Help Aaron Fix His Boat Motor

Motor: Yamaha F25MLHY 25HP 4 Stroke Outboard
Carb: Keihin BCM 65w10 nf15


I'm relatively sure the issue is carb related. When I pulled the spark plugs they aren't wet, yet they do spark when operating the pull start. I started by opening the drain plug on the lower bowl of the carburetor, a considerable amount of fuel came out. The consistency was something like tequila that has been in the freezer, kinda syrupy but still easy flowing. When I squeeze the fuel pump, the bowl is filling with fuel so I know gasoline is at least reaching the carb.

I completely dismantled the carb and cleaned all the jets with carb cleaner. I took care to try and follow the flow of gas from start to finish thru the carb to make sure I was cleaning everything. I bought a carb repair kit which consisted of a new float valve and a flat rubber seal apx 3" by 3" that apparently covers the upper part of the carb where there are channels for air/fuel to flow thru.

Upon re-assembly of the carb, I noticed a rod that's attached to the throttle linkage isn't moving as it appears it should. This rod starts from the outside of the carb and goes thru a collapsible grommet/seal into the interior of the lower bowl of the carb. From here it appears it should be operating a piston type assembly which I believe is seized and preventing the rod from moving properly. I believe this assembly is called or related to "starter plunger and/or accelerator pump" based on some carb diagrams I looked thru. I tried saturating the piston assembly with carb cleaner and leaving it over night but it's not budging.

Ultimately, I'm wondering if this is the reason my motor isn't starting and what I can do to fix it. I found an exploded view of my carb here: http://www.boats.net/parts/search/Yamaha/Outboard/2000/F25MLHY/CARBURETOR/par... The part I'm concerned with in this diagram is #23...that's what's apparently seized. If I can't free this up, looks like I'll be paying ~$115 for a new bowl assembly. Any tips/tricks...would it be cheaper to replace the lower bowl on my own vs. taking it to a mechanic? Thanks all for your help.

Category:

Science & Technology

Tags:

• Yamaha
• Boat
• Motor
• F25MLHY
• 25HP
• Keihin
• BCM
• 65W10
• Nf15
• Carburetor

[horshooer]

I assume you checked fire and compression 1st? what were they?

[Crypt1q]

@horshooer I was getting spark but replaced the plugs anyway. Didn't check the compression because it was running fine before I put it in storage. Based on all the crap that was under the plunger, I'm pretty sure it's a carb issue, or fuel lines could be gunked up too. Hopefully I can get back to work on it soon, I know my dog is upset we haven't put any bass in the boat lately :D

[8484cj]

Hey Aaron.... many thanks to you...My 4 stroke yamaha 25 hp would not start or stay running,..... I had the same part stuck and got it out and cleaned everything up and the motor is now running!! You are the man..I have been struggling fior weeks with nit-wit boat mechanics and decided to fix it myself, and you bailed me out...thanks again!! Carl Jervis-Florida

[Crypt1q]

@8484cj hey that's great to hear, I hoped that in addition to getting some good feedback myself I might be able to help others along the way. Thanks for the comments, you made my day.

[griggsb]

Is that hole a passageway for fuel? Or just a recess for shaft to slide into? Does end of shaft have hole in it, or just solid?

[Crypt1q]

It's just a recess. I was actually able to remove the plunger...there was a lot of gunk and debris below it. I've ordered a new plunger and plunger spring and hope to have a new video in a couple weeks with a working motor. Thanks for your reply.

[SuperJason4ever]

Dude how much coffee have you had:)sorry

[martyisabeliever]

hey Aaron that is the accelerator pump... it prevents a lean condition as the engine is transitioning from idle to power circuit. Hope that helps.

[CNNATHANful]

Your battery might be dead or you need a new battery or your motor is no good

[horshooer]

Something else you might check.. some older fuel lines have an inner lining that the ethanol eats away and causes to flake off... check any choke points like quick connects, filters and fuel pumps..  also pre molded sharp turns in the fuel line..

[luckynut22]

Great video I also really like the fast forward effects. Watching your video and following along in the exploded diagram from the service manual of a '98 Yamaha F25 I noticed that your missing a couple of parts. Attached to the bottom of the rod in question there should be plunger. Underneath that there should be a spring followed by a circlip and underneath that a ball. The screw you removed from the bowl i believe held this assembly down. Again check your service manual for the specifics.

[eringvo]

Great video. I had the same problem and what i did for moving the plunger was that i made some threads and mounted a screw in the treads and forces the plunger up and out. Then I removed the thing that hold the ball in the bottom of the hole and flushed the channel with oil and air. Mounted back together and it worked perfect again. I think the problem is due to water and corrosion which can be prevented by draining the bottom pot of the carborator.

[bubblerings]

SUBSCRIBED...

I wish more 'how to' videos were done this way.

Fast motion/ then good info in real time...

Thanks!