Results 1 to 12 of 12

Thread: 2008 Yamaha 25 mlh fuel problem

  1. #1
    Join Date
    Mar 2016
    Posts
    36

    Default 2008 Yamaha 25 mlh fuel problem

    I'm having some fuel problems and looking to be pointed in the right direction by someone with some wisdom. I took my carbs apart, cleaned them, and replaced fuel diaphragm. The motor ran perfect for a couple months. Then it's started bogging down when I get around 50% throttle. I can pull the choke half way out and it'll pick back up and run close to normal. It starts fine and runs fine until it gets a load on it and the throttle is opened up. I figure it's loosing vacuum somewhere but am not sure where to start. I also only run non ethanol in it and have already checked for water in the gas. Any help is appreciated as I kind of like to fix things myself.

  2. #2
    Join Date
    Nov 2008
    Location
    Scumter
    Posts
    21,804

    Default

    Not sure if this is your problem, but I had a similar issue and come to find out I wasn't unscrewing the vent on the gas tank cap. So it was cutting off air flow and enough gas couldn't flow time the carbs.

    Did you replace fuel diaphragm for a reason?

    Sent from my SM-G930V using Tapatalk
    Last edited by willyworm; 04-28-2017 at 07:27 AM.
    [SIGPIC][/SIGPIC]
    Delta in a nutshell: Breeding grounds + small wetlands + big blocks of grass cover + predator removal + nesting structures + enough money to do the job= plenty of ducks to keep everyone smiling!

    "For those that will fight for it...FREEDOM...has a flavor the protected shall never know."
    -L/Cpl Edwin L. "Tim" Craft

  3. #3
    Join Date
    Aug 2006
    Location
    Carolina Backcountry
    Posts
    12,265

    Default

    Sounds like carbs are still gummed up. My 25 had one ofvthose factory grey mercury tank lines. The ethanol was breaking apart lining in it and stopping up jets. If you have that hard grey line go to napa and get some black rubber fuel hose and then get a can of mercury power tune and run it throufh motor. Let it sit overnight then put non ethanol in it and run it on hose and should be good. Mine would run perfect up to half throttle, then would bog down. We cleaned carbs multiple times and it ended up being that dang hose particles breaking loose and clogging it up
    "Eventually, all things merge into one, and a river runs through it. The river was cut by the world's great flood and runs over rocks from the basement of time. On some of the rocks are timeless raindrops. Under the rocks are the words, and some of the words are theirs.
    I am haunted by waters" Norman Maclean.

  4. #4
    Join Date
    Jul 2004
    Posts
    3,641

    Default

    doesnt take much to stop up a carb. lint from rag used to wipe parts can do it. i'd suggest cleaning carbs and if you use a rag, use a lint free rag. replace fuel line from tank to motor if its suspect. blow out fuel filter on motor and make sure bowl is clean. hooking and unhooking fuel line can introduce trash too. so once you get it all together and its running good leave it alone. or just be sure connections are clean when hooking back up.
    Last edited by Redleg Camo; 04-28-2017 at 11:26 AM.

  5. #5
    Join Date
    Nov 2010
    Location
    Charleston
    Posts
    807

    Default

    Install a small clear plastic filter under the cowl and see what it collects.

  6. #6
    Join Date
    Nov 2008
    Location
    Scumter
    Posts
    21,804

    Default

    You talking a fuel filter or a air filter?

    Sent from my SM-G930V using Tapatalk
    [SIGPIC][/SIGPIC]
    Delta in a nutshell: Breeding grounds + small wetlands + big blocks of grass cover + predator removal + nesting structures + enough money to do the job= plenty of ducks to keep everyone smiling!

    "For those that will fight for it...FREEDOM...has a flavor the protected shall never know."
    -L/Cpl Edwin L. "Tim" Craft

  7. #7
    Join Date
    Nov 2010
    Location
    Charleston
    Posts
    807

    Default

    Quote Originally Posted by willyworm View Post
    You talking a fuel filter or a air filter?

    Sent from my SM-G930V using Tapatalk
    Fuel filter. Like the ones you see on a riding lawn mower.

  8. #8
    Join Date
    Jan 2004
    Location
    Irmo
    Posts
    4,248

    Default

    Check your fuel line, maybe sucking air?

  9. #9
    Join Date
    Mar 2016
    Posts
    36

    Default

    Willyworm I replaced the diaphragm because it would just bog down and cut off. I put new fuel air screws in it because the old ones were broken off and held in place with what looked to be jbweld. I could tell it was running rich so that's why I started messing with it. I just replaced the diaphragm and diaphragm gasket because I had it taken apart and figured I might as well because I know ethanol eats them up in weed eaters. It ran perfect after I cleaned it up, replaced parts, and got the fuel air screws set right. It ran fine one day last week and the next time I took it to the lake it started loosing fuel in higher rpms. I've had the vent screw on a gas tank problem too haha. My tank is one of those EPA deals that blows up like a tick so it doesn't leak fuel or vapor. It has a vent built into the cap that I knocked out with a screw diver because I don't like it expanding the way it does.

    Phoneman that's a good idea with replacing the fuel hose. I've got the grey hose too with plastic on the inside. It would probably be a good idea to put in one of those fuel filters with the screw off filter while I was doing it. The fuel line coming apart makes since too because it went from running good to bogging down all the sudden. I blamed it on my wife's attitude because it was running fine until she got in it. I'm going to clean it again, replace the hoses and see how it does.

    D's tees that's true about the rags too. I just soaked it and blew it out with carb cleaner and an air compressor. The bowls were pretty clean to begin with. I think the first issue with it was mostly what a previous owner had done to it. I know very well if it's not broke don't fix it haha. I just figured I might as well try to fix it myself first and if I can't do it I'll take it to the shop.

    Thanks for all the replys. I was kind of thinking it was the diaphragm, something clogged up or a gasket not making a good seal. Just thought that because it would run good when I got the choke pulled out to where it would draw fuel through the carbs. I hate paying someone to fix something that I can do myself.

  10. #10
    Join Date
    Dec 2010
    Posts
    28,018

    Default

    You need to rebuild them. I mean take apart, soak, blow air through all passages and reassemble with float set correctly
    and idle/air mix screw set correctly.

  11. #11
    Join Date
    Nov 2013
    Posts
    2,707

    Default

    If you cleaned them and it ran fine then next trip it's bogging again, I'd say you e got trash in your fuel somewhere. Most people replace the main fuel line and call it good. Don't forget the fuel lines from your quick connect to the carbs, they will eat up from the inside and plug jets

  12. #12
    Join Date
    Nov 2008
    Location
    Scumter
    Posts
    21,804

    Default

    I agree with GS on that interior gas lines. It's a good idea to replace em if their stock and have 10 years on em. Any small engine shop should have quality replacement fuel lines. I use Tygon lines, but if what they have isn't Tygon, it should be at least comparable.

    Plus they're transparent and you can see when you have fuel flow or not. I disconnected the fuel hose from the tank one time, pumped the bubble hard, motor wouldn't crank. Somehow I guess I got a bad connection and fuel wasn't flowing and I could immediately tell when I pulled the cowl. With those black lines I wouldn't have seen that.

    Sent from my SM-G930V using Tapatalk
    Last edited by willyworm; 04-29-2017 at 04:43 PM.
    [SIGPIC][/SIGPIC]
    Delta in a nutshell: Breeding grounds + small wetlands + big blocks of grass cover + predator removal + nesting structures + enough money to do the job= plenty of ducks to keep everyone smiling!

    "For those that will fight for it...FREEDOM...has a flavor the protected shall never know."
    -L/Cpl Edwin L. "Tim" Craft

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •