2005 90 TRLD Stumbling at idle

[DBank57]

Hope this is not a duplicate. I was almost done with the post and fat fingered the keyboard and it disappeared....

Engine starts up and goes through idle sequence. When it idles down it runs approximately 1100 RPM with muffs on driveway, approx 900 RPM in river. Idling along for a minute or so and it suddenly stumbles like it misfires. Usually it will recover and continue to run but occasionally it will stall and die.

Following troubleshooting analysis in my service manual, I have gone through the entire fuel system. Flushed the fuel tank, changed fuel/water separator, changed fuel filter on engine, cleaned carbs, even ran engine off of a portable tank thinking perhaps the fuel supply line was collapsing. When engine dies I have drained the carb bowls to make sure there is fuel in them. I am reasonably certain I have eliminated the fuel system as the problem.

Next the manual points to the electrical system. I have changed plugs. Ran the engine until it died. Pulled the plugs and Nr 1 was fouled black, 2 and 3 were still clean as a whistle. Possibly spark plug cap or wire? The ignition coil and wire is a little pricey to just be easter egging to possibly hit on the problem.

Any constructive comments would be greatly appreciated. Thanks in advance.

[boscoe99]

Hope this is not a duplicate. I was almost done with the post and fat fingered the keyboard and it disappeared....

Engine starts up and goes through idle sequence. When it idles down it runs approximately 1100 RPM with muffs on driveway, approx 900 RPM in river. Idling along for a minute or so and it suddenly stumbles like it misfires. Usually it will recover and continue to run but occasionally it will stall and die.

Following troubleshooting analysis in my service manual, I have gone through the entire fuel system. Flushed the fuel tank, changed fuel/water separator, changed fuel filter on engine, cleaned carbs, even ran engine off of a portable tank thinking perhaps the fuel supply line was collapsing. When engine dies I have drained the carb bowls to make sure there is fuel in them. I am reasonably certain I have eliminated the fuel system as the problem.

Next the manual points to the electrical system. I have changed plugs. Ran the engine until it died. Pulled the plugs and Nr 1 was fouled black, 2 and 3 were still clean as a whistle. Possibly spark plug cap or wire? The ignition coil and wire is a little pricey to just be easter egging to possibly hit on the problem.

Any constructive comments would be greatly appreciated. Thanks in advance.

You got three coils and three plug wire/cap assemblies that are identical. Why not take the number three coil and plug wire/cap and swap it with the number one coil and wire/cap assembly and see if the problem moves?

Did you use a spark tester to confirm that spark is occurring when the motor stumbles and dies?

Have you confirmed proper output from the charge coil, pulser coil and crank position sensors?

Have the carburetors been thoroughly cleaned (including the complete dismantlement of same)? Was a vacuumate or other similar device used to synchronize the carburetors? Were they set to idle mixture specifications according to the book?

[99yam40]

being that he did not say this was a F90, it must be a 2 stroke.
Did not know you could hook up a Vacuum mate to this motor to tune carbs.
But testing ignition system is the best way to eliminate spark problems, then work on fuel system if nothing was found wrong with spark.

Strange it idles fast after warming up. could be it is running lean. that may the reason it lean sneezes( stumbles), if that is what you are describing

[boscoe99]

being that he did not say this was a F90, it must be a 2 stroke.
Did not know you could hook up a Vacuum mate to this motor to tune carbs.
But testing ignition system is the best way to eliminate spark problems, then work on fuel system if nothing was found wrong with spark.

Strange it idles fast after warming up. could be it is running lean. that may the reason it lean sneezes( stumbles), if that is what you are describing

That is my guess as to what might be going on. A fuel issue and not an ignition issue. But hard to trouble shoot from a distance. Heck, hard to trouble shoot in person.

You may be right about the carbs. I forgot that some Yamaha two stroke outboard motor carbs don't have an attach point for a vacuum mate hose.

[TownsendsFJR1300]

Previous posts from the Op indicates it IS a two stroke...

[boscoe99]

I interpreted the motor as being a two stroke because of the absence of the letter F in front of the 90. Also, because he mentioned three plug wires. The F90 uses 4 plug wires.

[rodbolt17]

leave the ign system alone.
fix the carb issue.
most likely that will also involve drilling and removing the air screw plug.
or buy ign parts and have spares .

[Nautical]

My guess is that its a carburetor issue too. Sometimes you think you cleaned it good, but it has to be completely disassembled , soaked,and ultrasonically cleaned for best results..Gunk spraying it doesn't get it most of the time.

[DBank57]

Thank you very much for the inputs. I apologize for not specifying the engine is a two-stroke. I thought the TLRD suffix did that... my mistake.

I did not use a vacuum mate to sync the carbs. I am limited on special equipment and tools. A friend of mine who is factory trained through the USCG suggested using a strobe to check spray pattern on carbs. All three looked strong, thus I "assumed" the carb cleaning was sufficient.

The plates over the pilot valves have been drilled. I seated the valves and backed off 1 1/4 turns per manual.


I realize trouble shooting by forum is next to impossible, however all of you have given me food for thought. I do appreciate all the comments.

Do any of you have any direction on finding a comprehensive shop manual that will give more than an IPB and basic nomenclature? I am looking for something with a trouble shooting flow chart and an in-depth explanation of what to look for based on indications and symptoms.
I currently have the basic Yamaha service manual.

[boscoe99]

Thank you very much for the inputs. I apologize for not specifying the engine is a two-stroke. I thought the TLRD suffix did that... my mistake.

I did not use a vacuum mate to sync the carbs. I am limited on special equipment and tools. A friend of mine who is factory trained through the USCG suggested using a strobe to check spray pattern on carbs. All three looked strong, thus I "assumed" the carb cleaning was sufficient.

The plates over the pilot valves have been drilled. I seated the valves and backed off 1 1/4 turns per manual.


I realize trouble shooting by forum is next to impossible, however all of you have given me food for thought. I do appreciate all the comments.

Do any of you have any direction on finding a comprehensive shop manual that will give more than an IPB and basic nomenclature? I am looking for something with a trouble shooting flow chart and an in-depth explanation of what to look for based on indications and symptoms.
I currently have the basic Yamaha service manual.

You won't be able to find this from Yamaha. Unfortunately. Comprehensive data that is. Pity the poor Yamaha mechanic in training that is trying to work on many different Yamaha models and has no guide to direct him in the right direction. Does the term getting tangled up in your underwear come to mind?

You provided the full identity for the motor which told us it is a two stroke. Many folks however leave the letter F off when they provide us the model making us think it is a two stroke when it is really a four stroke.

The tune up specs for your model is idle RPM of 800 in neutral and 600 RPM when just in forward gear. Also, the specs for the idle mixture screw is 1 1/4 turns out from being lightly seated, plus or minus 1/4 turn. Maybe try enriching the idle fuel mixture by a quarter turn and see what happens.

[DBank57]

You won't be able to find this from Yamaha. Unfortunately. Comprehensive data that is. Pity the poor Yamaha mechanic in training that is trying to work on many different Yamaha models and has no guide to direct him in the right direction. Does the term getting tangled up in your underwear come to mind?

You provided the full identity for the motor which told us it is a two stroke. Many folks however leave the letter F off when they provide us the model making us think it is a two stroke when it is really a four stroke.

The tune up specs for your model is idle RPM of 800 in neutral and 600 RPM when just in forward gear. Also, the specs for the idle mixture screw is 1 1/4 turns out from being lightly seated, plus or minus 1/4 turn. Maybe try enriching the idle fuel mixture by a quarter turn and see what happens.

Thank you for your reply. I can see the can of worms that is trying to find reliable information sources that have in depth instruction. Certainly not like my years in the Navy where we had the NSTMs that could walk any literate person thru an entire engine change out and test op.

As far as adjusting the fuel mix, clockwise turn enriches or leans the mixture?

Do you suggest tweaking one carb at a time or all three equally?

Plans are to run a bottle of Seafoam in a portable tank with 2+/- gal of fresh fuel thru in 15 minute increments. I disassembled the carbs and cleaned them but did not ultrasonically clean them. If no avail may take carbs to shop and have them ultrasonically clean them then reassemble with new gaskets, etc.

I really appreciate your insight, thanks.

[rodbolt17]

on that carb design the A/F ratio is fixed.
that mixture screw simply allows more or less of the fixed A/F ratio.
careful study of the carb will bear this out.

that stumble at idle is most likely a lean "sneeze".

its actually caused by a lean condition allowing the A/F mix that is compressed by the primary compression(piston on the down stroke) to burn in the crankcase instead of the cyl trying to force that downward moving piston back up.

[boscoe99]

on that carb design the A/F ratio is fixed.
that mixture screw simply allows more or less of the fixed A/F ratio.
careful study of the carb will bear this out.

that stumble at idle is most likely a lean "sneeze".

its actually caused by a lean condition allowing the A/F mix that is compressed by the primary compression(piston on the down stroke) to burn in the crankcase instead of the cyl trying to force that downward moving piston back up.

So, will more of the same air/fuel mix result in an overall richer air/fuel mixture or not? That is, if it provides 13 parts air and one part fuel but then 13 more parts of air and one more part of fuel is added is the mixture exactly the same?

If not, what is the purpose of the screw? Why would Yamaha post plus or minus specifications if it does nothing?

Will turning the idle mixture screw outward not help a lean sneeze condition?

If turning the screw does not change anything why does the EPA mandate an anti-tamper plug?

Don't have a carburetor here in front of me to study and Yamaha sure as hell is not going to be providing exploded diagrams with words and arrows that explain the theory of operation.