Rough running first use of the year

[BlacksCove]

I have a 1996 DT115 engine, at the end of the year I flush the engine with fresh water and disconnect the fuel line and run the engine until it stops. When I put the boat away for the year I usually have the gas tank at least 1/2 to 3/4 full, I use Starbrite "Star Tron" each time I add fuel. The next year I replace the plugs, regardless of the hours from the previous season, replace the fuel filter/water separator and replace the lower unit oil. I then put the "ear muffs" on the lower unit, turn on the water, and start the engine. It appears to run fine.
Now the fun begins, for the last five years on the day of launching, the engine starts fine, I run out through the mooring fields, etc. at headway speed and when I am able begin to advance the throttle. The engine will rev up to 2000-3000 +/- rpm's and begin to "bog" down. It won't take any more throttle, I can feel the engine running rough and hear a more "flat" sound rather than the normal "smooth" sound. Now it usually takes me somewhere around 3/4-1 hr. to get to my destination, now it is more like 2 hours. The first three years, when I reached my mooring, I shut off the engine and did nothing until the next morning. At that time I pulled the plugs, not fouled, dipped them in gas and then started the engine and it ran all season like a new engine. The fourth year I said the "heck" with doing that and the engine ran like new the next day. This year the engine did the same thing! So I am wondering, does anyone have any idea what is causing the problem? Thanks in advance for your comments and help.

[Solarman]

First question, carbs or efi?
Next, is there any signs of rust around gear counting coil at the back of the flywheel? Or even the bracket that supports the gear counting coil?

I do believe it is fuel related, but carbs vs EFI are different when storing for longer periods of time (?).

Post back when able, good luck.

[BlacksCove]

Rough running

Thanks for getting back to me, the engine has carburetors. As for the question of rust, I will have to check that the next time I am using the boat, hopefully in 7-10 days.

[Solarman]

Carbs you should run empty of fuel when you store it. My carb motors still occasionally have to have carbs cleaned. I have since started running my carb motors every 4-6 weeks, each time running them dry. I seem to get better results and haven't needed to clean them the past several years.

There is a chance the throttle position sensor on your motor may also be going out. With you motor bogging the way you say, this or dirty carbs would be my best guess from what info you've given me.

I have replaced the gear counting coil and TPS several times on my motors. Most common items that fail. Another item is the low pressure fuel pump, they tend to fail almost every 10-14 years.

Mechanics at the dealerships don't work on 2 strokes these days, so I do it all myself now.

Good luck, post back when able.

[BlacksCove]

Rough running

At the time I put the boat away for the season I disconnect the fuel line and run the engine until it stops, I am assuming that there is no fuel remaining in the system. Is there something else that I should be doing to make sure that there is no fuel in the engine system?

Since I store the boat outside covered, and live in Maine, there is no way that I can run the engine during the winter.

My boat has an "in hull" fuel tank (55 gal. capacity) and fuel lines that run under the deck from the fuel filler to the tank and then from the tank to the engine. I am assuming, once again, that there in no way to empty the line of fuel from the tank to the engine. The thought occurred to me that this could be the problem, but this past spring I ran the engine at home for at least 20-30 min., to potentially clean the lines, but I still had the problem when I launched for the first time!

As far as the possibility that the problem is related to the "throttle position sensor" or the "low pressure fuel pump", wouldn't they continue to cause the problem after the initial launch? As I said previously, the problem does not occur again after the initial use, the engine runs without issue.

Thanks once again.

[Solarman]

Without issue? Do you mean it only happens when you first run the boat after storage? And after that it runs fine?

If this is what you mean, then most likely it is a slight film of old fuel left in carbs that has to loosen up and wash through the first time running.

When you run the motor out of fuel for storage, there is usually some fuel that remains in carbs. This leftover fuel would evaporate, but leave thin little flakes. When fresh fuel is added, these flakes become like jell drops and may interfere with running until flushed through the carbs.

Post back if this isn't what you meant? It is difficult on this side of a computer screen to diagnose problems, please be clear, descriptive, and precise. You are our eyes, ears, hands, and minds.

Good luck.

[BlacksCove]

Rough running

Without issue-yes! I first run the motor at home with the hose attached to a pair of "ear muffs" and it appears to run fine, no load on the engine and the RPM'S in the range of 2000-2500. The issue happens during the first run in the river/lake/ocean, after that it runs great the remainder of the season.

So if you think the problem is "a light film" left in the carbs, do you have a recommendation for a way to clean the carbs so the chance of it happening again is nil?

I do appreciate your time and comments.

[catacom225]

What position do you store your engine , tilted up or down ? and what type of fuel are you , evaporated Ethanol leaves a nasty film or residue on carbi parts and I found even using acetone makes it difficult to clean

[Solarman]

There is a plug at bottom of each carb that will drain any fluid left in carbs, but it might be better to use a small portable tank with non-ethanol fuel and a heavier dose of fuel stabilizer storing additive to run through all carbs Before storing. Might also increase amount in tank? Or maybe change to a different stabilizer, and/or heavier concentration in main tank(s), prior to flushing before storage.

Good luck, you shouldn't change anything except fuel additive or amount you use in tank before storage.

[BlacksCove]

When I put the boat away for the winter the engine is in the running position. As for the fuel I use it is regular gas with 10% ethanol, I put "Starbrite" StarTron Enzyme concentrated gas formula in the tank each time I add fuel. Thanks for comments.

[BlacksCove]

Solarman thanks for your help, I'll let you know how it runs next Spring/Summer when I put it in once again.