Mariner 1978 140HP carb jets

A

Aboattime

Recruit
Joined
Mar 6, 2005
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1
Serial# 5264708 3 carb system. Had a mechanic rebuild my carbs.He replaced original low jets with updated ones but left original highs in.<br />Original low jets had little plastic balls that from my understanding would stop fuel flow at high speed, allowing fuel only through high jets. Should the high jets be sized smaller so that in combination with lows they equal the same fuel volume as the original high jets?
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,838
Re: Mariner 1978 140HP carb jets

Aboattime, I looked up your carb on the web. It appears to be a common, "back-drag" sidebowl carb. These carbs used vacuum in the bowls to lean out the mixture at high speed. I never heard of the "little plastic balls" the mechanic specified. Also, the low speed jets have very little influence (if any) on the high speed mixture.<br /><br />Some merc mechanics also thought the high speed jets were too lean on these. If it runs well at both idle and high speed, and the plug color indicates proper mixture, I would leave it alone.
 
Clams Canino

Clams Canino

Commander
Joined
Jan 10, 2004
Messages
2,179
Re: Mariner 1978 140HP carb jets

Main jets are (should be) .080 in that motor from the factory - that's fine. Put a BB in the little hoses to the float bowl tops to cure the backdrag lean-out, this renders the jet over the bowl cover maningles. Then set the low speed mixture needles per the manual.<br /><br />That's all.<br /><br />-W
 
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