TOPIC: It Runs!

Hey All,

I've been posting on here quite a bit lately during the progress of my Mark 75 that I picked up a few months ago with a seized power head and cracked lower unit for $80. I installed new rings, new gaskets & seals, new impeller, and did a fair amount of welding and machining on the lower unit to get it right again. Finally this past weekend all the hard work paid off and I got to hear it run. It fired right up and starts easier than any outboard I have. I literally touch the starter button and it roars to life. Must have gotten the point dwell setting pretty close.

Just wanted to say thanks for everyone that helped me out through the project. Now I just have to rig it up on the old crownline and see how she runs on the water.

Scott

running in the barrel

VERY COOL!!!

doc

Nice work, look forward to seeing it on a boat!

And it actually has a telltale, amazing!! You know that's a rare sight in itself!

I think you're gonna like the way it runs, like you say if the ign is set up right, they start up really nice and idle like a dream.

Years ago I had a 700E on a 13-1/2' Sea-King runabout and it was the perfect, "cheep" ski-machine!

Enjoy and let us know how you like it!.......ed

ed-mc wrote:

And it actually has a telltale, amazing!! You know that's a rare sight in itself!

I've heard so many stories about people having a hard time getting these to pump that I was meticulous when I put the water pump together. The tell tale was plugged solid with mud and who knows what else, but I cleared it out.

I was nervous on the first start, but after I saw the strong telltale, it was a big relief.

Well, as a little update i got the motor rigged to the boat and it looks good

The weather was terrible on Saturday with rain and drizzle, but i decided to bring it down to the lake by my house and try it out anyway. The entire trip ended up being an epic failure

I last ran the motor last week in the barrel and it started great and ran awesome. I figured it would do the same thing at the lake, but i was mistaken.

First off, i went to prime it like usual, and the bottom carb was just puking fuel. I had gone through the carbs when i assembled the motor, and it had never done this during all my test runs in the barrel. Next, like an idiot, i must have bumped the key to on when i was mounting the controls earlier in the day and the battery was pretty much flat dead. Long story short i didnt get to make a run.

When i got home i dissembled the float-bowl of the bottom carb (PITA) and found that the float was "half sunk". this just goes to show how bad the "modern" fuel really is. After only a week or so of sitting with fuel, the float got saturated. (im sure it wasnt the greatest to start with either).

Anyway i am in the process of removing all of the floats (luckily i have spares) and am going to coat all of the replacements in airplane dope.

Will post some pics of the motor on the boat as soon as i resize them

Scott

Scott,
Sorry to hear that the maiden voyage didn't happen.
We have all been there I'm sure.

Since you are going into the carburetor(s) again - have you considered replacing the floats with new ones?
I use the Sierra Marine number 18-7208 float available through NAPA.
They are about $11 each.
Have you replaced the needles & seats yet?
The replacement ones from Sierra Marine work much better than the original style. Part number 18-7057.

It is always best to track down ethanol free gasoline because of the problems ethanol cause in the fuel delivery system. Original fuel hoses break down, fuel pumps fall prey to the ethanol, and original needle & seat units fail - causing the carburetors to flood.
This web-site should point out to you where the ethanol-free gas stations & marinas are in your area. Just enter your zip code.
www.puregas.org
doc

Scott, Where did you get your parts? I have a '60 Merc 800 that needs a full restore. Low compression in #4 cylinder (light scoring).
TIA
Larry

Hey all

I need some advice because I am starting to get to my wits end with the mark75. Last week I had it running in the barrel and it started up great and ran well in forward and reverse. After my trouble with the carbs, which I now seem to have figured out (they don't leak anymore) I can't get it to run on all 6 cylinderS. No matter what I do it will not run on cylinders 3, 5, and 6. I can pull the plug wires right off those cylinders while it is running and it does not change how it runs. 3,5,and 6 have good spark. Also it now will not run at all in reverse. Before it would start up both Ways.

I thought it might be a fuel problem but I do not understand why only 3,5, and 6 are affected? I have had the carbs apart so maNY times that I don't think I missed anything. Also, to get it to run at all, the throttle has to be pretty advanced.

All cylinders have 115 pounds of compression (checked tonight) all cylinders have bright blue spark,and all plugs appear as if they are getting fuel after it does run...

Is it possible that the distributor belt timing could be one cog off? Just trying to come up with ideas.

Any ideas anyone?

you problem is the ignition.it has 2 ignitions in 1 unit that is why 2 coils 1 system is down.

Thanks Dave... When i had the distributor off i set the dwell with the mercury synch plate, and i thought i had everything correct, but im wondering if forgot to tighten a screw holing in the points or something?

Whats really confusing me is that the three cylinders that do not run do have spark, im just not sure if it is happening at the correct time. I checked the coil and it ohms out the same as the other one, and it has a bright blue spark at the coil.

the only other thing i noticed that could be causing me trouble is the coil wire that goes into the side of the distributor cap. I believe it goes to coil#2. When i pulled it out, it seemed to be a bit worn(to the shape of the rotor) and the spring seemed a bit weak. i stretched the spring slightly so it would make better contact with the rotor. I have a spare distributor laying around, and i may try to swap that wire and contact.

I think ill also disconnect the ballast resistors and check continuity on both sets of points to make sure they aren't shorted or staying open.

Any other tips on things i should check?

Scott

Keep in mind that one coil & set of points runs cylinders 1-3-5, and the other set runs 2-4-6.

So you've got problems crossing both ignition sets. Maybe a combination of ignition problem and carb issues?

5&6 are running off the same carb so either flooding out or not enough fuel?? Spray some premix into the carb and see what happens. Check the plugs for fouling. Since you installed new seals, I wouldn't suspect a problem there.

It's possible to get crossfire on a dirty dist. cap. You might want to pull the cap and clean it. Carb spray will flush out any gunk in there.

Hopefully your points cam didn't have any worn lobes, that's another thing that can cause a miss at idle. I've seen new ones for sale on eBay for a reasonable price. Note that the Dockbuster cam is different than a FGS cam.

HTH........ed

Dumb ????? check and see if the wires are crossed.

I'm probably way behind on this troubleshoot.
'coil #2' is actually the front coil.
12vdc is delivered to both halves of the ignition during start up via the second small terminal on the starter solenoid.
To determine if in fact one side of the ignition is the cause of the cylinders that are not firing,...simply disconnect either the brown wire or the white wire from the (2) sets of points at the port side terminal block, and see if the missing cylinders fire are consistent.
Brown & White mayt not be the correct colors on the MK75 - one wire might be red (no manual in from of me at the moment)
Anyway,...If you can positively confirm that one side of the ignition is okay - The same (3) cylinders are not firing) - you can narrow down the cause of the other side by listed ohms tests.
If you decide that you need a fist full of the various components to use in a part-by-part swap to find the culprit,...I have "oh-plenty" of these components.
I believe you can track the cause down by ohms tests, but if that leaves you scratching your head (like what happens to me very often) my parts are here for your assistance.
This ignition is so-o-o-o-o sweet when it is right that it is totally worth the efforts to understand and trouble-shoot it.
doc

okay guys,

i got to spend some time with the merc last night and i think i have the problem fixed.

First, i tested continuity on both sets of points to make sure they were properly opening and closing, and both were working properly. I also checked to make sure the distributor belt timing was correct, and it was.

I then fired it up, and it was doing the same thing (not running on 3, 5, or 6). I started messing with the high speed adjustment needles and no matter how far in or out i turned the bottom carb's needle, it did not change how it ran. I also couldn't see gas coming out of the fuel tube in the bottom carb like i could on the top two. I disassembled the bottom carb and found the problem. The tiny spring, that is on top of the float, somehow came out of the float and perfectly wedged itself between the needle and seat levers, causing the needle to stay shut all the time. I put it all back together and magically cylinder 5&6 came to life, which just left cylinder #3 to figure out.

I was scratching my head with the cylinder #3 problem and just couldn't figure out what was going on. I had forgotten that when i put everything back together the #3 wire spark plug boot was melted, so i replaced it. Well it turns out that when i squeezed the new end on the wire, the sharp part that actually stabs the wire dislodged and came out. i took the boot back off and "re-stabbed" the wire and slid the boot back over. Fired it up again and it ran like a sewing machine. super smooth. It starts easily in forward and reverse now.

I bringing it down to the lake on wednesday night to test. Hopefully it goes well this time

great job well done.

Right on!!
doc F

How did the test run go!?!?!?

Hey Guys,

Sorry i didn't post earlier, i have been really busy, but i am happy to say that i think i have the Mark 75 running pretty good.

I tested it last week Wednesday as planned. It was freezing out (49 degrees), but i went anyway. The motor started right up and ran very well. I was impressed with the performance. According to the speedo on the boat, with two full sized guys and one smaller teenager, we hit 34MPH (compared to the 25MPH that i got out of my 40hp johnson).

I went camping in northern MI for the holiday and brought the boat along. It ran like a top for most of Saturday, and i was able to hit 38MPH with just me in the boat. Late in the day Saturday, it suddenly developed a bog. I opened the cowl up and noticed that once again the middle carb was just pouring fuel. Im going to order needles & seats along with floats for all carbs as Dr. Frankenmerc had suggested, and i think that my carb problems should go away.

i was able to tap on the float bowl and got the carb to stop leaking. I ran the boat for a bit on sunday with no problems.

overall i was very happy. it starts super easy in both forward and reverse, and after only a little bit i am pretty used to the controls.

Scott