My motor is acting weird. Can you help?

[kyle317289]

Motor is 99 200 Yamaha Vmax ox66.

Idles fine in neutral. Cranks no problem. Currently has fresh 93 octane with marine stabil mixed about 6.25 gal per ounce.

When I put it in gear and idle it starts running a little rough occasionally it will go dead. When I give it gas sometimes it will do fine and plane out normally. Other times when i give it gas the bow will rise and it will take the engine a couple of seconds to reach full power and plane out.

Once planed out boat runs normally. I can run WOT then let off and slow down or turn and accelerate again no problem.

Any ideas what the problem could be?  I'm thinking gunky injectors maybe?

Any help would be appreciated because i'm certainly no mechanic.

[JohnnyBigger]

add some seafoam to the gas, if that doesnt help it might be time for a tune up. Have you checked the fuel filter?

[kyle317289]

I haven't checked the fuel filter. I'll try to check it out tomorrow.

How much seafoam should i add per gallon?

[JohnnyBigger]

I cant remember the exact amount per gallon off the top of my head but you can go overboard and it wont hurt. I think one can does 15 gallons

[Fishing Rhino]

Could also be an intermittent ignition (wiring) problem.

My wife had a car that would cut out when driving on a highway.  Get up to speed, and when the engine wasn't pulling or holding back, it would die.  Then it would start again, on it's own.  Standard tranny, so the engine would keep turning when it shut down.

Floor it, it ran fine.  It started fine, and idled fine.  It was only when the engine wasn't under load that it shut down.

Turned out it was a wire in the distributor.  The insulation had worn off in one spot where it touched the housing.  When the timing advance plate was in one precise spot, the wire would short out on the housing.

Most engines today do not have distributors.  They use a "crank trigger" mechanism that tells the coils when to fire.

Take the cover off the engine and check all the ignition wiring for any loose connections or bare spots where the insulation has worn off.

Most intermittent problems are electrical/electronic.

[JohnnyBigger]

also check battery connections, on the injection motors loose connections will cause low power

[kyle317289]

Ok guys, i checked the connections and the fuel filter and both seemed to be good.

I put a can and a half of seafoam in one tank with about 23 gal left.

I went to the river to this morning and it seems like the problem has gotten worse. Starting out this morning it did fine good hole shot, 10 mile run, no problem. After that things went south, it would take 9-10 seconds to plane out.

I would give it gas and the rpms would immediatly go to about 2200 and slowly rise to about 3200 when it would plane out and do 4500-5000.

Ocassionally while running it seemed to miss and the tach would go up and down +/- 200 rpms for 10-15 seconds at a time.

I ran probably 30+ miles today so the seafoam should have had a chance to work if it was going to. I think i'm going to change the plugs and fuel filter and say a prayer. If that dosen't change anything i guess i'll put it in the shop.

[JohnnyBigger]

I think that would be smart, start small. let us know hot it runs

[kyle317289]

I took it down to a local lake today and fished a while.

Nothing seems to have changed. I probably ran 4-5 miles total.

A few more details that I haven't mentioned before:

it smokes a good bit more than usual right after i crank it, but doesn't smoke at all after a run.

it won't get over about 5200 rpms max. usually WOT is ~5500.

Any more ideas? If not, i'll probably go ahead and put it in the shop. thanks for the help btw.

[Bass_Fanatic]

Let me know what you find out because mine is doing the exact same thing...It left me stranded 20 miles from the ramp in a tourney last week!!! >

[Sam]

Kyle, the motor is telling you it is sick and needs some help.

Please take it in before it blows up on you and then you have big buck repairs.

Sounds like something is getting hot and either interfering with the gasoline intake or the compression is starting to fail.

Your certified dealer's repair shop can find out the problem.

Let's hope all you need are some new gaskets. 

[kyle317289]

Well I took it to the shop this morning. They said they should get to it thursday or friday.  The mechanic said it could be any number of things. Hopefully it won't be too bad.

To bass_fanatic, i'll definitely let you know.

[Bass_Fanatic]

I appreciate it...lets hope it minor for both our sakes!!

[acar555]

Does your Yamaha ask for 93 octane?  Most only require 87.  Higher octance fuel burns slower.  Don't know if this is your problem or part of it, but running the correct octane fuel is important.

[kyle317289]

It dosen't. It just says 86 minimum. I've thought about that and the octane could be a small part of the problem, but I doubt its the whole problem.

From now on i'll probably go with 87 at a more popular gas station than i've used in the past.

[JohnnyBigger]

In the higher HP motors ive always been told to run at least 89 octain

[GLADES]

In my merc 150, I always use 87-89 octane.

[kyle317289]

UPDATE:

I got the boat back today. The mechanic said the main source of the problem was the fuel injectors. 2 were completely stopped up. He said it likely just built up over time thanks to the horrible gas we're forced to buy.

He also told me to run minimum 89 octane and at least 1.5 oz per 10 gal gas of ring free plus fuel additive.