Simple questions for Yamaha 25hp 2 stroke

[SeanKent]

Hi

I have an old (1983ish) Yamaha 25hp 2stroke engine number starts 695.

Had a few troubles with it last time I went out in it, seems to be fuel, one seemingly knowledgeable chap on the beach told me that carb needed a clean up.

I took off what looks like an air filter box expecting to see a filter inside but its empty. Is this normal ? or should it have one ?

Any one know where I can get a (Haynes style) workshop manual, it's my first time looking at outboards !

Anyone able to recommend someone cheap (and hopefully helpful) for parts ? (mainly service bits).

Thanks alot

[spartacus]

I had a 1986 Yamaha 25hp and it was model 25D. It'll be two cylinder, etc. Really great engines. Manual here: Genuine 20C 25D Yamaha Outboard Service Manual 20HP 25HP 2Stroke 6A9-28197-E0 | eBay

Regards air box - there's no filter in them. By all means use a little WD40 on it (removed from engine) and clean up with a rag.

If it's new to you and you're unaware of the service history, then I'd look at the following service items:

1/ Remove propeller, grease splined shaft and refit thrust washer, castle nut and new split pin.
2/ Renew manual start cord.
3/ New sparks.
4/ Remove thermostat, wire brush, lightly grease and test (use new gasket)
5/ Lube grease nipple points.
6/ Test fuel pump for tears or leaks in diaphragm
7/ Drop leg, renew impeller, and gear oil, fit new drain and fill fibre washers.
8/ Drain carbs, remove from engine clean with carb cleaner, rebuild and refit.
9/ Electrics, unplug bullet connectors, lightly sand with 3M paper and reconnect
10/ Run strimmer wire into tell-tale hole and ensure it free of any blockage
11/ Check sacrificial zinc anodes and replace any that look worse for wear.

Good luck.

[SeanKent]

Originally Posted by spartacus

I had a 1986 Yamaha 25hp and it was model 25D. It'll be two cylinder, etc. Really great engines. Manual here: Genuine 20C 25D Yamaha Outboard Service Manual 20HP 25HP 2Stroke 6A9-28197-E0 | eBay

Regards air box - there's no filter in them. By all means use a little WD40 on it (removed from engine) and clean up with a rag.

If it's new to you and you're unaware of the service history, then I'd look at the following service items:

1/ Remove propeller, grease splined shaft and refit thrust washer, castle nut and new split pin.
2/ Renew manual start cord.
3/ New sparks.
4/ Remove thermostat, wire brush, lightly grease and test (use new gasket)
5/ Lube grease nipple points.
6/ Test fuel pump for tears or leaks in diaphragm
7/ Drop leg, renew impeller, and gear oil, fit new drain and fill fibre washers.
8/ Drain carbs, remove from engine clean with carb cleaner, rebuild and refit.
9/ Electrics, unplug bullet connectors, lightly sand with 3M paper and reconnect
10/ Run strimmer wire into tell-tale hole and ensure it free of any blockage
11/ Check sacrificial zinc anodes and replace any that look worse for wear.

Good luck.

Thanks for the response, I guess that manual will show me how to do all that ?

I notice the tittle says 25hp but in the ad it say 40 hp ? I have message the seller to see which it is but you sound like you can confirm it with confidence ?

[SeanKent]

can anyone confirm that the manual is for a 25hp rather than the 40hp ?

Advert says one thing, tittle says another, really don't want to miss it as have no idea how often they come up.

Also will it tell me how to set the carb back up etc ?

[SeanKent]

The bloke on the beach made it sound so easy lol

I've just got the carb back on, nothing seemed to be sticking or out of place (I'm far from an expert).

The fuel bulb still doesn't go hard, just seems to dump fuel out of the exhaust/water intake grills.

The engine looks really looked after and well serviced, I've had it running fine since I've bought it (been out a couple of times). I think it's probably something relatively simple (maybe I'm just being optimistic) but does anyone have any ideas or suggestions ?

Be nice to be able to get it going (sun is shinning) and the chap I use for this kind of thing wont be available till Tuesday

[SeanKent]

just started it up in a big bucket of water.

Runs really rough, stalls on idle

and turned that water dark really quick.

Any ideas anyone ?

[CJL]

Free manual here; Boatinfo - 1984-1996 Yamaha Service Manual

[SeanKent]

Originally Posted by CJL

Free manual here; Boatinfo - 1984-1996 Yamaha Service Manual

Thanks, I notice all the manuals are 1984 onwards

my outboard was sold new in 1983 so would have been made before this.

I guess 84 is when the design changed ?

[spartacus]

The water will get dirty, the exhaust gases are going in there. However if there's a petrol film on the surface, then something is leaking. Check the fuel pipes to the carbs are intact, no tears or pin holes. Next check the fuel primer bulb. The internal diaphragm can be damaged. It should prime the carbs and go hard. Quicksilver primer bulbs are good replacements.

If it continues to pump fuel when the primer bulb is pressed, either the fuel pump is goosed, the primer bulb is goosed or you have a leak elsewhere. Is the fuel tank properly vented? Run the engine, remove the fuel pump from the engine, then press the bulb. If the fuel comes out of the hole on the reverse (next to lower cylinder) - it needs replaced.

Check the fuel reservoir filter on the engine, remove and clean. Ensure the 'o' ring isn't broken. Use a little gear oil on the 'o' ring before re-tightening.

When the carbs came off - was there a gasket in place? Not sure with this particular engine if there's one or not.

Regards manual - pictures are for 25D manual, but agree listing says 40hp. Drop seller an email to confirm.

[SeanKent]

Originally Posted by spartacus

The water will get dirty, the exhaust gases are going in there. However if there's a petrol film on the surface, then something is leaking. Check the fuel pipes to the carbs are intact, no tears or pin holes. Next check the fuel primer bulb. The internal diaphragm can be damaged. It should prime the carbs and go hard. Quicksilver primer bulbs are good replacements.

If it continues to pump fuel when the primer bulb is pressed, either the fuel pump is goosed, the primer bulb is goosed or you have a leak elsewhere. Is the fuel tank properly vented? Run the engine, remove the fuel pump from the engine, then press the bulb. If the fuel comes out of the hole on the reverse (next to lower cylinder) - it needs replaced.

Check the fuel reservoir filter on the engine, remove and clean. Ensure the 'o' ring isn't broken. Use a little gear oil on the 'o' ring before re-tightening.

When the carbs came off - was there a gasket in place? Not sure with this particular engine if there's one or not.

Regards manual - pictures are for 25D manual, but agree listing says 40hp. Drop seller an email to confirm.

Pretty sure the fuel bulb is good, it does do hard as with the engine out of water you can pump it and see fuel coming out of the exhaust/water intake grills on the leg of the outboard. Guess this means it's getting plenty of fuel.

It is a film over the water, deffo fuel coming from the grills (you can see it when it's out of water) I could see a film of fuel on the water before I started it (had been pumping the fuel bulb for a while without it going hard). The engine started and ran lumpy, thought I'd see if it got any better if warm so let it run for a little while to see if it got better. Anytime you let the throttle back (it was only a little over idle that I had it) it would cough, splutter and die, I caught it a few times but could see it wasn't right and not getting better so let it die.

The water is very black (it was running lumpy though) almost looks like use engine oil on the top.

Not sure how well you'd see it in a picture:

I'm pretty sure it's not a leaking fuel hose.

Maybe I need to completely strip the carb (I just took it off made sure the butterfly valves opened and closed freely, and that the float was free(did the turn it upside down and blow thing)). All seemed ok.

Guess it could be fuel pump. I'm guessing it's definitely pumping fuel, pumping it all out ! lol

Someone else suggested the head gasket, though this feels a bit more drastic, have a feeling its something simple. Guess it's possible if the engine has sat around unused for a while.

[SeanKent]

picture attached

[SeanKent]

and yes was a rubber gasket between carb and engine and put a little gear oil round it when I replaced

[spartacus]

The picture could be deceptive but that water sure looks inky black!

To rule out cylinder head issues invest in a compression tester. Draper do one for £25 so it won't break the bank. Remove both spark plugs and screw the compression valve into the spark plug thread. Turn the engine over and take a note of the reading. Both cylinders should be within a few PSI of each other.

If that's not conclusive, run the engine and lightly feel around the head gasket for any fuel/oil once it's been cleaned up prior to starting.

The carbs needs to be removed and completely stripped down. Use the right size screwdrivers to remove the jet nozzles and ensure air passages are clear with compressed air. Soak in carb cleaner, thoroughly wipe down with a clean cloth and reassemble. Don't adjust the fuel/air pilot screw. If you are going to check, then screw in (counting the number of turns) until lightly seated. I'd have thought it would be 1 1/2 turns out.

If the 'o' ring where the carb meets the engine head block looks worn, then go ahead and replace.

[Davie]

Slacken off the fuel pump. 2x 10mm bolts and pull it away from the engine block. Pump the primer bulb and watch the fuel come out the small hole between the two bolts. You need a fuel pump diaphragm. And before you try run it again get a bigger bucket you need another 4 inches of water, your going to burn the impeller out.

[A1an]

Fuel pump is fubar. That's unburnt fuel in bucket.

[SeanKent]

Originally Posted by Davie

Slacken off the fuel pump. 2x 10mm bolts and pull it away from the engine block. Pump the primer bulb and watch the fuel come out the small hole between the two bolts. You need a fuel pump diaphragm. And before you try run it again get a bigger bucket you need another 4 inches of water, your going to burn the impeller out.

Thanks

I followed your instructions and sure enough the diaphragm had a huge split.

Thought I'd get a fuel pump kit. Probably a new impeller too (seems like a good idea to change this). I'll add a bigger bucket to the list too.

[BoatyMcRibFace]

Originally Posted by Davie

Slacken off the fuel pump. 2x 10mm bolts and pull it away from the engine block. Pump the primer bulb and watch the fuel come out the small hole between the two bolts. You need a fuel pump diaphragm. And before you try run it again get a bigger bucket you need another 4 inches of water, your going to burn the impeller out.

Just joined the site to say THANKS! bought a 20c. Hadn't viewed it first. Schoolboy error. Thing is pouring out fuel. Fiddled with the float valve repeatedly. Then google found this thread and did what you said. Boom. New pump ordered. Fingers crossed. Anyone want to buy a 20c?? Things bloomin heavy for my honwave

[SeanKent]

Originally Posted by BoatyMcRibFace

Just joined the site to say THANKS! bought a 20c. Hadn't viewed it first. Schoolboy error. Thing is pouring out fuel. Fiddled with the float valve repeatedly. Then google found this thread and did what you said. Boom. New pump ordered. Fingers crossed. Anyone want to buy a 20c?? Things bloomin heavy for my honwave

Everyone is very helpful and knowledgeable