Evinrude missing when hot

[TonyL65]

I have a 1995 Evinrude Intruder 175 HP, some days the bulb pumps up hard and it starts and idles well, other days the bulb is mushy and the motor is hard to start and tough to keep running, after warm up the motor idles fine. I can run 5200 RPM and around 61-62 MPH at WOT. After running for an extended distance and the motor being hot on slow down or restart it misses badly and continues to miss until the motor has sit for 20 to 30 minutes, it then starts and idles fine. I have had all 6 carbs rebuilt, new plugs, new wires, new stator, new vro pump, new coils, link & sync has been checked and adjusted, the vapor chamber has been checked, the compression is exactly where it should be according to 2 shops, some recirculation hoses have been changed, no improvement. The carbs have been cleaned twice since the rebuild, The missing always starts after an extended run. Does anyone have any idea what could be causing the problem? several local shops cannot find a problem.

[t-bone]

My guess would be the power pack starting to go. Bring a timing light with and check spark when it happens.

[TonyL65]

forgot to mention in 1st post, also has a new power pack.

[ChampioNman]

Hit the choke, if it corrects itself it is a fuel issue if not it is electrical.

[TonyL65]

Hitting the choke doesn't help, neither does pumping the bulb.

[TonyL65]

Does no-one have any idea what the problem may be? I have spent about $1300.00 on this motor. I had thought it may be heat soak but none of the post I read mention anything about a miss just stalling on acceleration or hard starting. Mine starts right up but sounds like it is running on 3 cylinders and it idles at around 1200 rpm when doing this and you can not give it any gas. when cold or after short runs it idles and runs perfectly.
Thanks for any help.

[ChampioNman]

If you have a new power pack, then test your stator's output.

[TonyL65]

Brand new stator.

[ChampioNman]

Could be a coil pack breaking down with the heat. Make sure none of your plug wires are touching the block. They could be breaking down and arcing to the block. You could check that by running it at night with the cowl off and look for arcing. A timing light shoot each plug wire when the motor is warmed up may pick off the offender.

[TonyL65]

already been done.

[316jughead]

Sounds like a timing issue, quick start malfunction or timer base hanging up. The part about not being able to give it any gas is confusing. I would think if it was a timing issue it would take gas. The fast idle when hot and rough running could also be that the carbs are not closing and causing a lean idle condition. Most of the time when these carbs are rebuilt it is only the carb body and not the carb bases. Given that all the parts replaced are good and working properley, the problem almost has to be in the linkages somewhere. If the carbs were open just a bit and the timing did not start to increase at the same instant as you gave it throttle the motor might stall and die. Just throwing out ideas and thinking as I type.

[TonyL65]

Is there any way to check the timer base or the quick start? The linkage seems to be functioning properly. Is it possible there may be a problem with the wiring harness, something breaking down when it heats up? I and 2 qualified techs are out of ideas.
Thanks,

[TonyL65]

Forgot to mention earlier, I have also changed the thermostats, and rebuilt the vapor chamber. I have tried unplugging the rectifier and the thermostat leads, as well as removing the main fuel line to check for fuel flow when it starts missing. Nothing that has been done has made any difference.
Thanks,

[ChampioNman]

No timer base on your motor, it is an OIS motor. When the pack was replaced was the EET replaced also? It is the optical eye that see the timer wheel and lets the PP to know when to fire. May also want to pull the flywheel and check the magnets.

[TonyL65]

The eye has been changed and the magnets looked to be ok when we changed the stator.

[316jughead]

What was I thinking? No timer base is right, I was thinking about the sensor support hanging up and the other moving parts sticking when hot. Dumb question: Do you have the right spark plugs?

[ChampioNman]

Run it with the cowl off but the air box on and see what happens.

[TonyL65]

right plugs. i will try running with the cowl off.

[316jughead]

Championman, I am thinking that the faster idle should be the clue. I think I might have been wrong about if the carbs were slightly open it would cause a lean condition. Would it cause a rich condition with these carbs because of the air jets? Maybe the only thing that hasen't been touched is the throttle sync. with 6 carbs it would be easy to get one off, or maybe the carbs are not closing when hot. I would lightly oil the throttle shafts and the linkage and sync the throttles.

[TonyL65]

update on the problem. I took the motor to a very highly regarded local mechanic he says all 6 cylinders have 50% leak down and that the motor needs to be rebuilt at a cost of around $3000.00. Does this diagnosis sound right, and would it cause the problems I have described in previous post? As a reminder the motor runs fine cold and after short runs but misses badly after an extended run, then fine again after sitting awhile. That is a lot of money to put into a 15 year old motor and I'm not sure it's worth it. Does anyone have any ideas? or does anyonr know where I can find a used motor? Thanks for the help.