friend of mine while I was in high school helped me build the boat in shop class. He was the craftsman. A lot of evening hours work went into this. The shop was open in the evening so we could get a lot done. Thanks for the complement! It did teach me how to work with wood. In my hydro days, I did have to repair the turning side on a Marchetti and the nose on another.

[DeanFHobart]

cpizze1,

What year did you build it?

Also, the older motors had fuel system parts such as gaskets, rubber fuel pump diaphragms etc that are not compatible with gasoline with ethanol in it. Check to see that those parts are still good. Then use ethanol free gasoline. Marinas, farm stores etc. have ethanol free gasoline. ‘Google’ ethanol free gasoline in your area.

[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.

[cpizze1]

Dean, built back in '76. Only been in the water once before. I had a neighbor bet that it wouldn't float since he had never seen it in the water. I told him, not only will it float, but it won't leak......I didn't! Unfortunately, I couldn't get it to run. A little surprised and disappointed since it sounds strong on land. Question: what fuel mixtures are you running today. I was told 16:1 mix for this engine. Seems a little rich. Also, I just tested last night with a test wheel in the water. Ran okay. I did fix the leak in the gas tank coming from the fitting to the fuel pump on the motor. Maybe that???

[squirrelboydeluxe]

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

[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.

[cpizze1]

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.

[ZUL8TR]

On those older Mercs the higher oil ratio will do it well to help seal it up. I run 16:1 on my Merc 25ss but I keep the revs up at 7000+ on the hydros where more oil is needed. If you plan on not so much high revs and average lake running then less oil like 25:1 will do it. The right plugs help as well as the right and correct mag timing. The prop depth at 1.5" is very deep for top performance with the 30H, depends on how you will use it, you can prop for the deeper depth if that is what you want but expect less from the 30H. Might be better off with a service lower unit for average lake running?

Take care of that Quicki gear case and service the gear lub often especially the outer cone bearings that are greased separately. I service my gear case after each use with new gear oil and outer cone grease, still alive with same gears and bearings except seals since 1973.

Do you know the weight of the boat rigged without engine and you?

[cpizze1]

ZUL8TR, I think fuel mixture is adding to my dilemma. I may need to go to 25:1. I'm not racing, just putting around a marina. Heights not an issue either since I'm not worried about top speed. And yes.....I greased my bearings after each use. Thanks for reminding me. So, leaning fuel mixture, fixed air leak in fuel tank to pump and smaller prop.....maybe that will work.

Thanks ALL for the suggestions!

[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.

[John Schubert]

ZUL8TR, I think fuel mixture is adding to my dilemma. I may need to go to 25:1. I'm not racing, just putting around a marina. Heights not an issue either since I'm not worried about top speed. And yes.....I greased my bearings after each use. Thanks for reminding me. So, leaning fuel mixture, fixed air leak in fuel tank to pump and smaller prop.....maybe that will work.

Thanks ALL for the suggestions!

As mentioned above, remove the prop & see if it will start in the water. Then go from there. Increasing the amount of oil will not help your starting issue. If it starts out of water, should start in the water with no load. Then you go from there with the other suggestions, some of which are very good but won't necessarily change your starting issue. BIG prop is an issue though especially if it is buried underwater when attempting to start. A 30H runabout prop should be about 6 3/4 x 9 1/2. My best hydro prop which was fast was a 7 x 10

[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.

[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.