90-Runs for 10 min dies

[hiflutin]

Have had a continuing prob with 2002 90hp Yamaha-
dies at 3500 rpm
Cranks up & idle’s fine
Run for approx 10 min at 3500 rpm motor “bogs” down, did not stall, but runs at idle very rough, I can let idle or shut down for a few min & it cranks up fine, run at 3500 rpm for awhile ,than will do the same thing

Fuel is fresh I maintain/treat & always use new fuel when I go out
Checked the audible alarm, tested good, dissconnected at helm, hooked to 12v “sounded off”
Changed spark plugs-Same results
Changed Racor filter-Same results
Changed small fuel filter inside cowling-Same results
Installed new fuel Pump-Same results
Installed new male & female fuel line connectors-Same results
Used an auxiliary tank with dif bulb-Same results
Removed all three carbs-Dissammebled/cleaned my self-Same results
Bought 3 Yamaha carb kits-Took to carb shop-had carbs tanked & cleaned assembled with the new parts-
Took the boat out today,cranked & idled fine, ran for approx 10 min stalled, than would not start, let sit for aprox 10 min cranked up ran, for approx 25min at 3800rpm with no probs than stalled out, would not start back-up, let sit for approx 10 min, cranked up but idled very rough & would not go past idle. Limped home on the rough idle. Not sure what to try next
CDI or stator
Any input would help
Thanks

[99yam40]

test voltages into and out of CDI like the manual calls for,
It will point you to where a spark problem is if it is spark problem

[hiflutin]

Before today it would run for long periods at idle, (I keep the boat in a LONG no wake zone). Today it would not idle good at all after running for long period

[greasyshaft]

90 don't have a oxy sensor

[greasyshaft]

Nothing monitors whats coming out, it's an open loop system.
The amount of fuel that goes in is simply based off the velocity & pressure of air being sucked through the venturi.

Also the oxygen sensor is only sampling no. 1 cylinder on yammies

[TownsendsFJR1300]

Agreed ^^. The carb is NOT changing mixtures like a fuel injected engine would with the help of sensors, ECU, etc.

To verify if its heat related, try running with the engine cowl off (if feasible) to allow cooler air to the engine while under way.

If it runs fine after that, you know its an electric issue...


Just for S&G's, try draining the carbs (drain plug at the botom of the float bowl) into a clean container and check for any debris, water, etc. A pump or two on the primer bulb wouldn't hurt either..

Not mentioned, will the engine run to 5,500 RPM or so WOT, or what is the highest RPM your getting out of it?

[greasyshaft]

Is it fouling one of the spark plugs? try pulling a lead off momentarily using insulated pliers to check running on all cylinders.
compression test and give the thing a good de-carb

[hiflutin]

2 stroke with carbs

The motor is a 2 stroke with carbs

Have had a continuing prob with 2002 90hp Yamaha-
dies at 3500 rpm
Cranks up & idle’s fine
Run for approx 10 min at 3500 rpm motor “bogs” down, did not stall, but runs at idle very rough, I can let idle or shut down for a few min & it cranks up fine, run at 3500 rpm for awhile ,than will do the same thing

Fuel is fresh I maintain/treat & always use new fuel when I go out
Checked the audible alarm, tested good, dissconnected at helm, hooked to 12v “sounded off”
Changed spark plugs-Same results
Changed Racor filter-Same results
Changed small fuel filter inside cowling-Same results
Installed new fuel Pump-Same results
Installed new male & female fuel line connectors-Same results
Used an auxiliary tank with dif bulb-Same results
Removed all three carbs-Dissammebled/cleaned my self-Same results
Bought 3 Yamaha carb kits-Took to carb shop-had carbs tanked & cleaned assembled with the new parts-
Took the boat out today,cranked & idled fine, ran for approx 10 min stalled, than would not start, let sit for aprox 10 min cranked up ran, for approx 25min at 3800rpm with no probs than stalled out, would not start back-up, let sit for approx 10 min, cranked up but idled very rough & would not go past idle. Limped home on the rough idle. Not sure what to try next
CDI or stator
Any input would help
Thanks

[99yam40]

The motor is a 2 stroke with carbs

are you going to take my advice and test peak voltages with the proper test equipment as the service manual calls for?
It is the easiest way to find out if it is a electrical problem with the ignition system

Test before and while the problem is there

[99yam40]

If you do not know what peak voltage is do some searching and reading.
it is what the service manual gives in the specs
if you want CDi electronics has basic info on test equipment and specs
here you go so you do not hurt yourself trying to look it up
Print Out This Guide, The Use of Electronic Test Equipment for Outboard Motors.

He was thinking his ignition system was failing after warming up,and I gave him what to do to prove or disprove ignition system
reading your comment on this thread and others tell me you know very little about the motors you talk about
Do better at your reading and learning before giving advice that is not for the motor in the thread
and do not add your condescending comments as some one might get offended

[rodbolt17]

can electronics heat up and break down?
yes.
however a simple test with a Kv tester can spot it almost instantly when its occurring.

most likely on a Yamaha its still a fuel issue.

[99yam40]

Again, you are the one blaming this on the ignition system, which will be the cause of a no start if faulty.

No one is going to buy your parts, nor test equipment, that you have no idea how to use. You can not understand how obvious that this is.

Just in case you keep overlooking or just refuse to read what he wrote
here it is again

let sit for approx 10 min, cranked up but idled very rough & would not go past idle. Limped home on the rough idle. Not sure what to try next
CDI or stator
Any input would help
Thanks

I sure looks like he is trying to blame it on ignition system to me when asking about stator and CDI.
I just gave him a way to check to see if stator or CDI has a problem

If you cannot read and understand what these trouble shooting procedures and test equipment I posted about are for or how to use them then take it to someone that does. Just because you do not comprehend what it written then do not think that the OP or no one else will.
I guess you still think this motor has all the things some EFI motor do also

[99yam40]

He said:

Run for approx 10 min at 3500 rpm motor “bogs” down, did not stall, but runs at idle very rough, I can let idle or shut down for a few min & it cranks up fine, run at 3500 rpm for awhile ,than will do the same thing

and you said this

Check your Oxygen sensor.

then when you were told it did not have one you said

What measures the exhaust mix then, to adjust the fuel mix? it's not like O2 sensors were a new thing in 2002.

Because, The Oxygen sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust as the exhaust exits the engine. Monitoring oxygen levels in the exhaust is a way of gauging the fuel mixture. It tells the computer if the fuel mixture is burning rich (less oxygen) or lean (more oxygen). Here is one for your viewing pleasure. Oxygen Sensors | Yamaha Outboards | Basic Power

I am not sure you know anything about this motor, so if you do not,
why throw this junk at him as it is all wrong?
Not sure why you think my answering his questions about stater and CDI upsets you so much

[TownsendsFJR1300]

Pass the popcorn please!

[TownsendsFJR1300]

LOL!!!

Pepsi, Pepsi, NO coke!!