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Old 11 June 2019, 15:24   #1
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Yamaha 15F 2-stroke. Purchase, check & Service.

As mentioned in another thread I realised after just a year with our Mariner 9.9 4-stroke... despite liking the convenience of no oil mix & quiet smoke free trolling... it was the wrong balance of weight vs power for us. 36kg is the sensible max lift for me so the 15hp 2-stroke hunt started.

I'd always liked the look of the Yamaha quality and heard good reports so as the Mercury/Mariners were well known to me (had 3) thought a change might be interesting.

Hence today this landed. A clean 2003 model with... for me... the benefit of my favourite 25l Quicksilver tank. Also instruction manual, emergency pull cord and flush adaptor. Oh yes and got lucky. It has the expensive... if bought from Yamaha... accessory 12v output.

Went against all the rules buying from a phone call and emailed images. Arrived on a pallet this morning and as follows below got straight on with checking it over and a major service.
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Old 11 June 2019, 15:30   #2
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Whoah! Thatís nice.

Looks brand spanking new.
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Old 11 June 2019, 15:42   #3
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Knowing I wanted a Yamaha 15F I bought a used workshop manual on Ebay the other day as there were no easy ones available online I could find and a real copy is easier in the workshop.

As the weather is so ghastly I've left the carb check, tuning jobs etc until I can get it in the tub so today was an erratic series of jobs.

I checked the plugs but they were new and correctly gapped. The gear oil was also new... this was obvious as the drain plug wasn't quite nipped up and possibly with the wrong seal so there were drips on the pallet. I have OE seals if needed.

The prop didn't come off easily so I engaged the three leg puller... with Jubilee clips to keep it behind the exhaust flange. It then took very little effort to remove as there was no corrosion just old hardened grease on the splines. The prop was acceptable so I tapped out a few dings and painted.

Oddly it has a 10.5" pitch fitted which would be high in our experience... perhaps it's been on a light skimmy boat.

I greased and oiled all pivots. The tilt tube/saddle pivots were fitted with original screw head plugs not nipples. But filling the thread recess with grease a couple of times and pushing it through by replacing the screws did the job.

For me with an older OB I like to see in the waterways at an early stage, regardless of if it pumps water or not. I removed the thermostat and was pleased to see the channels were free of anything other than tiny deposits. The thermostat tested OK in a saucepan so went back in.

The other thing that makes me nervous about an older OB until I know is... will the lower unit bolts come out OK? I'm putting a full pump/impeller kit in when it arrives tomorrow so for today I was pleased to find all the bolts came out easily. Similarly the bolt holding the large anode underneath the AV plate could be a snapper but came out OK. Anode will do another few years.

Other than that just a wipe down of the powerhead with a WD40 soaked rag and car polish on the leg and hood.

So far it's looking OK.
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Old 11 June 2019, 15:47   #4
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Yep Chipko it's tidy enough for what I like to see. There are a couple of scratches on the hood and leg that have been touched in with a fairy close match brush but in keeping with the age.

Tomorrow's tasks... Overhaul water pump. Fit "Tiny tach". Test run in tub. Compression test. Put correct gearbox plug seals on. Perhaps put the proper Yamalube gear oil in. Pressure test gearbox (routine, not because of leaks).
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Old 11 June 2019, 15:50   #5
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A friend had one on his Zodiac......ran perfectly for ages! Looks like a nice find
Fresh water use?
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Old 11 June 2019, 16:08   #6
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The anode looks to have done some work and it came from the coast.... but who knows really in its 16yr life. My experience is that 20hp and under leisure use OBs with just basic care/maintenance can stay in great order.
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Old 11 June 2019, 16:22   #7
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Welcome back - once a smoker always a smoker!
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Old 11 June 2019, 16:34   #8
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Yep and I can defer the test tub start up for a nice day when next door has his BBQ so we kind of blend fumes at the fence line.
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Old 12 June 2019, 04:21   #9
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lovely specimen David i did wonder about the 9.9 being fit for your needs looked after that will last years enjoy.
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Old 12 June 2019, 04:59   #10
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A nice bit of kit!
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Old 12 June 2019, 09:07   #11
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Not Yamaha stuff as such but despite liking the 25l Quicksilver tank they have a weakness I always check. The pickup pipe which is glued to the connector spigot can loosen and pull in air or fall off completely as the glue ages and fails. So I always take the assy off the tank to check.

Mine was still glued but only just as the seal broke with the lightest twist. I put some fuel resistant silicone on the spigot and a pipe clip for extra security. I vac tested it together with the whole fuel line for a few minutes to be sure.

When I pulled the outlet assy from the tank there was no float on the arm... and it wasn't in the tank. Odd but no matter they are only £7 so I'll get one.

I cut one of the fuel pipe ends just to check the condition as these grey Quicksilver pipes can delaminate internally and block the fuel flow but this one's fine.

Finally I'd noticed the outboard end is a Quicksilver fitting as used on Mercury/Mariner 2-strokes. It seems to seal on the Yamaha spigot OK but just in case that mismatch has potential to pull in air I'll get a proper Yamaha one.
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Old 12 June 2019, 10:01   #12
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Always the most interesting/nervous job of a new to me OB... the first tub start and run. Three pulls and it fired easily giving a strong idle on choke and then soon with choke in. Instant half pull to restart hot. Good pee stream but the postman has just delivered a full pump kit so I'll get onto that later so I start from a known position.

With the hood off I noticed a slightly odd character to the sound just off idle as revved but this turned out to be intake noise from the plastic chamber on the front of the carb.... and probably more noticeable after three plus years with quiet 4-strokes.

I did a compression test and both cyls were 120psi so that's great.

The throttle was quite stiff to return to idle despite the tensioner being loose and linkages oiled. Took the twistgrip off and dry grease plus light alloy corrosion dust were the culprits.

I test fitted the Tach which will live under the hood in the space where a starter could go after I've temp mounted it on the tiller for prop trials. Once the prop pitch is decided I only need it as an hour meter and tuning aid. Bought this model again... my third as they have been accurate on the revs and lasted OK... correct setting in tach menu for this OB is 2P1r.

https://www.ebay.co.uk/itm/Hour-RPM-...72.m2749.l2649

Now to go out and see if the lower unit will drop off OK to do the impeller etc.
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Old 14 June 2019, 17:03   #13
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Been distracted but got round to the lower unit today. I'd mentioned earlier the gear oil looked new where it had dripped from a not fully tight drain screw during transit. Decided as I already had a tube of the correct Yamalube I'd regard whatever had been put in as a flush and change it again. Gearbox capacity is given as 250ml... exactly the same as the tube. I filled from below until the tube could be squeezed no more but no oil from the fill plug. Once turned upside down and fully drained into a spray can lid the tube gave up another 20ml which I injected into the level plug with a syringe and then it ran out a little.

Drain & level plugs replaced using Yamaha OE seals.

Usual four bolts and gearchange brass collar to drop the lower unit which came off easily with no hammering or levering.

Unexpectedly the water pump bolts though were a pig to get out... so sluggish to move I really thought one or more might snap. They should be fitted with a drop of Loktite but the previous person had applied Sikaflex to the length of the bolts. New bolts come with the Yamaha pump overhaul kit but I used the old trick of putting a saw cut along one of the original bolts and running it in all the threads as a cleaning tap.

The pump housing liner was really tight to drive out so after cleaning the inside of the housing I heated it in boiling water then the new liner dropped straight in. Oddly the one thing missing from the pump overhaul kit was the O-ring for the housing to lower unit interface. The original had been re-used a few times I guess and was flattened but a replacement was found in my O-ring assortment box.

Replacement of the lower unit was trouble free.

While I was "underneath" I noticed the tilt mechanism was bone dry... they are commonly missed when lubricating. Now all greased and snaps nicely into the shallow water or fully up positions.
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Old 14 June 2019, 17:13   #14
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Only other job today was the proper fit of the small Tach. I made up a plate from a cut off section of kitchen chopping board which screwed to the optional started motor fixings and then mounted the Tach on this so it was well supported and spaced a little off the engine to reduce heat soak.

Getting through the jobs now. Just the ign timing to check... which is not entirely straight forward if requiring adjustment... needing a DTI through the spark plug hole. Then fuel filter to clean and however much (full strip) or little (set idle mixture) I do to the carb.
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Old 15 June 2019, 03:46   #15
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Thatís some properly tidy work there!
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Old 15 June 2019, 06:13   #16
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Have you got carpet in the garage or are you living life on the edge and doing O/board work in the lounge?
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Old 15 June 2019, 15:00   #17
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Well it dont matter where he works his attention to detail is to be commended well worth studying the process if you want to replicate or a least get near to
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Old 15 June 2019, 15:25   #18
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Cheers guys. No, not the lounge. Half the garage is concrete where the car stands and the other half is storage and workshop. I always carpet the workshop side and replace every 2/3 years. Current one is a £200 large Dunelm rug that had an iron dropped on it making a flattened mark and I bought for £4 in a disposal sale. Much more cushy on old knees than concrete.

Finished the service today with tuning checks.

Washed out the fuel filter which was nicely clean anyway. Bit more fiddly to access than the Mercury/Mariner 15 2st.

Checked the ign timing which you do at full advance and full retard... close to perfect so left alone. Decided as it starts/runs perfectly not to take the carb off until the season end when I'll probably do a full clean/check with new gaskets and a fuel pump diaphragm.

Ran it up in the tub again and set the carb idle. The mixture screw was 1.75 turns out of the allowed 1.25-1.75 and I couldn't better that posn. Set the idle to the high end of the 750-800rpm spec.

I mounted the Yamaha on our Aerotec for the first time and with the 45mm lift I modded last season the AV plate is just about 5mm down from the lowest part of the transom. Should be about right but proof will be on the water. Hopefully having a few days at the coast in a week or so for the full testing. Just wondering about buying a second 9" or 9.75" pitch prop as I'm sure the current 10.5" will be too much.

Often the look of older OBs can be spoilt by ratty tilt tube ends. So my final if slightly anal job was to push on a couple of generic black plastic caps bought from Ebay.

And that's it done.
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Old 16 June 2019, 02:03   #19
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Inspiring stuff, I have recently purchased a 90hp two stroke that I need to do all of the above to, so I too can start from a known position.

It has 90 odd hours on the clock, allegedly. I hope it's as good as I think it is. I bought it from a respected dealer and did see it running before my purchase.
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Old 16 June 2019, 04:32   #20
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>>>start from a known position

Yep for me that's the core point... and if there are problems in the future, particularly on the water, it gives a far better idea where to look if you know the status of all the items.
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