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    Rusted spark plug well/mating surface - is this a concern?

    You can clean it out with an old small screwdriver and a dremel/wire brush. First, get a long bolt (M14x1.25) and screw it into the plug hole about 5 or 6 turns, then just clean up the area. You can get rid of the remaining bits with a squirt of WD40 etc. Unscrew the bolt, put a little bit of...
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    Smelly 2-Stroke

    It's oil injected, and doesn't appear to be adjustable according to the manual. However, when I did the checks a while back, it was giving slightly more oil than the spec, but didn't seem to smell like it does now. It only smokes when I first start it up, but by the time it's hot, the smoke has...
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    Smelly 2-Stroke

    Hi, I have a Yamaha 70B, and the smell from the burnt fuel/oil literally makes me and the missus feel quite nauseous, and is starting to spoil our time out. I have tried normal and fully synthetic 2-stroke oil, and they both are off-putting, with the synthetic being the worse. How can I either...
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    Over heating at idle/low speeds

    Not quite the same, but a similar problem on my 70B. Eventually, I took the head and head cover off, and all the channels were blocked with crud. It also extended into the channels round the bores. It wasn't a complicated job cleaning them out, but it was quite time consuming.
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    50hp Yamaha 2 stroke outboard fuel problem?

    Also, check the colour of your plugs. Are they all the same ? Are they all brownish, or are they black, white, different, oily, etc.
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    50hp Yamaha 2 stroke outboard fuel problem?

    Agreed, but the OP stated : "I have tried new connections new hoses, diffrent size hoses, diffrent primer bulbs, diffrent tank, checked pick up tube" So I assume the path from petrol to pump is OK.
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    50hp Yamaha 2 stroke outboard fuel problem?

    I would say it's more likely to be your fuel pump.
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    Ex RNLI Yamaha 75 CETO question

    Agreed ! Changing from 50:1 to 100:1 will not make it run better. Other issues are afoot !
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    Yamaha 50 tlr 2 stroke throttle stiff at engine

    Looking at the picture you provided, it seems that your throttle linkage is wrong. With the carb butterfly's shut, the pointer on the CDI, should be pointing to I, not II. If you continue to push the throttle open beyond that point, you are in danger of shagging your CDI (££££!).
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    Synthetic gear case oil

    80W90 is fine, but make sure it is for marine use, not automotive. Quicksilver do a synthetic SAE90.
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    Lack Of Power Under Load

    The choke valve block is the part of the carb that has the red switch on. If it doesn't make any difference to the running of the engine when it is switched to open or closed, then I would say it's a fuel issue. Usually, if you switch a running engine to open, it will stall due to excess fuel...
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    Lack Of Power Under Load

    What was the condition of the spark plugs? Were they dry and brown, or black and wet? If they are black and wet, then it's going to be a fuel problem, like either the primestart isn't closing or the small 'O' ring in the choke valve assembly on No.2 carb is shot. If the plugs are OK, then...
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    Carburetor question on restoration I’m working on 1992 40 hp MSHQ Yamaha

    IF, these two engines have done the same hours, then they have obviously not been used in the same environment, or in the same way, so is not a good comparison. No decarbonizer on the market can make the water channels clean. Also, the mating/gasket surfaces are very different. Finally, I...
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    Yamaha 70B too much Autolube

    Extract from the manual (and exactly as I did it): 1. Start the engine and set the idling speed at 1500 rpm by adjusting the throttle-stop lever. 2. Remove the oil-pump link-rod and fix the oil-pump lever in the full-throttle position. 3. Measure the oil discharge from each port for three...
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    Yamaha 70B too much Autolube

    I have a Yamaha 70B (2005), and recently, I checked the 2T oil injection function as per the service manual. It says 2.20cm3 +-0.50cm3 / 3mins. Mine was 3.80cm3 / 3 mins for all cylinders. Now I realise it's not a big deal, and that too much oil is better than too little, but I would like to...
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    Bad Spark plugs?

    As the middle two are different than the top and bottom ones, it's very unlikely to be anything that's common to the engine (fuel line, tank, computer, timing, etc.) but rather, individual to them. Look at plug caps & leads, coil packs, etc. and follow it back, checking, until it becomes common...
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    2005 Yamaha 70B running rich

    YAY ! Its Fixed.... I'll put a quick description here so that anyone else with similar problems might be able to find it with a search, or Google. Opened her up, took off the splash guard near the coils and separated the wires. Started her up and set the idle to about 1500rpm. Checked for some...
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    2005 Yamaha 70B running rich

    I've found the specs for the lighting coil voltages and resistances, and for the Prime Start resistance, and now have a plan of attack. When I get back down to the boat, I shall be checking them all out to see what I can find. Cheers, Paul
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    2005 Yamaha 70B running rich

    I haven't checked the voltages yet - I'm still looking for the specs on that. I don't know if the battery is being charged while the motor is running as I have a solar charger in place, so the battery is always charged. I know the wire from the Primestart to the connector is OK, as that is the...
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    2005 Yamaha 70B running rich

    One step forward - One step back. I've now replaced the 'O' ring, (and diaphragm & gaskets) and it still isn't right ! So, after letting it run at a fast idle for 5-6 mins, I pulled the Primestart assembly, and the needle hadn't moved! Also, according to google/youtube, the Primestart housing...
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