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Discussion Starter · #1 ·
I have a 2004 225 4 stroke with about 1300 hours. Been having an issue where after an hour of trolling the engine starts to run rough like it has a miss. Normally troll at 900rpm and the motor will fluctuate between 700-1000rpm. I can goose the throttle up to about 1200 and it will clear but return again in about an hour. Here's what Ive done so far but the problem persists.

1. 4 cans of Sea Foam injector cleaner. 2 before fuel up and 2 after. Pumped 110 gal.
2. Had injectors pulled, cleaned and reinstalled
3. Replaced thermostats as there was a bit of a temp difference on each side of the block
4. VST was replaced in 2013

I trust my mechanic. He isn't Yammi certified but he know engines , has the equipment and a Yammi network to tap into....which he's been doing. Sure could use some ideas. Hard issue to solve but worst case is that i take it back to the dealer and let them have it. Likely they will do some of the same things but this is getting old.

Thanks,
John
 

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I would:

Change Filters - Change water sep filter, medium pressure filter (about $80 part), and clean high pressure filter under the fuel pump inside the VST tank. There should be ZERO residue on these. If you have stuff in there, clean/replace it all and polish your fuel.

Run ring free always and fresh fuel always. My boat always gets 93 octane.

Also check your fuel vent, primer bulb, the O-ring on your filler cap and fuel line.

Remove your o2 sensor, soak it in Ringfree overnight and blow it dry with compressed air. Clean the carbon out of it's housing and reinstalll with a new gasket.

Get a fly rod and quit trolling....
 

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I would:

Change Filters - Change water sep filter, medium pressure filter (about $80 part), and clean high pressure filter under the fuel pump inside the VST tank. There should be ZERO residue on these. If you have stuff in there, clean/replace it all and polish your fuel.

Run ring free always and fresh fuel always. My boat always gets 93 octane.

Also check your fuel vent, primer bulb, the O-ring on your filler cap and fuel line.

Remove your o2 sensor, soak it in Ringfree overnight and blow it dry with compressed air. Clean the carbon out of it's housing and reinstalll with a new gasket.

Get a fly rod and quit trolling....
A higher octane fuel is not better, it is harder for the engine to burn it. Whatever yamaha calls for is what octane you should use.
 

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Have you ever changed the O2 sensor ? If not - that might be the cause.

I'll assume you checked / changed spark plugs but if not - very easy to do and a dirty plug ( s ) could also cause what you describe.
 

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They have internal filters that clog. E10 fuel eats fuel lines and clogs the filters, water separator or not. Could be a culprit
 

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Discussion Starter · #6 ·
All - appreciate the suggestions. Will pass on to the mechanic.....can't hurt.
Plugs were checked when injectors were pulled....was hoping that it would provide a clue if a particular injector had an issue
Meant to add that I have no issues running at cruise. Problem only occurs when an extended period of low rpm.

Thanks,
John
 

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The above suggestions make sense, but 4 cans of sea foam for 110 gallons isn't going to cut it. I helped a guy hook up a temp 1 gallon tank to his engine with a full can of sea foam. He had to keep RPM's up to keep it running, but it worked. Definitely check plugs first.
 

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Had similar issue on a f250. Turned out to be hairline cracks in the porcelain on 2 plugs. Plugs would fire fine above about 1500 rpm but below that engine would run rough. Gradually got worse until I changed the plugs. Plugs looked normal except for a slight carbon trace on the porcelain.
 

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A higher octane fuel is not better, it is harder for the engine to burn it. Whatever yamaha calls for is what octane you should use.
This is not true at all. Higher octane fuel is more stable, and ignites when it's supposed to as opposed to lower octane fuel that is not. Lower octane tends to ignite before TDC, which is very bad for an engine.

I always run high octane 93 in my engine.

I know these 225 yamaha shad a lot of corrosion issues, might be something you wanna look into with your mechanic.
 

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Check out all the suggestions above and if they do not cure your engine do one more thing. I have the same model engine you have with 2700 hours on it. Also have a bud with the same engine with 2200 hours. That engine was introduced in 2002. It has been a great success but they had vapor lock problems big time in Fl when first introduced. Yamaha developed an anti vapor lock kit to cure it, and offered it free of charge for those who needed it. I never got a recall notice or heard anything about it from my dealer. I have had some stumbling in hot weather over the years and so has my bud. My dealer suggested I change fuel brands, which I thought was a weak response. I am getting the kit installed next week. Would have done it years ago if I had known. You can tell if you already have it by looking in back of the engine block to see if there is a black canister mounted horizontally there. If it is not there then you have a decision to make.
 

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You are right. The kits are no longer available. Individual parts are available at a whopping $1000.00. It was free at the time. Sucks that Yamaha did not make the info more available to owners. Remember that Yamaha made the Merc four stokes back then. At least the upper end. So if you want the kit you may be able to find a junk Merc or Yam with the kit. My mechanic claims to have one he can install. My bud got one off a Merc.

Wild Bill
I was told that vapor lock kit was not available anymore. is a dealer installing it
 

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There's only one cure for Ethanol and Gas from the station....

.....buy aviation fuel. Change the spark plugs every 50 hours. A certified Yamaha mechanic and dealer owner said you'll never have fuel problems again...and I don't. I run it in all of my small engines to include my lawn mower, pressure washer, weed wacker, and leaf blowers. I'm lucky since the baybridge airport is right near my house. I do sometimes go down to easton and fill my tanks with the non-ethanol Citgo fuel near the amish market, but at $5.00 a gallon, its the exact same $$ as the aviation fuel at the airport. A complete pain in the ass, and not an easy fix for a larger engine that requires a good bit of gas, but I would absolutely suggest running a 1/2 tank of AV-fuel for your last run of the season. Lastly, I don't change my filters often since the AV-Fuel is FAA certified to have no water and so few impurities that every time I remove my main filter, I merely put it right back on....its that pristine of fuel....just like bombay Gin.

You can run AV-Fuel in any engine that doesn't have a catalytic converter. Any combustion small engine basically...to also include 2-strokes w/proper oil mixture of course.

Say no to ethanol. There is no fuel stabalizer that cures ethanol fuel....it is terrible.
 

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I was told by my Yamaha certified mechanic troll for a while then run the $hit out of your motor to clear it out. Wide open throttle! These four strokes like high rpms much like a two stroke. He said they once loaded a boats tank with a dealer only fuel system cleaner and ran it wide open for an hour to clear out carbon and gunk in his motors. After that ran fine. just run ring free and burn them out after idling
 

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Discussion Starter · #17 ·
Appreciate the continued suggestions which I will pass on to my mechanic. His Yammi contact was fishing the WMO last week so hopefully things will happen this week.

I've run ring free since the motor was new and didn't have any issues for over 10 years. Motor runs fine at cruise and will get right on plane after this low rpm issue. The puzzling part is why does it take about an hour to show up? Was going to try an run it in the slip and see if it happens when not under load.
 

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The puzzling part is why does it take about an hour to show up?

The carbon builds up in the cylinders while trolling. While traveling to and from you are clearing them out
 
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