Rich on the high end

Discussion in 'Outboards' started by skytech, Jun 6, 2015.

  1. skytech
    Joined: Jun 2015
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    Location: Texas

    skytech New Member

    I have a 1974 25HP Evinrude that would not run when I got it. I new the carb, had been worked on so that was where I started and yes there was some mistake's that was made in it. I cleaned it really good, replaced all the fuel lines, installed a new fuel pump and new fuel tank. then I went thru the timing and new points and new plugs. Now she cranks up first pull all day long very good reliable idle but at the top end it seams a little rich but there isn't any adjustment needle for the top end. It will peek out for a few seconds and then fall back a few RPMs. It seams like it wants to peek out and run but it just wont do it. has any one here ever run in to something like this
  2. whitepointer23

    whitepointer23 Previous Member

    R u sure its too rich. I would have suspected too lean.. could be varnish in the main jet .sometimes that can be very hard to remove.
  3. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    I agree with Whitepointer. This is a common issue with vintage outboards; Johnson/Evinrude sells the cure, a spray can labeled "carb cleaner". It is a mixture of acetone and other carbon hydrates that removes varnish within 15 minutes.
  4. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    I agree, before worrying too much about it, run about five tanks of gas through it doped with a heavyish dose of "Sea Foam". Then see where you are at in a month.

    Check the port that drives the fuel pump, also.

    Are you sure you used the correct fuel pump?. They made a bunch of really similar ones. Check that the PN is correct. When I was in the Keys, it was pretty common to be told "they will all work fine - don't worry about it." Some did, some didn't.
    Last edited: Jun 9, 2015
  5. skytech
    Joined: Jun 2015
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    Location: Texas

    skytech New Member

    Thanks whitepointer23, CDK, philSweet. I am going to pull the carb tomorrow can I clean it with out pulling any of the plugs in the carb, are do I need to pull them as well? I was thinking it was rich from all the smoke and fumes at idle but yall got me thinking it isn't smoking on the top end so yep I bet it is lean. I have been running sea foam in it about 5 to 6 tanks now with no success and the new fuel pump I ordered by the model and serial number off the engine from fear that it had the wrong one on it already. thanks again I do thank yall may have me on the right track now.
  6. SukiSolo
    Joined: Dec 2012
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    Location: Hampshire UK

    SukiSolo Senior Member

    Most, if not all carbs run at the high end with a combination of needle and main jet only. Some more sophisticated carbs (and manufacturers) offer a wide choice of options. However you can be pretty certain the manufacturer will have selected the correct pairing, unless it was an export model motor for say high altitude or very cold conditions. Worth finding the original specifications ie needle type and main jet (size) with atomiser holes. Check this correlates to what you have.

    I agree with CDK, PS and Whitepointer re carb cleaner is often your best friend especially on smaller ie the atomiser holes and mixture screw orifices. Anything around 0.5mm or smaller is often blocked by the aromatic gum if left to dry out. Also the fuel pump diaghram if old may be too stiff or split as a result of modern fuels. I believe the increased ethanol espically in the US has resulted in more rapid deterioration of older 'rubber' parts. Basically they were not as resistant as newer materials.
  7. Easy Rider
    Joined: Oct 2009
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    Location: NW Washington State USA

    Easy Rider Senior Member

    Fuel line sucking air preventing max fuel flow at the top end.

    Dirt, chunks of thread sealer (both liquid and tape) could be limiting the output of the pump.

  8. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    has it got the correct main jet in it?
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