Yamaha V-X 76 250Hp 1992 mid range rpm problems and smoking at low rpm

[Warrior-VX76]

Yamaha V-X 76 250Hp 1992 mid rpm problems and smoking

Hello,

I own a Yamaha V-X 76 250Hp 1992 outboard, carb version. I have it for 6 years in storage but never fired it up it till last weekend.
Amazingly it fired directly after cranking, ran smooth at idle and also up till 1200 rpm in the Amsterdam canals, no smoke. finally arrived at the lake after a 2 hour at low rpm drive I took her up the 3500 RPM, ran smooth very powerfull and no smoke all the time. After 10 minutes or so it became hesitating and would not run smooth between the 1500 and 4000 rpm at all, boat is quit fast so difficult to investigate during the ride, but I'sure I heard it backfire as well. At idle it smokes now, doesn't run well and if you want to keep it going it needs to be above the 4500 rpm. above this RPM it runs smooth and is very strong.
It absolutly loves fuel as I burned 120 liters running 3 hours at idle (1000 - 1200 rpm) and 45 min at 4500 rpm.

I used to be a outboard mechanic in my younger years so I know the basics but i never worked on such an engine.
I googled and found there are known issues with the 61A-13910-01-00 fuel pumps......?? When the contact is switched on but the engine is not running this pump keeps making a clicking sound.

So before a grab my toolbox I wanted to ask you experts if this is a known problem and if there is a possible solution.

Looking forward to any reply.

Thx. Bas - Amsterdam - The Netherlands

[pstephens46]

Probably needs a thorough fuel system cleaning. Hope there was no old fuel in the system.

[Warrior-VX76]

Thank you for your reply. Engine was set dry of fuels and liquids by meself before storage. Carb are clean... I will do a ultrasonic clean if necessary , but I first like to see if anyone else recognise the problem at hand.

[99yam40]

that motor has 3 fuel pumps that run off of the pulses in crankcase as the motor is running.
I see no way they could be making a clicking noise when the motor is not running.

but checking them for a bad diaphragm would be a good idea, if one or more was leaking into the crankcase, it would cause problems

[boscoe99]

When the contact is switched on but the engine is not running this pump keeps making a clicking sound.

So before a grab my toolbox I wanted to ask you experts if this is a known problem and if there is a possible solution.

Looking forward to any reply.

Thx. Bas - Amsterdam - The Netherlands

Is it the fuel enrichment solenoids that are making the clicking sound?

[TownsendsFJR1300]

A video with audio (with the cowl off) might help narrow it down...

[Warrior-VX76]

Thanks again for the support, in anwser to the suggestions my comments is bold:

Is it the fuel enrichment solenoids that are making the clicking sound?
No it's the electric pump at the bottom of the carbs. see link for image:
http://www.southcentraloutboards.com...0-hp-28652-hdc

Are there any valves in it which are possible not closing and the pump can't hold pressure?
Is it possible that 1 or more solenoids staying open enriching a few cilinders at low rpm(therefore the smoke) and drain to much fuel from #6 (I believe I read on this forum that this carb supplies fuel to the enrichment system) of which a result is that #6 runs lean and do the backfire? Don't know the enrichment system yet, I'll take a closer look this week.

but checking them for a bad diaphragm would be a good idea, if one or more was leaking into the crankcase, it would cause problems
That's a good idea, never considered that they could be leaking to the inside.

A video with audio (with the cowl off) might help narrow it down...
Good idea, hope to get to the marina later this week and I'll try to record the sound.

[99yam40]

Your link does not show a fuel pump,only a pan.
but here is a link that shows a pump,
http://www.boats.net/parts/search/Ya...202/parts.html
but I have never seen this set up before.
Guessing that pump furnishes the enrichment system pressure to solinoids.

I would not think an electric pump would make a clicking sound, solenoids yes

those carbs look like a very complex set up
an electric fuel pump, pressure regulator ,and a bunch of solenoids with something to tell them to open just to furnish enrichment during certain times

[panasonic]

Your link does not show a fuel pump,only a pan.
but here is a link that shows a pump,
http://www.boats.net/parts/search/Ya...202/parts.html
but I have never seen this set up before.
Guessing that pump furnishes the enrichment system pressure to solinoids.

I would not think an electric pump would make a clicking sound, solenoids yes

those carbs look like a very complex set up
an electric fuel pump, pressure regulator ,and a bunch of solenoids with something to tell them to open just to furnish enrichment during certain times

Yam...looks like electric fuel pump is attached to the pan shown in pictures on the link the OP supplied...third row down.

OP ...can put your finger on the fuel pump when the clicking noise is heard and maybe feel if the pump is doing it.

[boscoe99]

Your link does not show a fuel pump,only a pan.
but here is a link that shows a pump,
http://www.boats.net/parts/search/Ya...202/parts.html
but I have never seen this set up before.
Guessing that pump furnishes the enrichment system pressure to solinoids.

I would not think an electric pump would make a clicking sound, solenoids yes

those carbs look like a very complex set up
an electric fuel pump, pressure regulator ,and a bunch of solenoids with something to tell them to open just to furnish enrichment during certain times

I am wondering if the fuel pump is the interrupter type. They can make a chattering sort of sound.

The enrichment valves are used for a cold start, during warm up, load control (low RPM/high throttle opening and high RPM/low throttle opening) and for knock control. A most unusual system IMO. I think of Rube Gooldberg. Give me one Rochester four barrel carburetor feeding all six cylinders. With maybe an electric choke.

[TownsendsFJR1300]

Your link does not show a fuel pump,only a pan.
but here is a link that shows a pump,
http://www.boats.net/parts/search/Ya...202/parts.html

those carbs look like a very complex set up, an electric fuel pump, pressure regulator ,and a bunch of solenoids with something to tell them to open just to furnish enrichment during certain times

And here's MORE fuel pumps for the same engine:

http://www.boats.net/parts/search/Ya...201/parts.html Jeez..

[Warrior-VX76]

Today checked diaphragm from all 3 fuelpumps, all good and the valves as well. Solenoids and electric fuelpump are working as well. If I disconnect the fuelpump it starts running very irregularly.
Further i synchronised the carbs, runs much better at low rpm and less smoke, left 3 carbs were closed while right 3 where already opening. Engine still starves between 1500 and 3500 rpm. IŽll check the fuel system outside the engine first. its a 6 meter (8 mm) fuel line. The manual handpump in the fuel line gets soft during running at mid rpm and requires 4 x squeeze to get hard again. Next time IŽll drive the boat while pumping see if it runs smooth then. keep you posted.