1972 Mariner / Yamaha 8A 8hp enricher question

S

silversniper

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Hi I have recently bought a 1972 Mariner / Yamaha 8A of the 647 series. I need some advice about its choke and how to start it.

The guy I bought it off said it has been recently re-serviced and it looks in good order. I replaced the impeller and it now has a good telltale.

I've had it going about three times since I bought it and each time it has been very hard to start. I have used primer in the air intake, and that got it working yesterday but today even primer wouldn't start it for more than a couple of revolutions then it would die. When I had it going yesterday it was purring along. Once started, it restarts with one pull. Today I pulled many times over the day, let it rest, cleans the plugs, but nothing would convince it to start.

So I am increasingly thinking this is a carb/choke issue. It has an unusual choke and I did some research tonight I think its an enricher, not a choke. It is a small brass barrel connected to a cord which shifts its position inside the carb. See here http://www.boats.net/parts/search/Merc2/Mariner/8A/655-000300 AND BELOW/CARBURETOR/parts.html the brass barrel is part #16.

If it is an enricher, is it correct that I should be starting the engine with low/no throttle to create a vacuum to allow the enricher to work? (up till now I've been trying with the throttle open as that's what I'm used to doing). I read somewhere that is how enrichers work.

Any help/tips would be appreciated as I am not able to find much out about this model motor, or this type of choke.
 
S

silversniper

Recruit
Joined
Nov 3, 2012
Messages
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By way of an update,

I have found a Mariner 8A 8HP manual by following these instructions (posted elsewhere on these forums):

Go here for the manual:

http://search.ebscohost.com/

User ID is marshall

Passwrod is public

When you have logged in, select Small Engine Repair

Then, select Marine/Boat Motors

Then, select Mariner

Then, select OUTBOARD 2-220 HP, 1976-1989 (INCLUDES ELECTRIC MOTORS)

Then select fuel system

Then you will find the 8A carburetor described as a "downdraft carburetor".

So looking at this manual, it appears the "choke" actually isn't a choke, it just moves a "starter plunger" out of the way - possibly to open an air passage at the lowest point of the throat. If so, its not even really a fuel enricher? Or does it allow a fuel passage to be opened?

This suggests that this engine must be started with the throttle butterfly in fully closed, or almost fully closed position (not half open like I have been doing with other older engines with a normal choke) in order to generate the vacuum needed to draw fuel into the engine.

What still has me puzzled is the part listed as the screw, air adjustment, #27. If the "starter plunger" is opening a passage and letting air in, and this screw also lets air in, then where is the fuel coming from at engine start? Is this carburetor using some sort of auxiliary carburation unit that is activated by pulling the 'choke' knob?
 
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