05' 300x stalling issue

[F29DCB]

Having an issue with one of my motors.
It's a 05 300X. rebuilt powerhead about 3 years ago.
It starts fine and seems fine at speed but it stalls every time I put it in gear.
forward or reverse.
compression is good on all six cylinders.
I just had all the injectors cleaned and calibrated about a year ago thinking that may be the issue.
Any ideas where to start in tracking down the problem would be much appreciated.

[F29DCB]

Helllooo anybody home ??????

[chewymalone]

May not be helpful, but I have a F26 with 300X's and mine does the same thing. New powerheads are in break-in mode, so I called my engine guy and inquired about it. His answer made sense... spinning a 32P prop at idle behind a relatively low torque motor (compared to big blocks) is no easy task. Most bass boats run pitches down in the 20's, so a 32P is somewhat out of the comfort zone for these motors at idle. His suggestion was to be sure to give the prop time to stop spinning if going from F to R (i.e. docking). It's a pain but seemed to help.

[F29DCB]

Thanks chewymalone.
My issue is a little different. I agree that these motors don't idle well anytime. after all they are 2 strokes.
My port motor stalls every time as soon as I put it in gear.
Never did this before just recently.
The starboard motor is fine.
I think it may just be a coil or something going bad and not getting a good spark at low RPM's.
after it stalls it seems a little flooded and is hard to restart.

Is there a way to test the coils to see if they are firing correctly?

[F29DCB]

Anyone else have any ideas??

[87starflite]

Have you scanned the motor? My motor was throwing a map sensor code that came up on my vessel view and the motor was a little grouchy at idle. These motors also cut back rpm during shifting, maybe in need of a good tune up

[msg11]

What do your motors idle at in neutral,they may be idling to low. You may have to adjust the stop screw to idle them up higher. That's what worked for me, I had the same problems. Mine idled at 450 RPMs ,then drop it in gear it idled around 300 with a 34 pitch prop.I now have it at 650. put it in gear and idle fine. Try it,you can always put it back.

[merctech5591]

Check your Reed blocks , u may have worn reeds or even a broken pedal or 2.

[F29DCB]

What do your motors idle at in neutral,they may be idling to low. You may have to adjust the stop screw to idle them up higher. That's what worked for me, I had the same problems. Mine idled at 450 RPMs ,then drop it in gear it idled around 300 with a 34 pitch prop.I now have it at 650. put it in gear and idle fine. Try it,you can always put it back.

MSG11, It seems fine at idle. same as other motor. doesn't stall or sputter at idle.

[F29DCB]

Check your Reed blocks , u may have worn reeds or even a broken pedal or 2.

Didn't even consider that. I will take a look. Thanks, merctech5591

How difficult is it to get to them?

[Nick225EFI]

Mark (Go Time) here is good at these things, use a DDT to read the ECU, they give a fair bit of information and allow a good few tests. They are a little primitive in modern terms of diagnostics, but they work. Maybe the diaphragm pump is worn but not dead, it wouldn't help the idle. Before you spend a bunch of money on parts use the DDT, or have someone help you.

[Catss]

hey dcb, I had the exact same issue with my Xs went a few years after the new powerheads and after trying multiple things as suggested above it ended up being the reed cages/pedals......i replaced all of them on both motors not cheap but now they idle perfect.....how many total hours on motors i had like 320 on what i believe were original reeds....i think your supposed to change them around 250 hrs or so is what i had heard.

[F29DCB]

Thanks Catss, did you replace them yourself? how hard are they to get to?

[Catss]

Yes I did probably takes a little over an hour or so for each motor....i bought them from merc which includes the pedals and blocks....you might be able to get away with just pedals but i didnt want to take any chances....all of my old pedals looked fine to me but once the new ones were in huge diff night and day...my Xs are on a 32 skater and they always friggn stalled when i was trying to dock...drove me nuts now i can dock without the stalling...

[kylesbdsmerc]

Yes I did probably takes a little over an hour or so for each motor....i bought them from merc which includes the pedals and blocks....you might be able to get away with just pedals but i didnt want to take any chances....all of my old pedals looked fine to me but once the new ones were in huge diff night and day...my Xs are on a 32 skater and they always friggn stalled when i was trying to dock...drove me nuts now i can dock without the stalling...

Did it make a difference on overall performance after you put in the new reeds?

[Catss]

Other than idle and and reduced coughing etc not really...maybe a little better milage but I really didnt compare..just a lot easier to drive slow...wished I hadnt waited so long or actually figured it out....

[Go Time]

Good call on the reeds...the 300X motors are hard on them. They beat up the rubber coating on the cages and will look fine but cause problems. Do you any issues with that engine beeing a little weaker coming on plane ..lagging the other engine?

I have also seen two 300X engines in the past year that completely died due to faulty crank position sensors. Never seen this on any other Mercs. The first time it took some time to figure it out because that is one sensor the DDT won't help with.