250 ProXS 2 Stroke Runs but Wont Idle

[ss]

Sorry in advance for the long post. 2015 250 ProXS 2 stroke 2B110587. Motor started fine and idled off the trailer. Idled out from the ramp and then ran about a mile. As I came off plane the motor died. I checked the kill switch to make sure I hadn't pulled it but it was fine. Tried to restart. Motor would crank and fire for about a second and then die. Tried holding throttle partially open with the hot foot while cranking and it fired right up until I let off the throttle and then it died. If I hold the throttle open and keep it at 2500 rpm, it runs fine. Smooth, no smoke, no funny noises or smells, no oil or fuel slick on the water. As soon as I let the rpm come down it dies. No cough and sputter, just like you turned off the key. Water pressure, water temperature and voltage are all normal. I noticed the fuel line primer bulb wont stay firm, so I am going to get and new one tomorrow and try again. But it can't be something that simple can it? Any suggestions are appreciated. I don't have the gauges to check fuel and air pressure.

[lpugh]

Normal for bulb to be soft after starting as the pulse pump pulls a low vacuum on it. Should only take one or two pumps to get hard though
do you have smartcraft gauge or merc monitor, any messages displayed?
Compressor belt in good shape and tight, do not rev motor above about 1500 in neutral
Think you will need the computer scanned and pressures checked
do a good visual inspection of all connections including the battery for anything that may have become loose or disconnected
On the port side fuel rail there is a shrader valve, as soon as it dies check the pressure with a tire gauge that will read 120 psi and note, crank for few revolution and depress the center, does it spray out liquid gas, do not confuse this with condensation water. Do the same thing on the starboard side shrader for fuel and note the pressure, Post you results
Pretty sure you are going to need dealer support on this one
Symptom does make me wonder about the TPS though, look at the tps linkage as you operate the throttle

[ss]

No alarms or messages on smartcraft gauge. The primer bulb loses pressure without running the motor. I pumped it up before I left the lake, and when I got home 45 minutes later, it was soft. Compressor belt was new about 6 months ago, but I will take the cover off and check it and turn the compressor by hand to check for compression. I pulled the cowl off and checked for anything unusual, but no loose connections or visible fuel leaks. Its not acting like a bad tracker valve, but if the new primer bulb doesn't help, I'll pull the tracker valve and inspect it.

[lpugh]

If it become firm in one or two pumps it wont be the bulb, by the time drove home some fuel would have been evaporated and I would expect it to be soft
Keep in mind there is about a quart of fuel in the vst, It would have to be almost empty to cause a no start, think you are barking up the wrong tree here
If it was low enough to prevent a no start at closed throttle, opening the throttle would still be a no start

[EuropeanAM]

Check the belt, tensioner/spring and air compressor for any obvious signs of failure.

Check COMPRESSION and AIR/FUEL PRESSURES (while cranking with NO throttle added).

Also note pressures at 5/10/15 seconds after you STOP cranking.

[ss]

Update: Replaced the primer bulb, but no change. Compressor belt is good. Turned compressor by hand and felt compression. No wobble in compressor pulley. While I was trying to start it after replacing the primer bulb, I noticed fuel dripping from the telltale hole in the fuel pressure regulator housing, indicating fuel on the wrong side of the diaphragm. I pulled it apart and found this. Also pulled out the tracker valve diaphragm and it looks fine.

[EuropeanAM]

Guessing that you actually pulled that from the AIR pressure regulator (it is the one with atmospheric vents (2) in the cover).

Strongly recommend the correct special tool be used when reinstalling (also need to verify pressures after replacing regulator diaphragm).

[ss]

Guessing that you actually pulled that from the AIR pressure regulator (it is the one with atmospheric vents (2) in the cover).

Strongly recommend the correct special tool be used when reinstalling (also need to verify pressures after replacing regulator diaphragm).

Tool is on order. I've done it before using longer bolts and gradually tightening the cover, but once I saw there was a tool for this, it looks a lot easier.

[trivialpursuits]

Tool is on order. I've done it before using longer bolts and gradually tightening the cover, but once I saw there was a tool for this, it looks a lot easier.

The tool makes it a LOT easier. Highly recommended.

[JOE54]

anyone had that apart recently ??????

[ss]

anyone had that apart recently ??????

If you are referring to the regulator, I was the last one to take it apart probably 2-3 years ago. Where the diaphragm is torn looks like it could have been smashed by the housing when putting it back together. But if that was the case, it held up for a pretty long time before it failed.

[JOE54]

agree for sure

[ss]

I checked all of the fuel rail diaphragms and the only one that was actually bad was the air pressure regulator. I replaced all of them anyway, just because. The motor now starts and idles just like it always did. I now have a tool and a pile of slightly used parts for future episodes. Optimaxes are fun.

[greauxpete]

Does the air pressure regulator need to be recalibrated like the fuel pressure regulator?

[EuropeanAM]

Either of the regulators must be checked with highly-accurate pressure indicating equipment. If pressure is not precisely within specifications, adjustments must be made. Information on this is included in the form of an instructions sheet (included in the box with new regular diaphragms).