Urgent Question For Rodbolt

[2MADAKAT]

RODBOLT,

I have had a recurring problem with my Yamaha outboard and it has been at our local Yamaha dealer for 4 weeks and they haven't been able to solve the problem. I am entered in a fishing tournament for next weekend and need my boat and wonder if you might be able to help the mechanic and I figure out where to look.

Boat = 19.5' Bayliner

Engine = 1990 Yamaha 115HP ETLD
Motor has been rebuilt three years ago
Oil injection was disconnected as I run a two stroke kicker

Problem = Engine starts great, idles great, but when you get to between
4500 and 4800 rpm it starts to cough and stutter and then
backs down to 4000 rpm.

The first time it happened I changed the fuel pump. It helped temporarily and then the problem came back. Turned out that the primer ball was missing a spring on one end so I changed that. Problem still there. Tested the coils and found one defective, so I changed that and the motor ran beautifully. It hit 5600 rpm at WOT and hit a top speed of 48 mph.

This lasted about a month. One day after a couple of hours of tubing and water skiing, the problem returned again.

The dealer tested the motor and said everything indicated the fuel pump.
He changed it and tested it in the water and it was still doing the same thing.
The mechanic called Yamaha tech and they listened to what he had to say and said the same thing, the fuel pump is bad and maybe he had a defective off the shelf.

A new one has been put on but it has not been water tested yet. I believe it will fail again. I will be talking to the mechanic on Monday. Is there anywhere else in the fuel system that could cause this grief?

I am really stuck here and would appreciate any suggestions you might have on where else to look?

Thanks!

 

[rodbolt]

Re: Urgent Question For Rodbolt

test spark, test compression if they pass repair the fuel system.
what water seperator are you running?
the 10 micron 90 GPH yamaha one has the least amount of vacum drop I have seen.
sounds almost like trash/debris in the carbs or a fuel resrtiction. run it at WOT with a vacum guage attached at the engine fuel filter outlet.
you can also use the fuel system vacum tester that is shipped to all Yamaha dealerships as part of the essential tool program.
remember, you can rebuild the carbs in the morning but if trash/drebris is introduced at noon you will have to rebuild them again in the afternoon
occasionally we see restrictions at the engine side of the fuel connector.

 

[2MADAKAT]

Re: Urgent Question For Rodbolt

Thanks Rodbolt,

I have printed a copy of your reply and will give to the mechanic to check out on Monday. I am leaning towards the carbs myself, as the engine seems to leak a minor amount of gas into the water, even when sitting still at the dock.

 

[2MADAKAT]

Re: Urgent Question For Rodbolt-UPDATE

Re: Urgent Question For Rodbolt-UPDATE

Hi Rodbolt,

The mechanics here are stumped. Here are a few more details of what they have done.

Compression check = all cylinders 140psi
Replaced fuel pump
New spark plugs
Vacuum check on fuel system = works great
Checked carbs = all clean and they even sprayed to make sure
Everything you mentioned to me in your post (I took them a copy)

When running the boat in the water, they can get the boat up to 4500 rpm before it drops out. He said if someone squeezes the ball, it will go up to 5600 rpm. But the ball is a new one I put on last year, (from an Evinrude hose system), and it worked last year perfectly.

They disconnected the fuel pump from the boat system and ran it direct from a tank of gas. Same problem at 4500 rpm.

They are going to try to hook up an electric pump and bypass the existing vacuum one.

They don't feel the boat fuel system is the problem, but that it lies somewhere in the motor. It seems to be starving at the 4500rpm mark, even though the vacuum is registering properly.

Have you ever run into anything like this before. The Yamaha tech line isn't being overly helpful at the moment.

Could there be anything from the old oil injection system that could be causing the problem?

I would appreciate any ideas as they are about to give up on it.

 

[2MADAKAT]

Re: Urgent Question For Rodbolt

Just keeping post on top due to time crunch.

 

[rodbolt]

Re: Urgent Question For Rodbolt

double check the tech's hands. make sure they have opposable thumbs. the fuel pump is driven by primary engine compression, if you lacked it it would never turn 5600.
by squeezing the bulb your forcing fuel past the pump, what were the specific vacum numbers at the pump inlet,what was fuel system pressure at the pump outlet? you can use the same guage for both tests.
my guess is the never ran the test or interpeted the numbers incorrctly.
did they use the fuel system in a box or an actual water test ?
your fighting a bad pump or a fuel restriction someplace.

 

[2MADAKAT]

Re: Urgent Question For Rodbolt

I will doublecheck their numbers today. Thanks for the reply. Yamaha tech says the fuel pump could be defective out of the box.

I will let you know.

 

[BruceAML]

Re: Urgent Question For Rodbolt

Get a genuine Yamaha fuel hose assembly. The quality is far superior to generic hoses.

 

[2MADAKAT]

Re: Urgent Question For Rodbolt

I am almost out of options Rodbolt. The two mechanics currently working on the motor have 28 yrs experience and 20 yrs experience (this one in racing) and neither no where to go from here.

The fuel pump registers 4lbs of vacuum on both ends of the fuel pump until it hits 4500 rpm and then it falls off to 2 lbs. They say when the bulb is pumped it gets to 8 lbs but then they also say if squeezed hard enough it could conceivably go to 20lbs. They are aware that this is bypassing the fuel pump.

The engine was sprayed with Acetylene to check for air leaks and it tested out fine. The fuel filter "o" ring was missing but it didn't help when it was replaced.

The engine was run again on a jar of gas and it had the same problem as running from the boat tank so they have eliminated the hose, bulb and water separator.

The carburaters were taken apart and sprayed again, but they tell me they are clean clean.

Yamaha tech has suggested changing the lower crank seal but there is no guarantee it will work and they are telling me another two hours labour plus parts and they already have 16 hours into the motor now.

They also said Yamaha tech doesn't care too much because the motor is a 1990 and most of the tech people aren't old enough to know enough about them.

They are at a loss of what to do and I am hoping you might have one last suggestion before they give up. Do you think there is anyway a crank seal would affect the vacuum at high RPM? They tell me it is #4 cylinder that drives the fuel pump, but like I mentioned earlier, the compression is good in all four cylinders.

I don't want to waste anymore money on this motor, but I know it is mechanically good, just this annoying fuel issue.

I hope you can help me??!!

 

[rodbolt]

Re: Urgent Question For Rodbolt

in the US we use pounds per square inch(PSI) on the pump output and inchs of mercury (Hg) for thye pump inlet.
4"Hg is to much at the pump inlet for a 115.
have the actually tested it at the fuel pump inlet?
you have to T into the line between the engine filter and the pump inlet, yes its very possible to have a bad pump. one lean sneeze can ruin a brand new pump.
20 years of doing something still doesnt mean you know what your doing, just means you made the same mistakes for 20 years.

 

[2MADAKAT]

Re: Urgent Question For Rodbolt

They said they checked both the inlet and outlet of the fuel pump. The pump was changed a second time to no avail. I will have to ask them what measurement they got at the inlet.

If it is 4"Hg at the inlet and you say that is too much, what would be causing it and how would you correct it.

What about the crankshaft seal change? Do you think that is a valid suggestion?

 

[BruceAML]

Re: Urgent Question For Rodbolt

What is the part number of the fuel pump that was installed? The correct fuel pump for your motor is 6E5-24410-03-00. When you ask the mechanic for the part number do not give them the part number, let them tell you. If a different part has been installed, it is not correct. Ask them if a new fuel pump gasket has been installed and ask them for the part number of that.

 

[rodbolt]

Re: Urgent Question For Rodbolt

if you have 4" Hg at the pump inlet on a 115 you have a resstriction some place. start moving the vacum guage back to each joint in the system until the restriction isnt appearent anymore.
pay close attention to the engine connector on the cowl.

 

[2MADAKAT]

Re: Urgent Question For Rodbolt

I will have them try the vacuum test back on the joints as well as the fuel pump gasket, although I would think the gasket is something they would be aware of.
I will let you know and thanks again.

 

[2MADAKAT]

Re: Urgent Question For Rodbolt

Another frustrating weekend!!! I went to see the mechanics on Friday. The fuel pump and gasket were correct. Vaccuum tested good as well on incoming side of pump and pressure was good on outgoing side until it hit 4500.

You might consider this sacreligious, but of of sheer frustration, I had them wire on a Mercury electric fuel pump that put out 5.5lbs pressure in place of the normal pump. I can now get to 4800 rpm before the problems starts, but it still is the same old thing.

This "mystery" is not making me think too kindly about Yamaha at the moment, even though I know others who have had great luck with them.

 

[rodbolt]

Re: Urgent Question For Rodbolt

you dont have a yamaha problem, you have a problem with techs doing a shotgun approach.
test compression, check CDI output at the problem RPM, then go fix the fuel system.
this aint hard, however it does require attention to details.

 

[Ray Neudecker]

Re: Urgent Question For Rodbolt

Not sure what year Yamaha did away with the quick disconnect for the fuel. but if it is still there, you may want to try bypassing it ,also the engine mounted filter has caused a restiction from the housing itself. Bypassing it may also be a solution.

 

[2MADAKAT]

Re: Urgent Question For Rodbolt

Rodbolt, how do you check the CDI output at 4500 rpm as you can only get this out on the water?

Ray, have you run into an actual instance of the fuel filter on the block causing restriction? My line runs right into the motor.

 

[noelm]

Re: Urgent Question For Rodbolt

20 years of doing something still doesnt mean you know what your doing, just means you made the same mistakes for 20 years.[/QUOTE]

Never a truer word was spoken (typed) I have seen a guy with more years than that on a product that I knew as much about as Rodbolt does Yamahas and I can assure you, this guy knew Jack sh!t, I think I might be looking for another dealer.

 

[2MADAKAT]

Re: Urgent Question For Rodbolt

As the only dealer within an hour's drive of us cannot help me, I have decided to start at the beginning myself.

I did a compression check which showed between 121 and 125 psi on the four cylinders. Plugs are brand new, correct part numbers and all were wet.

I checked the fuel line from primer ball to engine and it has no holes.

Currently the electric fuel pump is hooked from fuel filter direct to carbs. Pressure is constant 5lbs.

If you guys can help, how do I check the ignition at the trouble rpm which is 4500rpm, as you have to be on the water to get it that high. Not being a mechanic, how would I hook up a meter and do I need a special one, or can I use my digital one for electrical work? Can the coils or CDI work only at the lower rpms? Would there not be signs through the whole range.

Trusting that part works okay, and I change the fuel pump, again, to the proper one, what would be my next step in looking for the restriction?

I have a Seloc repair manual as well.