95 Sport Jet 120 Fuel recirculation

[MississippiBaja]

Model: 0E137433
I recently picked up a sport jet from a coworker that appeared to be a time capsule forgotten about in storage. With superficial tune ups and repairs it seems to be working as it should minus a mystery fuel recirculating/ crankcase pressure issue.
When idling in the driveway hooked up to auxiliary cooling, it seems to idle very high(throttle linkage adjustments are set to the minimum already and the timing is calibrated to about half a degree retarded from spec, along with the fuel air mixture being adjusted to spec then finely tuned for no delay throttle response)
along with the high idle there’s a pop of air intermittently through the fuel recirculating line coming from the elbow right below the bottom carb.(This only happens at an idle engine speed and any throttle up stops this issue)
This burst of air pulses through all the main fuel lines right up to the carburetor causing the engine to sputter for a split second almost as a single misfire. The video shows how I found it, the line for the fuel recirculation has been since replaced with the same intermittent popping.

 

[alldodge]

Welcome
Don't know much about the model ski but maybe it's the fuel pump diaphragm. If it uses a pump like some of the old outboards the exhaust pulses is what moves the diaphragm to pump the fuel

 

[racerone]

Really-----Why do you say it is EXHAUST pulses that move the diaphragm on old outboards???-----Crankcase PRESSURE pulses move the fuel pump diaphragm !------Sounds like the engine has classic lean sneeze.-----And some of these units rev high for proper cooling at idle.

 

[MississippiBaja]

Really-----Why do you say it is EXHAUST pulses that move the diaphragm on old outboards???-----Crankcase PRESSURE pulses move the fuel pump diaphragm !------Sounds like the engine has classic lean sneeze.-----And some of these units rev high for proper cooling at idle.

So this is actually a sport jet 120 that has been sitting for 7 years. The “lean sneeze” was right on point! At least that’s what I gather.

So I ended up replacing all the fuel recirculation hoses which are directly connected to different areas of suction and pressure points on the engine to collect unburnt fuel. The air leak in one of these lines caused a lean condition that kept exaggerating the problem causing it to idle high until a misfire.
Now with the read valves being able to seat properly with pressure changes here it is!!!

 

[racerone]

Sport jet is a FORCE powerhead.----Powerhead is no different than the outboard motor.-----Exhaust manifold is different.----Fuel systems must comply with Coast Guard rules for inboards.

 

[MississippiBaja]

Sport jet is a FORCE powerhead.----Powerhead is no different than the outboard motor.-----Exhaust manifold is different.----Fuel systems must comply with Coast Guard rules for

 

[MississippiBaja]

I was just clarifying the exact setup to this boat. I’ve heard they are one and the same powerhead through my research but 10 “merc.” Mechanics I spoke with through the restoration of this boat were no help claiming to not work on inboard jets..

Until the next issue that pops up with this boat just wanted to thank everyone for the input and I’m very happy a place like this forum exists!

 

[racerone]

I think the spline on the bottom of the crankshaft differs from the outboard version.