2016 Mercury 150 Pro XS miss

[skeetertj]

Hi everyone,
I'm pretty stumped and thanks for the help. I purchased a 2016 150 Pro XS on a 2016 Tracker 195 TXW from a private seller in California, which is about 1200 miles from my home. I had a reputable dealership check the motor prior to the sale. The report came back as no codes, 140 hours and Compression was 130 in all cylinders. Apparently the dealership did not start the motor. After arriving home, I started the engine and it had a substantial miss. It fired right up, but every 10-15 seconds sputters some, then returns to normal RPMS. I have always worked on my own motors and have a 200 Pro XS on my Skeeter tournament boat. I removed the old plugs and they looked perfect. I replaced these plugs with new, properly gapping each. The belt looked a little loose, so I replaced this along with the tension mechanism and spring. Fuel rail pressure in 100 PSI and air 90 PSI. Alternator puts out 13.7 volts at idle. Tracker valve looks perfect. New battery, new fuel, new bulb and fuel lines. No abnormal sounds and the engine looks brand new. I placed Sea Foam in the gas and ran the boat on the water for about 30 minutes. Great hole shot without loss of power or stuttering. WOT is great. The miss is most pronounce when at idle and in gear. Before looking into the fuel rail, injectors, VST, etc.. I'd appreciate any advice.
Thank you very much!
Tim
Model number - 1150P73EY
Serial Number - 2B229997

[EuropeanAM]

Need to verify those AIR/FUEL pressures again- they're not good. Test and record BOTH at same time: Stated as AIR: Fuel: (in that order).

What plug did you use, and what did you gap them to?

Have you inspected the REEDS?

[skeetertj]

Thanks for responding Don. I have learned so much from your posts over the years. AIR/FUEL were tested at the same time which read 90:100. No fuel expelled from the air Schrader valve. Plugs are IZFR6J gapped to .043. Have not inspected the reeds.

[JOE54]

remember when air psi rises fuel psi also rises , might want to inspect compressor and reed plate in compressor

[lpugh]

^^^^^^^ Plus one more

[skeetertj]

Joe, Thanks for responding. Can you elaborate on this a little more? Are my AIR:FUEL numbers off? I had to replace the compressor twice on my 200, but it was obvious that there was a failure. This 150 compressor seems to be functioning fine, but I have no idea how to determine if this is an issue or how to assess or perform a test. Thanks again!

[JOE54]

yes numbers are low , if you have a problem with air press fuel press will suffer also opti are very dependent on air press so a problem in the air side will result in low fuel press , there is a volume test in the serv manuals / pinch air dump hose test

[skeetertj]

Thank you. I have the service manual and will check on this. What do you show for the desired Air:Fuel PSI numbers?

[JOE54]

93 +-2/112+-2

[skeetertj]

Thanks for the numbers!
Joe, the numbers you referenced would leave an approximate 20 PSI difference. I am definitely low on the Fuel PSI (likely the result of low air pressure), but it was my understanding that a 10 PSI difference was desirable between air and fuel. Any thoughts on this?
I'm so grateful for your time!!!!!!

[JOE54]

those are output numbers, needs 15lb differential (95/110 )for gray DI

[EuropeanAM]

Air Pressure must be right there at 94-95 psi (technically at 1000 RPM's). Fuel pressure should be: AIR PRESSURE + 14.7 psi (+/- 1 psi).

[skeetertj]

Thanks Don and Joe. My fuel pressure is not even close. I’ll get working on this. Definitely learning a great deal and I greatly appreciate the information!
Tim

[JOE54]

lil low skeet

[skeetertj]

Hi Don and Joe,
I worked on the motor all day after purchasing new gauges etc.. At idle to 1000 RPMs my air pressure is 92 and fuel pressure 104. I switched gauges to confirm these were correct. Leak down after 15 seconds was air 88 and fuel 92. Both pressures then stayed at around 88 for the next 5 minutes. The compressor sounds fine and has zero play. I inspected the reed plate in the compressor and this looked fine as well. Tracker valve looks brand new. All hoses are secure and I do not hear or see any leaks. Pinch test (hope I did this correctly by pinching the fuel line) did NOT increase my air pressure. The motor sped up then died. Really struggling to get this miss figured out. Motor looks brand new and runs terrific at WOT with an incredible hole shot.
Hope you have a nice evening and thank you again!
Tim

[PatriotAW4]

How fast does the boat run with that motor on it?

[skeetertj]

Around 55-57 @ 5200 RPM’s. A jackplate and different prop would help a little. Really no bow lift, but the hole shot is immediate.

[EuropeanAM]

Tim- those pressures are far enough off to cause some performance problems. BOTH need attention, though I would be hesitant to alter ANYTHING without the appropriate instruments to accurately make the adjustments.

If you were at 94-95 Air and 108-110 fuel it would be happier. Air needs to be corrected FIRST, and adjustments made based on pressures at 1000 RPM's.

[skeetertj]

Thanks Don,
Is there anything else that I could check or do on my end prior to taking it to a shop. I’m going to double check my compression and plugs today and also pull the port side diaphragm on the fuel rail.
Thanks for taking the time to help!
Tim

[JOE54]

air dump hose needed pinched on port rail