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04 4HP carb lacks vacuum ports

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bugbitten

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I've got an older (January 2004) 4HP Tohatsu (model MFS4A2D 3H9) that I've had in the garage for a number of years and am trying to resurrect. It starts and runs well, but idles very fast. Research leads me to believe the carb needs rebuilding. Before I attempt that, though, it did come with a new carb, still in the box; however, that carb, while identical in every other outward respect, has two vacuum ports that my old carb lacks. Can I still use it? Should I just run a hose from one port to the other to effectively cap them off?

Thanks.

John
 

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NO. Do not cap them off. They are not vacuum ports. They are vents.

Each takes a hose that then exits the lower cowl to atmosphere.
Your old model is probably an MFS4A2 (year is irrelevant), and the newer carb is actually the wrong one -- for an MFS4C. It will work, but will not have as nice an idle, as it is built to a newer EPA standard. If I was going to change the carb, I would install one for the 6A2, and gain 50% power.

Yes, you probably have a restricted (or blocked) low speed circuit in the original carb; increasing the idle stop to the transition point will allow it to run, but way too fast. After a complete disassembly (including jets and emulsion tube nozzle), a 4-hour soak in real carb dip, followed by a thorough blow-out with generic carb spray, it may or may not come up OK.
 
Last edited:
pvanv said:
NO. Do not cap them off. They are not vacuum ports. They are vents.

Each takes a hose that then exits the lower cowl to atmosphere.
Your old model is probably an MFS4A2 (year is irrelevant), and the newer carb is actually the wrong one -- for an MFS4C. It will work, but will not have as nice an idle, as it is built to a newer EPA standard. If I was going to change the carb, I would install one for the 6A2, and gain 50% power.

Yes, you probably have a restricted (or blocked) low speed circuit in the original carb; increasing the idle stop to the transition point will allow it to run, but way too fast. After a complete disassembly (including jets and emulsion tube nozzle), a 4-hour soak in real carb dip, followed by a thorough blow-out with generic carb spray, it may or may not come up OK.
Click to expand...

I did a search and my primary source for boat bits, Defender, has what looks to be the carb you mention. Is this it?

http://www.defender.com/product3.jsp?path=-1|311|2349106&id=1829684

Thanks.

John
 
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