1996 Yamaha C25hp bogging

[Donman89]

Seems that I am having problems with this motor. It doesn't seem to have enough power to get my little 230lbs boat out on plane. I rebuilt the carb and adjusted the needle numerous ways but can't seem to get it running right. Does anyone know what the compression is suppose to be? Here is a YouTube video of me taking out the boat. Yamaha 25hp problem - YouTube

[99yam40]

compression, spark, and timing are easy to test

Have done any of that?

need to make sure motor is sealing properly and that the timing is advancing to spec when opening the throttle

[Donman89]

Checked the compression and it's about 55&60psi cold. Good spark. But haven't checked timing.

[99yam40]

sounds low, but it may be the gauge.

You can try the gauge on a different motor to see if it reads low on that one also

[Donman89]

Ya I borrowed the gauge from Oreillys but it maybe the gauge because that is weird to have both within 5 psi and be low.

[Donman89]

Yep went and got another gauge from AutoZone and the readings are 111psi on the top cylinder and 120psi on the bottom one.

[Donman89]

Its fouling plugs like no other. I got new plugs today and ran it today for 30 mins and already fouled plugs. I'm using Penzoil synthetic blend oil mixed at 50:1.

[Pas Bon F115]

Its fouling plugs like no other. I got new plugs today and ran it today for 30 mins and already fouled plugs. I'm using Penzoil synthetic blend oil mixed at 50:1.

Sounds like it's getting too much fuel and or running too rich. Wouldn't that be a carb issue?

[rodbolt17]

could be a fuel pump issue or a reed issue.

[Donman89]

Ya I rebuilt the carb and couldn't get the nozzle out so I think maybe it's clogged but Idk yet. I messed the nozzle up so I have to get a new one. Gonna see if this fixes it. If it doesn't then I'm not sure what's wrong with it.

[mitch00]

I had something like this on a yamaha 150. It turned out to be a small tear in one of the fuel pumps diaphragm.

[TownsendsFJR1300]

Its definitly misfiring and NOT running on all cylinders listening to your video. (fouled plugs as you stated)

Did you rebuild the carb AFTER the issue or BEFORE?(and the issue started after the carb re-build?)


(your not in SW Florida are you? The video looks like down here).

Also, please try removing your plugs from the head, plug them into the plug wires, ground to the head and check for spark. A bad coil/cap/wire/etc can cause a misfire and foul the plug (the plug will load up with fuel as its NOT burning it). All the plugs out at the same time will allow a little bit faster spin.

http://www.boats.net/parts/search/Ya...201/parts.html


Note, the spark plug caps DO spin onto the spark plug wire (clockwise) per the parts fisch. I would make sure you have a clean connection(no arcing) between the caps and wires, it should be snug. If any doubt and any arcing inside the caps are found, simply trimming the wire back 1/4", and re-installing the cap should give you a good connection...


A timing light clamped over each wire while running will also give you an idea about spark to thru/the wire but won't rule out a bad cap or connection to the cap.

[Donman89]

I rebuilt the carb after the issues. I just bought the motor about a week ago. And took it out for the first time and it was doing even worse than this. I rebuilt the carb and this is were it's at. So I took the carb back apart and took the nozzle and main jet out and messed the nozzle up so now waiting on that to come in at the local dealer. Na I am in South Carolina. Your the second person that mentioned firing issue. I checked to see if both were firing and they were. It was a blue spark but the lower plug didn't seem to fire as often as the top with just turning it by hand on the flywheel.

[Donman89]

Even though I really hate to do it but I may take it to a shop if it doesn't run very good after putting the carb back together this time. It's soaking in cleaner at the moment. And I did run a small wire through the holes.

[TownsendsFJR1300]

I rebuilt the carb after the issues. I just bought the motor about a week ago. And took it out for the first time and it was doing even worse than this. I rebuilt the carb and this is were it's at. So I took the carb back apart and took the nozzle and main jet out and messed the nozzle up so now waiting on that to come in at the local dealer. Na I am in South Carolina. Your the second person that mentioned firing issue. I checked to see if both were firing and they were. It was a blue spark but the lower plug didn't seem to fire as often as the top with just turning it by hand on the flywheel.

Is the lower plug the one that's fouling??

Either a timing light as noted will show a difference (if there is any) between the coils, wires (not the cap or cap connection) etc.

I would at least spin it over with the electric starter (much faster) visually checking the spark on each plug. Make sure each plug is grounded so you don't fry anything.

You can test the igntion coils however I'm not familar with your set up and you'll need the spec's if it turns out to be an ignition issue.

Just curious, did the original owner give you a heads up, or no sea trial I gather?