Help me troubleshoot my Yamaha PRO V150 it will not rev above idle.

[SigSaurP228]

I have turned a wrench successfully on a few older OMC's but the Yammy is a far more sophisticated animal.

I have a 1985 Yamaha Precision Blend PROV 150.

Background, I just pulled the engine off of an old junk rotten fiberglass boat, anyways I bought it for a whopping $400 sold the rotten boat and trailer for $200 the very next day. So anyways I have $200.00 in the motor.

Supposedly the motor ran when last time it was out Blah Blah Blah, we have all heard the story before.

I started by running compression check on the motor. 105-110 on all 6. Figured what the heck lets start it up and see what happens, it starts and runs fine at idle. Will not rev above idle at all.

I ran a spark check on all 6 spark is bright blue and jumping a 1/2" gap according to my spark tester.

I figured it has a clogged up carbs. Pulled them off tore them open they are surprisingly clean, soaked them in cleaner overnight and blew them out with the air compressor put them back together and put back on the motor, no change.

The fuel system on the boat has been completely gone through, (I am restoring an old StarCraft 18SS) as such I have completely emptied and cleaned the tank, I have replaced all the fuel lines with new 3/8" low permeation line, I have installed a new primer bulb, and a new Marpac Fuel filter. The primer bulb primes hard and stays hard.

In further troubleshooting, I decided to idle the engine open the butterflies on the carbs and spray gas directly into the carb throats, this resulted in no RPM change.

The engine idles smoothly, I am getting no spitting of fuel from the fronts of the carbs (indicating possible reed problem).

When I bought the motor the external oil tank was removed from it, all wiring was disconnected and laid to the side. I have done all of my testing running at a 50:1 premix.

It honestly feels as if the engine is somehow governed by something but I am just lost. I am getting no answers from another forum that I am a member of and was hoping that some of the experts here might be willing to lend a helping hand.


Sorry about the long first post but I figured a thorough explanation off all that has been done might be beneficial, in diagnosing.


Thanks in advance. NICK.

[mackeral5]

Is the timing arm advancing the timer base when applying throttle? The joint between the two is bad about breaking. Typically the motor will start/idle fine but bog and die when applying throttle due to no timing advance. Wnen you cleaned the carbs---there are 2 tiny transition jets in each bowl installed vertically from the bottom of the bowl. If they are clogged the motor will behave in the same manner....good luck.

[CharlieN]

I second the transition jets that are just behind the main nozzle.
You might consider changing the reed cages to the 8 petal reeds, yours have 4 petal. and install a bigger set of carbs, either 32 or 34mm from a 200 or 225 engine. You will see nothing but a gain. Mine came alive with the change and it gives you another set of carbs to work with.

If it revs to about 2000 and flattens this would be a safety in the CDI set by the oil system. Make sure the oil control box on the port side is disabled properly and that a thermosensor on ether head is not shorted.

[SigSaurP228]

There are no linkages broken, however advancing the timer arm results in absolutely no change. What should I look for specifically with the oil tank being removed all the searching i have done results in an answer of dont disable it or zop tie the float up up in the oil tank but I am not seeing a way to do so, I did however fill the reserve tank with oil. Is there a way to bypass the oil switches on the motor side since the boat side tank and harnesses are gone. Can i ohm out the head temp sensors or bypass them temporarily for testing.


Also I am getting no temp or oil alarm horns.

[CharlieN]

For fishing use I would get the oil system working. There has been an upgrade from the Keihin pump to a Mikuni. Might have been done on that motor or might be worth looking into in the long run.

The boat side tank should not be hard to come up with. The harness is just a 4 wire cord that I have seen both on ebay buy you might have a more economical local source. If you are going to run the oil system I would want the in hull tank.

For the time being the switch in the motor tank will lift out the top of the tank, it is a floating magnet that you could tie wrap up top. The shaft has 3 reed switches in it, you want the upper one active. Just having oil in the tank does that.

If the engine is not accelerating then I expect there are blockages in the idle circuits that are not cleaned out yet. I have fought with these for a few years and just got my motor to run sweet at the low end.

If you can put the boat on water or at least back the trailer into water see in the engine will accelerate through the dead spot.
With pluged up idle circuits the engine can still get onto the main jets if you open the throttle far enough.
The power will come on hard so you want the prop in the water.
If it will make power with advanced throttle then you just need to chase what is in the idle-mid range circuits.

[SigSaurP228]

It actually idles perfect just wont rev anywhere past idle. I have ordered a replacement tank pump and harness. I can easily blow air through all of the carb jetss.

[CharlieN]

The issue is probably up in the top of the carb where the progression circuits are. I find it interesting that it could be all 6 cylinders.
Might be possible that it is a stator or CDI issue, but it should rev up a little.
This to me is where I would get the boat somewhere that you can load the engine down in water and open the throttle up. See if it will pull through onto the main jets or stall out.
Look through all the CDI testing here, http://www.cdielectronics.com/support/ and see if there are issues with the wires up into the trigger coils or stator.

I would think the engine would die out if there were electric issues.

[SigSaurP228]

Ok everyone I am now 100% sure it is electrical not carbs. This morning I unhooked the white and blue wire thqt runs from the control box to the power pack. As soon as I did I was able to tun it all the way up to 5000 rpms and could have easily kept going. I am kind of lost as to where to go from here.

[CharlieN]

Disconnecting the blue wire made a difference? That is interesting, that is the choke solenoid.

The white wire is the engine kill. First, do you have a lanyard inserted in the safety switch at the bottom of the control?

Then check continuity across the ignition switch with the key on and off. Check between white to black.

[mackeral5]

Charlie I believe he is referring to the rev limiter lead at the power pack/cdi. He is getting closer, bad sensor, oil injection wasn't properly disabled, or the ignition control box is bad?

[CharlieN]

I was trying to determine if he meant the 703 control or as you refer to the control right by the CDI. If so I answered wrong thinking as I wrote that the control box should not be rpm sensitive at low speeds.

I am still curious if the engine was gaining any RPM from idle such as being limited to 2000 revs by the controller.

[SigSaurP228]

Sorry guys I meant the control box, underneath the CDI/PowerPack, and the wire that I disconnected was the white wire with a light blue stripe.

[CharlieN]

Yes, I read it wrong, M5 had this right.

On the CDI unit the white w/ blue trace from a screw terminal on the right side is a #5 pulser coil.

White wire from the small box below the CDI is the RPM limiter and this wire would limit the engine to 2000 revs if there were an overheat signal or oil system issue.

Neither of these would prevent the engine from reving at all.

[SigSaurP228]

Figured out the idle was set just below 2,000 so it wasn't revving at all because idle was WAY to high to start set the idle down to 700 then it would rev to 2,000 and stop. Removed the white wire from the box below the power pack and it revs to 5,000 easy.

[CharlieN]

There we go, I was expecting you had a high idle.

Chase down the cause of what is triggering the safety and you will have it.
Easy check will be the two thermosensors up high on each head. Make sure they do not have continuity. They are probably good.
Then on to the oil system that has it's previous issues that you have repairs in process.
Once that is restored then hook up the white wire again so the safety system is there to protect the engine.

In the long run a set of Chris Carson's reeds on lapped cages will make the idle sweet, helps with trolling all day long.