I've been having a issue with acceleration ever since I bought my boat. The motor is a 2003 ox66 250 model vx250tlrb. I'll start from the beginning so this may take a bit. My motor has been bogging on holeshot since I bought it. Some suggested lp pumps so I replaced them. Problem slowed but did not go away. Another suggested the exhaust manifold may be broken. I checked and it was, so I replaced it with a hydrotec performance tuner. Problem is still there. I have also replaced ALL filters and screens, all lp pumps, and plugs. I sent the injectors off and had them cleaned, tested, and calibrated. I have checked all plug wires, caps, and coils. So the other Sunday I was cruising alone and up came a noise that sounded like the starter was hung in the flywheel but it was coming from the bottom of the powerhead. Turns out the crankshaft balancer completely shelled out, so I had it replaced along with the oil seal while they were there. I was hoping that was throwing everything out of wack but no luck. I had told my shop about the issue and I guess they had some extra time and another tech had stopped by. They showed him and he said he had one do that years ago and had a Yamaha tech come look at it and even he could never find true out exactly what was causing it. But he knew how to make it run better, just not cure the issue. So he takes a pair of pliers and pinches the return line from the fuel rail to the vst and that fixes it. They even did it while it was bogging and it instantly cured the issue. They had a fuel pressure gauge hooked up and said pressure was in spec and never dropped or went above. The other tech said he put a orifice in the other motors return line and never had the problem again, but it did use more fuel and oil after that. I want to fix it right. Does anyone know exactly what is wrong? They think either the fuel pressure regulator or the cdi. I'm leaning toward pressure regulator as I don't think it's a injector control issue but I may be wrong. Heck it could be as simple as a check valve. I have tested the fuel pressure at the ramp on the trailer and it was 35-36 psi and the motor would rev to 1800 rpm. When I would squeeze the return line with pliers it would rev to 2000rpm and I was reading 34 psi. I have checked all the spark plug caps and they were in spec. I tested the fuel pressure regulator as stated in my Yamaha manual and when I applied 25kpa of vaccum the fuel pressure dropped to 33psi. I also checked the knock sensor per the manual instructions and could get no ac voltage from it when tapping it with a screwdriver. This may be the culprit, but I am told they rarely ever fail and I'm not exactly sure how that would effect the fuel. I'm just lost and confused at this point and just want to get it fixed. I am reluctantly willing to take it to someone who could figure it out. If I must I will, but I don't know of anyone reasonably close to me who knows these motors well enough that I wouldn't be paying them for hours on end of diagnosis. I am in Brenham and would drive up to maybe 2 hours if I have to, but I would really like to figure this out without it costing me a bunch of money since I've already spent quite a bit on it. I am willing to buy any special tools or test leads for this motor as I don't plan on getting rid of this motor for a long time.

I guess you've replaced or cleaned the screen/filter inside VST?

Look up a user "Rodbolt" on (iBoats. com) very knowledgeable Yamaha master tech

Yes I have put a new screen filter in the vst, cleaned filter behind regulator, replaced filter on motor, and spin on filter in boat. Rodbolt has been responding somewhat on another forum that I posted on, but sometimes I get no response, and other times I check what he says to check. His responses are sometimes hard to follow. For instance he said it could be the knock sensor so I checked it and reported back. Then he says they hardly ever go bad and it's not a magical device that would cause this. I'm waiting on some orings to get here then if it's not fixed I'm going to have to take it somewhere. I'm not sure where, but I need to find somewhere good with these motors and hopefully fairly close to me.

Well, there is a lot of post on the hull truth about hidden filters on the injectors?

Filter screens on the injectors were cleaned when I had the injectors cleaned and calibrated. I am going to try swapping parts from my buddies 225 this week or next and try to figure this out. If I can't figure it out swapping parts I will just have to find someone to take it too and hope I don't get raped on the hourly charges for them to figure it out.

The O2 Sensor can cause a lot of problems on these. Try your buddies and if his works then replace yours. You can try to clean it but sometimes that makes it worse.

Ships marine Gladewater Texas they can fix it.

I have already replaced the o2 sensor with an aftermarket one and had no change. I will try his if all else fails. I will also keep ships marine in mind if swapping parts doesn't solve it. I'd hate to have to drive 4 hours one way to take it there, but if necessary I will.

Hughes Marine Service
McKinney
214-796-0373

He's Boatman025 here on the boards