Running Lumpy

[Lizz R]

I have a 50hp Deto Yamaha engine (90's model- not sure of age) and when you start the engine it runs perfect and will take the revs for the first minute-minute and half then you can hear the engine change tone, after it changes tone it will not take the revs and usually stalls. When you start it back up it runs fine, once again for the 60-90 secs then goes lumpy.
Any ideas? it has had the carbs striped and cleaned, all new plugs.
Also anyone know where I can get a workshop manual for this?

[boats.net]

Check the timing to make sure timing advance is working in CDI unit.

Check the timing to make sure timing advance is working in CDI unit.

ya same suggestion from my side....

[bigfish1229]

take it back to where ever the carbs were done. the engine sounds to be running good while the primestart is working, once it stops the motor stalls. those carbs are tricky. i believe your problem is there

[hans1159]

I had a Honda kicker that would do the exact same thing. My filter inlet to the fuel pump was mostly clogged. Check all of your fuel filters. My honda would run great until it drained the carb bowl, then die off in different ways.

- Craig

[Lizz R]

Thanks for all your replies.

Today we have stripped out and replaced inline filters, drained all 3 carbs and checked fuel lines, but still doing the same.

Any ideas on how to check CDI unit?? Am hoping it isn't this and that it is a problem with the carbs.
Plan on getting the guy out next week to take a look!! A BETTER look!!!

i have a 50hp doing the same thing, all started with last tank fill.
so far i have drained and filled with non-ethanol, i have parts from
a blown 50hp so trying to find problem i have
cleaned main filter
checked for air leaks in fuel line
changed plugs
changed all coils
replaced all carbs from other motor
changed cdi unit

this one has me stumped, today i am going to change the fuel pump.

when it is running bad i pulled the plugs only the center plug is burning
hot top plug looks wet, and bottom looks full of carbon
if this helps good if you locate your problem please post it
because i dont have may more parts i can swap

changed out fuel pump and also checked for more fuel leaks
still left me stranded at the dock, but a good note "runs like a champ
on the trailer"!

[Lizz R]

Hi,
Just wanted to let you know I managed to get my hands on a second hand cdi unit and once plugged in all is well- runs like a dream . Can't wait for the weather to warm up a bit so fishing trips here we come!!!