replace all Yamaha carbs Chapter 2

[rodbolt]

Re: replace all Yamaha carbs Chapter 2

that engine has 3 carbs.
each carb is actually 2 carbs sharing a common body casting.
thats why ech carb has 2 floats,two float bowl chambers,2 main jets,2 pilot fuel jets,two pilot air jets and two bowl vent jets.
the trottle sutters,2 again, share a common shaft, if one plate opens so does the other.
if one is misadjusted would mean two cyl on opposing banks would have white plugs.
the setup is mechaniclly driven so engine runnig or not would not affect carb linkag

 

[rodbolt]

Re: replace all Yamaha carbs Chapter 2

wrong button, to early.
anyway its possible a bowl vent jet is missing or you still have blockage on a main jet.
did you ever test the plug cap resistance or check ign coil primary voltage?
WOT timing I an not as concerned about as long as from the time it used to turn 5800 to now no one has moved the WOT timing stop screw.
there again its 2 pulser coils mounted on a movable plate driven by the magneto control lever and unless something mechanically breaks it cant move unless monkeyed with.
instead of dropping 1400 on carbs drop 300 on test wheel YB1626, then you can do all your testing at the boat ramp or tied to the dock.
the test wheel simply places a known load on the engine but produces no fwd or aft thrust.

 

[99yam40]

Re: replace all Yamaha carbs Chapter 2

A inductive timing light should show if the spark is dropping on that cylinder at the problem RPM

and if you can spray fuel into that carb throat on the port side, bottom cyl and it picks up the rpm like you originally stated then you prove it is a lean fuel problem and you need to be looking inside that carb before running much more or you will cause piston problems

 

[colayn]

Re: replace all Yamaha carbs Chapter 2

wrong button, to early.
anyway its possible a bowl vent jet is missing or you still have blockage on a main jet.
did you ever test the plug cap resistance or check ign coil primary voltage?
WOT timing I an not as concerned about as long as from the time it used to turn 5800 to now no one has moved the WOT timing stop screw.
there again its 2 pulser coils mounted on a movable plate driven by the magneto control lever and unless something mechanically breaks it cant move unless monkeyed with.
instead of dropping 1400 on carbs drop 300 on test wheel YB1626, then you can do all your testing at the boat ramp or tied to the dock.
the test wheel simply places a known load on the engine but produces no fwd or aft thrust.

I have not performed the test suggeste yet
I have to get a manual because I don't know what the bowl vent, plug cap or ign coil primary is
I know it is basic but I don't have the experience
That is why I ask if a yamaha manual will illustrate the parts

 

[rodbolt]

Re: replace all Yamaha carbs Chapter 2

the yamaha shop service manuals are set up for a tech that while not nessasarily trained in yamaha products, has an understanding of how the ign system subsystems work, how fuel delivery works how and why carbs are desined the way they are and a basic understanding of a 2 stroke articulated rod engine works.
the tune up spec guide page that DonS posted is your friend.

 

[colayn]

Re: replace all Yamaha carbs Chapter 2

OK, I know what to check on the coil and plug cap now and will check as soon as I can.
Still not sure about the bowl vent. I tried to attach a schematic of the carb but no luck.
Will let you know what I find on the electric.
Also going to put my timing light on each plug wire at idle and just see if there is anything funny looking

 

[rodbolt]

Re: replace all Yamaha carbs Chapter 2

timing lamp wont tell you much, thats why I use my Kv tester and my DVA meter.

 

[colayn]

Re: replace all Yamaha carbs Chapter 2

timing lamp wont tell you much, thats why I use my Kv tester and my DVA meter.

Here are the test results:
Plug caps - resistance low was 5.10k and high was 5.38k with others in between

Ignition Coil - I checked all of them wire to wire and they were 0.0 ohms
Between each wire and the lead to the plug wire was 3.95k for the low and 4.07k for the highest, with others in between.

Pulser Coil - unplug at CDI box and checked at plug
W/R to W/G was 302 ohm
W/Y to W/Br was 301 ohm
Should I check it across any other leads ?

Any other electical points I should check.
Also I attached blow up of carb. Can you tell me which part number is the "bowl vent jet" you spoke of earlier?
Thanks,

 

[rodbolt]

Re: replace all Yamaha carbs Chapter 2

resistance tests is a last resort.
use loaded output peak voltage tests AT the problem RPM and load.
its the ONLY way to test it.
its also why it sometimes cost so much.
a stevens CD-77 is about 269 dollars and they dont swim well.
a snap on Kv tester is about 239 dollars,they eat 9V batteries and they dont swim well.
my snap on bore scope is about 960 dollars and doesnt swim well.
my tech mate vacum mate was about 700 dollars and its water resistant but I try not to test that.
I own 3 Cd-77,one of the merc peak reading analog meters and 2 CDI DVA adapters for anyone of the 4 DVM's I own.

 

[colayn]

Re: replace all Yamaha carbs Chapter 2

what do you charge to come to Ky and fix this thing
Looks like I am going to have to try and find someone, I can't buy all the tools needed.

 

[colayn]

Re: replace all Yamaha carbs Chapter 2

forgot, did you look at the attachment of the carb blow up?
can you tell me which part it the "bowl vent jet" you spoke of ?

 

[99yam40]

Re: replace all Yamaha carbs Chapter 2

I have no idea what the "bowl vent jet" is either but the pic is too small to see anything, where did you get it?
It would be better send a link to the page if it is on the web.

You do not need all that he was saying he has, depends on what you are trying to do as to what is needed.
You have a meter will it read dc voltage? If so then get a DVA adapter if you are wanting to take peak voltage readings like your manual says to.

Have you given up on the idea that you could get the cylinder to fire when you sprayed fuel mix into that certain carb throat?

 

[colayn]

Re: replace all Yamaha carbs Chapter 2

Here is the link to the carb blow up
http://www.boats.net/parts/search/Yamaha/Outboard/1999/P150TLRX/CARBURETOR/parts.html

Pretty sure it is the jets #17. If so I have checked them, they are all there and passage way to the bowl is clear.

I hope to go to the lake this weekend and try spraying fuel into each carb at WOT and see what happens (this is what the shop said they did to determine it needed 3 carbs!)

One thing , if the RPM picks up is this a definite indication of fuel deprevaiton or would the engine pick up anyway even if all is well just because it was able to get more fuel?
I don't know.

 

[colayn]

Re: replace all Yamaha carbs Chapter 2

yes, my meter will read DC voltage.
I just haven't been able to figure out how or what to check.

I say one good thing about this mess, I have learned a lot about my engine. And that is good cause I plan to keep this boat about 15 more years, like my last one.
Thanks to all of you for the help

 

[99yam40]

Re: replace all Yamaha carbs Chapter 2

Did you say you had a manual? It should give the steps and where to hook up the meter and DVA adapter to read the different voltages for inputs and outputs of the cdi.
the problem is you need to read them at the problem RPM which can be dangerous hanging off the back of a boat running at WOT

For a motor to run properly it needs good compression,good spark at the proper time (Timing), and the proper air/fuel mixture.
Too much fuel or too little fuel will not let the cylinder to fire properly. By spraying a fuel/ oil mix into the different cylinders it will tell you if one is running without enough fuel if the RPM picks up when you spray it.

But be aware that if you are running lean it can and will eat a piston if run too long that way.
The timing light thing I talked about before may show if the spark is being lost if hooked up to the problem plug wire and monitored at the problem RPM as I stated before

 

[colayn]

Re: replace all Yamaha carbs Chapter 2

I don't have a manual but will buy one. I have seen there are a few different brands, from OEM to aftermarket.
Which is best ?

I don't possibly see how I could check voltage at WOT on the water. Even running bad it will do about 50 mph and there is no place to stand or hold on.
It is a Skeeter bass boat.

I don't care about the speed, rarely ever use it. Wouldn't even worry about it if I wasn't afraid of doing long term damage.

The oil supply line are behind the carbs, on the intake. Looks like good design to supply oil even if fuel supply is low. Am I correct to assume that the cylinders are getting good oil even if one of them is starving for fuel?

 

[rodbolt]

Re: replace all Yamaha carbs Chapter 2

dude
welcome to my world.
its also why I told you to use a trusted helmsman thats NOT on your life insurance policy.
not the first time I have nen on the aft casting platform at 70 MPH, or between a pair of 250's running 60+.
dont like it, most times I dont have to, occasionally its that or admit defeat.
defeat doesnt happen.
dont wanna go to kaintuckyy to many banjoes, but if ya wanna drag it here all I would charge is parts.
to expensive either way.
on your reference page, #10 is pilot fuel,#14 is main fuel,#17 is pilot air.
the bowl vent jets are not shown but are located under #26 plate.
pilot air and pilot fuel determine the actual air/fuel ratio at idle. the mixture screw simply allows more or less of this A/F mix into the intake at idle.
its a fixed setup for the actual fuel to air ratio.
yes, oil is injected independent of fuel.
you can do the voltage checks while sitting at the helm, wire is cheap.
while there is about 150 to 250V on the ign coil primarys there is only a few milliamps of current.
make up a 6 wire harness that can stretch from the engine to you.
peel off about 1/2" of insulation at the engine side.
pre solder the wires to make them stiff.
slip this into the coil primary bullit connectors.
have the other end of this octopus avalible at the helm.
now run a ground wire and you can test all 6 ign coil primary voltages,also known as CDI outputs, from your seat.
pay careful attention to the plug that is white, compare that ign primary voltage to the other bank.

 

[jeffersondodson561]

Re: replace all Yamaha carbs Chapter 2

I have never seen a Yamaha service manual. Are they fairly easy to use if you don't know all the termanology?

Well I will put it to you this way, imagine you are in Japan waiting for crosswalk signal to tell you when to cross the street...they are so simple they are intimidating

 

[rodbolt]

Re: replace all Yamaha carbs Chapter 2

and this from the mouth of babes.

 

[Don S]

Re: replace all Yamaha carbs Chapter 2

Rodbolt
What do you see in the picture below?