125hp ELPTO 2+2 miss/hesitation at high speeds

[GeneralIke]

I have a 2000 Mercury 125hp (ELPTO 2+2) that is driving me crazy. Last fall it started to hesitate when accelerating and was generally running rough so I took it in for service this spring. Carbs were cleaned, new carb kits installed, spark plugs replaced, fuel filter replaced. Compression was tested and was 125-130 on all 4 cylinders. Timing was set to specs. Engine starts and idles great. When accelerating, it starts to miss at 3/4 to full throttle. If you back off a bit, it seems to run better, but never quite makes full power compared to before having the work done. It just doesn't have that "crisp" sound of firing on all 4 cylinders and seems I've lost 5-7 MPH at top end. The plugs all look good (nice golden tan color).

I've had it back to the shop several times. They have gone through it again including replacing coils and the issue persists. Unfortunately, they are really busy and every time I take it back it takes a while to get my boat back. (Minnesota summers are very short so I'm trying to minimize time out of the water.)

I have some experience working on snowmobile engines and carbs so decided to try some troubleshooting on my own. I purchased a service manual and have been slowly working through some theories. Here is what has been done so far...

1. Fuel - fresh 91 non-oxy fuel is being used. I have drained some fuel and it does not appear there is any water separation.
2. Fuel lines - the fuel lines from tank to the engine were checked by the shop. No deterioration in the lines was detected. The lines and primer bulb are Quiksilver brand.
3. Carbs - I took the carbs off, disassembled and verified that they are all clean. All seem to be assembled correctly. I re-installed and synchronized according to the manual.
4. Synchronization - I synchronized the throttle cam and roller and adjusted WOT stop. Question - do the butterflies in the carbs open completely so they are perfectly parallel with the carb body or are they supposed to stop a bit before they are fully open? Seems carb #2 has a stop that will prevent them for opening 100%.
5. Accelerator Pump - Since it seems to run really well when at lower RPM, I was thinking it could be related to the accelerator pump and fuel delivery to cylinders 3 & 4. I rebuilt the accelerator pump and replaced the fuel filter on the accelerator pump path. I made sure that the metal restrictor was clear in the fuel line on accelerator pump circuit. The normal hesitation from 2 cylinders to 4 cylinders is gone (thats a win!), but still have the issue at higher RPM. I didn't replace the accelerator check valves into cylinders 3 & 4. Could that be the culprit? Seems unlikely since I now have the smooth acceleration from 2-4 cylinders, but I'm not sure how much a role they play at high speeds.

So, after all this, the issue persists. Any ideas on next steps?

 

[flyingscott]

Check the stator.

 

[Faztbullet]

Could be bias in switchbox bad

 

[Texasmark]

Could be bias in switchbox bad

Would you explain that sir? Is the 2000 the same engine as the 2002? My serv manual seems to think so.....like 1996 was the big change and nothing till the series was terminated in 2004-5 time line. I use CDMs connected directly to the Stators....no switchbox.

 

[Texasmark]

I have a 2000 Mercury 125hp (ELPTO 2+2) that is driving me crazy. Last fall it started to hesitate when accelerating and was generally running rough so I took it in for service this spring. Carbs were cleaned, new carb kits installed, spark plugs replaced, fuel filter replaced. Compression was tested and was 125-130 on all 4 cylinders. Timing was set to specs. Engine starts and idles great. When accelerating, it starts to miss at 3/4 to full throttle. If you back off a bit, it seems to run better, but never quite makes full power compared to before having the work done. It just doesn't have that "crisp" sound of firing on all 4 cylinders and seems I've lost 5-7 MPH at top end. The plugs all look good (nice golden tan color).

I've had it back to the shop several times. They have gone through it again including replacing coils and the issue persists. Unfortunately, they are really busy and every time I take it back it takes a while to get my boat back. (Minnesota summers are very short so I'm trying to minimize time out of the water.)

I have some experience working on snowmobile engines and carbs so decided to try some troubleshooting on my own. I purchased a service manual and have been slowly working through some theories. Here is what has been done so far...

1. Fuel - fresh 91 non-oxy fuel is being used. I have drained some fuel and it does not appear there is any water separation.
2. Fuel lines - the fuel lines from tank to the engine were checked by the shop. No deterioration in the lines was detected. The lines and primer bulb are Quiksilver brand.
3. Carbs - I took the carbs off, disassembled and verified that they are all clean. All seem to be assembled correctly. I re-installed and synchronized according to the manual.
4. Synchronization - I synchronized the throttle cam and roller and adjusted WOT stop. Question - do the butterflies in the carbs open completely so they are perfectly parallel with the carb body or are they supposed to stop a bit before they are fully open? Seems carb #2 has a stop that will prevent them for opening 100%.
5. Accelerator Pump - Since it seems to run really well when at lower RPM, I was thinking it could be related to the accelerator pump and fuel delivery to cylinders 3 & 4. I rebuilt the accelerator pump and replaced the fuel filter on the accelerator pump path. I made sure that the metal restrictor was clear in the fuel line on accelerator pump circuit. The normal hesitation from 2 cylinders to 4 cylinders is gone (thats a win!), but still have the issue at higher RPM. I didn't replace the accelerator check valves into cylinders 3 & 4. Could that be the culprit? Seems unlikely since I now have the smooth acceleration from 2-4 cylinders, but I'm not sure how much a role they play at high speeds.

So, after all this, the issue persists. Any ideas on next steps?

Could be sticking. due to non-use or old fuel....metal to metal, lubrication in the fuel...I don't see a wear component on check valves. You'd think the 3-4 filter would keep crud out of the line. On linkage all mine open fully....parallel. On the transition zone I think it's more of how you drive rather than how the engine operates. If you use the pump as a pump, like advance the throottle past where you want to be (fast motion) and as the boat is responding and you are wanting cruise then easing back as you are coming up on the intended speed. On firewalling it, the pump squirts and the cylinders respond all in the blink of an eye and yes there is no lag.
Did the service dept replace the main fuel filter? Anybody cut it open and check what's inside? On carb cleaning, were the carbs totally disassembled and cleaned with solvent and 100# compressed air, fine wire down the little tubes? High speed jets free and clear? I had a problem with my 90 when I had it and the problem was accidentally found with compressed air in #2s high speed jet cavity. A blast of air at the right angle dislodged a tiny bit of black fuel line that was intermittently partially clogging that jet.

 

[GeneralIke]

Could be sticking. due to non-use or old fuel....metal to metal, lubrication in the fuel...I don't see a wear component on check valves. You'd think the 3-4 filter would keep crud out of the line. On linkage all mine open fully....parallel. On the transition zone I think it's more of how you drive rather than how the engine operates. If you use the pump as a pump, like advance the throottle past where you want to be (fast motion) and as the boat is responding and you are wanting cruise then easing back as you are coming up on the intended speed. On firewalling it, the pump squirts and the cylinders respond all in the blink of an eye and yes there is no lag.
Did the service dept replace the main fuel filter? Anybody cut it open and check what's inside? On carb cleaning, were the carbs totally disassembled and cleaned with solvent and 100# compressed air, fine wire down the little tubes? High speed jets free and clear? I had a problem with my 90 when I had it and the problem was accidentally found with compressed air in #2s high speed jet cavity. A blast of air at the right angle dislodged a tiny bit of black fuel line that was intermittently partially clogging that jet.

The main fuel filter was replaced, but I don't know whether it was opened to check inside. When I inspected the carbs, they looked very clean. I'll pull them again and check.

 

[Texasmark]

Ensure that your floats are per the manual...usually carb upside down, main support of the float is parallel to the flange where the bowl touches the carb casting.

 

[GeneralIke]

Ensure that your floats are per the manual...usually carb upside down, main support of the float is parallel to the flange where the bowl touches the carb casting.

I'll plan to take the carbs off next week and make sure the floats are set correctly. I didn't check that when I had them off before. Hopefully will also try to determine if there is an adjustment to allow the butterflies to fully open. They they are all sync'd with the butterflies closed, but there is a tab on carb #2 that seems to prevent them from fully opening. Hopefully it is something obvious when I get them off the engine.

 

[Faztbullet]

Would you explain that sir? Is the 2000 the same engine as the 2002? My serv manual seems to think so.....like 1996 was the big change and nothing till the series was terminated in 2004-5 time line.

The bias is in the trigger circuit, only way to test is to index flywheel and check timing on each cylinder at problem RPM. Below is from AMTEC training manual

 

[GeneralIke]

The bias is in the trigger circuit, only way to test is to index flywheel and check timing on each cylinder at problem RPM. Below is from AMTEC training manual

View attachment 344302

Thanks for this additional information. Indexing flywheel and checking timing on each cylinder might be a bit above my skill level. Are you aware of any instructions that would help a layman mechanic do this?

 

[flyingscott]

Thanks for this additional information. Indexing flywheel and checking timing on each cylinder might be a bit above my skill level. Are you aware of any instructions that would help a layman mechanic do this?

You have to have a factory manual to work on this motor. That should be your first purchase.

 

[chimneycarp]

I have a 1999 125hp that I just fixed with the same symptoms. If the service manual you bought is the mercury service manual go to section 2b and start on page 26. That's where troubleshooting for the cdm module(instead of older switch box/coil setup) engines starts. My question to you would be were all cdm's replaced or just certain ones? My issue was intermittent spark on cylinders 3 and 4 witch makes sense with your description because on 2+2 engines 3 and 4 don't come in until around 1800 rpm. I had to replace cdm on cylinder #1 because of a bad stop diode in cylinder 1#. Cdm's 3 and 4 get their ground path through cdm's 1 and 2. So even though cylinder #1 was firing the diode built into it that was bad, kept 3 and 4 from firing. This is explained in the manual section 2b starting on page 26. Hope that helps and is not too confusing

 

[GeneralIke]

I have a 1999 125hp that I just fixed with the same symptoms. If the service manual you bought is the mercury service manual go to section 2b and start on page 26. That's where troubleshooting for the cdm module(instead of older switch box/coil setup) engines starts. My question to you would be were all cdm's replaced or just certain ones? My issue was intermittent spark on cylinders 3 and 4 witch makes sense with your description because on 2+2 engines 3 and 4 don't come in until around 1800 rpm. I had to replace cdm on cylinder #1 because of a bad stop diode in cylinder 1#. Cdm's 3 and 4 get their ground path through cdm's 1 and 2. So even though cylinder #1 was firing the diode built into it that was bad, kept 3 and 4 from firing. This is explained in the manual section 2b starting on page 26. Hope that helps and is not too confusing

Thanks! I replaced 2 CDMs. I'll try to get the factory service module and do some of the additional troubleshooting. (I've been using the Clymer manual so far).

 

[Texasmark]

I got the 2015 revision of the original manual covering 1994 or 5 to the end of production on ebay for a decent price. In the revised edition I found the timing starting in section 2C. 2B-26 was still covering starter maintenance.

The bias is in the trigger circuit, only way to test is to index flywheel and check timing on each cylinder at problem RPM. Below is from AMTEC training manual

View attachment 344302

Thanks for looking that up sir. Will copy and include in my serv. man.

 

[GeneralIke]

Doing some additional troubleshooting this morning. Eliminated rev limiter as a source of the problem. Tested the ignition stator. The resistance on the green/white to white/green is out of spec. Spec shows 660-710 and mine measured 751. Before I spend more money throwing parts at this, does this seem like it would be a contributing factor? Also noted that one of the bullet connectors on a yellow wire from the stator seemed burned. I cleaned it up a bit suspect that may also play a role??

 

[GeneralIke]

I have a 1999 125hp that I just fixed with the same symptoms. If the service manual you bought is the mercury service manual go to section 2b and start on page 26. That's where troubleshooting for the cdm module(instead of older switch box/coil setup) engines starts. My question to you would be were all cdm's replaced or just certain ones? My issue was intermittent spark on cylinders 3 and 4 witch makes sense with your description because on 2+2 engines 3 and 4 don't come in until around 1800 rpm. I had to replace cdm on cylinder #1 because of a bad stop diode in cylinder 1#. Cdm's 3 and 4 get their ground path through cdm's 1 and 2. So even though cylinder #1 was firing the diode built into it that was bad, kept 3 and 4 from firing. This is explained in the manual section 2b starting on page 26. Hope that helps and is not too confusing

I tested all the CDMs and they seemed OK based on my novice testing. I didn’t have the Mercury test tool, so just used alligator clips to the pins in the CDM. I don’t think that would affect it, but this is my first time through this process.

 

[chimneycarp]

I tested all the CDMs and they seemed OK based on my novice testing. I didn’t have the Mercury test tool, so just used alligator clips to the pins in the CDM. I don’t think that would affect it, but this is my first time through this process.

I downloaded the factory mercury service manual from (emanualsonline.com) for about $20. It is the complete manual from mercury in a pdf form. Easy and cheap

 

[GeneralIke]

I downloaded the factory mercury service manual from (emanualsonline.com) for about $20. It is the complete manual from mercury in a pdf form. Easy and cheap

Thanks! Certainly seems like a worthwhile purchase. I've ordered a new stator today and hopefully it will arrive prior to the weekend. Since I'd already have the flywheel off, I also purchased the trigger. Hopefully between the two I can either solve the problem or eliminate a couple other causes.

 

[GeneralIke]

Thanks! Certainly seems like a worthwhile purchase. I've ordered a new stator today and hopefully it will arrive prior to the weekend. Since I'd already have the flywheel off, I also purchased the trigger. Hopefully between the two I can either solve the problem or eliminate a couple other causes.

Finally had an opportunity to work on the boat. Replaced the stator and trigger. Unfortunately, same issue persists. I'm running out of parts to swap.

So... After all this. Compression is good. Electrical *should* be good (mostly all new parts), and I'm back to suspecting fuel delivery.

While testing tonight, I did notice a significant fuel leak so pulled the carbs off. I disassembled all carbs and checked float height. Floats were good. However, it looks like one of the carb kits installed by the shop is bad. Gaskets are broken and disintegrating. (I wonder if they actually replaced them or if they reused the original...) Now trying to source a gasket kit today so I can get this back on the water for the weekend.

 

[GeneralIke]

Finally had an opportunity to work on the boat. Replaced the stator and trigger. Unfortunately, same issue persists. I'm running out of parts to swap.

So... After all this. Compression is good. Electrical *should* be good (mostly all new parts), and I'm back to suspecting fuel delivery.

While testing tonight, I did notice a significant fuel leak so pulled the carbs off. I disassembled all carbs and checked float height. Floats were good. However, it looks like one of the carb kits installed by the shop is bad. Gaskets are broken and disintegrating. (I wonder if they actually replaced them or if they reused the original...) Now trying to source a gasket kit today so I can get this back on the water for the weekend.

It has been a while since I posted, but thought I would follow up.

The new carb kits did not solve the problem. The fuel leak was fixed, but still having hesitation/miss at higher speeds and can only get about 4000 RPM at WOT. I saw another post about the check valves on 3 & 4 cylinders possibly contributing. I'm not sure I understand why that would affect performance at higher speed, but willing to try replacing... Anyone have experience or explanation how that would contribute?