help rodbolt

[1stpriority]

I have twin 1994 yamaha 250 txrs outboards on my boat. The right motor runs strong up to 5700 rpm and the left is having problems at wot it will go to 5400 rpm. They used to both hit 5700. When I gun just one motor at a time the right runs strong to 4300 by itself and the left feels sluggish and hits 3700. I ran all new fuel lines , new fuel fiters and rebuilt the carbs. It has good response off idle but just doesnt have the power. like the right one. good compression 115 to 120 all cylinders. The next step I am guessing is the timing not advancing for some reason. Any help would be appreciated

 

[rodbolt]

Re: help rodbolt

I would check the low pressure pumps and reinspect the carbs.
I suspect somethig is leaning the fuel out. a stuck thermostat can do that as well.

 

[1stpriority]

Re: help rodbolt

Thank you Rodbolt , I will check tstats first

 

[1stpriority]

Re: help rodbolt

Ok I replaced the tstats, new fuel pumps, went through the carbs again , I even ran the boat wide open , the timing advanced to 18btc and I squirted a gas oil mix into each carb while wide open and it didnt make a difference. I am totally puzzled. Any help would be appreciated. Thank you

 

[1stpriority]

Re: help rodbolt

I forgot to mention I also put a new tps on. I realize I probably did alot here that it didnt need but I am covering all the bases

 

[rodbolt]

Re: help rodbolt

did you use a temp gun and test the head temps while running?
the fatal flaw is if the stbd head stays cool it drains the fuel bowl for #6.

 

[99yam40]

Re: help rodbolt

the fatal flaw is if the stbd head stays cool it drains the fuel bowl for #6.

OK Rodbolt, my curiosity has kicked in again and I am clueless as to how that can happen.
Just how does that happen? and why just #6?

 

[1stpriority]

Re: help rodbolt

thanks rodbolt I will give it a test run and just bought a new laser temp gun. Do you think the new tstats could be defective?

 

[rodbolt]

Re: help rodbolt

dunno
your the one testing, I am behind a monitor.
if you wish to be your own tec .
read.
understand how your system works.
the reson I asked about the temp, certian situations can drain the #6 fuel bowl faster than the lift pumps can fill it.

 

[1stpriority]

Re: help rodbolt

OK I checked the temp on each head on both motors , according to my laser temp they are reading 110 and 112 on both motors. I also put a timing light on each spark plug wire on port motor and the are all fireing. I thought maybe I was dropping a cylinder at high rpm. The timing is advancing right at 18btc at wot also. I am stummped. What else should I look for. I also ran the boat wot and squirted oil and gas mix in each carb with no results. Oh according to my fuel moniter the port is burning about 4gph more at normal cruising speed of 4000 rpm also. What else should I be looking for. Do you still think I should go through the carbs again. I was thinking can I squirt starter fluid at the fuel lines going to each carb at wot to see if I might be sucking air in one?

 

[rodbolt]

Re: help rodbolt

cold start enrichment wont let go until after 115*.
use a winky blinky to verify its going out of cold start.
then read and head how your system works BEFORE posting about detonated pistons.

 

[1stpriority]

Re: help rodbolt

Rodbolt you seem to know what you are talking about and I am sure that everyone here appreciates your help,but I have read the shop manual from cover to cover and there are no details about what you post in there. You seem to be gifted in your ability to troubleshoot outboards but that doesnt mean you have to be arrogant in your answers. I only posted the troubleshooting that I did to find out if all the cylinders were firing at wot.

 

[rodbolt]

Re: help rodbolt

not being arrogant.
however you have an ign system with 3 basic subsystems,a fuel system with about 5 subsystems.
you have to understand whats going on.
the reason #6 goes lean if the stbd tstat fails and sticks open or is missing is obvious if you understand how the enrichment system works.
below 113* the ecu controls the enrichment by opening the solinoids,cold engines need more fuel.
however at high speeds and low temps the solnoids can add up to 20% richer mix.
the solinoids all feed from #6 fuel bowl and the feed system isnt designed to operate cold at high RPM leading to the fuel in #6 bowl being sucked dry leaving nothing for *6 carb circuits.
leans out *6 cylinder and leads to detonation.
if the knock detect grabs you RPM falls,if its unplugged timing defaults to 7* BTDC and RPM is lost.
tstats are set at about 120*.
that engine requires lots of fuel and if it cannot get it it doesnt like it.
a quick run with the diagnostic test lap instaled will eliminate a lot of ghost chasing.

 

[99yam40]

Re: help rodbolt

Thanks Rodbolt, I knew if I kept watching and reading I would eventually find out about the #6 fuel bowl going dry before the others.

 

[rodbolt]

Re: help rodbolt

its cause if the ECT never tells the ECU its warm the ECU reacts to the ECT telling the ECU its cold and the ECU opens the fuel enrichment solinoids.
then #6 goes dry.

 

[1stpriority]

Re: help rodbolt

Once again thank you rodbolt I think I will switch tsats with the other motor and see if that clears it up and I will also put them in hot water to see what temp they all open at.