2008 250 PRO XS, rpm surge

[lwgbully]

serial number 1B690589


Experienced momentary increases in rpm 100-150 rpm, at all on plane throttle positions, this past weekend. Looking for input on potential causes.

Boat/Motor history:
Purchase from a friend who had it sitting with little to no use over past three years. I placed in shop, and had the VST cleaned, filter replaced, injectors cleaned, and plugs replaced. Shop said they drained fuel tank, however I have reason to believe that they might not have. There is currently an external inline fuel filter in place, which I will be removing. It appears that the fuel lines are original and need to be replaced. Found short section (2') of gray fuel line between filter and primer bulb. This past weekend was the first time I had it on the water since purchase and shop work.

Thanks!

[Savage]

Follow all these steps EXACTLY as they are written.

Click on this >>>Performance problems? Read Here and Upgrade Fuel Supply System FIRST!

[lwgbully]

Savage,
Thank you, saw this earlier and intended to follow it. Thanks.

Wes

[EuropeanAM]

+1... start there (and get rid of the extra filter). ALL items recommended in that link, all at the same time.

[lwgbully]

Gents,
Did the above as instructed. Surge still present. Next steps??

Wes

[Savage]

What is the fuel pressure when the surging occurs?

[lwgbully]

Savage,
I do not know. I haven't seen any indication of the rpm surge at idle, and can't really say that I've seen it below 2000 rpm's. It seems to show itself intermittently starting at 2000 rpm's and up. Also, It possible that i have an issue reaching the upper RPM limit. I have not been able to reach in excess of 5000 rpm, and I don't believe that the rig is over propped. It's possible, but not likely, the rig is new to me so I don't have any history with different props to pull from.

Back to the pressure, I assume I will have to set up gauges to measure this?

Wes

[Savage]

Yes, that's how a technician would test.

[lwgbully]

Is this something I can do while running on the hose, or do I need to some how manage this testing on the water and at various rpm?

Wes

[Savage]

On the water testing, as the problem is occurring.....

[EuropeanAM]

On the water testing, as the problem is occurring.....

+1

Good idea to monitor low and high pressure fuel pressures, LIVE, via video.

Have a passenger video the engine, with sound, showing the gauge readings (pressure gauges).

[lwgbully]

Is there a way to do this without purchasing the $400 test kit reflected in the manual? I assume I could identify the connection sizes and configure my own.

[lpugh]

The last time I responded to post similar to this it was taken out of context the party was highly offended so I will try to word this a little different. I think you should take this to a qualified Pro with a good reputation with Optimax motors. Do not run it on the water until it is checked out. If the RPM loss is due to a lean run condition, continuing to try to on the water test it could cost you a motor.
There is another post on here where the Op had this type of warning and it looks like he may have lost his motor due to ignoring the RPM loss and kept running it. Protect your investment by knowing without any doubt that the fuel system is at 100%.
The term cleaning injectors is a very vague, misused term regarding these motors, Send the complete assy. to Don to be restored to like new conditions, then proceed. His link is at the top of the forum See post #11

[lwgbully]

lpugh,
Understood, and I appreciate the advise. For what it is worth, it is an intermittent/momentary increase in rpm of 100-200 rpm. I am sure that doesn't change the recommendation, but just adding clarity to the condition.

Wes

[Savage]

If the problem is intermittent, as you stated, then on the water testing is the only way to determine the cause, without guessing its a hundred different things. See post #10 and #11.

[lwgbully]

Gents,
Curious is the a poor connection to the battery could result in this symptom? Had a trip where the issue was not present, followed by a trip where the it became apparent again. At the same time had a low fuel alarm on the vessel view, despite having a 1/2 tank. Once of the water, realized the connection to the battery was poor. Fixed and low fuel alarm went away. Have not had a chance to get back on the water with verified good connection to battery to see if surge can still be witnessed.

Thanks,
Wes

[Savage]

Possible.

[tmmfont]

I had this same problem before. I know you said the plugs were changed, but you might want to check them again. If they aren’t gapped correctly it can cause the motor to surge. Also, a friend of mine had his motor do the same thing and we found that one plug tip was broken. Replaced all the plugs with properly gapped ones and it ran awesome. Think the gap should be .042-.044. Might be worth a look.

[lwgbully]

Excellent, thank you.

[Kb444fishing]

Yes I had a similar issue plugs not gapped correct can cause it.