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At my wits' end with a 30hp mariner

C

chrisgt

Contributing Member
I bought a boat with a 1996 30hp mariner 30 that has oil injection and I cannot get it to run well. The boat is a 14ft aluminum Lund.
It was accelerating very slowly. It would eventually reach a plane, but it took a long time to get there, this engine should have snappy throttle response, but when I put the throttle down it just bogs, then slowly accelerates.

While taking the carburetor apart for the 3rd time I noticed that it had an 066 main jet, which is for the 40hp; I thought "hey that's the issue," so I ordered the 054 jet for a 30hp. Now it runs worse, it won't run over part throttle without stalling. If I go wide open and hold the key it would run properly for a second, then bog, so it appears to be a lean condition.
The engine idles and starts well, though.

Things i've done:
- cleaned the carb and installed the correct jet.
- checked the compression: 135psi both cylinders.
- Checked the spark, strong on both cylinders.
- The fuel pump gives a nice squirt of fuel when cranking the engine.
- The oil injection seems to work fine, the carb bowl is always full of blue fuel.
- Squeezing the primer doesn't change how the engine runs which helps reiterate that the fuel pump works and the needle in the carb isn't leaky.
- checked the reeds, see below.

I finally ripped the reed box off the front of the engine even though the problem is almost never reeds. One cylinder has the reed valves closed all the way touching the plate. The other cylinder has a few reeds with some play, I can't find the specification for how much play is acceptable, it doesn't seem too excessive.

Anyway, I am having my butt kicked on this one, any help appreciated.
 
I also checked the ignition timing, it's 3 degrees at idle and 25 degrees over 3000 rpm, which is exactly to spec.
 
It has a brand new 10.5x15 propeller that the PO installed, apparently they chewed the old one up on a rock or something.
I have pulled the flywheel and the key is in place. The timing is correct anyway so that shouldn't be the issue.

They said "it runs perfectly." It was out of the water but it started fine on muffs, so i took it home. Now obviously they have blocked me and don't wanna talk so... yea.
 
On many motors ( with sheared key ) the timing will be correct when a timing light is used.----That is why I suggested the check.-----Good luck with the motor.
 
Well, i may have solved my problem. I took the reed plate off and some of them weren't closing so I flipped the reeds over to make them seal.
Now it starts right up, runs beautifully, and accelerates just fine.

I am absolutely aware that doing this WILL break the reeds and destroy my engine, I ordered a new set, just did this for testing.
 
Just as a final update, I have an early serial number (pre 96-1/2) which means the only difference between 30hp and 40hp motors is the reed stop vs reed retainer... Since I already had to take this apart, and since the reed stops are only $7 each, why wouldn't I :)

So with the 40hp airflow mods and CCMS reeds this thing is INSANELY smooth. It starts the instant I turn the key, idles so smooth I can barely feel it, and goes like a bat out of hell. I need a higher pitch prop (or maybe a 4 blade) because I'm hitting the soft rev limiter ignition retard.

The engine could be a hole higher and a few other adjustments to be made, but the 14ft lund is now running 29kts wide open; overall this thing was really cheap for a reason, but now that I got to the bottom of it, it's pretty fun.
 
I put a Yamaha F40 on my 14' Mirro Craft and it was an E ticket ride. I would imagine the same with your Lund.
 
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