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Merc 260 issues

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Bryan morey

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I have a 1986 Sea Ray sundancer this is only my second year owning a boat and I don’t know much about them I’m a pretty good mechanic but obviously boat engines being a little different there’s some things that could potentially be plaguing me that I don’t understand and I’m not afraid to admit that. The boat started by leaving us stranded and needing a tow when the ignition coil cracked and I did not have a replacement on the boat at the time got towed home put new coil on boat started right up and seem to run fine took it out in the water that afternoon boat seem to be running great out of nowhere engine started surging lifted the cover to find that I had a riser gasket that had failed got towed home again put new risers gaskets and bellows on because the risers did not look in good shape inside change the oil boat start it up seem to be running great so back out on the water we went boat was actually running very well seem to be free of all of its problems five minutes into our journey from dock Engine started to surge seems to run fine at an idol and just above an idol but if you ask anymore out of it it starts to die almost like you’re reaching up and shutting the key off but then comes right back and it continuously does this as long as you’re just above an idol it actually stalled on us twice but fired right back up I had a friend out on the water with us with his boat and I did not want to push the issue in case something was hurt so we shut down and had him tow us in again I’m just stumped we really enjoy our boat we have six kids that love to go out on the boat with us but the last few go rounds have been a catastrophe and would like to get this problem solved anybody that could point me in some sort of direction would be extremely helpful
 
Change the fuel filter/water separator. When you unscrew the filter/separator, be careful not to spill the contents. Dump contents into wide mouth GLASS jar and let sit for 20 mins... Gas should be clear and no evidence of water as a layer at the bottom. Install new filter/separator. Be sure to wipe a thin film of engine oil on the filter's rubber gasket and tighten per instructions and NO TIGHTER.
If you are in a ethanol in gas state, did you stabilize the fuel last fall?
 
sandkicker said:
Change the fuel filter/water separator. When you unscrew the filter/separator, be careful not to spill the contents. Dump contents into wide mouth GLASS jar and let sit for 20 mins... Gas should be clear and no evidence of water as a layer at the bottom. Install new filter/separator. Be sure to wipe a thin film of engine oil on the filter's rubber gasket and tighten per instructions and NO TIGHTER.
If you are in a ethanol in gas state, did you stabilize the fuel last fall?
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Just a silly question about my boat but the ignition coil took a crap on me so I ran down to the local auto parts store because they were the only ones that were open and I got a Chevy ignition coil and put in the boat the one that was in my boat was an XL Superstat I did not get one of those I just got your standard run-of-the-mill 12 V coil could this potentially be some sort of problem because we were not experiencing any problems until then
 
Bryan morey said:
Just a silly question about my boat but the ignition coil took a crap on me so I ran down to the local auto parts store because they were the only ones that were open and I got a Chevy ignition coil and put in the boat the one that was in my boat was an XL Superstat I did not get one of those I just got your standard run-of-the-mill 12 V coil could this potentially be some sort of problem because we were not experiencing any problems until then
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Nope,..... By yer description, it's starvin' for gas,.... follow Bob's advice,.... I'm bettin' ya find water, 'n crud,...
 
bondo said:
Nope,..... By yer description, it's starvin' for gas,.... follow Bob's advice,.... I'm bettin' ya find water, 'n crud,...
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I pulled fuel filter off and dumped it into a container it did have a lot of stuff in it Peppa Pig including brass metal shavings I’m just a little unsure about where they are coming from since the filter is catching everything directly off of the tank before the fuel pump that is some thing I’m going to have to dig deeper into I’ve already pulled the Edelbrock carburetor apart and the bowls were spotless probably the cleanest carburetor I have seen. I’m also going to replace the fuel pump since it’s mechanical and appears to be original and am unsure of diaphragm condition
 
Bryan morey said:
Just a silly question about my boat but the ignition coil took a crap on me so I ran down to the local auto parts store because they were the only ones that were open and I got a Chevy ignition coil and put in the boat the one that was in my boat was an XL Superstat I did not get one of those I just got your standard run-of-the-mill 12 V coil could this potentially be some sort of problem because we were not experiencing any problems until then
Click to expand...

it depends upon which run-of-the-mill coil you got...you should have a TB-IV distributor and they run best with the proper coil (primary resistance). There may have been other mods done so, without know what's there its hard to say.

On your fuel pump, there should be a TYGON hose from the pump to the carb...its there to let you know if the fuel pump diaphragm is ruptured...
 
makomark said:
it depends upon which run-of-the-mill coil you got...you should have a TB-IV distributor and they run best with the proper coil (primary resistance). There may have been other mods done so, without know what's there its hard to say.

On your fuel pump, there should be a TYGON hose from the pump to the carb...its there to let you know if the fuel pump diaphragm is ruptured...
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Thank you guys for all the help I’ve been a mechanic for many years it has been a while since I’ve messed with the older stuff and I’ve never messed with about and all the different things that it has on it we are working on it we are going to do a new fuel filter I’m going to buy A better coil‘s and just because the fuel pump is for sure to be old I may replace it because they are cheap and throw it all on there at once and put it back in the water and we will go from there I will keep everyone updated on how things go definitely frustrating but not giving up once we entered the boating world We became addicted and don’t wanna throw in the towel just yet
 
Your ignition is a Thunderbolt IV Mercruiser electronic ignition.

The coil for this is a INTERNAL resistor coil. Any will work. I have purchased many from NAPA. ~$30.00

The other coil choice is EXTERNAL resister and that type is used typically with point ignitions systems with a Ballast resistor


The Water separator filter is only for large particulates and water. Any crud in this is from gas tank.

There is a fine filter at the carb fuel inlet. You have to use a 1" open end wrench and hold inlet fitting and use a FLARE NUT wrench to loosen steel fuel line fitting.
Remove from inlet fitting and then remove inlet fitting to expose carb inlet fuel filter. Either clean/replace as needed.

Last week I had to rebuild a 1986 Rochester 4 bbl which was a mess! it took me hours to get it properly cleaned and some parts had to be replaced due to corrosion. Yes corrosion.....I believe this was the OEM carb and never was touched.

After he reinstalled on boat he had similar issues. Mutli filter changes/cleanings and same with Water separator filter and he actually added an inline filter between tank and water separator soft fuel line to help keep the crud from getting into carb inlet fine filter. (carb inlet filter should be about 1 inch long and made of plastic and the screen is also very fine plastic screen).

(Note, There is a paper washer like gasket that the inlet filter rests on inside the fuel inlet fitting so be sure to check that and replace if needed)
 
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Still messing with this boat after changing the entire fuel system from the fuel tank to the carburetor and everything in between boat is still doing the same thing starts up runs great stalls at 3000 RPMs or around there finally decided to hook an auxiliary fuel tank up to the carburetor in the boat ran like a dream but I noticed some thing in the process of all of this. I took my fuel line that goes from the fuel pump to the carburetor and stuck it in a container to catch fuel while I was running the engine off the auxiliary tank and I noticed that once the engine came up off an idle the fuel pump would start pumping fuel and would go back to pumping fuel when I return the motor to an idle When I first started having this issue I change the fuel pump because the fuel pump was original and the brand new fuel pump is doing the same exact thing and I literally have changed every single component in the fuel system including a brand new carburetor and I’m not any further ahead than I was before it doesn’t make any sense to me that the fuel pump pumps just fine at an idle but stops pumping fuel when the RPMs are raised I’m starting to lean towards the fuel pump push rod but I really don’t have a direction to go in on what could potentially be the problem any help would be amazing
 
Although your methods are rough you seem to be getting somewhere.

What you should be doing is using a fuel pressure gage teed into line connected to carb.
This will give you specifics of fuel pressure. It will show when and how much fuel pressure is being produced.

If the results bring you back to the same place where you suspect fuel pump push rod then you can trouble shoot that area.

First thing i would do is confirm rod is being moved by the cam lobe which controls this.

I am not sure what that distance is, but I would say it should be about 1/2 inch.
I am also not sure what the push rod lenght is (I forget)
But if you can remove it at least you can inspect the ends to see if there is exessive wear.

Just because you replced the fuel pump does not garrentee it works.
Where did you get the pump from?

One thing you could do if you have the resources,

Get a electric low pressure fuel pump, use your remote tank, connect and see if issue is resolved. Then reconnect boat fuel system with elec pump and see if issue remains resolved.

But all that being said, I would start with using a fuel pressure gage teed into carb feed line and get real numbers on fuel pressure.
Pressure should be ~ 4-7 psi steady from idle to high rpm.
 
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Totally understand what you are saying with fuel pressure gauge and I will get one to test that out. But like I said we have determined that the boat runs amazing no more stalling no more skipping often auxiliary tank straight to the carburetor. And even without a fuel pressure gauge I visually saw the fuel stop coming out of the fuel pump while the engine was running once it came off and idle So I do know that I’ve got some sort of fuel pressure issue without even putting a gauge on it yet because I should not lose fuel at all. And I’m a pretty decent mechanic but this particular situation has got me stumped considering that I replaced the original fuel pump for this reason and the new fuel pump is doing the exact same thing that the old one was doing which is leading me to believe that I need to dig deeper into something The fuel pump that I purchased was from our local boat repair place near me and was quite expensive not saying that I didn’t get a bum part because I’ve seen it many times but my old fuel pump was doing this exact same thing and when I remove that pump and took that apart to check it out it was immaculate inside there was no signs of any malfunction with that fuel pump. But I will try the fuel pressure gauge today just to see what fuel pressures are
 
If you are 100% confident on loss of fuel flow out of pump. You may be looking at cam lobe wear considering it is a 1986.

This is rare and I have never seen this in 30+ YEARS but it could be the first for me.

Also the pump rod could have failed in the sense that the hardened surface went bad and started to wear...also rare but this has been seen before.


If all this fails to give you resolution, you could convert to a electric MARINE fuel pump system..


You can rig up a Holley or other aftermarket MARINE RATED low pressure electric pump BUT you need to order and install a Low oil pressure switch which gets installed at oil filter housing.

The wiring for this is easy and can be attached here if needed.

By going this route you permanently eliminate the mechanical pump/rod and any associated issues.

The only down side in my opinion is you loose the steel fuel line from pump to carb which I feel is the correct way to do this.
If you have the skills and tools and can make an all steel fuel line from pump to carb that would be best otherwise you will need Marine rated fuel line and an FYI- Two hose clamps per soft line connection on pressurized side of fuel lines. Many dont realize this is a coastguard regulation.......Steel lines remove this issue
 
kghost said:
I thought he got the same fail from pump when using remote tank???
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The Boat ran fine running off an auxiliary fuel tank it did not mess did not cut out did not lose fuel engine stayed running and ran great at all RPMs while I was running it off the auxiliary tank I had my main fuel line which I took off the carburetor in a container to catch the gas that the mechanical fuel pump was pumping out and that’s when I noticed that once the engine came off and idle it stopped pumping fuel but when the engine was idling the mechanical fuel pump was pumping fuel like crazy I was getting lots of fuel but once the motor was brought off and idle and the RPMs raised the pump stopped pumping fuel into the container this is where I am at the loss of knowledge because both of the fuel pumps were doing the same thing which leads me to believe that the problem is much deeper I’ve been out messing with the boat since 630 this morning and pulled the entire fuel system apart yet again and everything is clean I just replaced every component on the fuel system and the boat has not left my yard because of this fuel situation that I cannot get narrowed down
 
You need tp clarify a couple things.

1. With Aux tank, did you have that connected to the fuel pump and the pump was connected to the carb and it ran OK?

2. You did NOT have the Aux tank connected to the fuel pump when the engine ran ok?

You need to be very clear and specific sobwe dont waist time asking stupid questions.

Your responses leave out specific details.

Start over and leave out anything that doesent pertain to you exact connections when it ran coreectly.
 
The boat ran fine with an auxiliary fuel tank hooked directly to the carburetor and it was gravity fed as I explain in the last post I had the fuel system ran into a separate tank to catch any fuel that the fuel pump would be pumping out while the motor is running so to be specifically clear I had an auxiliary fuel tank with a rubber fuel line going to the carburetor directly I remove the fuel line from the carburetor and my existing fuel system and put that into a catch container and the boat ran fine
 
It was then that I noticed that the fuel pump my mechanical fuel pump that is on the motor that I had disconnected from the carburetor and pumping into a separate canister because I was running the boat off of an auxiliary tank that was hooked directly to the carburetor which was gravity fed it was at that point I noticed above an idol that the fuel pump my mechanical fuel pump which is new stopped pumping fuel above an idle nothing was coming out of the hose into the cat container
 
Ok now that that is clear,
Follow CHRIS'S post and check anti syphon barbed fitting on tank and you may need to remove and blow some AIR thru pick up tube that anti syphon fits into. To see if pick up tube is clogged up.

I would replace anti syphon with new and if pick up tube was clogged you may need to remove sending unit and with a FLASH Light look to see whats going on inside take.

It may be the source of low fuel flow.

I know it sounds like a lot of work but tjats what we would have to do if you brought it to us to troubleahoot.

If tank is clean and no restricrions in pickup tube and new anti syphon does not allow pump to pump gas then you are back to pump rod or cam lobe
 
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