1999 mercury 30 hp 4 stroke made by Yamaha

[Chewybmt]

Hello all and thanks in advance to the input I receive!!

i have a 1999 mercury 4 stroke with 3 carbs and they are kicking my butt. Everything I’ve read says that Yamaha built these motors from 1999-2005

I removed the breather and can see gas shooting out of the tall stem in the carb when I rev up the engine, but as soon as I let off the gas the gas will quit coming out even if it’s full throttle and the motor bogs down and eventually dies. If I keep messing with the throttle, I can see gas goin in and it continues to run. Not much I haven’t checked on this dude. New gas can, new lines all the way to the carbs too. Disconnected the line at fuel pump and it shoots out of it fine while running. It starts and idles fine. Plugs are clean and compression is 110 on all 3.

If someone can just give me a clue what to check next I’ll be more than happy to try it.

I’ve tried just about everything I read about, need new ideas.

Thanks in advance
Brandon

 

[Texasmark]

Why don't you order 3 carb kits (iboats probably has them) and install after you do a thorough cleaning of your carbs. A good soaking in a good carb cleaner, scrub as required, and blow out with compressed air. Ensure that any of the little holes you find get a blast of air and that there is an exit point somewhere on the carb for the air. The flow control "jets" are usually brass and are removable. Remove and ensure that you can see through the little hole and there is no contamination present.

110 is getting iffy on compression (opinion) but since you are happy with WOT performance then it must be adequate for your requirements.

 

[Chewybmt]

I’ve been all through the carbs 4 or 5 times and synced them every time afterwards.

I’ve took this motor to 3 different shops and always pay big money for nothing. That’s why I’m trying to do it.

 

[boscoe99]

Would it trouble you too much to give us a serial number?

Was the motor hot, throttle wide open, battery fully charged, when the compression test was performed?

 

[Chewybmt]

OG906509 is serial number.

Motor was warm, honestly don’t know about the battery being fully charged and it was full throttle.

 

[Chewybmt]

Just checked it with cold motor and all 3 were at 115. Battery is 12.62, throttle was wide open.

 

[Chewybmt]

All the same with warm motor

 

[Texasmark]

Just checked it with cold motor and all 3 were at 115. Battery is 12.62, throttle was wide open.

"Motor was warm, honestly don’t know about the battery being fully charged and it was full throttle." Did I get sidetracked here.....Battery was at 12.62 at full throttle??????? If I read this right, your alternator isn't charging your battery. Assuming a '99 4 stroke is late enough design to have a regulator which, at WOT should have your battery up at around 14 to 14.5 unless you ran it down cranking and it hasn't had time to catch up.

I realize triggers come from one coil and the alternator has it's separate coils neither interacting with the other except at low speeds you could have low voltages at your CDI circuitry resulting in unreliable firing....but you said it starts and idles fine so that blows that concept out of the water.......thinking........

 

[Chewybmt]

battery was at 12.62 when I did the test, I didn’t check the battery while doing the test.
I’ll check the battery while it’s running in the morning and report back in the morning

thanks for the replies guys!!