Mid-Range power surges in humid weather

[LSC101]

Boat: 2000 Challenger 1800

Motor: Mercury M2 jet 210hp

*power head replaced new in 2013. One valve block replaced at time of power head replacement.

Current issue: Typically in very humid weather when coming off plane (between 3000-4200 rpm) the power level surges up and down. Mostly feeling like it is loosing power only to come off plane. After I come off plane it idles fine. Take off (acceleration) and top end is excellent. This only happens when de-accelerating. I don't know if the humidity has anything to do with this issue, but I just happen to notice the majority of the time it is a very humid day or evening when this issue occurs.

Could this be one or more of the (reed) valve blocks is bad?

When I replaced the power head in 2013 it was because of a blown cylinder. The mechanic replaced only one valve block because it was corrupt because of the cylinder seize. Since this is a mid range issue I can only assume this may be the problem. Anyone have any other suggestions?

 

[LSC101]

Well, so far the only thing the service manual states about surging is loose reed housing or bad gaskets. I will have to read further on the bleed hoses.

 

[LSC101]

Can anyone recommend a very good mechanic in the Metro Detroit area that I can speak with that really knows these engines?

I have been in search of a mechanic that is the upmost expert on Mercury jet motor engines for a long time. Seems to be they are hard to come by.

 

[LSC101]

91 views and no input... hmmm:facepalm:

 

[racerxxx]

I looked in the manual and also read about the reed cage. Have you actually pulled them to check them? The reeds could have a piece broken off or they're just getting tired, or, something is loose from the install. That's where I would start. Sorry man, the only guy who really knows them was Dr Honda and he doesn't visit too often. We can try to help but unfortunately those engines in a Doo are like the black sheep.

 

[Seadoobuddy]

Calling [MENTION=16022]Dr Honda[/MENTION]
sometimes tony takes a peek here.

 

[racerxxx]

Calling [MENTION=16022]Dr Honda[/MENTION]
sometimes tony takes a peek here.

Been over 2 months since last activity SDB. That's why I did summons him.

 

[biffdotorg]

Since you have not gotten much response on this, I will throw a real "stupid simple" response in the middle. Do you run your boat with the blower on?

Our 240efi was showing some of these symptoms a while back, and it seemed to be on very humid day. And I thought about the blower only for the fact, that I ran it before starting to clear the engine compartment, but always shut it off. Until that day that it seemed to bog down.

Now we run it anytime that engine is on or soon to be on. And we have yet to experience it again.

This is obviously no mechanics answer, I'm just sharing what we experienced.

Good luck.

 

[Waterluvr]

OP, you own the very last generation of Mercury power heads that were carbureted and typically if the only performance issue your having with it is a rich bog when bringing the throttle down on very humid days don't lose to much sleep over it after an inspection of the reeds shows them to be in good order and not missing any pedals.

The stock jetting and reed combination at factory settings were designed to provide an air fuel ratio of 12.5 to 1, on really humid days that ratio goes down on the air side of the equation and leaves you with more fuel in the circuits than the engine can atomize and use. It can be tuned right out of there pretty easily, but the downside is you're going to have to retune it for average operating conditions or face the music from lean acceleration and top end operation.

It was a very common issue on that particular powerhead and I had many complaints on them, having gotten my Mercury tech rep involved several times with different engines, their edict was to send them back out that way tuning them rich to the point it didn't negatively affect acceleration or idle to avoid lean seizures.

Be careful getting rid of it all together that's one of biggest causes of early engine failure on that powerhead, and it's very easy to tune it away.

 

[LSC101]

Thanks for the responses fella's. I have been on the fence about running the blower while on plane or not, and for the most part I have been running it before and during the engine is running. It has not been quite a problem lately, however it is still evident occasionally. Only twice so far this season. I really want to inspect all the reed blocks but that in and of itself it quite the task having to remove the carbs and intake block etc. And, very costly to replace all of the blocks like I probably should since all but one are original.

That leads me to a question: What is the typical age of reeds before they need to be replaced? You mention that they may be getting tired. Just wondering if there was a typical age or certain hours that I should consider replacing them all.

 

[LSC101]

Well, it has been almost 2 months with no issues until yesterday. It wasn't terribly humid out, but it was acting up all day. I made a couple changes to the bilge blower since May. 1) installed a new blower. More powerful. 2) Ran the blower tube more toward the carbs. Also have been running the blower the entire time the engine is running ever since biffdotorg stated his reply.

I always burn midgrade fuel and burn AMSOIL HP Premium. I am giving this boat some good stuff. Just want to run right.

I have noticed the small amounts of oil collect in the air intake housing. Almost like it is coming from one or all of the carbs. It is not much at all, but it is evident. Could the oil injector be set too rich? I wouldn't run it past the situation. Not very confident that my mechanic did everything as he was suppose to when he installed my new engine.

Any thoughts?

 

[Dr Honda]

Sorry I've been gone, but I needed to clear my head after selling off my shop.

OK, I have a few thoughts......


1) They posts above are right about the rich condition when coming off high RPM's. It's not the "Jetting" per say, but it's the emulsion tubes. They inject air into the main circuit, and help maintain a proper mixture. When you chop the throttle... the vacuum goes high, and the air flow is cut. That in turn, makes it rich. This is an issue with ANY carb of this style.

When that happens... there will be some popping, but it really shouldn't surge that much.

If you pull the throttle back to where the issue happens... and don't move it anymore (either up or down) will it eventually stabilize? Or does it continue to surge?

2) The oil injection could be off... but it won't flow enough oil to cause surging. BUT, it not a bad thing to check. Just put the throttles to idle, and make sure the mark on the arm lines up with the mark on the body.

3) That engine has an "Auto Enriching System" opposed to a regular choke. If it's leaking... then it will be dumping extra fuel into the engine.

4) The oil in the air box is normal. Basically, the reeds are open a little, as the piston is coming back. AND, there is back-flow before they close. So, the carbs will spit some. This is also why it won't run properly without the airbox. The reeds could be a little weak, but since it's running well at idle, I'm going to say they are fine.


So, what does this all mean?? If it was my boat.....


I would check the enrichening valve... and I would verify the oil pump. And if the engine is running well at idle, high RPM... and steady at any throttle setting otherwise.... AND, it wasn't fouling plugs all the time... I personally wouldn't worry too much.




OK... there is one last thing.

Because of the RPM range... it could simply be a switch box that's going a little soft. On the 210 engine... there's a set of charging coils for low RPM's, and a set for high RPM's. at around 3000 RPM (Don't remember the exact speed right now) it switches between them. BUT, if the high RPM set of coils are going bad... when the RPM gets close to the switch over point... the spark may be weak. (that would feel like a sag in power) But once it switches to the low RPM coils... the spark power would come back.



Hope that helps some.

 

[LSC101]

1) They posts above are right about the rich condition when coming off high RPM's. It's not the "Jetting" per say, but it's the emulsion tubes. They inject air into the main circuit, and help maintain a proper mixture. When you chop the throttle... the vacuum goes high, and the air flow is cut. That in turn, makes it rich. This is an issue with ANY carb of this style.
When you state "Emulsion Tubes", do you mean the Bleed system? I cannot find anything in the service manual about Emulsion tubes.

When that happens... there will be some popping, but it really shouldn't surge that much.

If you pull the throttle back to where the issue happens... and don't move it anymore (either up or down) will it eventually stabilize? Or does it continue to surge?
It's a situation that I am pumping the throttle so I do not come off plane as suddenly so not sure. I would say, in most cases it continues to surge.

2) The oil injection could be off... but it won't flow enough oil to cause surging. BUT, it not a bad thing to check. Just put the throttles to idle, and make sure the mark on the arm lines up with the mark on the body.
I checked this in the spring, but will make sure it is dead on.

3) That engine has an "Auto Enriching System" opposed to a regular choke. If it's leaking... then it will be dumping extra fuel into the engine.
I have the procedure for testing the Enrichment Valve. Get back to you on that.

4) The oil in the air box is normal. Basically, the reeds are open a little, as the piston is coming back. AND, there is back-flow before they close. So, the carbs will spit some. This is also why it won't run properly without the airbox. The reeds could be a little weak, but since it's running well at idle, I'm going to say they are fine.


So, what does this all mean?? If it was my boat.....


I would check the enrichening valve... and I would verify the oil pump. And if the engine is running well at idle, high RPM... and steady at any throttle setting otherwise.... AND, it wasn't fouling plugs all the time... I personally wouldn't worry too much.




OK... there is one last thing.

Because of the RPM range... it could simply be a switch box that's going a little soft. On the 210 engine... there's a set of charging coils for low RPM's, and a set for high RPM's. at around 3000 RPM (Don't remember the exact speed right now) it switches between them. BUT, if the high RPM set of coils are going bad... when the RPM gets close to the switch over point... the spark may be weak. (that would feel like a sag in power) But once it switches to the low RPM coils... the spark power would come back.
Is there any way to test these coils?

 

[Dr Honda]

1) The Emulsion tubes are in the carbs, and it's part of the main jet circuit.

2) Next time out... pull the throttle back, until it surges, then stop moving it. See if it stabilizes.

3) Yes, you can test the coils. In the manual, there are resistance checks on the charge coils. Make sure they are in spec. If they are starting to "Cook"... then the resistance will be low, or a ground.