sport jet 120 this could be a tough one

[`Mike Burke]

I have a 94 sea rayder f-13. The boat originally had a 90 horse power sport jet in it. I put in a 96 sport jet 120 xr. The only problem that I have now is at wot the boat goes 36 mph. If I back off the throttle a little bit the motor picks up rpms and tops out at 41 mph (this is with one adult). So why do I have to back off the throttle to get more rpms. I just rebuilt the carbs and put them back on, they are in sync. I just don't understand because it has a throttle stop so it's not like the butterflies are starting to close from over throttling. Throttle cam is in line with roller. I know the timing is 32 deg. btdc while cranking and 30 deg. at wot. I don't know if it's retarding itself too much at wot. I plan on checking timing soon. Here's what I've done so far. New plugs, rebuilt carbs, new fuel pump, new fuel filter, new starter, new starter selonoid, and it already has the blue stater. Impeller to wear ring is fine and would'nt cause this problem anyway. Could the rev limiter be doing this. Engine starts great (hot and cold). The only thing I have'nt replaced yet is the plug wires. And probably will just order anyway. Any help would be greatly appreciated, I have a service manual and I'm stumped!

 

[Lion hunter]

Re: sport jet 120 this could be a tough one

I would have guessed over throttle but you say it's not that. Exhaust restriction or a partially plugged (or to small ) high speed jet?

 

[`Mike Burke]

Re: sport jet 120 this could be a tough one

The motor has a throttle stop so it seems impossible to me that it could be too much throttle. When I rebuilt the carbs I soaked them overnight and then installed rebuild kits. I verified via part number that I ordered the correct kits. No blockage on exhaust either. I appreciate the reply. Anybody else have any suggestions?

 

[Lion hunter]

Edit -delete

 

[CharlieB]

Re: sport jet 120 this could be a tough one

Double check that throttle stop, set the control to WOT and physically LOOK down the carb throats.

Also try momentarily bumping the choke/enrichener while running at WOT to see if that makes an improvement, indicating that the carb jetting is slightly lean OR float levels a bit too low.

Possibly even a fuel line restriction, a zip tie holding a line in place a bit too tight, the fuel pick-up tube have junk in it, small air leak into a fuel line.

 

[`Mike Burke]

Re: sport jet 120 this could be a tough one

The auto enricher can only be used when the carbs are fully closed. I replaced all the fuel line on the boat. And I checked the throttle stop, at wot the shutters are in the correct position. I took the boat out this weekend and somehow I lost 4 mph. I can only get 37 mph out of it. This doesn't make sense to me because the boat is overpowered with a 120 hp. I think I may just buy two more carb kits and see what happens.

 

[j_martin]

Re: sport jet 120 this could be a tough one

The auto enricher can only be used when the carbs are fully closed. I replaced all the fuel line on the boat. And I checked the throttle stop, at wot the shutters are in the correct position. I took the boat out this weekend and somehow I lost 4 mph. I can only get 37 mph out of it. This doesn't make sense to me because the boat is overpowered with a 120 hp. I think I may just buy two more carb kits and see what happens.

I used to train computer field engineers. The hardest thing for them to learn was this. If you walk up to a running machine, do something to it, and it now doesn't run, IT'S WHAT YOU DID.

The symptoms you describe are probably high speed lean, which is about the shurest way to burn down your powerhead known.

Recheck your work.
Float levels right
Gaskets installed right (not blocking something)
The right fuel line.
No fugative pipe dope or tape in the fuel system.

etc. etc.

hope it helps
John

 

[CharlieB]

Re: sport jet 120 this could be a tough one

I suspect that there is a restriction in the fuel supply, possibly at the tank fitting.

That 120 should flow approx. 12 gallons of fuel per hour. Fuel lines are CRITICAL. Install a NEW 3/8's line and bulb, connected to a portable O/B tank and retest. If that cures your WOT problem then pull that fitting and dip tube from your main tank and clean it out. Sometimes a piece of gunk will stick the check ball in the outlet fitting, causing a restriction and burning your pistons at WOT.

 

[`Mike Burke]

Re: sport jet 120 this could be a tough one

That sounds like a good idea, I'll try that. I already replaced all the 3/8 line. Thanks for al your replies I will update soon.