25hp Yamaha Bogging Down

1990 25 hp manual start tiller oil injector<br /><br />Recently bought this motor used from local ebay seller. Have used it 3 times. Problem has been intermitent each trip and seams to "fix" itself eventually but makes me quite nervous. Engine starts easily (first light pull) and has run like a dream with plenty of power and smooth acceleration. I ran one 6-gallon tank of premix through it because I had no idea how long it had sat or if the oil injection system needed priming. No problems there - just changed the plugs after that first tank. <br /><br />Problem is this:<br />I can be running along just backed off of WOT just fine and suddenly the engine will bog down and only run properly at lower rpm's. At first I suspected the engine protection system for overheating or low oil reserve where it limits your rpms. Cooling system was fine, engine was not hot, oil tank was full, and alarm light was not lit. problem lasted for about a minute first time and then cleared up and ran fine on its own.<br /><br />Same thing next trip - fixed itself - ran fine afterwards.<br /><br />Third trip problem stayed until back to port giving me time to try and analyse. ran seemingly fine at lower rpms but when trying to accelerate up on to plane engine bogs down and won't run right until I reduce throttle. Checked vent on tank - open. Pumped fuel-line bulb - was already pressureized and pumping didn't help rpms at all. Partial choking helped quite a bit - got me up on plane and back to port. <br /><br />What's my problem and what do I need to do to fix it?

Re: 25hp Yamaha Bogging Down

Welcome to iboats.<br /><br />I'll bet you have some varnish or dirt in the carb floating around and clogging the main jet occasionally. Or maybe some water in the gas. If it's easy to do, drain the carb. That might let whatever is causing the problem to come out with the gas. Definately worth a try. Just put a rag under it to absorb the gas. A clump of paper towel might help you analyze what comes out better. With a lot of Yamaha carbs, you only need to partially loosen the drain screw to let the gas out. But remove it completely. Once it's drained, give the primer bulb a squeeze to help flush it a bit more. Then put the drain screw back in and refill the carb with the primer bulb.

Re: 25hp Yamaha Bogging Down

Hi!<br /><br />You seem to have the same problem as we have with our 20Hp -87 yamaha. It can run fine for a while and then suddenly it "bogs" down and only run on low rpm. After a minute or two it runs better again, or not. We think that it's the fuel pump that is causing the problem. The diaphragm in the pump should be changed every 5 year. We are going to change it and hopefully it starts to run great.<br /><br />Good luck with the problem solving!<br /><br />Regards,<br />Robbi

Re: 25hp Yamaha Bogging Down

Ocean Sun, I would have to guess it is the fuel pump. The diaphragm is made of a rubber type material and they will deteriorate with out modern day alcohol additives in the fuel. If you are inclined I would also clean the carb(s) out as it would give me the piece of mind knowing they were gum free. Especially after buying from an ebay user. Is the fuel pump part of the carb? On some of the smaller yamis they have the two attached.

Re: 25hp Yamaha Bogging Down

The clue in this discussion is that pumping the bulb does not help so it is not the fuel pump. And choking it does help so it is a lack of fuel. By elimination it has to be the carbs and the likey culprit is what WillyBWright has suggested. Drain the bowls and it that isn't enough, thoroughly clean/rebuild the carbs, cleaning ALL orifices with carb cleaner AND compressed air. Install the rebuild kit parts, set the floats and idle mixture screws to manual specs.

Re: 25hp Yamaha Bogging Down

what jimd says

Re: 25hp Yamaha Bogging Down

Looking at a 1995 Oil Inj Yammie 25. Any suggestions besides the usual (compression, visual appearance, spark plug condition, lower unit condition? All comments welcome. have owned 3 OBs of varous size in the past never a Yammie.

Re: 25hp Yamaha Bogging Down

Hi again!<br /><br />Changed the diaphragm but it did not solve the problem. It's probably the carbs that should be cleaned as it has been mentioned earlier in this post. <br /><br />Robbi

Re: 25hp Yamaha Bogging Down

I have had the same prob with a 1998 25 yamaha and it is water in the carb. it sits there in the bowl and lets fuel run across the top hence the good performance at low rpms and when you need some fuel it just dont happen, actually bloody scary in a following sea when the damn things bogs. And for the life of me cant work out why the carbs wont drain out the drain , i have to remove the carbs completely and the second and last time was at sea and its not pretty, change the fuel in your tank regularly especially when it has been hot and there is a chance of condensation forming and just for measure i run approx 200ml of methylated spirits in the tank when i first launch the boat and this allows to burn the water in the fuel rather than have it sit in the bottom of the tank and carbs. Hope this helps.<br />Dave

Re: 25hp Yamaha Bogging Down

OK - Drained the bowls - didn't notice anything coming out after capturing in a paper towel. So Rebuilt both carbs as suggested soaking all the parts, spraying out all the little passages and both jets in each carb, blew everything out with compressed air, replaced all the newly supplied parts/seals from the carb rebuild kit, and two beers later I'm done. Took it out last night and it ran flawlessly and with more responsiveness than ever for 5 hours. Thanks a lot for the help guys!! If you were local I'd share some of the haul of crab from last night.<br /><br />Thanks again!!<br />Dan

Re: 25hp Yamaha Bogging Down

Followup - my idle is a little too slow - almost wants to die - since the carb rebuild. Do I adjust the needle valve on the carb or the throttle stop in the linkage?<br /><br />Both carbs are synced properly. I'm thinking that with some passageways cleaned out the the idle mixture has changed with the screw set at the previous location.<br /><br />Any tips?<br />Dan

Re: 25hp Yamaha Bogging Down

If you didn't remove the idle screws you didn't do a thorough job on the carb rebuild. How are you gonna clean the passages if you don't have access to them. Regardless, after a carb rebuild you have to reset the idle mixture screws, starting at the manual's recommended number of turns out from lightly seated. IF the carb to ignition advance is correctly synchronized to manual specs as you said, adjust the idle mixture for best idle in the water in forward gear at the proper rpm (see manual probably ~700-900 rpm).

Re: 25hp Yamaha Bogging Down

I did remove the idle screws - I just re-set them to their previous setting as it was also the recommended initial setting. I used to do warranty reel repair for shimano and Penn so I wasn't shy about completely dissasembling the carbs - everything that could be disassembled was. It appeared that the needle valve seat was pressed in so I didn't attempt to remove that - otherwise everything was thouroughly cleaned. It fixed my problem and made a noticeable performance increase.<br /><br />Anyway... thanks for the answer! I need to adjust my idle with the IDLE screws - DOH! Now that I think about it you would of course not want to rely on the throttle being opened for idle but would want it to idle correctly with the throttle backed off. It's not dying and is idleing smoothly - just very slow - I don't have a tach but I'd say it's about 150 - 200 rpms low. Should I adjust it under load tied to the dock or moving through the water with a normal load in the boat?<br /><br />Thanks for the help<br />Dan

Re: 25hp Yamaha Bogging Down

They are all a little different, this is where a manual is handy. I don't know how to set the idle speed on your engine. On my Suzuki you set the idle speed with the ignition advance, yours might be with the throttle stop. Hopefully, someone will know precisely. Once you find out which knob to twiddle, put the boat/trailer in the water and leave it on the trailer. Make sure the engine is in enough water and is approximately horizontal and put it in forward and adjust the idle speed (while its still on the trailer).

I have a 1988 Yamaha 25hp outboard and I’m having a problem with the motor bogging down past 3/4 throttle. It seems like it’s a fuel issue. I have cleaned the carb, put new ignition coils on, new fuel pump, new primer bulb and line, and all new fuel lines, and new impeller. Any suggestions on what it could be thanks.( The motor runs like a top and fires right up other than that)

use a timing light to check the timing.
make sure it is in spec and advancing as it should

I will look into that. I also wanted to note that when I switch my plug wires around the motor runs better but still Boggs at high rpm.

I am also not very sure on how to make an adjustment on the timing. I wanted to figure out how to make an adjustment before I hooked a timing light up to the motor thanks.

why.
if it in good, in spec you do not need to do anything
just check it