Pop Quiz Time...

M

madbanchee

Seaman
Joined
Aug 17, 2004
Messages
52
Do Evinrude/Johnson motors have accelerator pumps on them like Mercury's do?<br /><br />What fuel component on an '89 Evinrude 150XP (E150STLCEM) compensates the carb jets with a shot of fuel when the lean condition from accelerating off idle is created?<br /><br />In other words... When the throttle is pushed wide open from a dead stop, what provides the extra fuel required to keep the motor from stalling by having too much air intake from the wide open throttle plate?
 
W

Walker

Captain
Joined
Jun 15, 2002
Messages
3,085
Re: Pop Quiz Time...

No accelerator pump, and I've never seen one on a Mercury either.<br />The Carbs work on the venturi theory. If you look in the throat it gets smaller where the fuel orifices are. The smaller throat make the air velocity increase and actually creats a vacumn at that point which sucks fuel into the air flow.
 
M

madbanchee

Seaman
Joined
Aug 17, 2004
Messages
52
Re: Pop Quiz Time...

I know of a '72 115hp Merc with an accelerator pump. The pump was located on the side of the carbs.<br /><br />The point to the question is this...<br /><br />How is the lean out condition during acceleration avoided when the butterfly is opened?<br /><br />Is the choke primer used some how to handle this or is the low speed idle circuit just set so rich so that it won't stall?
 
W

Walker

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Jun 15, 2002
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Re: Pop Quiz Time...

The carbs on that 150 have 3 sets of orifices. Idle jets that feed fuel at idle and very low RPMs, intermediate jets that feed fuel through mid-range, and high speed jets that feed fuel at high RPMs. When accelerating, even thought the butterflies are fully open, the engine is not requiring the same amount of air as when at full throttle. Air is pulled in with each upstroke of the piston, so the faster a piston is cycling the more air it pulls over the same amount of time. Does that make any sense.
 
W

Walker

Captain
Joined
Jun 15, 2002
Messages
3,085
Re: Pop Quiz Time...

I think you need to do a thorough cleaning and overhaul of your carbs. Thorough means tearing down, a good soaking in carb cleaner and finishing up with aerosol carb cleaner and compressed air. Put new carb kits in them and set the floats according to manual specs.
 
J

jim dozier

Lieutenant Commander
Joined
Jan 8, 2003
Messages
1,970
Re: Pop Quiz Time...

Because each cylinder has its own carb and the intake length is short, the vacuum pulse at the carb venturi is sufficient to keep the mixtures adequate when moving from idle to intermediate to main jets as the rpms increase on a 2-stroke outboard. On a multicylinder car engine (or outdrive boat) with a V8 there is usually a single carb (multiple barrels) feeding a large plenum intake manifold. The intake vacuum pulse is diluted and an accelerator pump is usually necessary for improved throttle response. If you put 8 Webbers on individual intakes on a V8 you might not need an accelerator pump either.
 
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