2000 Yamaha 150 hp 2stroke no top end

ermess

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2000 Yamaha 150 hp 2stroke no top end,good compression, good spark, timing right on the money,at idle sprayed fuel down throat of each carb with two plug wires off, each carb bogged like it is supposed too. Ran motor without cowling and flame arrestor, fuel spray thru emulsion tubes looks good and uniform thruout all six cylinders at WOT, but engine wants to race and bog race and bog. Problem starts just before WOT- cam position is about 1/2 before raised knob.<br />Customer had boat for sale - sat in hot sun on a parking lot - August - December, brought back home - sat 6 weeks and now has this running condition. ?
 

brownies

Chief Petty Officer
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Jul 5, 2004
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495
Re: 2000 Yamaha 150 hp 2stroke no top end

I may not be one to give advice here, but, Won't hurt to check all the fuel lines,filters, and connections. <br />I've encountered similar and took me forever to find a split in a fuel line. It wouldn't leak, but, it would suck air. <br />Changed fuel line cured the problem.
 

Ray Neudecker

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Re: 2000 Yamaha 150 hp 2stroke no top end

Brownies on the right track. Sounds exactly like a fuel restriction. The hard part is finding the cause. The obvious starting place would be the filter. If it has an inline filter in the boat change it. Do not run that same fuel that sat in it or you are likely to burn a piston. Bound to have moisture in the tank at best from all that sitting. that is what the water seperating filter is for. Fuel pumps are due to be replaced by now also and can cause the problem.
 

rodbolt

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Re: 2000 Yamaha 150 hp 2stroke no top end

had some issues with the engine side of the fuel connector as well. the oring will swell and restrict fuel, can be quickly found with a vacum guage. or you can attach a remote tank to the engine mounted filter. <br /> do all testing in the water, visual spray is decieving and why would you run it with two plug wires off ?<br /> if you suspect a main jet issue its quite easy to pop them out for inspection as well as removing the bowl drains and inspect for crud, if the drains are cruddy so are the jets.<br />but the old low tech vacum guage is a techs best friend, also one of the most ignored friends.
 

ermess

Petty Officer 3rd Class
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Re: 2000 Yamaha 150 hp 2stroke no top end

Eliminated everything on the boat yesterday evening, attached a remote tank that eliminated existing fuel tank,water seperator filter, and primer bulb - still has hi speed sputter - he is fine almost up to WOT and right before, he gets a slight miss and this continues thru WOT not much but it is there.
 

rodbolt

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Re: 2000 Yamaha 150 hp 2stroke no top end

have you inspected the main jets and drains?<br /> and have you tested the plug caps ?
 

Ray Neudecker

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Re: 2000 Yamaha 150 hp 2stroke no top end

Now it is time for the fuel pumps replacement and carb cleaning. Plus go back and change the water seperator filter. This is an almost routine process where the motor was not serviced prior to being allowed to sit.
 

ermess

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Re: 2000 Yamaha 150 hp 2stroke no top end

What kind of Fuel pressure reading should I see on these two pumps,<br />and what is the best way to test resistance (and what should it be) on the plug caps? are they removable from the wire or will this damage them. <br />Thanks for your help<br />ED
 

rodbolt

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Re: 2000 Yamaha 150 hp 2stroke no top end

dude I know your an independant, as I am most the time, however ya gotta buy test equipment and service manuals. yes they are expensive put quit winging it.<br /> the red caps unthread from the wire. the resistance should be 5Kohms plus or minus 1 Kohm.<br /> fuel pressure is irrelevant diaphram intergrity and pump intake vacum is what your looking at, at the pump intake system vacum must be less than 4"Hg at WOT.<br />shoot a list of all the electronic and diagnostic test gear you have and ill try to help.
 

ermess

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Re: 2000 Yamaha 150 hp 2stroke no top end

I appreciate any help I can get. I have most of the diagnostic and shop manuals, it is just such a slight hiccup that I wanted to make sure. The boat sits on a lift at the owners house with the owner looking over my shoulder the entire time-(comes with the job),just like to have all the bases covered when I am in those type of situations. This is a 2000 Yamaha 150 with yellow plug caps I wasn't sure if these pulled off(plug cap spring) or unscrewed. Vacum is less than 3"hg so I feel that is within spec I just was wondering if there was an accurate psi to go by on the other side of the pump. <br />Thanks for all your help<br />Respectfully<br />ED
 

ermess

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Re: 2000 Yamaha 150 hp 2stroke no top end

Rodbolt,<br />I have a couple of inline spark testers I got from Precision a couple of years back - wondering if they would show this hiccup.<br />Thanks<br />ED
 

seahorse5

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Jan 24, 2002
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Re: 2000 Yamaha 150 hp 2stroke no top end

A common problem on Yamaha motors like that one that has sat for a while is varnish deposits that accumulate in the float bowl and float around at high speed causing all kinds of intermittent problems.<br /><br />Another area of concern is between the fuel inlet fitting and the needle valve seats in each carb. There is a small brass screw on the side of the carb to access this cavity for cleaning. On the older carbs, there was no way to clean it out unless you drilled an tapped an access hole in the side.<br /><br />If the fuel lines are starting to rot, specs of rubber can lodge in that area.
 

rodbolt

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Re: 2000 Yamaha 150 hp 2stroke no top end

never seen the yellow caps so I cant comment, the suzuki's had some with yellow caps. all the yamahas I worked with had orange or black caps, some of the oil control module kits come with black resistor caps that dont show up in any service literature.<br /> best thing would be to rebuild the carbs and replace the pumps and continue.<br />test whell YB1626 would help tremedously at this point.<br />its expensive but fits a lot of V6 yamahas and it lasts forever.
 

ermess

Petty Officer 3rd Class
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Jun 25, 2005
Messages
96
Re: 2000 Yamaha 150 hp 2stroke no top end

Took your advice Rodbolt & Seahorse, cleaned carbs flowed all circuits -varnish looked minimal, only thing noticable was a layer of varnish on lip of nozzles. Runs like a bandit, customer happy.<br />Thanks for the help.<br />ED
 
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