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  1. J

    9.8 Running on One Cylinder Only

    9.8, 2 stroke. Serial A901055. Top cylinder not contributing. Compression at 125 psi, spark plug does fire and spark energy will jump 3/8" air gap. With the engine running I can pull the spark plug lead from the top cylinder and the engine performance does not change in the slightest. If I...
  2. J

    Badged as 9.8, Serial A901055 Running on One Cylinder Only

    racerone, thank you for sticking around. This story is so long. I'm short on the diagnostics. Timing, stator signal, trigger and crankcase pressure measurement techniques I'm not familiar with. I'll have to look for videos on how to. 1 Spark at the right time One of the big clues I have is...
  3. J

    Badged as 9.8, Serial A901055 Running on One Cylinder Only

    Intake cover. Yes. Seals the intake paths between the sump and cylinders. Looks like access was for machining the casting. Could leak vacuum, yes? Gasket was squeezed right out of position, bulging like a figure 8 instead of parallel sides. Reseated with much better surface area contact. Had...
  4. J

    Badged as 9.8, Serial A901055 Running on One Cylinder Only

    Without anything else to try, I'm going by the words used in the parts list. I see things called an intake cover and intake cover gasket. If this is leaking could it spoil the intake vacuum for the top cylinder? J
  5. J

    Badged as 9.8, Serial A901055 Running on One Cylinder Only

    Any other components within the crankcase that could leak resulting in vacuum loss at top reeds? Should I replace the o-ring on the top bearing housing just because it's cheap and easy? Get it off the list? J
  6. J

    1973 Mercury 40 4hp: Compression, Spark, Fuel - No Start

    Condenser: Unfortunately, a competitive website. marineengine.com I see aftermarket cdi, part number 994-4463 (takes the place of Mercury 336-4463), $55 before shipping. Must be one helluva condenser @ $55. J
  7. J

    RPM won't go over 4000

    May not be running on all cylinders ... ? Is it worth trying to pull each spark plug lead while running and see if performance changes? If you pull a wire while running and operation changes, then that cylinder is working. If you pull a wire and nothing happens, then that cylinder is dead...
  8. J

    1973 Mercury 40 4hp: Compression, Spark, Fuel - No Start

    First off I'd say replace your condenser. Clean and regap your contact points. Stick with Champion L78V. They show on the parts list. Expect them to be design intent. J
  9. J

    Badged as 9.8, Serial A901055 Running on One Cylinder Only

    Thanks racerone. lol I always fly too fast by Mercury cylinder castings not having head gaskets. Trick design. You've caught me the last few days. Gotta slow down. I've seen enough. I should get it. Alas! Removed the recoil starter, flywheel, electrical gear and top bearing housing. I...
  10. J

    Badged as 9.8, Serial A901055 Running on One Cylinder Only

    Cheers! Thank you. J
  11. J

    05 Merc 25m

    If designed right, the component failure mode will be predictable. If not, unfortunately, it'll be seemingly random among the other wear outs and failures. I would talk to a couple repair shops to see how prevalent this failure is. Your problem will be breaking the studs of you try to pull...
  12. J

    Mecrcury 9.9 HP shifting issues

    A good carburetor cleaning with spray cleaner and a small diameter wire (florist wire) to reem the jets. Maybe compressed air to further clean and dry the parts. There are a couple places to clean out. First is the idle mixture adjustment needle and seat. Remove the needle, inspect for tip...
  13. J

    I need help on my 85 hp force. Plz &thx I’m kinda new to boating and fishing but I can wrench on my own stuff

    If you have little to no history with the engine, cover the basics with a compression test and ignition test just so you have an idea of where you stand with the rest of the power head. J
  14. J

    I need help on my 85 hp force. Plz &thx I’m kinda new to boating and fishing but I can wrench on my own stuff

    Is the boat new to you? Any history with it? First impression is that you're starving for fuel. Verify fuel pump by disconnecting carburetor feed and wrapping it with a rag. Turn the engine over (if the starter spins) and you should get fuel spurting into the rag. From there, get into the...
  15. J

    1988 Mercury 25hp 2 stroke repeated stator failures

    Signs of excessive heat on the coil? Is the engine itself overheating? J
  16. J

    Mecrcury 9.9 HP shifting issues

    What's your serial number? Sounds like the first thing is to get the revs down. Stop the gear slamming. I think once this happens you'll be able to shift forward to reverse. Do you have a barrel you can drop the engine in? You can work it on the boat but it may be easier on an engine stand...
  17. J

    Badged as 9.8, Serial A901055 Running on One Cylinder Only

    I do not see a reed plate in exploded view parts lists that I am looking at. Is there no reed plate in this block? How is fuel distributed to the cylinders? J
  18. J

    2006 60 ELPTEFI Spewing Fuel from Vapor Separator Vent

    Bueller? ... Bueller? I looked at a video on swapping out the VST and it did not mention any post-swap set-up procedure. Looked like plug-n-play. Any input? J
  19. J

    1973 Mercury 40 4hp: Compression, Spark, Fuel - No Start

    Input somehow posted twice. Disregard this entry. No head gasket? Serial number would help get me to the right parts diagrams. J
  20. J

    1973 Mercury 40 4hp: Compression, Spark, Fuel - No Start

    Please provide serial number so we can look up configuration. That said, compression seems a little low. Try putting a little 2 stroke oil into each cylinder and recheck compression. If number increases, rings are wearing out. Check the condition of your head gasket, may be leaking. Spark...
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