40 ELH Misfiring bogging down

[DraganTine]

A random problem, the boat did it two trips ago, then did not do it last trip but did it today.... I cannot get higher RPMs it sounds like it's missing. I squeezed the fuel bulb to try and get gas pushed inside in case it was fuel-related. That didn't help any. Yamaha experts have any idea? I checked the over heat temperature sensor buzzer that still works so I don't think it's overheating. I pulled the spark plugs they look good. I emptied out the fuel filter on the motor didn't see any debris in it. Motor will always start up fine so I don't think it is a battery if that could even add to this problem. I can rev it up a little when in neutral but don't want to go high RPMs in neutral. Underpower it starts to miss, first it will do it at higher RPMs then it loses power and I can't even get past like probably 3,000 RPM. But I'll turn the motor off sit for like 30 seconds and start it back up right away. I can throttle up a good amount before it starts missing again. If I keep it low RPMs 3/4 throttle I can go for a bit no missing sounds, but if I try to get a little higher RPMs and begins to miss. I could run ok at like 1/2 throttle or lower, idles fine. Got home ran on the hose just fine too, idle and a little bit of throttle in neutral on the hose works okay. Full oil tank. New water pump, spark plugs, lower gear oil, just rehubbed the prop, always use non ethanol gas.

First time it happened three trips ago I was full throttle running fine and it bogged down a couple of times so I throttled back and just eased into my fishing spot that I was getting close to anyways. I fished for about an hour and then ran back fine with no missing or bogging back to the dock. Last trip not a hitch at all ran perfectly, today nothing but problems..

I replaced the fuel line and bulb added more gas 2 or so gallons to the two week old fuel. Carbs were rebuilt 2 or 3 years ago. Checked all the electrical fittings and connectors today. I charged up the battery. All cylinders have 120PSI. Different new spark plugs. Today I tested the spark and coil with a multi meter I think I did it right. coil off motor, leads on the ground ring and power plug I get 1.8 on all 3. Leads on the power plug and then in the spark plug boot I get 6.69 6.82 and 6.68.

If I read right the shop manual says that it should be .54 Primary and 6.3 Secondary +/- 15% the secondary is good but the primary is way off if I did it right.

If that's true all 3 are bad but how could the motor even run. It starts fine and will throttle up about 1/2 throttle.

Photos and videos if it helps. Im going to go out again tomorrow and run again after I cut a bit of spark plug wire off and make sure they are tight and re-gapped spark plugs.

Sorry run-on sentences and rambling .... it's been a bad week any ideas....


Spark testing
https://youtu.be/UvCWSyyAIos
https://youtu.be/rLT66hAzbdE
https://youtu.be/163m1_Ivp-I

Day 2 problems
https://youtu.be/oKhIwkIGc-c

New fuel line plugs not much change still missing got a little more speed but it still missing badly
https://youtu.be/2o-I41l7a1Q

Thanks for any ideas

[99yam40]

did you measure the lead resistance and then subtract that from your ohm readings?
I do not think that is your problem anyway tho

a timing light hooked to individual plug wires will show if a plug is not getting spark while the problems shows up.
that will eliminate spark so you can chase something else.

too much fuel to air and too little fuel can both stop a cylinder from burning properly even when it gets good spark.

check fuel pump maybe.

also could be something floating around in a carb bowl that gets into a main jet restricting fuel flow

[DraganTine]

Well I just realized that my cheap MM was out of zero ( I didn't even think about that, getting beyond what I normally do also haven't worked on motors for years so Im rusty ) so I used another and it looks like I have .50 +/- on all 3 primary coils.

I just changed the fuel today and added sea foam it gets running but its not got full power. it struggling to get power, I ran today 25MPH but I normally do 30MPH. I ran for about 5 - 10 mins going from low to WOT but it would not get any faster and going from low speed to WOT starting off plane it would bog and struggle to get on plane, not as it used to go 3 trips ago. It would jump right up to high RMP's and go. But once going it would get to 25 but sounds horrible. would an out of balance prop or slightly slipped hub cause the poor power, misfire feeling? It was rehubbed like 7 or 10 trips ago / in July. its not jumping up in the RPMs as fast as it would normally under power. At idle in neutral it will rev fast just playing with the throttles on the carbs.

I about to throw in the towel and get it in a shop. I don't have a timing light but might be able to borrow one. It does feel like its out of timing kinda. the studdering horrible sounding. But it always starts up fast and easy no struggling to get started. Just problems past idle under power.

As far as I know the carbs were rebuilt about 3 years ago. not sure about the fuel pump.

when I came home today I cleaned a few electrical connects and played with the throttle, it coughed a few times when revving up a bit now ... Now I don't know if I caused more problems.

So Im thinking/guessing its probable fuel now .... guess Im going to have to break down and take off the carbs. not looking forward to that. would the precision oiling that Yamaha has caused any of this, it's still on the motor.

Im just confused as when this all started I was WOT and it hiccuped and lost power. Made me think electrical not fuel-related.

Thanks for any ideas.

[zenoahphobic]

Just a quick observation, that lower plug looks dry to me, and maybe that cylinder is not getting fuel, just a guess.
So I think a carby clean might be in your future, no matter when they were last cleaned. Could be bad fuel last time filled.

[99yam40]

I agree now that I looked closely at the blown-up pic, there is also a hair hanging in there too in that pic.

you really need to fix that before you harm the motor