What is the proper plug gap for this engine? By serial number this (689 s 108XXX) is a 100% Yamaha made in Japan (Yamaha logo is on engine block). I bought the Seloc Mariner repair manual for 2-60 hp 2 stroke. The chart in the manual list .024 as the plug gap and list Champion L82 or NGK B7HS as approved plugs.
The Yamaha owners manual for the same year and engine list the plug gap as .035 - .039 using NGK B7HS....Yamaha list 100:1 mix ratio.

Whats the correct fuel/oil mix? Seloc/Mariner does not have the mix ratio listed in it if you can beleive that. Oil Options; Pennzoil Synthetic blend or Quicksilver Premium?? I use syn. blend in my high mileage truck and wonder if the same concept is good for older outboard?

The engine sputters, I've replaced plugs (NGK), new fuel tank, hose and bulb, fuel pump, engine fuel lines (3), new carb kit and cleaning, cleaned fuel filter, new fuel. It fouled the plugs after a couple of hours lake test and would never run well even at low RPMs. I used Quicksilver Prem. at 1.5 oz per gallon = 100:1. I think I may have added a little too much oil, maybe no more than 2 ounces over in 5 gallons , I also added Seafoam at 1 oz per gallon. The plugs were a little oily and it used a lot of fuel, i put in backup plug and limped back to the ramp... So I dumped the fuel to another can and got 2 fresh gallons of 93 octane, 2 new plugs to start the process over.......open too suggestions..Please Help!!! I'm not mixing or installing plugs until I'm sure about it!!

Well, I've decided to let a professional tune the engine up and instruct me on the proper tune settings. I've purchased quite a few parts from this site for both of my engines and have NEVER gotten one reply from boats.net......

I think the questions I've posted should be fairly simple to answer for a professional like boats.net

I also posted the same questions on the Yamaha side of this forum and got the same results.

I guess I will seek info from another forum or website. Boats.net HAS been very good as far as parts availability and delivery but there are several competitive options to purchase parts on the internet.

C'mon man!! I'm a desperate crappie jigger thats got to hit the water soon!!
Boats.net......if you have a real person that actually reads or screens these forums then show me a sign!!!!

C'mon man!!

Doesn't sound like a spark plug problem. the NGKs will fire in about anything.
Does the motor spit/puff back out of the carb?
What speeds if any does the motor run OK?

The spark plugs have always fired, spark is good. It does not seem like it spits back throught he carb, no backfire. It took three different trips before the plugs fouled out, maybe 3 hours run time. I havent messed with it in a few days...

Any idea where your timing is set at at low speed? High speed?
How is the carb adjusted?
Does it only sputter at idle?
What happens if you hammer the throttle?

Thanks for the reply.

I have no idea on the timing, dont have a light I guess I need to get one cause I really want to learn the engine.

I just installed new NGK's new and new fuel at 50:1. Plugs set at .035 or so. It idles better and seems to run better now at high idle. When I idle down it's smoother also.

The Seloc say's that there's no mixture screw on carb my carb "J" and I don't see one, only the pilot and idle which I cleaned.

I've been checking the plugs every 5 minutes or so and they're not dry but they're not as oily as before, still workin on her.

Mercury Mariner Outboard Parts 30A 689-105325 THRU 689-530100 (ML) CARBURETOR Diagram

Item #12 is your idle air mixture screw. Good rule of thumb, GENTLY run screw in just until it stops then back it out 1 1/4 turns, good starting point.

The throttle plate should be completely closed to start and then you might open that screw (#11) maybe 1/4 turn.

So can the idle screw affect top end and hole shot performance? I had no idea that the idle controlled the mixture since my Seloc manual said carb "J" didn't have air/mixture adjustment....I have been messing with the idle screw to smoothe things out....

UPDATE; I took her out Saturday but before I could do any adjusting, the Yamaha 703 remote had a malfunction and got stuck in reverse 200 yds from the ramp!!! I got home and found that a snap ring that holds the cable on the shifting pin was missing and it finally worked its way off....

I'm still getting different opinions on the proper oil ratio as well as thje proper plug gap. This Mariner/Yamaha thing is getting old....My biggest fear is spending $150-200 bucks for someone to make a simple adjustment that I can do...

Thanks boatman for the help...I'm going to fix the control then get back on the motor..

Boatman, I forgot to mention that the model number of my unit is a 30EO (Electric start/oil injection). The oil injection is removed. I cant find any documentation on my model number.

30A is the closest model on record to mine.

Seloc manuals are pretty generic, no where near the detail you get with OEM books.
The idle/air screw mainly affects idle and off-idle performance. It will not have much affect at all on high speed operation. It will affect holeshot.
Try the 1 1/4- 1 1/8 setting on the mixture screws and go from there.

I suggest a 50:1 mix of manufacturers name brand oil (Mercury, Yamaha) not what's cheapest.
Also try a double dose of Mercury Quickleen for a tank of fuel.

But 1st MAKE SURE YOUR HIGH SPEED TIMING IS SET RIGHT AND MAKE SURE ALL OF THE CARBS HAVE FUEL FLOW FROM THE HIGH SPEED ORIFICE BEFORE ANY HARD USE!