40 hp Mariner 2 stroke bogs down at first then runs great

[SAABologist]

Thanks for your advice, I am a little stumped. What could cause running bad at first, then running great?

Here is the situation:
Starts instantly and idles great at all times.
During first accelerations, it bogs down on acceleration, then runs rough like it's not getting constant fuel.
After a few minutes, all is well and it runs great, including backing off and accelerating again.

The Motor:
- 40 hp 2 stroke Mariner 1987
Fuel connector to motor is brand new and the hose from tank to motor is 3/8" fuel line in great shape. All hose clamps tight.
Scepter 6 gallon tank with the pickup tube repaired a couple weeks ago.
I did open the vent on the cap.

Thanks in advance for your suggestions!

 

[PGRChaplain]

The Motor's Lean at low RPM's. The Carburetor needs Cleaned/Rebuilt. I'd guess Crap left from running E10 Gas.

 

[SAABologist]

Thank you, I can handle that. It's only got 2 carbs and should not be a big deal.

 

[GYPSY400]

After it starts running good, can you bring it back down to a troll and accelerate back on plane?

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[SAABologist]

After it starts running good, can you bring it back down to a troll and accelerate back on plane?

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Yes, once it is running well it will not show any symptoms at all. But it might take about 5 minutes on the water before it settles down to run smooth and do well accelerating. It will go from trolling to top speed like it should after it has gone through the hiccup phase.

Thoughts?

 

[GYPSY400]

Hmm, that's weird. Has it happened once, or does it do it every time? ( I'm thinking water in the gas)

If every time , check all you electrical connections- maybe something is a little loose or corroded.
Put in a new set of plugs.. the other scenario is one plug is fouling and the motor runs on one cylinder until the plug clear up.

Try it again with new plugs, if it happens again, pull the plugs and check them for one that is wet. Since you have ruled out plugs with new plugs it might be a weak coil. You can probably swap coils to see if the problem follows. Check all connections while swapping coils.
If the problem doesn't follow, then it might be carburetor issues.

One step at a time, don't jump to conclusions.

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[GYPSY400]

Oh and while your idling ( trolling ) it.. dip your hand in the lake and touch the spark plug caps... if you get a jolt, change that spark plug cap.

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[Pappy]

Okay, Right off the bat.....if the engine can be idled down and is smooth at idle it is not lean and there should be no need to rebuild the carburetor(s).
Typically your symptoms are consistent with an engine that is over propped or your carburetor to ignition pick up point is too early.
What RPM are you running at WOT with your typical load onboard? If you are more than around 3-400RPMs below what you should be running at you may need to adjust pitch (prop shop) or change props.
On the sync and link side adjust your carb pick up point to come in later. This will allow a bit more ignition timing to occur before the carbs begin to open. I would try this before doing anything else.

 

[airshot]

Lots of good suggestions here, but I believe in starting with easy stuff first....add a healthy amount of Sea Foam and see what happens there, might ve some crud in the carbs..easy to try...then go with new plugs, again easy to try, if those two dont work then get into things deeper with more work and expense. I have seen fairly new plugs fail, and with todays crappy fuel, you never know what your getting. Clean your fuel filter or ad an inline filter if you dont have one. Unless the problem identifies itself right away, start with simple easy things and work your way up to more indepth scenerios.

 

[SAABologist]

Thanks for these great suggestions. I took off the carburetors and have cleaned them- not rebuild kit, just disassemble and clean. They weren't bad, but now they are very clean. These carburetors are so easy to take apart it is no trouble at all.

I checked fuel filter in the motor and it is clean.

I know the spark plugs are at least several years old. I did not change them when I bought the boat 6 months ago. (However, it did not start having this issue until the last 3 outings.) I will change plugs too, to rule out both of these factors and take it for a test run.

I will report back.

Thanks again,

 

[SAABologist]

Problem solved.

The 40hp Mariner (model 40EL) ran better than ever today. Set a new speed record and zero hiccups.

I guess I should have known, but it was dirty carburetors. I can't rule out the plugs because they were old and dirty and grimy. I changed them at the same time. But considering that it runs so much smoother and higher top end, I think it wasn't getting good flow from one or both carburetors.

It was easier to take apart and clean these carburetors than any I have done on my 15hp mercury and 8 hp Evinrude. It's a quick and easy job on this 40hp.

Thanks for taking time to point me in the right direction.

Happy boating,

 

[Stove Iron]

Thanks for these great suggestions. I took off the carburetors and have cleaned them- not rebuild kit, just disassemble and clean. They weren't bad, but now they are very clean. These carburetors are so easy to take apart it is no trouble at all.

I bet your Mariner is a Yamaha built Mariner. Those Yamaha carbs are very easy to rebuild and I've found they respond well to simply taking the bowl off and cleaning ultrasonically. In similar fashion as your motor, I have an 1984 Yamaha built 30hp Mariner that really came alive with a simple carb cleaning.

 

[SAABologist]

I believe you are right about my 40hp being built by Mariner. I first got confused trying find a Mercury fuel connector, but it turns out that the Yamaha fuel connector is what fits.

I am happy with it's power and reliability, but it sure uses a lot of gas and is noisy!

Onward,

 

[Stove Iron]

I believe you are right about my 40hp being built by Mariner. I first got confused trying find a Mercury fuel connector, but it turns out that the Yamaha fuel connector is what fits.

I am happy with it's power and reliability, but it sure uses a lot of gas and is noisy!

Onward,

Yes! Those 80s-90s Yamaha/Mariners scream at WOT. You might be able to quiet it down with some foil/foam matting made for sound deadening or butyl rubber. I've seen some older folks layer swamp cooler water pan coating inside the cowls as well.