Sportjet 90 low power

[basilfaulty]

I have a 1994 Bayliner Reflexx with a SJ90. Boat starts and runs, idles fine no hesitation when throttling up. Seems to me that it isn't getting full RPM. Here is what I have so far: Red Stator 696 ohms, CDI electronics switchbox, new regulator (Mercury), trigger White wire 1264 ohms, purple 1148, brown 1173. No rev limiter. Replaced carbs with a set of used matching carbs cleaned and adjusted. Throttle plates fully opening. Initial and full timing checked and adjusted. Compression on all 3 cylinders around 120 +-3 or 4 psi. Reverse gate is adjusted properly. New, not reconditioned (Mercury) Impeller, wear ring is in good shape, almost zero clearance to new impeller. Ride plate is sealed and undamaged, intake grate is undamaged. The boat is difficult to plane and will run only 27 or 28 mph on the speedo 2 people 1/2 tank of fule no other load (cooler boxes, etc.) I am at my wits end with this thing, don't know what else it could be. Almost forgot, new diaphragm in the fuel pump as well.

 

[basilfaulty]

Re: Sportjet 90 low power

I gues everyone is stuped on this one?

 

[calledinsick]

Re: Sportjet 90 low power

Most everything sounds good except I'm curious how you checked 'initial timing'. These can only be timed at WOT from my understanding.

If the butterflies are fully opened, throttle cable should be good. Ride plate, wear ring, impeller, reverse gate all sound good (gasket/seal around ride plate?). Does the engine sound like it's slipping/reving when WOT?

Check Fuel flow where the fuel line enters the carbs. I know you replaced the diaphragm but a valve may be stuck or the pump housing may be cracked. Place the end of the hose in a jar/can and crank engine (**DON'T TRY TO START OUT OF THE WATER WITHOUT FLUSH KIT!!**) It should be a steady flow...no pulsing. If this checks out I'd put the end of the hose under the fuel in the jar/can and look for air bubbles. This would show a leak in a fuel line (or cracked pump housing).

Hope this helps.

 

[basilfaulty]

Re: Sportjet 90 low power

Most everything sounds good except I'm curious how you checked 'initial timing'. These can only be timed at WOT from my understanding.

If the butterflies are fully opened, throttle cable should be good. Ride plate, wear ring, impeller, reverse gate all sound good (gasket/seal around ride plate?). Does the engine sound like it's slipping/reving when WOT?

Check Fuel flow where the fuel line enters the carbs. I know you replaced the diaphragm but a valve may be stuck or the pump housing may be cracked. Place the end of the hose in a jar/can and crank engine (**DON'T TRY TO START OUT OF THE WATER WITHOUT FLUSH KIT!!**) It should be a steady flow...no pulsing. If this checks out I'd put the end of the hose under the fuel in the jar/can and look for air bubbles. This would show a leak in a fuel line (or cracked pump housing).

Hope this helps.

I checked initial timing with throttle closed and full timing at WOT. Both can be adjusted as well.. I checked the valves when I did the diaphragm, I did not however check flow yet. I will check flow next. Also I am going to pull the reeds and check them...so maybe this weekend sometime. I doesn't over rev like it is slipping. Performs pretty much the same as it did with the old impeller that was out of spec. It definately feels like something is holding it back. Possibly fuel flow (but it doesn't stutter or sound like it is starving) possibly a broken or stuck reed? I didn't check resistance on the coils yet either....does anyone know the specs on the coils? (I don't think it is the coils though it doesn't feel like a miss at all but it won't hurt to check) What is the compression supposed to be? Is 120 ish on the weak side for these?