Nissan 30HP engine trouble

Hi.
Thanks for looking at my post.
I own a 30hp nissan outboard 4 stroke engine. It has problems running properly. Here are the problems.
It starts ok with LOTS of choke. If I run it with low choke it usually dies. IF it doesn't die and IF i can get it in gear, then it runs at very low rpm and has no power. It purrs beautifully with high choke. Runs rough with low choke or dies.
The air intake is clean. New spark plugs didnt help. I got new fuel and ran a carb cleaner through it at high choke.
I have had the engine come out of the water in a turn at high power and the engine reved high. Is ESG (rpm limiting)a player?
The manual says that if it happens to see a dealer. What does it do to the engine?

Also, is there a high power and low power portion of the carb? Seems that OCCASIONALLY, I can get it to run great with lots of power, but then if i hit a wake or something....it defaults to running poorly and not wanting to idle again.
Thanks again for looking at this post and any help you may have to offer.

PVANV I wish you lived next to me at the lake!!!

Aviator,

Sounds like you have an MFS30A, with 3 carbs. The 30B is fuel injected, so doesn't have a choke... so you must have the 30A. So here we go... If you need to have choke to run right, you are either starving for gas, or drowning in air. Typically it's a matter of varnishing in the low-speed circuits of the carbs. You may want to see a dealer on this one unless you are handy with carbs, as there are 3 to go through, and they all need to be synchronized when you're all done with cleaning. Yes, the carbs do have both low-speed and high-speed circuits, and usually the low-speed sides is what gets gunky. In general, it's getting critical to run the carbs dry at the end of every day now, since the fie;ls are so poor. That helps a lot.

The ESG could kick in if you bounced off a wave, or cornered too fast, and over-revved, but it clears after you shut down and re-start, so that is not the problem.

Just running spray carb cleaner through the thraots of the carbs won't do much. First get a good diagnosis, with the aid of the factory service manual. Then, if it seems to be low speed fuel starvation, the carbs need to come off, be disassembled, soaked and blown out, then reassembled and synchronized.

Drop by the lake any time

Paul,
Thanks for the reply. Everything sounds about right, with one exception. The engine is a NSF30A. Tell me that that means I dont have 3 carbs. (after a little research i found out it DOES have 3 carbs )
I was looking for the carb to take apart and was not finding what looks like a typical carb. I need a service manual, for sure, if I am going to tackle this. I guess the sevice manual shows clearly how to repair the carbs?.?.

Finally, if I do get the sevice manual, are you pretty sure I can tackle this myself or is it for sure something a licensed tech should look at? I am mechanically inclined and like a bit of a challenge.

And Paul, I am on a lake in Alabama. The water temp in AL is probably higher already than your highest air temp this year in NY. Buffalo is cold. Come see ME at the lake anytime Caught a nine# striper last week.

Thanks again for your help and suggestions,
Paul B

Paul,

Sorry 'bout the nomenclature (MFS vs NSF). The Nissan units will be NSF, as you noted. While it is a 4-stroke, it is a 3-cylinder motor, not a 4-cylinder. One carb per cylinder. The correct service manual covers 25A & 30A 4-stroke models. These are the carbureted 4-stroke models. Part # 003N210530. $27.58, available from any dealer, including me.

As long as you follow through the carb removal and disassembly carefully, you should be OK. Cleanliness is very important. Remember that the 3 carbs must go back on in the same position as they came off. The upper carb has the choke or auto-by-starter mechanism. After you are done with the 4-hour soak in carb dip and the blow-out with carb spray, and the reassembly of the carbs, you will need to synchronize the carbs so they open and close simultaneously. If the inlet needle valves have damaged viton tips, you will need carb kits. The kit includes gaskets, float & needle valve. Note: Must purchase 3 kits (one for each carb) Part # 3R3871221M, $52.67 ea. If the job looks daunting to you, consider enlisting the help of a local dealer.

BTW, Buffalo seldom gets below 0 degrees F in the winter, and has never gotten to 100 degrees F in the summer, so is fairly temperate. Lakes Erie and Ontario help to moderate the temperatures.