brainstorm

[tshupe5]

Ok guys,I rebuilt the carbs very carefully and Ifeel I did a great job. Did not see any type of gumming or any sign of wear anywhere. They looked great but i at least know they are done and good to go for a while. Here is the deal. My intermitent is still there. What do you think? In nuetral I can rev motor to any rpm with no hesitation, get on plane fine and run good up to about 4000 rpm then suddenly the motor starts to loose rpm and limit power. When i sharply turn left and right i gain quick bursts of power and then low again. Ball?Pumps?Fuel line connect?Power pack.Fuel line dry rot?

 

[cousinabe]

Re: brainstorm

Will it ever get above 4k rpm?
Have you tried using an external fuel tank for testing? Trying to omit a fuel restriction issue.

You can also T into the fuel line between the engine filter and lower fuel pump. Hook a vacum gauge to see if you have between 1 and 3 hg, more indicates a fuel restriction.

 

[birdbrain]

Re: brainstorm

As a quick check look at the fuel priming bulb when the problem happens. If the ball is collapsed you have a restriction between the ball and the tank, maybe debris blocking the intake in the tank... the engine is pulling more fuel that the line can deliver, causing the ball to collapse. If the ball is soft then you could have an air leak in the line, the system is sucking air. Keep in mind, you could have an air leak in the line which would never leak fuel. If the bulb is hard then I'd take a closer look at the carb(s)
This quick test will at least give you some direction. Verify your findings using a second tank, swapping hoses or attaching gauges so you don't waste time and money.

 

[llbt]

Re: brainstorm

If the aux tank seems to work check your anti siphone valve if its a built in tank.

 

[tshupe5]

Re: brainstorm

Thanks I will check it. Where might the anti siphon be? A yamaha tech suggested that it sounds like the system is shutting down. Possibly has a bad waterpump and is going into protection mode when it gets up in temp. Makes sense since i can run it about 200 yards at wot then starts intermitent and takes my RPMs down to less than 4000 when it first started a few months back it was right at 4000. I am wondering if the waterpump has gotten weaker.The thing is, is that i am not getting an alarm. maybe i have a bad buzzer or fault in it. I am going to tear apart the control arm tonight and look for a possible loose wire.

 

[tshupe5]

Re: brainstorm

I sqeezed the ball while running it and it did not make a difference but i did notice that the ball was not very hard to squeeze?it was not flat or anything it just felt very jellyish.

 

[yamamarinetech40]

Re: brainstorm

Ok, tell the Yama tech he's stupid, that doesn't even make sense....you have probably got fuel restriction....protable tank will tell you if it works....sounds to me you may have a blocked vent on the fuel tank...either there is a vent on side(or gun'l) of boat or the cap is(should be) vented....often people replace the gas cap with regular(unvented) cap and have this problem...or 'dirt dobbers'(wasp) build nest in vent if mounted on boat....hope this is your problem, free to fix.

 

[yamamarinetech40]

Re: brainstorm

Sorry, forgot to say, since sloshing fuel in tank changes things, your pick up(tube attached to fitting on tank that submerges to bottom of tank) may be cracked, isn't uncommon.

 

[tshupe5]

Re: brainstorm

10-4 on the fuel restriction possibility.I was ready to replace the water pump thinking it was not pumping enough to cool to yamaha spec's and was setting off an alarm during temp fluctuation.Speculation at this point but you are the marine tech not me so i am going to search from the motor to the tank and see if anything looks questionable, oh yeah and the pickup tube. Thanks

 

[James R]

Re: brainstorm

Looks like no one has heard of the gallon jug test. Disconnect the fuel hose at the tank and remove the fitting from the hose. Stuff the end of the hose into a gallon jug of fuel, pump and run. This will prove the tank and pick up.
Alternatively get another hose and stuff that into a gallon jug. Dont spill any now.

 

[tshupe5]

Re: brainstorm

Here is the latest. I bought a new primer ball and hose, hooked it to the motor and ran the other end into a gas can and ran the boat. The intermitent still there. Now it is more of a contant low RPM instead of a steady up and down of RPM> Figured i would pump the ball to see if it might change anything even though i had done it once or twice before with the old ball. To my surprise, the motor would pep up and stay there if i continued to apply very stong pressure to the ball.Is this a sign of weak fuel pumps?

 

[cousinabe]

Re: brainstorm

When was the last time you replaced the low pressure fuel pumps??
They are good for about three years.

http://www.boats.net/parts/search/Yamaha/Outboard/1987/PRO_V_150LH/FUEL SYSTEM 1/parts.html

parts #15 and #28 in the diagram.

Sounds like you have isolated your issue to fuel restriction.

 

[tshupe5]

Re: brainstorm

Not exactly sure when they were changed last. I have had the boat about 4 years and have not replaced them.Sounds like i need to get down to the shop and buy two of them this week so i can put in this weekend and run wide open.

 

[tshupe5]

Re: brainstorm

I replaced the two fuel pumps and it is running faster now but still acting like something is holding it back.RPMS are somewhat spuratic.Changed fuel line, bulb, and connector to motor.To date: previous items changed,carbs rebuilt,plugs,water separator. Wish i could figure this out. Please help guys?

 

[cousinabe]

Re: brainstorm

can you provide more details of your test setup...

did you use an external tank in the lastest test?
did you pump the ball during this test?
have you considered putting in a T to the fuel line and connect to a vacuum guage as describe in an earlier post to see if there is a restriction?

Will it hold a consistant rpm.... at what rpm range does it start to fluctuate?
is this only happening at WOT

 

[tshupe5]

Re: brainstorm

First i would like to thank you cousinable for takeing time to help me with this issue. My two young boys love to fish and i am not confident about the takeing them with me while the boat is not par.Ok, I have not done another external tank test since replacing the fuel pumps.The external tank test last weekend was what lead me to change pumps because i pumped the ball while running with the external and the tighter i could squeeze the new ball, the better it would run.It will hold a consistant RPM at lower RPM but still seems like it is bogged, then when i give more throttle it kicks in real strong for short burst and then levels out at 4000-4800 and stays there as if there is a governor???? I will borrow my neighbors vaccum guage this weekend>where can i get a t and what am i looking for?

 

[JUSTINTIME]

Re: brainstorm

you want less than 4" of vacuum
before the fuel pump

 

[tshupe5]

Re: brainstorm

yesterday we took it out and found that when I sqeezed the ball it was not blowing back up. It would stay collapsed while trying to prime to start. So i got on plane and found that the ball was staying flat. Restriction right? My boat has two built in tanks that the flow is regulated by a turn style valve where you can set to main,aux, and off. Do you think the valve may be the problem? I ran it using the main and the aux tank and the problem still there. In fact, the fuel level in each was down yesterday and i noticed an even worse hesitation.How about the water fuel separator, the filter is new but the unit is probably original, do those tend to fail?

 

[JUSTINTIME]

Re: brainstorm

well it could be the primer bulb
could be clogged water sep also