J50PLSTD miss fire over 3000RPM Idles fine. Compression is good

[JerryDH]

Engine idles fine all day, but when trying to get boat on plane, engine drops a cylinder and when returned to idle will miss fire for 20 to 30 seconds and then return to normal idle with no miss fire. I have replaced stator, ignition trigger, coil, plug wires, overhauled carbs, new plugs. Engine runs great when out of the water with muffs on for cooling, very responsive, no miss fire. I have eliminated the VRO system and tried mixed fuel. Compression is 120 to 125 PSI on both cylinders. this problem occurs in warm weather, water and air temps above 70 degrees, runs great all winter. I am out of ideas.
Does anyone have any suggestions?

 

[oldboat1]

What's the operating temp in the lake, not on muffs? Check surface temp at top of head.

 

[JerryDH]

What's the operating temp in the lake, not on muffs? Check surface temp at top of head.

Currently surface lake water temperature is in mid 80s.

 

[tphoyt]

Do you have thermostats installed or have they been removed ?

 

[Faztbullet]

disconnect rectifier and retest, if OK replace pack

 

[JerryDH]

Do you have thermostats installed or have they been removed ?

I just put a new one in. Problem still exists.

 

[JerryDH]

disconnect rectifier and retest, if OK replace pack

 

[JerryDH]

The latest attempt did not correct problem. I have now replaced the stator, timer assy, coil, plugs and wires, power pack, and cleaned and checked every power and ground wire on engine, and cleaned all the contacts in the connectors. Just rechecked compression on both cylinders and have 125 PSI on both. I went thru the carbs again, and raised the power trim and tilt up one hole to limit angle of motor when tilted all the way down. It took off the first time I tried, but did not sound like it was consistently running on both clyinders cleanly. When I slowed down and went to idle, all was good, but as soon as I tried to take off again, back to missfire. Could a bad reed valve possibly cause this? I looked at them when I had the carbs off, but they are hard to see. At this point I am open to any suggestions.
Jerry

 

[racerone]

Lot of money invested and I believe you have a box full of good spare parts.----So are the high speed jets in carburetor bowls clean.----They are screwed horizontally into the bottom of the bowl.----They are about 5/8th inch long with 1/4-20 thread.----What elevation are you running at ?----What type of fuel pump is on this motor ?----If running with VRO has the oil output been verified ?

 

[jakedaawg]

Fuel lines from pump to carb? Flywheel key? Run on auxiliary tank?. Sick of throwing parts at it? Are these new parts OEM, CDI, or Chinese internet wonders otherwise known as Sierra?

Better yet, start at the begining.

1. Comp test.
2. Open air gap spark test. In your case do this with the throttle advanced.
3. Fuel test. Pump so.e into a clear jar.
4. Unplug every little connector and inspect the pins and sockets. Make sure they are all in place.
5. Every where a wire hooks to the motor take it off, wire brush it and reinstall.
6. Inspect Fuel lines. Not just the one with the bulb.
7. Try with a timing light to figure which cylinder is dropping. Then switch the coils. Does the dropping cylinder follow?

 

[jakedaawg]

I just reread the thread...#9 is good advice. I'd still inspect every pin and socket in each connector. Especially the amphenol connectors. They are famous for having pins and sockets not fully seated. Aftermarket, especially cdi and Sierra, I have run into many many with improperly located wires in the terminals.

 

[hgxsilver]

It sounds like faulty alarm circuit like I had on my 91 evinrude VRO 60. I had replaced most the electronics and on my first day to try it on the water, as soon as the skeg touched the water the alarm would go off and run terribly.
Yes I should have replaced the temp sensor and what have you but i knew it was running at temp, (new empeller, thermostat etc). Instead I disconnected it from the throttle controls inside, and disconnected the senders at the outboard. Finally it ran well. In my case the safety system was stuck on and wouldnt allow me to rev very high either.

 

[Faztbullet]

Serria parts are not Chinese they are Taiwan and are 2X times better than the CDI brand parts. The CDI are notorious for miswires and socket problems. Serria is the only one that have a lifetime warranty if you a selling/installing dealer and will pay you if their parts break. Only problem parts Serria sell is the carb kits as sometimes gasket material is too thin and the OMC points

 

[JerryDH]

Lot of money invested and I believe you have a box full of good spare parts.----So are the high speed jets in carburetor bowls clean.----They are screwed horizontally into the bottom of the bowl.----They are about 5/8th inch long with 1/4-20 thread.----What elevation are you running at ?----What type of fuel pump is on this motor ?----If running with VRO has the oil output been verified ?

 

[JerryDH]

Luckily all the parts were spare parts I had from previous repairs on this and former engines. If the jets you are referring to are the ones hiding behind the carburetor drain plugs, I have run a wire through them and carb cleaner and compressed air. I think that I have got every passage clean since I have had them apart 3 times trying higher and lower float levels. Elevation in Charlotte is about 500 Ft above sea level. The engine has the VRO system pump still on it, but I disconnected it and am running 50 to 1 mixed fuel at the moment. I removed and capped the oil line to the engine, but nothing else yet as far as disconnecting the VRO is concerned. Someone else mentioned something about the warning system. About a year ago the warning buzzer did start going off constantly, but none of the tell tail lights on the Tach. were on. The warning lights go thur their self check at key on, and then go out. I know the low oil and no oil lights have been working. The no oil lite will come on if you run the engine out of gas at idle, after switching tanks, but after pumping the bulb on the oil line and cycling the key, it will go out. I've got a set of reeds (used) coming tomorrow, so I will have the carbs off again, so I will recheck the jets. Thanks for your help. Jerry 704-779-5436

 

[JerryDH]

Fuel lines from pump to carb? Flywheel key? Run on auxiliary tank?. Sick of throwing parts at it? Are these new parts OEM, CDI, or Chinese internet wonders otherwise known as Sierra?

Better yet, start at the begining.

1. Comp test.
2. Open air gap spark test. In your case do this with the throttle advanced.
3. Fuel test. Pump so.e into a clear jar.
4. Unplug every little connector and inspect the pins and sockets. Make sure they are all in place.
5. Every where a wire hooks to the motor take it off, wire brush it and reinstall.
6. Inspect Fuel lines. Not just the one with the bulb.
7. Try with a timing light to figure which cylinder is dropping. Then switch the coils. Does the dropping cylinder follow?

Compression 125PSI both cylinders. My last repair was replacing the CDI with one I had replaced previously trying to fix another problem (it did not fix the problem) then or now. I removed and sanded and sprayed all terminal, grounds, and B+ connections also, and installed a different battery. This engine uses a double coil, not individual one for each cylinder. It is new. I'm trying to diagnose this by myself on the boat, so it is hard to get up and see what is going on while driving the boat. I bought a pair of in line spark testers, but they both failed the first time I used them. I do have a timing lite I'll try if reed valves don't fix it. Fuel lines are original and all look good, but I have not removed them and tried to look inside of them, but I did pump fuel thru them with the fuel bulb when the carbs were off and all was good. Fuel bulb stays firm when this is happening. At one time I discovered that I could unplug the fuel hose and as soon as engine began to falter, hook it back up quickly, and engine would take off normally. Ill let you know what happens tomorrow.
Just a side note, this engine is run almost daily 365 days a year. Thanks, Jerry

 

[juno pierrat]

don't know if you have manual, didn't find a 2003 online but a 2004, try
PDFforLess.com

 

[Faztbullet]

Dont waste your time on reeds..if it idles fine reeds are good. Disconnect the rectifier and retest

 

[oldboat1]

assume fuel is fresh, and no water or other contamination in tank?

 

[JerryDH]

Fuel is fresh, tank is clean. I may have stumbled on a possible solution. I’ve discovered that this engine has a low power mode activated when temp sensor says the engine is running too hot. It doesn’t ever turn on the temp warning lite, but it makes sense since this problem is temperature sensitive. Information sheet that came with a CSU module that I purchased previously says RPM limited to about 2500, severe engine vibration when sensor says it’s too hot. Water pump is still the original, and pumps plenty of water out Pee tube, but 16 years and probably over 5000 hours, I think that I’ll replace impeller. Thermostat was just replaced. I’ll put it in the water tomorrow, and when it acts up, I’ll disconnect the temp sensor and see what happens.