99 Yamaha tough to start

[pfire]

99 Yamaha vmax ox66 does not want to turn over. Seems like starved for fuel. It will start some times but runs rough. If I disengage the gears pre start so the throttle is up it will start and then when I return it to the center runs rough and stalls. Checked plugs new last fall looked good. Thanks.

 

[rodbolt]

Re: 99 Yamaha tough to start

test spark,test compression fix the fuel system.
when was the last time the lift pumps were replaced? when was the last time the VST was serviced?
when was the last time the injector filters were serviced.
when was the last time the O2 sensor was cleaned and the voltage output checked?
lots more to this engine than plugs once a year.

 

[pfire]

Re: 99 Yamaha tough to start

Thank you for the info. now I need to find someone in my area Youngstown, ohio who has the knowledge to do all that should be done. What are the lift pumps you refer to? What is the VST? Thank you.

 

[rodbolt]

Re: 99 Yamaha tough to start

lift pumps are the low pressure pumps that place fuel in the vapor seperator tank(VST) VST is located on the front port side of the engine,its a big aluminum tank and the lift pumps bolt to the block kinda behind it.
use the yamaha marine dealer locator function.
try to find a shop in your area with at least one master tech and with school certifications from yamaha for electrical and fuel at a minimum, if not take a pass.

 

[pfire]

Re: 99 Yamaha tough to start

Thanks Rodbolt. I wish you were local enough to bring this to. I will take your suggestions and see if I can find a certified tech as you suggest.

 

[rodbolt]

Re: 99 Yamaha tough to start

I do live in a geographic anomally. I am two weeks from anywhere.

 

[pfire]

Re: 99 Yamaha tough to start

Why does the motorstart up when I disengage the gears and push the throttle up? Also, if the lift pumps were bad would I have trouble running because once I get going it runs fine until I come back to idle then still rough. Could this be as simple as a fuel filter? I think I have a line on a tech and am asking around for others who have been there. Sorry if these questions are naive but this is my level of comprehension of these things.

 

[FishinFreaks]

Re: 99 Yamaha tough to start

I do live in a geographic anomally. I am two weeks from anywhere.

Awesome "O Brother" reference.

 

[rodbolt]

Re: 99 Yamaha tough to start

cause when you open the throttle what happens ?

cause if a diaphram is ruptured and gas is leaking into the crankcase what happens?

trying to make you think a bit.
gasoline engines have a very very narrow air to fuel ratio to burn.
much above 16 parts air to 1 part gas its to rich to burn.
much below 13 parts air to 1 part gas its to lean to burn.

what does a throttle do on a gasoline engine?
answer my questions and ill answer more of yours.

 

[pfire]

Re: 99 Yamaha tough to start

I appreciate your approach and so I have done some research and discovered that the throttle controls the air flow in the engine. Therefore, the more you increase the throttle the more air. Does this answer the question? So what does this tell us? With the throttle in the neutral position I am not getting sufficient air to enable a good start. Beyond this I dont know what it means. I really do appreciate your teaching and knowledge and I look forward to your reply.

 

[rodbolt]

Re: 99 Yamaha tough to start

you got it.
so if there is an excess of fuel,possibly from a leaking fuel pump, in the crankcase and the throttles are closed the mix may well be to rich to burn.
by opening the throttles your allowing more air.
the ecu knows the TPS value changed but at cranking it will ignore it and start using the coolent temp sender and the engine start signal to actually fire it up.
by adding air and your engine starts it logically leads one to belive the air fuel ratio is rich at start up,for whatever reason.