Please look at my Yamaha plugs

[yammie15]

Hope everyone is enjoying the holiday season.

Ok... here are the long awaited numbers from my new compression tester:
Upper Cylinder - 120 psi
Lower Cylinder (the one that is suspect) - 125 psi.

Reading were taken on a cold engine.

Appreciate any and all comments.

Thank you,
Bry

[TownsendsFJR1300]

Well, you have compression(that's good, no major internal issues likely).

Now we just need steady, good, spark and ascertain the fuel pump isn't leaking fuel into the engine case fouling the spark plug..

We're you ever able to locate a timing light or better yet a spark tester tool?



With this one, you can plug it inbetween the plug and wire and run the engine. You would be monitoring the spark especially when it starts acting up..

[yammie15]

No. Never found an ignition tester but I got a compression tester for sale. Only used once. Ha! Ha!

I did as you suggested, disconnected all the grounds and cleaned them with a diamond nail file, blasted them with contact cleaner and gave them a smear of dielectric grease. Also did as many connectors as I could reach.

Engine still misses on a cold start, seems to improve at about one-quarter throttle, but maybe it's just harder to tell at that speed. Once warmed up, it seems to run well but I'm slowly going nuts listening to the thing: I don't trust my own judgement anymore!

I am getting some blow-by at the lower spark plug and the bottom of the air cleaner is moist with fuel.

I'm thinking of buying a new coil and a couple of gasket kits before tearing the carb apart. That sound reasonable?

Best,
Bry

[TownsendsFJR1300]

In posts 23 and 24 you mentioned the plugs being "wet after running" and also the wet spot on the intake(you called it an air cleaner).

IMO, I would NOT be throwing money at coils, you swapped them around already and the problem remains with the lower cylinder.

I think you already checked the fuel filter(too lazy to go back and read) but pulling that carb apart shouldn't be difficult.

Either refer back to your SHOP manual or worst case, parts fisch. I don't know how familiar you are with carbs however their NOT terribly difficult to clean, etc. you should have the float level measurement and know how to check it. Pay attention to the needle and seat. Should either be worn, fuel will flow into the bowl even with the NEEDLE CLOSED, causing a rich condition / fouling plugs, etc.
Make sure the float itself is NOT leaking, compromised.

In most cases, you can pull that carb apart without replacing gaskets however I'm suspecting you may very well have a leaky needle /seat, or crap(sand) stuck up in there causing the bowl to overflow. You won't know the needels condition until its out.


Just as a side note, with the carb off the engine(empty) and upside down, you should NOT be able to blow any air (by mouth) into the fuel line intake. (your simulating a closed needle/full float bowl). If you can, its leaking(not good)...

Flip the carb over, the float drops, you should be able to blow thru it(as if it was filling with fuel)

[yammie15]

Thanks Scott: I'll concentrate on the carb. There are a lot of Yamaha 15's here in the DR; the fishermen, who can afford an outboard, buy the 15's so it stands to reason that parts are available locally. The language barrier aside, I should be able to find a gasket kit.

Just feel safer having a gasket handy. If I can't get the carb back together, I'm stuck on the sailboat. (Have to remember to buy an extra bottle of rum, too!) Let me try pulling the carb and do the blow test you mentioned.

Thank you and have a great New Year,
Bry

[TownsendsFJR1300]

Thanks Scott: I'll concentrate on the carb. There are a lot of Yamaha 15's here in the DR; the fishermen, who can afford an outboard, buy the 15's so it stands to reason that parts are available locally. The language barrier aside, I should be able to find a gasket kit.

Just feel safer having a gasket handy. If I can't get the carb back together, I'm stuck on the sailboat. (Have to remember to buy an extra bottle of rum, too!) Let me try pulling the carb and do the blow test you mentioned.

Thank you and have a great New Year,
Bry

Back at ya and good luck! Hope you not stranded at sea!

[99yam40]

before there were motors there were oars, so maybe you will not be totally stranded if you have oars.

Not sure what kind of seals the kit has or your motor uses on that carb, but a lot of Yamaha carbs have o rings so they are usually good to reuse

[Yamahataos]

I'm interested to find out your problem as I have a very similar problem on a 2010 2 stroke 9.9 hp changed to a 15 hp ( the only part different on this engine is the reed valves) mine ran like it was loading up a plug at idle to 1/4 throttle it did it when new until now , also does it cold or warm choke on seems to make it worse so I try not to run it too long on the choke , I tried new plugs the same, I cleaned the carb( full dissasembly) blew carb cleaner through all oriffices to make sure clear, checked idle circuit and off idle low speed circuit for any problems all good the same , I remouved the idle mixture screw ,and plug cleaned and adjusted it same, spark test 28000 volts ,good, compression check 135 max on both cylinders this is with about 10 compression strokes, checked and cleaned fuel filter,lines to and from fuel pump, checked fuel pump diaphragms ok, the only thing is my engine doesn't seem to be as bad as the problem your having with yours but sounds very similar but I never notice any gas or wetness at carb,my runs fantastic at 1/2 throttle and above, I was at a boat show yesterday and asked one of the yamaha service guys and he said these engines need to run at 100 to one fuel oil mix , I'm running 75 to one mix , I haven't checked timing but don't have the specs , I really think the problem is with fuel ,like the float not sealing 100% causing in my case a slight rich mixture at low rpm but not enough to cause flooding and the problem is minor so at 1/4 to full rpm it's not a problem and seems to clear up when you rev engine up or run at high speed , but comes back at low rpm . Never noticed if one plug got black as I run engine high rpm most of the time then slow down when coming to a dock for only a few minutes then shut the engine down .

[yammie15]

Well I guess you thought I had fallen overboard. Nothing so dramatic as that.

I ordered a new head gasket and it arrived in Miami, but after that... who knows! The shipper has lost it.

Still hoping it will show up.

Bry