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  1. K

    Stubborn To Start 1979 9.8

    To clean the piston grooves I broke off a piece of the removed piston rings. I used it to scrape out any carbon. Honestly the engine was pretty clean in general when I tore it down. If extra scrubbing was needed I used Some steel wool and scotch-brite abrasive pads. Washed and blow-dried the...
  2. K

    Stubborn To Start 1979 9.8

    I used a 3 finger, sprung, straight-style home. I performed a quick hone. Not over-doing it. The carb float was set as per factory service manual. The engine does not have a decompression system. For break-in I warmed up the engine then worked it at various speeds. No full throttle for an...
  3. K

    Stubborn To Start 1979 9.8

    Someone told me they were low compression. I am doubting that. I have since seen folks on-line measuring 110 psi. The break-in exercise on the lake yesterday, it wouldn’t start. I squirted some raw fuel in the carb. It flashed up then. High idle and up, it seemed to run quite good. Wide open...
  4. K

    Stubborn To Start 1979 9.8

    I spent 2.5 hours out on the water today. Breaking-in the engine. When I got home I measured 75 psi still. Seems odd to me after a light hone and new rings. I measured bores and also used a dial bore gage. The cylinders measured to be well within specs. I re-used the pistons. There is no...
  5. K

    Stubborn To Start 1979 9.8

    Thanks for your responses folks. I feel like I solved it. It was indeed low compression. I lightly honed the cylinders and installed new rings. Compression test dry, netted 75 psi. I pulled the plugs and put some oil into the cyliders. I pulled it over a few times to coat everything. All the...
  6. K

    Stubborn To Start 1979 9.8

    The issue appears to be compression. I put oil in the cylinders and raised compression to 110 psi. She’ll run. I’ll see if seating the new piston rings will improve it. The cylinder taper and out of round was well within spec. Pistons looked great. Stock bore. New rings and honed cylinders...
  7. K

    Stubborn To Start 1979 9.8

    Affer a powerhead refresh, my 9.8 won't start unless I squirt some raw fuel into the carb intake. Then it'll fire up first pull, sound wonderful for a second or two, then die. It seems fuel starved. I have done a couple of real good cleanings of the carb in my ultrasonic cleaner. I pulled apart...
  8. K

    My 1979 9.8 Project

    With the weather improving weekly, I look forward to getting out and testing my Merc rebuilds. I’m curious about the HP rating at the prop and at the power head. My 1991 8 HP 2 stroke is rated at the prop. My ‘79 9.8 is measured at the powerhead. I’ve yet to use either of these as I picked...
  9. K

    My 1979 9.8 Project

    My local Mom & Pop shop had 2 full sets of brand new original Mercury reeds. Under about 3” of dust. The shop has been awesome with almost everything I need for these old Mercs, in stock. He’s says nobody can afford to pay him to rebuild them any more.
  10. K

    My 1979 9.8 Project

    Thanks for that max clearance spec on the reeds. I’ll measure my gaps. Pretty sure its over 0.010”
  11. K

    My 1979 9.8 Project

    Cleaning up my 1979 9.8 noticed an engine SN on the powerhead. Canadian build. Was it typical for the SN to end with the year of manufacture? As seen here, maybe 41st build of ‘79? Maybe not. I’m only curious as I picked up spare 9.8 parts outboard. Someone may have put together a mix parts...
  12. K

    My 1979 9.8 Project

    I’ve not fired it yet. Engine is still apart. I’ll deal with spark if needed, once I can turn it again.
  13. K

    My 1979 9.8 Project

    I started my second Merc project. This one is a 1979 9.8 that I paid about $60 USD for. (I’m in Canada, $100 CDN) The seller told me it had been sitting outside in all seasons un-protected, for about a year. I figured, for the price it would at least give me a good supply of spare parts. The...
  14. K

    1981 Mercury 7.5 2 stroke

    Re pisser and thermostat on 7.5 and 9.8 engines. Thermostat housing is seen here circled in red. Hose to pisser, red arrow indicating water flow direction. Thermostat housing open in next photo. When thermostat is closed water only spits through by-pass port, seen within red circle below...
  15. K

    1981 Mercury 7.5 2 stroke

    I’d like to discuss 3 ring vs. 2 ring pistons in the 7.5 and 9.8 engines. The ‘74 9.8 I have, has 3 rings. Same bore and stroke as my ‘81 7.5 HP. Yet the 7.5 has 2 piston rings. Is this possibly required on the 9.8 to seal a wider section of the cylinder walls? The section of the cylinder...
  16. K

    1981 Mercury 7.5 2 stroke

    Hi @racerone I want to apologize if I offended you in a response in this thread. You seem to have a ton of knowledge and experience to share on these old Merc engines. I appreciate your posts in my threads. I believe that both of us are not the “clueless beginner” when it comes to mechanical...
  17. K

    1981 Mercury 7.5 2 stroke

    Point taken guys. I will ensure I run it in a larger bucket with more water whenever I fire it up at home. I thought I read somewhere that it will sputter until the thermostat opens. This one has a thermostat.
  18. K

    1981 Mercury 7.5 2 stroke

    I’ve gotta stop looking at these engines on the used market. I’ve now acquired 4 small 2-stroke outboards. All Mercury. All very low prices. ‘90 8.0 ‘81 7.5 ‘79 9.8 ‘74 9.8 That happened quick.
  19. K

    1981 Mercury 7.5 2 stroke

    The 9.8 engine free’d up after about 10 hours of soaking. I’m thinking I’ll take it apart. Clean it all up. Scotch-brite any remaining rust. Check seals, bearings, rings. Take some measurements. Inspect cylinders & pistons and settle on a plan from there.
  20. K

    1981 Mercury 7.5 2 stroke

    I picked up a ‘74 9.8 for $65. Owner stored it on its side for the past 8 months. Rings are rusted to the cylinder walls. I had an opportunity to compare intake ports on my 7.5 to my 9.8. Thought I’d share a photo of each for comparison. 9.8 is the lower pic, ports are considerably larger...
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