Water Getting in Top Cylinder Yamaha 40hp Twin

[joesnuffy]

I appreciate the help I am always open to someone helping me and I like to help others. I do enjoy a good challenge and this has been one for me.

When I first rebuilt the engine it ran very well and idled very well and had a ton of power. Right now it feels to have half power like its missing a cylinder. The engine has 2 carbs one for each cylinder.

The carbs have a linkage that clips onto the side of them that open the butterflies I did not alter their sync because she was running so well I just un-clipped one carb when removing and installing them. I had adjusted their low speed screws both were set to 1 1/2 turns out while she was idling perfect from factory they were 1 1/4 out but she ran best at 1 1/2 out on both and spark plugs looked good after long idle periods on pontoon. I even turned the idle screw that touches the bottom butterfly all the way till it wasn’t touching the bottom butterfly screw meaning both butterflies were completely shut and she was still idling fantastic I then turned the screw to where it was barely making contact with the butterfly acting as a stop and left it. My buddy and his girlfriend were coming to visit I had started the pontoon boat several times that week to make sure it was ready and within 60 seconds she was idling as she should. When he arrived the day we were going boating he helped me put the insulation in the hood and the new hood decals on. We proceeded to the boat put the cover back on and tried starting the boat and that is when the problem occurred and the boat required a partial choke and the throttle lever to be pulled up a bit to idle. I have sync’d carbs before on my buddies MGB and my motorcycles etc I have a good ear for that stuff and have been pretty successful at it. I will read the manual today on that and investigate it when I reassemble the new reed valves. I will also switch the carbs at that point if motor still doesn’t run right to see if the problem switches cylinders right now it is the top cylinder with issue. I have the carbs and reed assy off right now waiting on parts etc.

What I think is happening and happened to the engine is the reed valve cage screw/s was hit by the rod and did damage to it. 3 of the 6 reeds for that cylinder (top cylinder) have light coming through them I think when the piston is going in direction of the reeds it is drawing some water from the exhaust ports (since reeds are not closing fully) and fuel but a tad of water also making that cylinder not hit as it should. That might also explain how the cylinder is getting washed and possibly why I am having to partially choke it to give that cylinder a bit more fuel since it isn’t drawing fuel as it should. Do you think this could be my problem?

Thanks,
Joe

ps Sometimes a pic helps as you can see it took a nasty hit. These are the reeds and manifold I got coming to put back on. I also have new gaskets coming.

http://www.ebay.com/itm/311280859355?_t … EBIDX%3AIT

With new screws in the reeds and cage the motor did run a lot better so I think this should help a lot sure can’t hurt.

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[fleetwin]

Yes, if the reeds aren’t sealing, the primary compression/crankcase pressure isn’t being developed and won’t be forced into the combustion chamber. And yes, the cylinder won’t fire properly and will appear wet/washed, but with fuel, not necessarily water. My only question is whether or not it is normal for the reeds to show a bit of light through in the static position…This isn’t uncommon for some of the OMCs, the reeds seal up when the piston is on the down stroke and pressurizes the crankcase. You have had the intake off, can you see the cylinder walls at all? It is possible that the debris got caught on the exhaust side of the cylinder wall gouging it up, this would create a primary compression/crankcase leak as well, this might not affect the compression readings you are seeing. Let’s hope this is not the case.
Not being familiar with the Yamaha linkage set up, can’t really comment on the methods you described. But, there is one thing I know which is universal to any carb….Just because the linkages are disconnected, this does not ensure the carb butterfly is closing completely. The throttle shaft could be jamming, or the butterfly could be jamming/not closing completely, perhaps due to debris from the initial failure ending up in the carb.
The only way to ensure the butterfly is closing completely/properly is to remove the carb and look at the butterfly after snapping it slightly, the return spring could be weak as well. It sounds like you don’t have the Yamaha manual with the sync instructions, let’s hope someone can help out by posting these pages.
Once sync has been set up properly/confirmed, swapping carbs will be the next step….

[joesnuffy]

Thanks,
I will get my strong flashlight this evening and see if I can’t look into the cylinder through the manifold hole to look for gouging on top and bottom cylinders where the exhaust ports are (they are mid cylinder on the bottom of cylinder). When I had the exhaust plates off I didn’t see anything but I should be able to see better through the intake manifold hole where reed blocks mount using a strong light. I will also check the carb butterflies they are on my workbench right now to see if their is debri in them and if they are snapping shut like they should.

Here is the manual I have been using.

http://boatinfo.no/lib/yamaha/manuals/1 … ha.html#/0

Also put the spec sheet on an attachment it shows specs for reeds also. Most these motors are 3 cylinder motors before 1995. I think the spec for my reeds would be .008 inch warpage. Not very much. Here is an auction of the reeds used in the 3 cylinder set up I think their warpage is considerbly more .028 inches you would see a light gap at that point like on the omcs you mentioned.

http://www.ebay.com/itm/YAMAHA-6H4-1361 … Xm&vxp=mtr

Thanks,
Joe

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Attachments:

My40hpYamahaOutboard Specs.pdf

[joesnuffy]

I checked the carbs out yesterday and the butterflies were all the way closed and snapped shut very well. I didn’t get a chance to look into the cylinders yet but hopefully will this evening when the sun isn’t so bright.

I have a yamaha 2 stroke golf cart and I had a similar problem with it and I got to thinking about that early this morning when I woke up from a dream where I was dreaming about the cart. It has 1 cylinder. It would not want to run at high rpm’s. I rebuilt the fuel pump, cleaned and fined tuned the carb like 6 times, and a new fuel filter it still wouldn’t run steady at full rpm’s. This was one of those things you pull your hair out. It had plenty of spark and compression. I noticed that the wires coming from the pulsar unit or what I call the pick-up area (under flywheel) were burn’t looking. If I remember right it had 3 wires 1 of them was a ground the other 2 went to the coil if I remember right. I decided to make a ground harness that grounded the 1 wire that was a ground from pulsar to the ignition coil ground then to battery ground then to the solenoids ground. The cart has 2 solenoids since the crankshaft turns reverse for reverse and this fixed my problem and I had never had that issue before then for like 3 years or since then for like 3 years. I think Yamaha copied the Harley Davidson golf cart concept on this. This was their 1st golf cart they produced and sold the G1 they say their bullet proof and I love mine use it daily for mail and take trash off.

I started reading the manual for the ignition. It has several grounds that may/will need cleaning. I have the ignition with one pulsar coil some yamahas have 2 pulsar coils one for low speed and one for high speed mine is just the one pulsar coil and one igintion coil one cdi unit and one charge coil.

Best I can tell is 1 coil fires 2 cylinders. Both cylinders fire at the same time and this is called wasted energy since one piston is in the non-compression stroke. It says one plug may not fire correctly due to low coil voltage output and coil leads can be reversed to spark plugs to easily see if this is the issue switches to other spark plug. What happens is the spark goes to the first plug through the plug wire then it goes through the cylinder head itself to the other plug and returns to coil through other coil wire this takes 30 percent more energy to do and do it right. I will attach the pdf of this look in the 2 cylinder part. I am good at checking electronics so I won’t bore anyone but I intend to check the pulsar coil, cdi, charge coil, ignition coil and clean grounds, check connections etc. I due have an old school meter that will check the strength of fire being produced so I will need to leave one spark connected when checking the other lead to see if I have a low output on one the top cylinder wire first before cleaning grounds and checking connections and doing ohm tests etc.

This is the model of my motor 1995 C40PLRT Yamaha Outboard 592cc 2 cylinder 2 stroke

Thanks for the help,
Joe

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Attachments:

ignition specs.pdf

wiring diagram.pdf

ignition.pdf

[fleetwin]

Well, weak ignition is surely a possibility. But the only thing that steers me away from the ignition is your comment about being able to keep it idling OK by tickling the choke. Needless to say, your lack of power at high speed might be a problem not related to the poor idle, weak ignition is surely a possibility…Doesn’t take too long to check grounds and do basic ignition meter tests, so that is always a good idea.
I remember that waste spark stuff, nice to see other manufacturers shooting themselves in the foot with cost cutting crap, not just OMC. We had that system on some large stern drive engines, slowly had to change them all back to conventional distributors. Had the waste spark on early four strokes also, learned to say that backfiring on acceleration was a "normal" condition for these engines….
OK, the carb butterflies are working as the should. I looked at the online manual you posted, seems like kind of a generic one, but not familiar with the way Yamaha lays out their service literature….So, I’m not sure I completely understood the synchronization process for your engine.
But, I did notice that Yamaha seems to control their idle speed on some engines by "cracking" the throttle plates open to increase idle RPM….So, my comments about both throttle plates being completely closed at idle don’t apply to your Yamaha. Did you check TDC? Don’t forget to properly set the idle and WOT timing. If problems are still present, temporarily swapping carbs will help steer you in the right direction.

[joesnuffy]

Thanks interesting about the stern drives using the wasted spark and the backfiring. I ordered a bore scope off ebay that will allow me to look at the cylinders from the intake manifold side using my laptop as a monitor to see what if any damage occured when those screw heads on the reeds came loose. .
I can also look from the spark plug hole side to inspect cylinders but I did look at them when I had the head off and they looked good but I couldn’t see below the pistons that part of cylinder scouring might be before exhaust port. I will put piston at TDC and look from intake manifold side for that using this scope. This tool will come in real handy on a lot of motors and didn’t cost a whole lot around 17 bucks and will sure beat taking an engine apart to look. It has 2 mega pixel and might be something someone else here would be interested in so I will post it. You have to select the 8mm 2.0MP with 5 meters of cable which costs 16.99 It also works on an android phone but I use an I phone so I will just plug it into my laptop I keep in shed.

I will wait on this tool before putting replacement manifold and reeds on. They aren’t here yet so its a waiting game at this point. I will get started on cleaning grounds etc. I don’t think its the spark either but couldn’t hurt to check it out while I am waiting. It did have over 1/4 inch of spark jump per cylinder that’s a lot of spark but I didn’t try it with one plug still connected and I also have a meter with needle that registers strong and weak spark. I will use that to help me.

When I get the engine back together I will check engine timing at idle and WOT using the manual. I did not make any changes to the original timing of motor meaning the magneto linkages just pop off and I was very careful not to alter the original timing of engine. The engine was running like a champ when I got it all back together. The engine looked like a new one under the hood with very low hours so I thought the timing would be correct. When you say check TDC I not sure on what to do on that except put engine at tdc and make sure the pick up is just opening with an ohm meter at idle position full retard on magneto? or when butterflies just start to open? need some help on that. I know I re-did my buddies 1962 50hp Mercury and the points needed to just be opening when throttle butterflies started to open or engine would stall.

http://www.ebay.com/itm/2-in-1-6LED-And … 1952062759

Thanks again for help,

Joe

[fleetwin]

Well, the big thing to worry about is if the flywheel key sheared….And, the only way to confirm/rule this out, is to verify TDC with a dial indicator or the OMC TDC tool. If the flywheel key had sheared, chances are the timing would be retarded causing poor idle and lack of WOT power. Again, this situation is not something you could verify with a timing light. I hear what you are saying, you did not alter any of the original adjustments, but who knows what may have happened since it initially ran nicely after the rebuild…
THANKS for the lead on the affordable bore scope, sure need one of those! Funny how I used to be able to look in the cylinders with a little flex light and be able to see scores/scuffs, those days have sure passed me by!

[joesnuffy]

Excellent point I never thought about a sheared flywheel key. I was thinking of removing flywheel when I check the ignition I could inspect the flywheel key at that point. Wouldn’t that be something if that is what my issue is.

Thanks,
Joe

ps below is how to time this engine I will check it.

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Attachments:

timing motor.pdf

[joesnuffy]

I think you may have figured it out.

Its raining off and on today so I went out between the rain. I took a pencil and spark plug wrench. I pulled the plugs out and rotated the flywheel to the tdc was lined up on the pointer. I put the pencil into the number 1 spark plug hole and the piston was close to the bottom of cylinder. I put the pencil in the bottom plug hole and the piston was close to tdc for the bottom hole. On the 2 cylinder ignition notes (not 3 cylinder) I posted it showed using the top cylinder and the pointer to 1-3 atdc at idle speed (using timing light)which would still be close to the tdc mark. This could mean the key is sheared and the flywheel is almost 180 degrees out and would explain why it its not running correctly since the coil fires both cylinders at the same time it could run just not run right. I will pull flywheel tomorrow if it isn’t raining.

I also rotated the flywheel until the bottom cylinder was very close to tdc using pencil several times and looked at pointer it was very close to tdc. I guess this could mean that it is tdc for the bottom cylinder but I will have to check to see if the key is sheared at this point. I wouldn’t think the tdc and pointer would be for bottom cylinder?

On the 3 cylinder notes it shows using dial indicator for number 1 piston and running it to tdc then check the pointer/flywheel and adjust it if need be to where pointer points directly at tdc mark. So I wouldn’t think the tdc mark on my 2 cylinder would be for bottom cylinder.

Thanks,
Joe

[fleetwin]

No, I’m sure the TDC mark is for the top cylinder….I guess the easiest thing to do at this point would be to remove the flywheel….

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