Merc 225 midrange stalling

[rprichoux]

If this posting looks familiar to some of you, it is posted on several other forums. Thanks to those of you who responded with some good ideas but I am still having the same problem. Hopefully someone viewing on this discussion will shed some light on my problem.
I have a 1996 Merc. 225XL (carbureted) S/N 0G429317 on a Wellcraft 220 Coastal with a stalling problem.
The motor starts, idles and will run all day at most throttle settings. The problem is accelerating to a speed.
When I move the throttle up slowly, the engine will stop responding between 1500 and 2000 rpm. If I continue to move the throttle up it will stall and die. The engine will start right up. The only way I can accelerate is to move the throttle quickly from idle to wide open then the engine will make the boat almost jump out of the water. It will accelerate very quickly to about 42MPH @ 5300rpm. I can back off as low as 3000rpm. If I reduce rpm any further, it will come off plan and gradually die unless I come down about 1500 rpm. An authorized Merc. repair shop here has rebuilt the carbs., fuel pump, changed the temp sensor and the throttle position sensor. They ran & tested the engine in the shop and found nothing. They put the boat in the water and it does just what I have described above. Now they are thinking that it could be the ECU and/or the stator. An online Merc tech said it sounds like an exhaust restriction. That doesn't make sense, it would surely bog down at a wide open acceleration. I took the boat home.
If anyone has any input or experience with this problem, please help!!!

[captcarb]

Carburetors have an idle transfer circuit that allows them to transition from the idle jets to the mains that is supposed to eliminate this problem. I have not worked on those particular carbs, but it is usually a series of passages or a slot that uncovers as the butterfly opens.

Some of them have very tiny passages that are the first to plug up from sitting. Soaking the carburetors sometimes will not clean them. They often have to be cleaned individually by forcing solvent through each passage, all the way from the throat to the float bowl. I don't know if this is your problem, but in my experience it is the single most common problem with carbs.

jim

[rprichoux]

I am familiar with the transitional passageway. When the tech rebuilt the carbs I pointed that out and they said that they would make sure that all passageways & holes were free and clear. (of course I didn't watch them)

[rprichoux]

Thanks Jim for your response. Where is everyone else? Any ideas, info, thoughts, possibilities etc. would be greatly appreciated. Could the ECU not be processing the TPS signal at midrange, could the stator break down only at that RPM range etc. etc. I have spent over $900.00 on repairs and replacements paid to 2 Merc repair shops that did not solve the problem. Again, any input would be greatly appreciated.

Ralph

[HighVelocity]

Just reading your senario makes the problem seem like dead electrical advance spot. I'm sure they tested the TPS for smooth voltage increase through the range, but maybe double check it. You can do it with a digital meter.

This is a real tough problem because of the cross over in technology. TPS sensors, computers, with carburetors----I don't kow what merc was thinking at the time. Electronic advance is a lot better with fuel injectors.

The other question is though, can you sustain high speeds indefinatly?? If not, maybe you're back to a lack of good fuel supply, or a bad float adjustment.

I hope my thoughts are more help than confusion,
HV

[rprichoux]

As you suggested, I checked the TPS with a digital meter. It showed a smooth increase with no dead spots or hesitation from .95V to 3.78V.
I recently made a non-stop run for about 15 miles running at 4800RPM and a speed of 35MPH with no problems whatsoever. I can slow down to approx. 3000RPM and pick back up slowly with no problem. If I drop below 3000RPM it will gradually slow down and die within about 30 seconds. Once it starts to slow down, I have to open the throttle all the way or pull back to idle to prevent it from killing. If it does die, it will start right up.
I also decided to take the carbs down myself (I know the shop just did that) and checked the float adjustments and used the aerosol gumout with the small tube to blow through all jets and passageways to verify that they were clear. Took it out for a run and it ran with exactly the same problem.
I hope that you, or someone out there can shed some light on this problem.
Thanks
Ralph

[HighVelocity]

Ralph,

I don't want to pretend to be an expert here, some people get upset when you do that. LOL It does seem that your fuel supply is good, so ruling that out we are left with a calibration problem, I think. "Open the throttle all the way or pull back to idle to prevent it from killing" is what you said. Somewhere along the line there isn't enough spark or fuel keeping up at that RPM. Which could also mean that your running too lean at higher RPM, and as you know, that's no good either. I have read the merc manuals on a few older 3.0L EFI and it seems the voltage they state is higher than the what you have come up with at WOT. They are saying .68-4.68 range. Please verify where you need to be at for that year.

Lastly-if we are suspecting calibration problems, you could experiment a little with the TPS sensor position. I would suggest marking your voltage starting point now then either lower or increase your starting voltage in very small increments, and see if it cures the problem or makes it worse. Obviously if it makes it worse you went the wrong direction.

If you want, shoot me an email with some pictures.

[email protected]

HV

[HighVelocity]

Ralph,

I don't want to pretend to be an expert here, some people get upset when you do that. LOL It does seem that your fuel supply is good, so ruling that out we are left with a calibration problem, I think. "Open the throttle all the way or pull back to idle to prevent it from killing" is what you said. Somewhere along the line there isn't enough spark or fuel keeping up at that RPM. Which could also mean that your running too lean at higher RPM, and as you know, that's no good either. I have read the merc manuals on a few older 3.0L EFI and it seems the voltage they state is higher than the what you have come up with at WOT. They are saying .68-4.68 range. Please verify where you need to be at for that year.

Lastly-if we are suspecting calibration problems, you could experiment a little with the TPS sensor position. I would suggest marking your voltage starting point now then either lower or increase your starting voltage in very small increments, and see if it cures the problem or makes it worse. Obviously if it makes it worse you went the wrong direction.

If you want, shoot me an email with some pictures.

[email protected]

HV

[props4u2]

Replace your fuel line from the tank to the engine including the primer bulb. Also remove the check ball from the barbed fitting on the fuel tank if it has not been removed previously.


Lee