Low Speed Trouble

[Tim Haines]

I just purchase a boat with a 2001 Yamaha 225 OX66. The engine hours are only 295. The boat has sat for long periods of time without use in dry storage.
I am having a low speed problem around 1000 to 1400 rpm's. At those RPM's the engine runs very rough and has vibration. As I speed up and all the way to 4000 RPM's the engine runs very smooth at cruise. I have only been able to run at 4000 rpm for less tan 2 minutes because of wake zones. I have just added Startron Fuel treatment to about 60 gals of remaining fuel with no effect yet in 3 hours of use since treatment. Tune up was performed 11/08 according to previous owner. Does anyone have an idea what the probelm could be. Thank you.

 

[Mas]

Re: Low Speed Trouble

I would think that carbs are gunked up with varnish due to non-use. The idle passages are very small and can become easily gummed up.

MAS

 

[Tim Haines]

Re: Low Speed Trouble

How would you suggest I treat this problem?

 

[Mas]

Re: Low Speed Trouble

If you have gummed up carbs, that would mean rebuilding them and cleaning all the passages.

But, before you even attempt that, do a compression check and spark check on all the cylinders. You want all the compression nubers to be fairly even and spark to be able to jump a 7/16 inch gap with a strong blue arc. You can buy a spark checker at most auto stores for about $10-15. Make sure you ask for a spark "gap" tester with adjustable gaps.

Also, you can try removing each spark wire one at a time to see if any changes in rpm occur while the motor is running. Allow the spark to ground harmlessly to the engine block and keep it away from your ignition. If rpm doesn't drop when you've pulled a plug, that cylinder is not producing any power...which is another possibility for poor running.

Tell us what you find out on your tests,

MAS

 

[cousinabe]

Re: Low Speed Trouble

First off, your motor is fuel injected, not carbed.
If you're gonna be fixing this motor yourself, get a manual and read up. I can't stress that enough.

These are great motors if maintained correctly.
This motor incorporates a CCS ignition; which will shut down cyl #5 until about 2000 RPM and #2 between 800 and 2000 RPM. They do vibrate a little at lower rpms.

test compression, test spark. if both pass the next step is test fuel rail pressure at the trouble RPM, having the diagnostic test lamp attacthed when testing rail pressure may give even more information.
if the VST cannot get the fuel due to a restriction between the liquid level in the fuel tank and the lift pump the VST runs dry.
so a fuel system vacum test is also in order.

vacuum must be less than 4"Hg at about 60 liters per hour at the lift pump intake.
your describing a classic loss of fuel in the intake manifold.

break the fuel system into 3 main parts, the supply side, this covers everything from the liquid level in the tank to the lift pump output.
then the VST ,this includes everything from the inlet needle at the VST to the 6 injector screens at the injector rail.
then the 6 injectors.
be aware that ALL lubricating oil is injected with the fuel via the injectors.
failure to have an adequate fuel supply in the intake manifold can and will result in a detonated piston and/or connecting rod bearing failure.
you have mostly gone as far as you can without buying or making certain test equipments.
if for whatever reason,the fuel rail cannot maintain 33PSI minimum the engine runs lean.
the lower the pressure the leaner it runs.
all of the above is assuming your not getting any alarms and the alarm system is working.

Not knowing what preventative maint has been done, I would
1) replace low pressure fuel pumps
2) replace VST screen and o-ring.
3) clean pressure regulator screen
4) clean fuel injector screens
5) clean/test O2 sensor for proper output voltage.
6) replace water pump
7) replace engine filter and water separator filter.
8) inspect/clean out popit valve; PRV.
9) link and synch and set TPS.
10) replace thermostats.
11) check that resistance of spark plug caps are in spec.
12) properly adjust the oil linkage rod.

If all of those items are completed and you run with fresh fuel, you will have a sweet running machine that can take a beating!

 

[salvagesolution]

Re: Low Speed Trouble

sounds like fouled plugs when its running "smooth" its prolly only running on 5 cylinders and from what it sounds storage/low hours/ and not being used often

you might be able to clean them out by reving the **** out of it or pull the plugs and look for that black oily coating

they dont like to sit at idol very long

 

[rodbolt]

Re: Low Speed Trouble

rev the **** outta it and it most likly will puke parts.
when running correctly that motor will idle longer than your bladder will allow you to remain at the helm.
if its running on 5 cylinders or even 4 it still may be running correctly as far as the ECU is concerned.
unless its a VX225.
VX motors did NOT incorperate CCS.
on the 3.1L motors and larger lift pump intake vacum max is 6" not 4"Hg.
I would still like to see less than 5"Hg.
the 3.1L motors were hard on fuel pumps.
glad to see someone actually reads some of my posts though