No throttle response - only idle if you push throttle forward some

[edwilk55]

Guys/Gals,

I've searched and found several similar issues, but nothing that points me in the absolute direction, so I'm going to ask for assistance before jumping in the back of this hell'beast.

1999 Challenger 1800...twin Rotax. My boat sat up for two years. Long story, don't ask.

The starboard engine had to be replaced so it's not even out of break in yet. Carbs were supposedly cleaned, but not fully rebuilt. RAVE valves are new as well, or course.

Been running fine for the last 6 hours of break in, but this past Sunday, we went into a cove to swim. After starting, the new engine wouldn't rev up when throttle applied. Wouldn't idle unless throttle moved up some. When pushing it to idle up, a more smoke than normal.

I was limping to a friends house and the issue cleared. Ran fine again. Took it to the docks at end of final run and issue returned.

Couldn't keep engine running long enough to put on trailer properly. (that's fun!)

I haven't started to diagnose yet, but I'm starting with the fuel filters.

I validated the throttle cable is working fine. Nothing obvious from lake inspection.

Is this a common issue I've missed in searching or do I start with step 1 and go until I find the root cause. Already dumped a load of cash into her, so trying not to just replace everything at once.

Thank you all for taking the time to read and/or respond.

 

[Upallnight]

The more smoke could be that the oil pump was injecting more oil into the mixture, but the engine wasn't revving fast enough. I had a similar problem with my rotax engine. Started fine, but wouldn't rev or get the boat on plane. After rebuilding the carbs a couple of time and buying another set of carbs and rebuilding them.

I decided to bite the bullet this year and rebuild the engine. Remove the engine from the boat and upon disassembling the engine when it came time to remove the nut for the flywheel, it came undone very easily. While pulling the flywheel off the crank I heard a metallic clink as something fell off the engine. Turn out it was the wood ruff key. The key must have sheared and the movement of the flywheel was enough to throw off the timing.

Rebuilt the engine and it been running like a champ this entire summer.

 

[edwilk55]

Being a new engine, I hope that's not the problem. But I didn't assemble / install, but I believe the shop that did knows there stuff. (fingers crossed).

I'm going to start with the idle screw and make sure everything I can test is tested. Hoping for a simple fix, but I don't mind a carb rebuild if needed. Just hope I can find the problem prior to putting more money in fixing things that aren't broken.

 

[Upallnight]

If the builder used the flywheel to hold the crank while he was torquing the nut onto the crank that 100 ft lb of torque is translated to shear stress on the woodruff key since that is what is preventing the crank from turning.