Question on Yamaha Prime Start System

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99yam40

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For anyone that has a 3 cylinder Yamaha with the Prime Start System I have got a question or 2 for you. Mine is a C40TLRX but I am sure any others would be the same.
Pull the line off the prime start system where it attaches to the intake behind the top carb and see if you can get any fuel out of it when you turn over the motor cold with it in the normal position. I do not, only when it is in the open position does fuel get pumped out by the prime start pump. Thinking that the passage ways were plugged up, I blew air (by mouth not compressed air)into the line I took off and with it in the normal position, air is coming out of the vent on top of the center carb without much back pressure.
I am wondering if this is normal or is there some type of problem with my carb?
My motor normally starts on the 2nd or 3rd 2 or 3 second turn of the key when cold, whether or not I have the line even hooked up. Of course cold here is usually in the 70s or 80s here in Texas during the summer.

I was just wondering if anyone else's does the same thing, air will vent out of the top of the middle carb, or if you get fuel pumped through and out of the line when cranking in the normal position with motor cold.
 

robert graham

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Re: Question on Yamaha Prime Start System

Are you having a problem with starting your motor? My 90HP Yamaha has the prime start also, but I have only a vague idea how it works, but hopefully one of the real guru's on here can help you. Good Luck!
 

99yam40

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Re: Question on Yamaha Prime Start System

Robert,
I am not having a starting problem that I know of right now, but it does not get very cold around here and if it does I probably will not get out in it.

I am trying to understand how the system works and if there is a problem with mine,since I do not get any fuel out of the system while in normal position.
If you get a chance try what I talked about to see if you have fuel pumped out when in normal and cold.
 

BadBowtie4wd

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Re: Question on Yamaha Prime Start System

From what i understand under normal mode it will only put gas around to the intake if it is cold? what temps you running? I will know more how this things once duck season gets here. yes it should dump around when in OPEN mode, but normal is supposed to work off the silenoid
 

99yam40

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Re: Question on Yamaha Prime Start System

Nick,
I am just trying to get some people to check theirs and report back as to whether or not they get fuel out of the hose when 1st turning the motor over and if they can blow air into the hose before the motor runs for the day.
The morning air temps here have been in the middle to upper 70s lately, maybe I need to put a ice pack on the unit for a while to see if that makes a difference or not. I still do not think I should be able to blow air through it and have it come out of the vent on the carb.

I do not think you would call it a solenoid , maybe a heating unit, The books call it a Prime Start assembly.
 

99yam40

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Question on Yamaha Prime Start System for Rodbolt

Question on Yamaha Prime Start System for Rodbolt

Just bumping up to see if Rodbolt or anyone else can give some input on the subject.
 

JustJason

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Re: Question on Yamaha Prime Start System for Rodbolt

Re: Question on Yamaha Prime Start System for Rodbolt

You won't get fuel out of that hose by cranking, its not attacted to the fuel pump. Basically crankcase pressure "sucks" fuel through that line when the engine is cold. Inside of the starter assembly is a thermoelectric valve. As the engine runs a wax pellet inside of the valve heats up and closes the fuel off from the vaccuum supply, and the engine can no longer "suck" fuel through that line.
Hope that helps explain it.
 

99yam40

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Re: Question on Yamaha Prime Start System for Rodbolt

Re: Question on Yamaha Prime Start System for Rodbolt

JJ,
Thanks for the reply.

Most of us are still learning a lot from this forum and welcome all the input.This system is a real learning experience for me

I think it is strange that the switch turned to open pumped fuel out, but not when in normal position, is that because the pump only works during the emergency or open position? It has a diaphran pump in the Prime Start system itself , so I thought it would pump it out in the normal position also.
I thought it is also strange that the line was not restricted when I blew into it and it vented through the middle carb vent. I will have to pull a vacuum on the line and check to see if it pulls fuel to see if I have a break in the suction.
 

JustJason

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Re: Question on Yamaha Prime Start System for Rodbolt

Re: Question on Yamaha Prime Start System for Rodbolt

put 12 volts to the starter assembly for a few minutes (light blue wire i believe) You'll feel it start to get warm. Then try blowing through it, if the thermoelectric valve is good then you shouldn't be able to.
 

99yam40

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Re: Question on Yamaha Prime Start System

JustJason,
Thanks for your time and all the info you give. My curiosity is getting the best of me like always and I need one more answer.

I just looked at it again this evening and with the motor cold I pumped up the primer bulb until hard making sure the fuel bowls were full, and I could not suck any fuel through the primer line just air or fumes and I could blow through the line and it vented through the vent on carb 2. I cranked the motor and ran for a while on the muffs, shut down and pulled the line off and it did close off.

This leads me to believe mine if functioning correctly, but also leads me to believe the Prime Start System does not feed liquid fuel into the motor during start up or warm up just fumes from the top of the middle carb.

Is this the way the system is designed to work or is it suppose to pull liquid fuel in and mine is not functioning properly?
 

JustJason

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Re: Question on Yamaha Prime Start System

honestly i have no idea, i have to have 1 in front of me to tell you. I have the SM at the house (at the womans right now) 1 of these days i'll upload it and post a link in here.
All I can say is that if your engine starts easily (the way its supposed to) i'm assuming the valve/prime start is working. When it doesn't work they can be a bxtch to start and they run to rich.
 

99yam40

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Re: Question on Yamaha Prime Start System

Thanks for the input JustJason,

I have not found anything in my manufacturers Yamaha Service Manual that would say is it is or is not suppose to be pulling liquid fuel or just fumes through that line.

All of the older OMC motors I have owned dumped liquid fuel into the carb through a solenoid or manual pump to prime for start. I just supprized me that this Yamaha did not. Like I said before my motor will start with the 2nd or 3rd turn of the key when cold even if I have the line disconnected, but it does idle a lot better with the line hooked up.

I have not had anyone else that would say if theirs acted the same way as mine, so I was concerned that I had a problem.
 

99yam40

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Re: Question on Yamaha Prime Start System

I thought I would post a few sketches I made of the Prime Start System to help others see how it works and find out if others think these are correct or not.
This is the way I believe the system works judging from what passages are open and which are closed during the different switch positions while the system is cold.
My findings are that in the normal position the motor sucks a fuel and air mixture into the manifold through the line (I installed a clear vinyl line in place of the factory one for testing, but did not see any liquid flow.) http://forums.iboats.com/attachment.php?attachmentid=39809&d=1256314500
I did see a solid stream of liquid fuel pumped into the manifold when switched into the open position.http://forums.iboats.com/attachment.php?attachmentid=39810&stc=1&d=1293464763
when in the closed position both the vent line and the line to the manifold are plugged off and have no flow.http://forums.iboats.com/attachment.php?attachmentid=39811&stc=1&d=1293464763
When warmed up the needle will plug the orifice to stop the fuel flow in the normal position and also restricts the air flow through the vent to the carb..
The layout may not be exact, but the flow concept should be correct.

any comments on corrections are welcomed
 

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rodbolt

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Re: Question on Yamaha Prime Start System

your reading way more into a simple system than you should.
 

99yam40

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Re: Question on Yamaha Prime Start System

You are probably right, but my curiosity has always run wild and sometimes I just have the need to understand how something works, not just that it does.
Since I have not been able to find anything saying if the system is designed to push or pull liquid fuel or fumes in the normal position, I thought I would try to figure it out myself and put it out there for others to see and see if they disagree.
 

Gary13

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Re: Question on Yamaha Prime Start System

Since this thread was referenced in another recent post, I thought I would bump it up with a little information I got from a Yamaha mech.
I was having starting problems with a 2008 F40TLR. I would have to crank it several times to get it to start and idle. After starting, I had to wait several minutes before it would run above idle without stalling. Other than that, after warm-up, it ran fine.
I mentioned this problem to the mech and inquired about the choke system used on the F40, since depressing the key switch on the remote did not produce the choke solenoid valve click I had come to expect and love. At this time I was introduced to the Prime Start Fuel Enrichment system. Since there was no solenoid, I had quit depressing the key to the choke system and was informed that even though there was no choke, depressing the key actually energized the prime start system. This is good information and should have been in the owners manual, or so one would think.
Long story short, this solved my cold-start problem and worked fine for the few months that the engine actually ran before developing other catastrophic problems.

Gary
 

99yam40

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Re: Question on Yamaha Prime Start System

Gary,
I have to disagree with you and your mechanic,"depressing the key actually energized the prime start system" is not a true statement.
The prime start system is active all the time, with no need to push the key or any other action from the operator. It is heated up, from voltage while the motor is running, to close it off when the motor has run long enough to warm up. If you want more info on the system do a forum search and read what Rod Bolt and other experts have to say.
 

rodbolt

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Re: Question on Yamaha Prime Start System

gotta go with 99 on this one.
the prime start on the small inlines and carbed F motors derives its operating voltage from either a power coil or the lighting col depending on which engine,
once the engine is running voltage is supplied to the electrothermal valve until the flywheel quits turning or something breaks.
on a prime start engine the only thing the dark blue wire in the 10 pin main harness switch does is take up space.
on the two stroke prime start 40 there is actually a diaphram pulse pump operated off the #2 cylinder located on the #2 fuel bowl, to aid in fuel enrichment. needs to be checked or replaced periodically.
your tech needs both outboard systems class and a fuel class.
I hope he or she is enrolled this year.
that electrothermal valve is simply a wax pellet heated by current that pushs a tapered rod into a seat.}
no clicks squeks or beeps are ever heard from it and its rare they fail.
on the F40. you have to allow about 5 mins of idle time before trying to accelerate or they simply lean out and die.
just the way it is.
 

Toltec

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99yam40.and Rodbolt. Am I understanding that there is no voltage to the electrothermal valve until the engine is started? If so, that sounds a little counter intuitive to getting a cold engine to start and remain running? Unless, of course, that power supplied when the flywheel is turning heats up the electrothermal valve very quickly? I have a 2005 F40TLR that is very difficult to start and keep running until it gets warm enough to continue to run. There is no power to the valve with the key in the in position. And, I thought I read somewhere in this forum that the plunger of that valve, when the engine is cold, is in the correct position for starting the engine?

thanking you in advance for your response.
 

GA_Boater

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99yam40.and Rodbolt. Am I understanding that there is no voltage to the electrothermal valve until the engine is started? If so, that sounds a little counter intuitive to getting a cold engine to start and remain running? Unless, of course, that power supplied when the flywheel is turning heats up the electrothermal valve very quickly? I have a 2005 F40TLR that is very difficult to start and keep running until it gets warm enough to continue to run. There is no power to the valve with the key in the in position. And, I thought I read somewhere in this forum that the plunger of that valve, when the engine is cold, is in the correct position for starting the engine?

thanking you in advance for your response.

Awfully old thread. Please start a new thread of your own.

Closed.
 
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