Mercruiserbackfires no power

"Mercury 5.0 litre in a 23&#39

"Mercury 5.0 litre in a 23' Trophy. I just took my boat out of storage. It ran great when I put it away, and it was carefully winterized. I put a fresh tank of gas in it before I put in the water, and replaced the fule filter/water seperator. The engine starts fine and can be revved at the dock. When I try to drive the boat; put any load on it, it starts to lose power and begins to backfire. When I reduce the rpm and the load it runs fine.

I pulled the carb abd emptied it out in the event there was any condensation, but no change. Any other suggestions? I'm in a pretty isolated area with almost no one to help unless I trailer it quite some distance. Not sure what to even look at at this point. Thanks,
PaulM"

Paul.
Did something build a n

Paul.
Did something build a nest in the exhuast? This sounds like back pressure. Look at the exhuast as you move at a idle and if it has what looks kind of like bubbles that you see when dry ice is put in water the exhuast is blocked. Good luck.

I could be wrong but i would c

I could be wrong but i would check fuel filter again sould like she starving for fuel? just a quess.Had a camaro that ran fine till it was in gear and found out i put the fuel filter in backwards.

Fuel lines are clear. Exhaust

Fuel lines are clear. Exhaust is clear. Does it osund like a fuel pump?
Paul

"Paul.
I guess it could be th

"Paul.
I guess it could be the fuel pump but I kinda doubt it.
Just so I understand.
The engine runs great until you load it then it looses power and backfires but doesn't stall out it just will not go,but(now this is important) AS SOON as you pull back on the throttle it recovers and runs smooth. Is that correct? No lag like it is out of fuel? If this is the case
the plug wires may have a problem. It may be the spark is jumping from one wire to another or the distributor cap is cracked or has a touch of water in it. Something like that.
You did not state the year of the boat. Is it safe to think it has electronic ignition? If so the amp for the ingnition may be going bad. I do doubt this as well but you never know. If there is a tach is it working correct? Could be the mechanical advance in the distributor is not moving holding the timing back. Just a few more ideas for you. Hope one gets it going."

"Not Me,
You're right it&

"Not Me,
You're right it's not the fuel pump verified it yesterday. The guy in the next slip seemed to know something about motors, and watched the carb as I drove the boat. He indicated that fuel was being "dumped" into the carb, and it seemed like a problem with the accelerator pump. My son is bring up some parts so can try it tomorrow.
Your question about timing is interesting, since we did find that the distributor was not fully tightened and had to advance the distributer to get the motor to start.
Funny that you should mention the tach. It is not functioning at all; I assumed that this was a coincidence.
The boat was new in 2003. It does not have electronic ignition. Thanks for the advice. Sitting on some of the best fishing in the world and can't get out to it,
Paul"

Paul.
How could a boat made i

Paul.
How could a boat made in 03 not have electronic ignition? What does it have?
If you have fuel being dumped into the carb it may have a sticky needle & seat and is not stopping the fuel flow to the carb.
Check that the tach wire is not grounding out.
Save some fish for me would ya?

"I think that you're right

"I think that you're right. We will replace the needle valve and seat and the accelerator pump.
I was a little surprised too that it didn't have electronic ignition. It's a 2003 Trophy and it has a standard ignition system with distributor.
I bought the boat new but in a somewhat circuitous way, so I don't know why it was configured the way it was. Probably Trophy getting rid of old inventory."

"I would go back and verify th

"I would go back and verify the timing after looking at the tach leads, on the motor and under the dash. Just getting it to start by advancing it does nothing to guarantee that it's correct. Also, if the tach isn't working at all, it could be that when you accelerate, the tach lead is touching ground. If you ground the coil (-), it won't develop the field, therefore weak, if any, spark. Make sure the tach lead is tight and you see RPM on the gauge.

Re: the electronic igntition, look at the rotor- if it has a stainless disc that looks vaguely like a star mounted to the rotor, you have electronic ignition. Mercruiser gave up on points a long time ago, IIRC. If it has points, I doubt the gap and dwell are set correctly."

"Thanks Jim, Where does the ta

"Thanks Jim, Where does the tach attach on the engine; at the coil?"

Paul.
Did you get that boat

Paul.
Did you get that boat going yet?
You have electronic ignition. Having a distributor does not mean it has points. It is not a true electronic ignition but better than points.
Just make sure you use a timing light when setting the timing.
The tach wire goes on the coil. The best thing is to look on the back of the tach and see what the wire looks like then find it at the engine.
What time is the fish fry?

"No, I am sorry to say that it

"No, I am sorry to say that it is not going. Replaced the needle valve and accelerator pump. At this point fuel or carburation sems to be elimnated as a problem. Fuel lines are clear, new water filter, carburator good. Seems like no place to go but ignition."

Paul.
I take it this boat is

Paul.
I take it this boat is a dock sitter.
If this is the case how did you check the exhuast?
There can be exhuast from the engine but it can still be blocked.
I still think this is part of the problem.
A vacuum test will give you the answer if it is or not. If the boat ran fine when you stored it it should now.
I've seen everything from birds to rats nesting in the exhuast ports.

"Not Me,
Yes it is in the wat

"Not Me,
Yes it is in the water. I haven't checked the exhaust. When I put the boat up, I take the prop off and wrap the prop shaft with plastic and duck tape. It pretty much bloacks off the exhaust. That being said, I didn't pull the cover off the shaft this year, my son in law did, so I'm not sure if he looked hard at anything. I may pull the boat today just to take a good look.

Plan to buy a distributor cap and plugs to eliminate possibilities. You were right about the distributor not having points.

Tach still does not work, but don't know if it is a conincidence or symptom, There are only two wires to coil, so I assume one must be the tach. Both look to be in good shap.

Thanks for the advice,
Paul"

Paul.
One wire is for the int

Paul.
One wire is for the interupt switch.
There are 2 exhuast ports that are on the transum mount. One on each side. Mice could have gone in through these ports.
Mice can really pack a lot of crap in thier nest. I've had this problem with snowmobiles. If they get the nest built in the right place it is very hard to get out.
You would think that the pressure from the exhuast would blow it out but this is not always the case.
If something was able to get in the exhuast and build a nest by the flappers the flappers may not be able to open holding the exhust back.
Hard to say if this is it or not but there is not much else that can cause what you have.
You've checked most of the things that cause this.

"not me, i have simalar proble

"not me, i have simalar problem with a 75 120 merc tach not working idles great but falls on its face after 12 mph timing set at 7 degrees tdc it has points"

"I finally convinced a boat me

"I finally convinced a boat mechanic from the next town to come over this morning and troubleshoot the problem. I've pretty much done what I can. It'll cost an arm and a leg, but at this point whatever it is will be worth it if it gets me back on the water.
I'll report back what he finds. Thanks for your advice,
Paul"

"Going nuts.
The mechanic spe

"Going nuts.
The mechanic spent several hours testing the ignition system. Ssid that coil was good, spark was good, ruled out the ignition.

Went through the fuel system working our way back from the tank. Used an auxillary tank to rule out the tank; problem still occurred.

Symptoms:
Motor idles and can be accellerated at dock. When you put it under load gradually, it starts to backfire and lose power. When you punch it, the boatv acceleratesd at first and the loses power. If you keep the throtle forward the engine will die.

The mechanice concluded that it could only be the fuel pump based on the symptoms, even though it tested with good power and good pressure. He suugested that I buy a fuel pump, which will be here tomorrow.

This afternoon, another mechanic came by who had workded on some outboards for me previously. With only a few test he indicated that it was the ignition module and not the fuel pump.

At this point I'm lost. The fuel pump is $280 and the module is over $500. It seems that both mechanics are suggesting sticking parts in to see if they fix the problem.

Clearly the boat is not getting enough gas, but can that be caused by the ignition module? We stuck in a spare coil and that wasn't the problem.
Not me, I have not checked the exhaust ports, but that wouldn't explain the gas problem would it? Can I open those from inside the boat?
Any help would be greatly appreciated."

"Paul.
If when you pull back

"Paul.
If when you pull back on the throttle from wide open when the engine is ready to die does the engine recover and chug for a second or 2 then idle smooth? If so it is not running out of fuel. This next test is going to make a mess but if you loosen the clamps on the exhuast boots at the exhuast manifolds and slide the boots back enough to expose the exit of the manifold the engine should take off if the exhuast is plugged. Other than taking out the boat and pulling it apart, this is about the only way to tell if it is blocked. Did you do a vacuum test? Higher rpm (2200 2800) and low vacuum can mean blocked exhuast. From what you say I do not think the vacuum test is going to tell much. Vacuum needs to be taken past the throttle plates."

"If I may chime in...First off

"If I may chime in...First off all I am no expert, but your symptoms sound somewhat similar to ones I’ve had. Have you preformed a compression test on each cylinder? And how is the engine backfiring? Through the carb or out the exhaust?

JS"

"Not me. I'll give it a tr

"Not me. I'll give it a try tomorrow. Do I need to open both sides at the same time. What will cause the mess; old carbon?
The engine does recover if you throttle back. on a couple of ocassions we have had to pour gas into the carb to get it to start.
Jason, the engine only has 100 hours on it so we have not done a compression check. It is backfiring out the carb.
Paul"

Paul.
The mess is going to be

Paul.
The mess is going to be from the wet exhuast blowing everywhere from the manifolds. You can try just removing one side and see if it helps any. If it does you're on the right track. I must say replacing parts at 3-500 bucks a pop is not a good idea. These parts can be tested to see if they are working. Not wise too just start guessing and replacing parts in the hope it will be cured. This is not that old of a boat. Something minor is worng and is being over looked. If you do think it is running out of fuel spray a LITTLE starting fluid in the carb when it starts to die. If it takes off then you know fuel is the problem. Don't just replace the pump when it shows good pressure.

"Maybe I didn't mention th

"Maybe I didn't mention that. We did spray gas into the carb when it wanted to die and it did bring the engine back and keep the engine running. I think this is what finally sold the mechanic on the fuel pump after we tested evey other aspect of the fuel system.

Both guys who looked at it are known as excellent boat mechanics. The first one was very methodical and tested and eliminated one possibility at a time.

Getting a little desperate since my son is up visiting for a limited amount of time to go fishing. This is our once a year get together.

It seems that it comes down to 3 possibilites at this point:
fuel pump
igniton module
exhaust blockage

I already bought the fuel pump so I'll stick that it. If that doesn't I'll check the exhaust as you suggested, doesn't sound like anything that won't wash off.

If that's not the problem it sounds like I may need to replace the igniton module. Both mechanics said that unless they are dead there is no way to bench test the module.

1st mechanic said that power to the fuel pump was constant while engine was losing power so was unlikly to be the module.

Thanks for hanging in there, it does help to have someone to bounce things off of,
Paul"

"Paul.
Were you able to get t

"Paul.
Were you able to get there engine to get past the trouble zone by adding fuel when it was trying to die or did it continue to stay at reduced rpm?
I do not doubt the experince level of the people you have checking the engine. But as I said before just changing parts is not a good idea. A pressure guage in the fuel line will tell if there is a loss of fuel pressure at the point the engine is failing to gain rpm. I do not remember if you checked this but there may be a filter where the fuel line connects to the carb,in the carb. The module can be tested with a ohm meter and voltage output can be taken at the ignition at the time the engine is failing.
I will be off line for a day but please post what you find."

Replaced the full pump; same p

Replaced the full pump; same problem. We peeled back the boots a little and didn't improve the situation.
Don't know what to do at this point short of replacing the igniton module to "see" if it is the problem.

"Hey Paul,
I really do not kn

"Hey Paul,
I really do not know what to say at this point.
There is something very simple wrong that is being over looked.(can't see the forest)
Did you ever replace the distributor cap as you said you were going to? I am just out of ideas at the moment. This makes no sense at all.
What did it sound like with the exhuast open? Could you tell if it was missing on one side more than the other?
Did the tach ever work? If it did work at one time disconnect it at the coil. The tach may have an internal problem. I'm reaching at this now because all the normal things have checked out. Has the ground wires at the ignition module been checked? Have all the ground wires been checked for that matter? Is there a safty switch in the remote control?(emergency tether)

There is a huanting thought that I have had this problem at sometime in the past but I'll be go to heck if I can remember what it was. This would have been in a much older boat than you have but it may be the same problem.
I am going to my books and see if by chance I made a note of it.

Sorry I can't be of more help to you at this point Paul.
It has me baffled.
If I find anything I'll sure post it for ya."

"Thanks Not Me.
We didn't

"Thanks Not Me.
We didn't have the boots all that open but there was enough water and exhaust coming that we should have seen a difference. I can't see how to get the boots open any more, there isn't really any play. I did replace the distributer cap and plugs. Replaced the water filter. Put a new needle valve and excellerator pump in carb. Isolated the gas tank by using an auxillary tank.
The mechanic eliminated the ignition module by testing the ignition components and seeing steady results.

At this point, it seems like the module is the only variable, but as I said its $500. I wouldn't hesitate if I knew that was the problem, but I don't.

Any ideas would be appreciated,
Paul"

"Paul.
I spoke with two other

"Paul.
I spoke with two other very well informed Mercruiser master mechanic's. They both said the said the samething. First the module either works or it doesn't. No question about it.

When asked what could be the problem they again both said (you're not going to like this) the exhuast is blocked.
I told them you had removed the boots to see if this was the case.
Thier answer was you can not get the boots off enough to tell if the exhuast is blocked.
It was almost word for word and this is at two different shops.
Again they both felt that one or both of the flappers in the Y pipe had come loose and lodged in the exhuast port.
Myself I think that your boat is not old enough for this to happen yet but if you are using it or it has been used in salt water it could have had a flapper come loose.
I've known both of these mechanics many years and they do know thier stuff.
I gave them the list of things that you have done and again they both still felt the only other thing is the exhuast.

I do not know what to tell you other than save the $500. the module is not going to help,that they both were sure of. I'm sorry to say that if the flapper is the cause the only way you can find out is to remove the out drive from the boat.
It will be stuck in the exhaust port where it enters the out drive. The shift rod keeps it from getting out and holds it side ways in the port blocking the exhuast flow.
If this is the problem and there is only one flapper,look for the other. It's not far behind. Everytime that I removed one and couldn't find the other sure enough it showed up on either the next time out or close to it.
Anyway that is about it. Everyone here seems to agree on this.
I wish you the best and please let me know what you do find is the problem when you find it."

"Not Me,
Thanks for that info

"Not Me,
Thanks for that information and for the research on your end. I spoke with the mechanic this evening and he said that the next step would be to test for a vaccum leak, The problem is he isn't available again until next week.
When I bought the boat, I bought the boat new from a guy who bought it from a dealership bankruptcy auction. He said that there had been a problem with something not having been torqued properly at the factory and I didn't pay much attention since it was fixed and the warranty was good. Could this be related?

This will be a dumb question, but can I pull the outdrive? Is there any special equipment required? Is it a matter of undoing some bolts or does it require special tools? Is there any way to verify that this is the problem in advance? Can I remove the top of the exhaust manifold?

Finding someone to do this work up here, north end of Vancouver island, is tough.

One other question:
I seem to have a collection of oil where the exhaust manifold the block and valve cover come togther. Very clean fresh oil. I wipe it up and it comes back. Any clues in this?

Thanks again for all of your help,
Paul"

"Sorry to be a nuisance, but h

"Sorry to be a nuisance, but here is a little more information.
When I installed the new fuel pump, I could hear it running. Now I can't. When I look into the carb when I accelerate, I do not see gas. This evening my son and I took it out and accelerated the boat until it flattened out and then I poured gas it and it pick up again. I had the feeling that if I kept pouring gas in it would get up and plane. In other words it is acting just like it did before we put the fuel pump in.
In answer to your previous question, "Were you able to get there engine to get past the trouble zone by adding fuel when it was trying to die or did it continue to stay at reduced rpm?" When we added fuel it accelerated past the problem until it ran out of gas again. When we back off on the throttle, the engine will keep running. I'm thinking of trying to put togther some fittings so we can safely gravity feed the carb.

I'm now wondering if there isn't some sludge on the bottem of the gas tank. Removing or even inspecting the interior of the tank is of course an impossibilty. Do you know of any addititive that would dissoveany and all residue?

If you ever get up this way, I owe you a fishing trip. Been watching them bring 25-30 lb salmon all day,
Paul"