backdraft carb

mr roach

Seaman
Joined
Jul 5, 2010
Messages
68
i have a 1977 merc 115 i6 thunderbolt ign. engine with the backdraft ( backdrag ) carburators i have been cruising posts and a lot of people suggest replacing the cross over tubes on the carbs economizer system and blocking the tube with a .177 bb as this will keep from ruining the engine as this midrange economizer system seems to do more harm than good under the right operating conditions. Also does the bb go on either side or one side specifically or possibly one on both ends ? Lastly can i just block off the tube connection with the vacumm line caps sold at auto parts stores after all blocked is blocked so why but new tubes and block them or is this not a good idea as i am missing something that may cause damage to my engine ?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: backdraft carb

You may cap the carb venturi side, instead of using the bb. The carb bowl side doesn't matter, as long as it doesn't leak fuel.

FYI - I never had an oz of problem with my backdrag carbs. I never modified them.
 

merc850

Commander
Joined
Jul 7, 2010
Messages
2,022
Re: backdraft carb

I bought a 1975 850 2 yrs. ago with b/d carbs and they are still configured as the factory did it, I asked a Merc dealer about them and he (has been in business since the 60's) said he didn't see any service bulletins about the problem and would they have used these carbs for 10+- yrs. if they were a problem.
I feel that bad oil and improper mixing procedures could cause more trouble, when you see pics of the motors on this forum they don't look like they've been well taken care of in the past.
 

mr roach

Seaman
Joined
Jul 5, 2010
Messages
68
Re: backdraft carb

thanks chris1956 i talked to a couple of mechanics and they say leave it be just mix the fuel right and i should be good to go i think the old adage if it is'nt broke don't fix it applies here and thanks for the fyi part of your reply
 

mr roach

Seaman
Joined
Jul 5, 2010
Messages
68
Re: backdraft carb

thanks merc850 i agree with you and a few mechanics i talked to say the same thing plus mine are working pretty darn well so i'm just going to run them like they are
 
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