2004 Sportster 155 Missing 1000 RPM

[JLOBO941]

Hello all,

I have a tough one here. First things first, the boat is a 2004 Sportster 4-tec 155 with 200 hours in Denver CO at approximately 5500 ASL. The goal for the boat from day one was to have an easy, low running cost way to tow wake boards, and rip around for fun. The law for maximum speed of operation for watercraft in any body of water in Colorado is 40 mph, and it's radar enforced constantly where I go. I've never been bothered by the CWP for anything 50 mph and below, so that was my targeted top speed. The boat had a cracked pump housing when I bought it, so I modified a few things right away:

-Impros, LLC pump rebuild with dual impeller (inducer), new metal pump housing, wear ring, bearings, etc
-RaceLab ECU tune optimized for altitude and 8200 rpm redline
-Solas intake grate (the stock one was broken)
-AquaSport exhaust spacer
-Wet Jet Performance water box mod

Here's where it gets weird... I got everything together, and it ran perfectly right out of the box. Over half tank of fuel, wife, and myself had no problem whatsoever making over 8k rpm, to the point I was worried it might start hitting the limiter at full throttle when it got lighter. The boat cracked 50mph, and got there in a hurry. After about an hour on the water out of nowhere I got what felt like a driveline vibration (like what seaweed feels like on a ski). I backed off, checked it out, nothing there, so I got back going. From that moment on, the vibration never returned, BUT the boat would not, and has never again broken 7000 rpm and about 42mph. I have troubleshot basically everything I can think of, including:

-Tested compression hot, cold, wet, dry, etc. Numbers always nearly identical across cylinders, and more importantly same as before the issue.
-Replaced spark plugs
-Replaced coil packs
-Changed oil to 5w30 and ensured proper fill amount
-Checked throttle linkage to ensure full operation
-Used Candoo to verify RPM accuracy against the onboard tachometer
-Removed and cleaned fuel injectors (battery and throttle body cleaner spray method)
-Removed and serviced fuel pump, replaced filter and sock

I am now completely out of ideas, the boat really does run great, but having had it to it's full potential, and now being left with 20% less is truly driving me crazy. I have owned and serviced every iteration of the 4-tec SC motor from the 215 to the 300 in one or more ski, so I'm no stranger to them, however this is my very first NA, and I have to say (especially before this issue) I'm quite impressed with the performance (probably mostly due to the dual impeller). I appreciate any help, feedback, criticism, etc. I'll try anything at this point.

 

[BGS]

So does it seem to be laboring at all or is the acceleration same / good ?
ie is drive train causing too much drag ?

 

[nesnfred]

On this model, does the impeller shaft need to be aligned when reassembled? That could cause vibration at speed.

 

[Speedster 150/215]

I wonder if boost pressure has changed, ie supercharger slip washers are slipping too much under high load/rpm.

 

[JLOBO941]

So does it seem to be laboring at all or is the acceleration same / good ?
ie is drive train causing too much drag ?

It really doesn't seem to be laboring, pulls well, just missing the last thousand or so RPM, so I only notice it at top speed, and sometimes when I'm being aggressive in turns, and the pump has to re-bite at high RPM, there's definitely a difference between the pump re-grabbing the water and pulling out at 7000rpm vs 8200.

On this model, does the impeller shaft need to be aligned when reassembled? That could cause vibration at speed.

I'm not quite sure, maybe someone knows better than I, but the pump removal and reinstallation is pretty straight forward. Maybe the alignment procedure must be performed when installing the shaft into the engine, but it stays in place when the pump is removed.

I wonder if boost pressure has changed, ie supercharger slip washers are slipping too much under high load/rpm.

This one is a 155 NA, no supercharger.

Thanks everyone for the replies!

 

[BGS]

It really doesn't seem to be laboring, pulls well, just missing the last thousand or so RPM, so I only notice it at top speed, and sometimes when I'm being aggressive in turns, and the pump has to re-bite at high RPM, there's definitely a difference between the pump re-grabbing the water and pulling out at 7000rpm vs 8200.



I'm not quite sure, maybe someone knows better than I, but the pump removal and reinstallation is pretty straight forward. Maybe the alignment procedure must be performed when installing the shaft into the engine, but it stays in place when the pump is removed.



This one is a 155 NA, no supercharger.

Thanks everyone for the replies!

If engine is fine, then possibly the momentary "driveline vibration" caused damage to driveline / pump assembly / bearings / wear and even though does not seem to be laboring is eating your 1k rpm.