Motor problem....

tod osier

tod osier

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My 2000 Yamaha F40 is acting up. It is running rough at idle and belching gas in the exhust, it bogs a bit above idle, but is fine at mid to high RPMs. #3 plug is wet. I can unplug the coil for the #3 plug and get no further degradation in idle, but unplug #2 or #1 and it almost stalls out - so no or poor spark on #3. I can also switch the #2 and #3 ignition coil and plug wires so that I can isolate that the ignition coils and wires are not at fault, so it is not ignition coils, wires or plugs.

I've recently done a bunch of maintaince stuff, but the motor ran fine a couple trips after that (I put on a new fuel pump (because I broke a hose barb off the origional), checked/adjusted valve clearances, changed plugs, changed theromstat, anodes, etc...).

Suggestions for next step? I'm thinking wiring harness or CDI, an I way off?
 
Todd:
I am no mechanic, but I do have the same motor as you. In fact, I have a Snowgoose as well. Anyway. I am sure you tried this, but run some Seafoam through the gas tank. The ethanol made my motor bog down more than once and a few runs with quality motor oil and seafoam did the trick. A few years ago the motor was running very rough and found out that the carbs needed replacing. Something about a very narrow passage..... Spent the $ and now it runs fine besides a small chirp it makes when the choke kicks down. I hope this is helpful. Probably not.
Stern
 
It's been a couple years since I worked at the boatyard but this motor has three carbs right? Pull all the plugs out and put the #3 plug back into the boot and then ground the metal part of the spark plug to the head to check for spark while turning over the motor. Careful touching the wire or you may get a surprise. After verifiying you have good blue spark my best guess is that your carb is a bit gummed up and its dumping fuel into the head. Try this and then come back here, the more you rule out the easier it will be to fix-

Will
 
It's been a couple years since I worked at the boatyard but this motor has three carbs right? Pull all the plugs out and put the #3 plug back into the boot and then ground the metal part of the spark plug to the head to check for spark while turning over the motor. Careful touching the wire or you may get a surprise. After verifiying you have good blue spark my best guess is that your carb is a bit gummed up and its dumping fuel into the head. Try this and then come back here, the more you rule out the easier it will be to fix-

Will
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It has 3 carbs, yes.

I have spark on 1 and 3, but not 2? #3 Plug was wet when I pulled it and fuel is rolling out of #3 when I turned it over.
 
Strange. Did you switch around the wires earlier? Are the plugs decent- no cracks or burnt spots?

There's something wrong with the bottom carb- maybe the float is stuck down and flooding the motor out. The fuel pump pulls off the bottom cylinder I think, maybe you have a faulty one and it's dumping fuel.
 
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I can unplug the coil for the #3 plug and get no further degradation in idle, but unplug #2 or #1 and it almost stalls out - so no or poor spark on #3.
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Not a correct conclusion. Only thing known by the above is that the # 3 cylinder is not producing power at idle speed. Lack of spark is only a possible reason the #3 cylinder is not producing power.


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I can also switch the #2 and #3 ignition coil and plug wires so that I can isolate that the ignition coils and wires are not at fault, so it is not ignition coils, wires or plugs.
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So what you are saying is that with coils #2 and #3 swapped, (#2coil to#3 cylinder and #3 coil to #2 cylinder) the engine performance is the same? or Did you actually check for spark, as opposed to observing for power from the affected cylinder?

If you get no spark from a known good coil ( in this case coil#2) when hooked to the #3 input lead, then yes, there is a problem "upstream" (electrically speaking) from the coil.

If it is just a case of the # 3 cylinder still producing no power, then it could be either spark related or carb related.

At this point I'd just be guessing until actual spark or no spark condition is confirmed.



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Strange. Did you switch around the wires earlier? Are the plugs decent- no cracks or burnt spots?

There's something wrong with the bottom carb- maybe the float is stuck down and flooding the motor out. The fuel pump pulls off the bottom cylinder I think, maybe you have a faulty one and it's dumping fuel.
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Plugs are new today.

When you say "faulty one" do you mean a pump? I had two good trips after changing the pump.

I didn't consider it but my fuel consumption is through the roof. I had a couple guys out Monday and Tuesday and attributed it to the load, but didn't really think about it, my fuel consumption today was crazy as well for the run I did.

I don't know if I can take the carbs apart without getting them out of sync. I know they are a PITA to adjust and need special tools I don't have.
 
New thermostat- motor is prob running to temp
New fuel pump- two good runs after changing
New plugs and motor ran to speed after getting through rough idle

My money is still on the float in the carb is stuck down and pouring fuel into the motor. Tap the bowl with the end of a screwdriver and see if that makes any difference. Taking th carb off and then removing the bowl isn't a big deal, but don't try it if you aren't comfortable and don't turn any screws that have springs behind them(air fuel mixture).

Do you have a fuel water separator? We used to reccomend them on all motors. Racor and Honda make smaller sized ones that are reasonable in price.

Good luck-
 
New thermostat- motor is prob running to temp
New fuel pump- two good runs after changing
New plugs and motor ran to speed after getting through rough idle

My money is still on the float in the carb is stuck down and pouring fuel into the motor. Tap the bowl with the end of a screwdriver and see if that makes any difference. Taking th carb off and then removing the bowl isn't a big deal, but don't try it if you aren't comfortable and don't turn any screws that have springs behind them(air fuel mixture).

Do you have a fuel water separator? We used to reccomend them on all motors. Racor and Honda make smaller sized ones that are reasonable in price.

Good luck-
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I have a racor fuel water sep. I changed the fuel lines when I changed everything else - could have got some crud in the system or dislodged some in the process.

I'll look at taking the carb off and apart tomorrow after I try tapping it with a screw driver.

Thanks for the help, I appreciate it.
 
Kick it. If that doesn't work kick it harder.
That's the total of my mechanical knowledge. You're welcome.

Tim
 
Tod,
the cdi requires a special tester and I dont own one. If you get to the point you feel it is not electric there are some very good video tutorials on carb take down.
Search yamaha carb rebuild and you will get a bunch. Most are motor cycle or quad but a minkuni is a minkuni.

I do know the guys who do a lot of it are all using the ultrasonic cleaners now. You might find one someone has for doing jewelry that fits.

The Yamaha is not as tough as the Early Honda was in this regard. Carb cleaner in a can is OK but the ultrasonic really gets in the nooks and crannies.
 
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I didn't consider it but my fuel consumption is through the roof. I had a couple guys out Monday and Tuesday and attributed it to the load, but didn't really think about it, my fuel consumption today was crazy as well for the run I did.
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Todd,

Couple reasons for the increased fuel consumption.
(A) First off you have two cylinders doing the work of three, meaning the two cylinders have to run at a higher RPM or longer to accomplish the work of three. During this longer or faster rpm running time, fuel is still being drawn thru three cylinders, thus more fuel is drawn thru the engine.

(B) As has been mentioned a float stuck in the down position will allow excess fuel thru the #3 cylinder.

I'd still confirm that you indeed are getting a spark to the #3 cylinder before working on the carb. If you have spark, then it almost has to be the carb given the info supplied. Your local auto parts shop should carry a simple cheap spark tester similar to one like this. There is also a spark tester which looks like a modified spark plug which has a clip on it for grounding the tester so you do not have to hold it with your fingers.
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Dave,
I have one of those and they dont always work on the New CDI type systems. Looks like no spark but the unit is fine. The test equipment for the electrical side of the outboards is a few bucks and Specialized or I would own it.

Not needed for diesel power.

Bob
 
Update... Motor is seems fine. I drained the bowls before bed last night to look for stuff and found nothing. I put it all together this morning and pulled it and could tell it was normal. Running it in the driveway at idle I'm getting a nice smooth idle and smooth running when I rev it and no gas moving through it, #3 plug was dry.

I'm going to go out on the lake and run a heavy dose of seafoam and maybe see if I can get it to break again.

Thanks a million thus far.

T
 
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I didn't consider it but my fuel consumption is through the roof. I had a couple guys out Monday and Tuesday and attributed it to the load, but didn't really think about it, my fuel consumption today was crazy as well for the run I did.
Click to expand...
Todd,

Couple reasons for the increased fuel consumption.
(A) First off you have two cylinders doing the work of three, meaning the two cylinders have to run at a higher RPM or longer to accomplish the work of three. During this longer or faster rpm running time, fuel is still being drawn thru three cylinders, thus more fuel is drawn thru the engine.

(B) As has been mentioned a float stuck in the down position will allow excess fuel thru the #3 cylinder.

I'd still confirm that you indeed are getting a spark to the #3 cylinder before working on the carb. If you have spark, then it almost has to be the carb given the info supplied. Your local auto parts shop should carry a simple cheap spark tester similar to one like this. There is also a spark tester which looks like a modified spark plug which has a clip on it for grounding the tester so you do not have to hold it with your fingers.
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http://duckboats.net/cgi-bin/forum/gforum.cgi?post=180432;sb=post_latest_reply;so=ASC;forum_view=forum_view_expandable;#180432

#3 has spark, see above.
 
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