2002 Yamaha 250 oc66 surging and loss of top end speed

[aus10b50]

Hello all, I know this topic has been covered time and time again and I just went through 15 pages of the topic and still nothing seems to fit.

I have a yamaha 250 ox66 motor that was recently rebuilt and hasn't run right since. (rebuilt because water got into the oil) It is bogging down on take off and not reaching top speed. Only getting about 5500 RPMs out of her. I should mention that I had the fuel pump and fuel regulator replaced 6 months before the rebuild and it never reached top speed after that but did run smooth. Have since taken it to a different mechanic than the one that did the rebuild. First thing he did was leak down and compression test, tested like new. He found a pinched fuel line and I had him replace all fuel lines, filters and all, also LP fuel pumps checked the VST, etc and replaced the O2 sensor, not cleaned. Then I tested it and it was still bogging down on take off and not getting past 5500 rpms and even dropping down to 5200 rpms. Took it back to the shop he pulled the injectors and sent them for a flow test and two tested bad, fixed those. (this was supposed to have been done with the rebuild but somehow didn't get done) Tested it on the water today and the problem isn't nearly as bad but it is still bogging down while getting up on plane and still wont go past 5400/5500 Rpms and still drops back and forth to about 5200 rpms. Mechanic said TPS bench tested fine. Thinks maybe the strator now but thats his best guess at this point. Can the TPS test good but still be bad? Can the REV limiter cause this? Any suggestions will be greatly appreciated as I am now several thousand into this and he is many hours into it as well and surly getting frustrated.

Thanks in advance for any and all replies

[CJ1]

Test fuel pressure. No imho on the Rev limiter. Cj

[aus10b50]

Thx for the response.
Mechanic said fuel pressure was good, but it just seems weird that it was never right after the fuel pump was replaced originally. The mechanic that replaced it did say that it was evident that it had been strained. Which i guess could be explained by the pinched fuel line, unless they pinched it putting everything back together. I've always felt like something was wrong with that install since i lost 10 MPH off top end after that. Thinking of just replacing the TPS despite it testing ok. mechanic is trying to find another engine to pull parts from to test on mine so I don't have to keep buying everything.

[CJ1]

What is his idea of ok, was it in Yamahas spec. Or??? I wonder when the pump crapped out if something got into the regulator. Like you are saying it makes no sense that after the fuel system was messed with you lost speed and alot of it. Cj
And thinking out loud here. Why did you need a rebuild? Water in oil? Did it sieze or burn down from not having enough fuel pressure?

[marinetechnician]

Did you and the mechanic take it out on a wfo run and check fuel pressure ?

[aus10b50]

No it doesn't make sense that I lost 10mph after the fuel pump was replaced, I took it back to them twice and they couldn't find anything. I'm thinking when they replaced the pump and put it all back together they are the ones that pinched the fuel lines. I was thinking this caused the loss in top end. maybe not, I don't know. The 2 injectors could have been bad then as well. As for water in the oil, I let my brother use my live wells for his bait and the drains got clogged overnight, came down to find my boat half sunk and the battery compartment where the oil tank is, was full of water. My auto bilge never kicked on. like a jack ass i got all the water out and didn't even think about water being over the oil tank and seeping into it. I ran it without draining the oil and she blew about 15 minutes into it. Standing behind the motor, looking at it, it's the top left cylinder also cracked the block. Mechanic that did the rebuild found lots of water in both the oil and fuel and drained both.

Mechanic that is working on it now said fuel pressure was in spec after he replaced all the fuel lines, he lake tested it himself. Mind you this is the 3rd mech working on it and trying to clean up what everyone else has put together, I'm thankful he is even willing to look at it at this point. I'm in Louisville KY and it's damn near impossible to find anyone thats knowledgeable and willing to work on these. He still feels it's a fuel issue of some sort, but has tested everything he can at this point. I Just put the winky blink on it and not throwing a code at idle, gonna try it at speed tomorrow and see if it's any different. I know they don't show much but it's at least something. IMG_9030.jpg

[CJ1]

looks like piston locked in the bore. lack of lube could surly have caused it, BUT lean seize can also sooo if it is not running good full out I would not do it too much until it is fixed. Like Marinetech said fuel pressure at W/O, lp fuel pumps, try a small aux tank. Keep looking, something is there. CJ

[aus10b50]

Thx, LP pumps have been replaced twice now. Mechanic did say he wanted to try aux tank. Just sucks, don't want to give up on it, i'm deep into the rebuild and I know this thing will run for years to come if I can get it taken care of. Can a TPS randomly work? Thinking about just having him replace that for shits an giggles....

[vicsservice]

How do the spark plugs look? Any signs to read on them? Gear lube ok as well?

[aus10b50]

Plugs looked good, haven't checked the gear lube. Will post the flow test results so anyone that knows what they are looking at can see if there is something missed there?

[aus10b50]

Flow test results, for anyone that knows what you are looking at? IMG_9035.PNG

[javelin90]

Did mechanic check the reeds?
Sounds like fuel issue

[aus10b50]

Yes he did, They are all there and intact.

[Amistad Tackle]

Could it be a fuel restriction at the tank? I had one tank that had a anti-siphon valve and one tank that didn't. When I switched to that tank I had all sorts of issues. Removed the valve and no more issues. If you have a valve remove it and just use a straight barb. Running it on a five gallon aux tank will tell you something.

[aus10b50]

Aux tank is the next step, but I had all new lines put in from the tank to the motor because it was pulling something like 7lbs of vacuum to begin with. When he got into it he found a pinched line so I had him replace everything with factory equipment.
For what it's worth I made 3 passes today with the winky blink on it hoping that somehow it might throw a code when it bogged down, It didn't. Also ran it with the shift interrupter switch disconnected just to see if that made a difference, it didn't.

[rat0502]

Aux tank is the next step, but I had all new lines put in from the tank to the motor because it was pulling something like 7lbs of vacuum to begin with. When he got into it he found a pinched line so I had him replace everything with factory equipment.
For what it's worth I made 3 passes today with the winky blink on it hoping that somehow it might throw a code when it bogged down, It didn't. Also ran it with the shift interrupter switch disconnected just to see if that made a difference, it didn't.

the valve mentioned above is sometimes built into the fitting that comes out of the tank, so unless that fitting was replaced it could be an issue if you have one there. Also, I'm not sure about your boat, but sometimes they put a little strainer at the bottom of the pickup tube in the tank. I had a friend who got some junk in his tank and it would plug up that little screen. He got very good at removing his seat and the pickup tube while on the water until all of the junk cleared out. Not fun! Some things to look at if you think it's a fuel delivery issue.

[marinetechnician]

A remote tank should have been tried a while ago. Also you say he ran the boat and checked fuel pressure ? I must say that driving a bass boat wfo and trying to turn around and look at fuel pressure gauges might be a bit tricky. Most don't have hoses long enough to reach the drivers seat. It's a 2 man job for us especially with a high speed boat. I would question it at least. I will have my lead Yamaha tech read this this thread tomorrow. Be curious to get his opinion. Do you have a parts list for what was replaced during the rebuild ? Also did you have the rebuild done by a machine shop or someone that is well known for Yamaha repair/rebuild ?

[Amistad Tackle]

Aux tank is the next step, but I had all new lines put in from the tank to the motor because it was pulling something like 7lbs of vacuum to begin with. When he got into it he found a pinched line so I had him replace everything with factory equipment.
For what it's worth I made 3 passes today with the winky blink on it hoping that somehow it might throw a code when it bogged down, It didn't. Also ran it with the shift interrupter switch disconnected just to see if that made a difference, it didn't.

The valve is in the barb on the tank that the hose connects to. Remove the seat (if that is where your tanks are located), remove the barb, and see if it is there. It will be a ball with a spring inside the barb. If so, replace with a straight barb.

[aus10b50]

yes it is a two man job, someone from the shop went with him. I will have to ask if the valve was replaced, My boat is a 201 Stratos ProXL.

[aus10b50]

The current mechanic only lake tested it once, as its an hour each way and their test tank where they can run at speed is drained for the winter. Thus the Aux can wasn't tried because it was me lake testing after each repair and I didn't know about it.

As for the rebuild the block was sent to a machine shop to be welded and re-sleeved. The mechanic is well known in the area for doing quality rebuilds and standing by his work if something fails. However, he obviously failed to send the injectors off for a flow test which makes me question everything, now that i think about it. I only switched mechanics because his shop is an hour and 15 minutes from me. The person working on it now knows the person that did the rebuild and also states he does quality work. As for a parts list I will have to dig that up, off the top of my head I know all 6 pistons, 1 sleeve, bearings, 1 rod, 02 sensor. Since rebuild, all new yamaha fuel lines, M kit fuel filter, primer pump assy, fuel pump asy, mar-10mel-00-00 (<-whatever that is) injectors flow tested and 2 tested bad replaced, fixed...