OX66 2002 250 HP Sputtering/stalling problem!!

[Gill7858]

I have a 2002 250 HP OX66 saltwater series 2 stroke. Just a little back ground, about 50 hrs ago I had the powerhead rebuilt, new O2 sensor, New fuel Lines, and replaced thermostats.

From idle when i start to throttle up to get on plane, engine starts to stutter/sputter/stall at about 1600 rpms. if i leave it at 1600 rpms, its will fluctuate between 1600-2300 rpms. when i continue to power up the engine "kicks in" and runs completely normal. If i didnt like to ***** at 1700 rmps this wouldnt be a problem but *****ing is next to impossible. When they rebuilt the powerhead they cleaned the VST and injectors and replaced the injector filters.

this problem was happening BEFORE and AFTER the powerhead rebuild.

I dont know what else to do? Any suggestions?? Thanks in advance

[99yam40]

If it was happening before the rebuild, then it could be what caused you to have to do the rebuild.
What was the reason for the rebuild? low compression one one or more cylinders?

Take it back to the ones that did the rebuild or find a shop with a Yamaha Master Tech to have them troubleshoot and fix it before it ruins the motor again.

could be loosing spark, wrong timing, lean fuel/air mix
Monitoring fuel pressures should show if filters/screens are a problem.

Strange it goes away at higher RPM.
Some motors have different charge coils for low and high RPM

Hopefully Rodbolt17 will give some thoughts on the off idle problem

[rodbolt17]

on that engine charge coils are bank to bank.
that engie also uses CCS.
means below about 800 RPM #5 cyl does not fire,from about 800 to about 2000 #s 2 AND five dont fire.
the list of issues could be long long.
however a quick look with a diagnostic test lamp can rule some of it out.
with the surging without moving the air valve(throttle) your either adding ign timing OR fuel.

[Gill7858]

Rodbolt,
My mechanic, who is the same guy that did the rebuild, hook it up to the lamp and it didnt show any errors whatsoever. He specializes in rebuilds, not just yamahas and doesnt have a computer to hook the engine up to. I cant say i understood all or any of what you said, but what should be my next step? i though that i might be a fuel restriction issue so i chenged out all my lines from tank to engine and no change.

[rodbolt17]

use yhe yanaha dealer locator function.
find a shop with a master tech or at least with fuel and electrical certs.
cannot use a laptop on this engine.
however it will trouble shoot itself for the most part if you know what is right and what is not.

some years back a dealership that the owner and I have been friends for years called me.
they had spent two days trouble shooting a lack of spark at #5 at idle on an OX66 250.

wanna guess my answer?

[madharchod]

i would suggest you buy your self a YDS from E bay and hook it up to the computer and your motor it will vitiate few of your problems

[rodbolt17]

OX66 cannot will not and never will support YDIS.
ONLY the diagnostic test lamp.

[Gill7858]

Thanks rodbolt. Test lamp was good to go.

I took her out today and its still doing the same thing. A couple of people said that surging is normally cause by a fuel restriction. I've changed out the fuel lines so I'm changing out the filter element which looks dirty to see if that's a simple cure and go from there.

[99yam40]

Did they use the lamp on it while it was surging?

Problem has to be there to light up, I believe it will not store problems, That coming from someone without the proper knowledge about this.

monitoring the fuel pressures will show if there are restrictions in filters, etc.

If it uses CCS to drop cylinders it may be it not getting proper info.
Not sure but it may think it is not in gear if that is part of what causes the cylinders to drop.

Maybe Rod will give a little more info.

Anyway you look at it you need someone with the proper knowledge to troubleshoot this motor. take the advice and find a Yamaha shop with the proper people

[Tucker]

How the heck can it be a fuel restriction if it runs OK above 1700RPM? At 1700 RPM 2-cyls are not firing, by design. I would ohm out the plug caps for starters. Did mine last year because I saw a post by the rodbolt suggesting it and had 4-caps out of spec. Easy test, but those suckers are a little expensive, about $12 each.

[99yam40]

monitoring fuel pressures will make sure he has steady in spec fuel pressures and that is not a problem.
Then he can be looking else where.
As Rod said maybe timing or fuel could be causing surging

If ECU is dropping cylinders at low RPM by design and he is trying to ***** at that RPM transition point it will be a problem, but should not cause motor to stall/die.
Good thought on the caps to make sure they are in spec too

[FabricGATOR]

on that engine charge coils are bank to bank.
that engie also uses CCS.
means below about 800 RPM #5 cyl does not fire,from about 800 to about 2000 #s 2 AND five dont fire.

What how are the cylinders numbered on my 2000 150hp ox66's?
Are the port head all odds 1,3,5 and the stbd head all evens 2,4,6? Top to bottom? Are they numbered on the casting?

Do I have the CCS?

How do they do selective cylinder fire? Injectors, sparks, both?

Thank you....

[seavee1512]

Yamaha 250 066

I know this is a old post, but having the same issue and if any found a solution.
Steve

[seavee1512]

anybody have a idea

[rodbolt17]

start a new thread.
post the complete model number.
not all OX66 motors used CCS.