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  1. #41
    CB750 Member Old Okie's Avatar
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    Been away for a while, lots of company this summer, problems with the weather, hotter than...
    Got back to the bike today and began with a compression check, very disappointing.
    1, 2 & 4 at 120 psi, 3 @ 90/100. What does that mean and what are some of the causes??
    I can do a lot but I am not comfortable rebuilding this motor. Will the bike run at those numbers???
    Going to check valve clearances, may be a problem there. When I started the bike it hissed at me
    through a carb, not sure which one yet, that could be a sticky valve or bad adjustment on #3.
    So much for cleaning this thing up and riding it.

  2. #42
    CB750 Addict Dave's Avatar
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    120 is fine for cold dry cylinders.

    Set the valve clearances on the loose side.
    96% of the time I edit my replies so check back for updates if it isn't at least an hour old

  3. #43
    Moderator dirtdigger's Avatar
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    120 is on the ragged edge for running, 90/100 is a no go. Do check valve clearance make sure not holding valve open but I doubt it on a sohc. Use standard valve clearance on sohc motor, go too wide and you will beat up the valve stem tips.

  4. #44
    CB750 Member Old Okie's Avatar
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    I will get back on this project on Monday. The bike has electronic ignition, a round black plastic module.
    So there is no points or any of that stuff so what do I use for determining TDC?? I have not looked at the
    stator side of the motor, anything there that I can use?? I need to download another manual, my computer lost the one I had.

  5. #45
    Moderator dirtdigger's Avatar
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    Even with electronic ignition there still has to be a way to check ignition timing.....timing marks which are on the ignition advancer assembly. post some pictures of what you have sometime so we know what you are working with

  6. #46
    CB750 Addict Dave's Avatar
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    Hook a timing light to #1 wire and shine it in the hole. For points you repeat on wire #2 but I can't remember if the solid state units can be separately adjusted.

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    @DD I always go 'on the loose side' (but within specs) on OHV Hondas with medium or high mileage (car and bike).
    96% of the time I edit my replies so check back for updates if it isn't at least an hour old

  7. #47
    Moderator dirtdigger's Avatar
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    @DD I always go 'on the loose side' (but within specs) on OHV Hondas with medium or high mileage (car and bike).[/QUOTE]

    The sohc is not like the dohc with the issues of valve clearances tightening. The sohc like to get looser as time goes on because of all the extra parts associated with the rocker arms. The valves seldom sink in the head so the clearance hardly ever gets tighter unless you get a fluke problem with a soft seat or ingest a lot of dirt and wear the valve face. Honestly cant say I have ever had a valve clearance go tight on the sohc, the rocker pivots seem to wear the most especially on the later models of the sohc where they dont allow the rocker pivot shaft to rotate. The valve stems do tulip and pit from excessive clearance on these...

  8. #48
    Moderator dirtdigger's Avatar
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    There has to be marks somewhere, somehow you still have to do an initial adjustment for the electronic ignition. Even on electronic you still have to be able to adjust them separately as 1,4 still functions as a separate system from 2,3. They still have to do the job independent, still two pickup units and two coils. Hiding somewhere there are timing marks.

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