About ready to give up

[supermuff]

I have a f115tlrd Yamaha
I took boat last sept. after sitting 3 weeks. First thing i do is fill it up with fresh gas.
We get a mile up the river and it hesitaes and back fires?
After this the boat would not plane. Stuck on 300rpms.
Turn around and go back to dock.

Change fuel/water seperator, fuel filter.
Take it back out it and the boat would plane but rpms would not go above 4200.
So i take it in to a buddy who does boat repairs.

He says bad gas!!! I agree.

He drained all of the gas. Cleaned the tank.(removed sending unit)
He test the boat and says it is fine.

I take boat out 2weeks later. Same problem!!

I call him and let him know.
I take it back to him. He water test it and he has the same issue.
Wait over the winter till spring!!

So he sent the injectors to be cleaned. Changed all of the filters(including vst)
Water test the boat. Says it good.

I take it out a week later. The boat is running better but doesn't get out of the whole very fast and now the rpms are jumping around. The will vary from 4400-5800.

Currently the boat is slow to plane and rpms are sitting at 4200?

I have bought a tank and new fuel lines.
My plane is to take boat and try this.
My guess it is a bigger issue.

How do you no if it is a fuel pump? How do you know which one?(high or low)Can they be intermitten?

Any ideas are welcomed

 

[waffles1]

Re: About ready to give up

How long have you had this boat? Any work or changes been made to the boat since it ran good? Same prop?

 

[rodbolt]

Re: About ready to give up

by purchasing the correct test equipment and the tech having the proper training on the systems and how to interpet the test equipment.
what is the fuel rail pressure at the problem RPM ?

 

[supermuff]

Re: About ready to give up

The fuel pressure at the rail was 36 psi.

I am taking it back to have it checked again.
He is also saying he can blow back the injectors if there is any debris in them.
Does this sound right?

 

[rodbolt]

Re: About ready to give up

I have blown back through them using compressed air,yamaha combustion chamber cleaner and a battery pack with two jumper leads so I could toggle the injectors while blowing through them.
doesnt always work.
when you checked the rail pressure was it at the problem RPM? if not check it at the problem RPM.

 

[supermuff]

Re: About ready to give up

they checked theh fuel pressure at 4200rpms and it was fine.
i took the boat out this weekend and it was started out with 5800rpms and 38mph.
i ran it Sat for around 5 miles.
Filled the tank up with non-ethanol gas. then went home put another 5 miles on it.
Then on sunday went out again.
I notices it had dropped 3mph on Sunday but i had another person with me.
We went around 4 miles and stopped for lunch.
When we came back out to head home. It didn't lump out of the hole and maxed out at 44rpms and dropped another 7mph.
I checked fuel dilters and they look fine.
I guess i am going to break down and buy new injectors.

Rodbolt- Just wanted tio say thanks for the help you provide on this board.
I know i appreciate your post and that u take time to try and resolve issues from your experinces!!!!!

 

[supermuff]

Re: About ready to give up

Latest update
Took the boat out after i cleaned the injectors and replaced the fuel lines from the fuel water seperator til right after the filter bowl on back of engine. The lines that are left are gray lines.

Blew 120psi in the oppisite direction of fuel flow.
Black spec were in my hand afterwards.

All the hoses looked fine.

The boat came right out of the hole like she should.
As i started to reach top speed i looked down and the rpms were 6800!!!
I backed her off and ran around 5600 for 5 mins.
It was getting dark so i headed back in and opened her up again.
She hit the top speed but the rpms were 6200.

i do not believe the prop is slipping.(i checked this when it was in gear i tried to turn the oppisite way and could not budge the prop and i could barley turn the prop the same direction it was in gear.)

It didn't sound like the egine was reving that high?
This was the first time i have ever taken the fuel rail off and blown injectors out.

The question i have is the injectors push into the fuel rail and do not push into the manifiold? I just wan to make sure i put everything back together correctly.

The other thing i can not figure out is how i am getting little black spec in fuel bowl but when i dump the fuel/water seperator i do not see any of these specs? If the hoses are good where is this coming from?