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**boats.net** · 12-29-2009, 11:59 AM

Probably not a problem in controls, it just has a neutral switch to prevent starter from working if in gear.
Do a compression test to make sure compression is even.
A hestitation or stall on acceleration is usually a fuel or carb problem.

**Steve Helmrich** · 12-29-2009, 04:03 PM

OK...thanks Boat.Net....I would have to agree with you but, new fuel filter/new water filter....gas looks very clean...and the carbs have been cleaned 3 times including re-build.....I can not figure out how it could be fuel or the carbs at this point...however, I am grasping at straws after investing nearly 2 grand in the issue (including 1400 of it by Yamaha Certified mechanics) and the issue still persits albeit intermittantly...usually after the engine warms up for a 1/2 hour or so....any thougths other than the fuel or Carb....

**99yam40** · 12-29-2009, 08:30 PM

Does it have good compression?
Does your temp/oil alarm work?
Have you tried checking the timing when the motor starts having problems to see if the CDI is retarding the timing? that is how it reduces the RPM on overheat or oil problems.

Have you hooked up a fuel pressure/ vacuum gauge in the fuel system to see if everything is in spec and there is no air leaks or restrictions in the fuel delivery?
And have you tried it when the problem is showing up?

**Steve Helmrich** · 12-30-2009, 08:30 AM

Thanks 99yam40....the oil alert works because on two separate occasions when I ran low on oil it slowed the boat to about 5 miltes per hour....I do not think the temp alert works....I know the engine has heated up (when the pee hole was clogged with some pebbles) and it ran hot for a few minutes until I cleared the water hole ...and no alert sounded.....

Do you think it has something to do with the hot alert switch... a new CDI was instaled by the Yamaha mechanics...which we thougth resolved the issue...but, after 3 or 4 times out...it has come back....

The problem I have is that this is intermittant...it will do it 5 or 6 times...then ...take off and run ok....then 20 minutes later...it repeats the 1/3 throttle issue....then will magically "fix itself".....that is why I am thinking electrical/faulty switch/soemthing in the throttle, etc....I will rerun compression on it...but, previsouly they were all even and within specs.....

The only other thing I can think of is soemtimes the vent tube get's gas in it...bad design....i generally fill up the take when the boats out of the water and I do see a fair amount of gas exit the vent hole when I fill up....it could be laying in the vent hose and causing a vent issue...possibly....

Could that do it...if there was excess gas in the vent line....

**dorf** · 12-30-2009, 10:36 AM

Hook up another external(6 gaL) gas tank and see what happens.

Did you check out(or remove) the anti-siphon valve in the gas tank as I suggested before????

**99yam40** · 12-30-2009, 11:02 AM

I really don't know if or how the vent would cause your problem, but you need to find out what is going away when the problem shows up.
A motor needs compression, a good spark at the proper time, and the right mix of fuel and air to run properly. Something has to be changing one of those to shutdown the motor. Or is it just stumbling real bad and will run fine after you get it up in RPMs

The tell tail getting plugged will not overheat a motor it is just an indicator that there is water being pumped. I believe the pink wire on the temp switch on your motor will cause the alarm and put it into safe mode when grounded to the block. An easy thing to check for proper operation with the key in the on position

I myself would think it is in the carbs or fuel system from what your have written, but is hard to see. The timing and spark can be checked with a inductive timing light to make sure what is going on with them when the problem shows up. And a fuel delivery problem can be tested with a pressure / Vacuum gauge and a piece of clear tubing can be temporarily installed after the fuel pump to see if there is air being sucked into the system

**Steve Helmrich** · 12-30-2009, 11:57 AM

Thanks Dorf and thanks YAM.....

No I did not remover the anti syphon valve....but will check into it

For what it is worth I have a center console Cape Craft boat...when i first got the boat (used) I had a very difficult time fueling it...it would only take a gallon or two...I called Cape Craft and they advised me that the vent line may have gas in it and to disconnect it and blow it out...which I did and thereafter could fill up OK....however, I do notice that when I fill up a fair amount of gas comes out the vent...directly above the fill hole......at least 3 or 4 tablespoons of gas on each fill up.....I also know that there is a full curl (loop) in my vent line...Cape Craft said the loop is intentional (why I don't know) ...my thought was there may be gas collecting at the bottom of the air vent hose loop...which could impede air flow and possibly gas flow...I would think as the boat attempts to plane or moves or rolls...when I throttle forward...that could be effecting venting and maybe fuel delivery...it could be intermittent too and clear itself and then re appear...

It's jsut a thought ...as I read through yoru comments about vacuum and fuel / air delivery....it got me thinking about this "gas in the vent line issue"

Is it normal to have a little gas in the vent line...and be dispersed when you fill up...again, it's not alot but it is definitely there...I see it disperse just about every time I fuel up....?????

**dorf** · 12-30-2009, 12:29 PM

If there is a loop,(and fuel in the line) seems like the fuel would puddle in the bottom of the loop.

It would be the same as a trap under you kitchen sink, or toilet. It won't let air in and out. Can't breathe.

Seems like a test portable tank would clarify this.

In my experience with airplanes...if no open fuel tank vent ...no gas will flow..

Cheers !!!

**Steve Helmrich** · 12-30-2009, 02:55 PM

Thanks Dorf...I do have a 3 or 4 gallon tank I could use ....and see what happens...by the way where is the Anti Syphon valve and what should I look for? Thanks for your help by the way ...

**dorf** · 12-30-2009, 03:14 PM

The anti siphon valve is a ball /spring affair that is located in the outlet fitting of the fuel tank where the rubber fuel line connects to the fuel tank. The engine fuel pump is supposed to suck the ball off seat and then prevent fuel from being siphoned when the engine is shut down.

After removing the fitting you should be able to punch it out with a punch or just purchase another similar type fitting.

I'm also guessing you are having starting problems ??????

Again... the vent should be clear to allow air in and fuel out. There are a multitude of vent fittings available to re-plum the vent line where water will not get in and allow air movement.

Tell us what you find and the fix !!!!

**cjdc2000** · 09-28-2020, 07:56 PM

Hi - Wondering if this ever got resolved. I'm having a very similar issue. Engine stalled out after about 15 minutes of running two days in a row. Just rebuilt carbs and now it won't get above a low RPM. Turns out I forgot one plug in a carb. Hoping that will fix the issue but doing some research and came across this thread.

**Keithbaja** · 09-29-2020, 02:05 AM

You might do a high speed shut down

**Keithbaja** · 09-29-2020, 02:24 AM

dorf, the "loop" is on the topside if done right
BUT, billie bob comes along and messes with it while installing bilge pump, bait tank pump. There are standards that are "SET" on vessel's. Dosnt sound like anyone here studies. CK out ABYC and CFR'S part 33. What do you fly ? Me
180's. My 2nd grade teacher had a cub, so I started early. OUT

**Keithbaja** · 09-29-2020, 02:47 AM

Last post. Getting late. To all mounted tank boat owners. Check your vent screen for blockage. bugs like to plug them up. It's on outside of da boat

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2004 yamaha 2 stroke 50TLRC Problem...HELP

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