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Carter BB1 Updraft Carb on a 109

Old Marine Engine » Gray Marine Gas Engines - 4, 6, and 8 cylinder » Carter BB1 Updraft Carb on a 109 « Previous Next »

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Eric Peggs
Advanced Member
Username: epeggs

Post Number: 34
Registered: 02-2017
Posted on Monday, May 21, 2018 - 12:44 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

I ran my boat with the 109 in this weekend. She will not idle down to 500 rpm as the book states and requires choke to stay running. Currently idles at about 900-1000 rpm.

I was making adjustments to the carb in neutral at the dock for the idle setting. The engine would not respond much to any adjustment.

I know the main jet needs to be adjusted at full throttle and under load(per the maintenance book I have). Does the order in which the jets and screws are adjusted matter? Meaning should the main jet be set first and then the idle?

Thanks in advance!
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J.B. Castagnos
Senior Member
Username: jb_castagnos

Post Number: 1377
Registered: 07-2002


Posted on Monday, May 21, 2018 - 04:06 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

Sounds like a vacuum leak or plugged low speed circuit.
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Eric Peggs
Advanced Member
Username: epeggs

Post Number: 35
Registered: 02-2017
Posted on Thursday, May 24, 2018 - 11:20 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

in the pic, I am pointing at a copper hose that runs from the top of the carb to the bottom of the carb. What is this for? Could this be clogged and causing these issues??
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Ned Lloyd
Senior Member
Username: ned_l

Post Number: 165
Registered: 08-2012
Posted on Saturday, May 26, 2018 - 09:11 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

I would agree with JB.

That piece of copper tubing,...... if it runs to the very bottom of the bowl/horn, it should be to prevent a flooded engine from dumping fuel - gas into the bilge. When the engine floods, the extra gas puddles in the bottom of the bowl, that little tube then leads to a small opening above the throttle plate. There is vacuum in that tube so it will constantly suck the extra gas out of the bowl and prevent the gas from getting to the point of overflowing and spilling into the bilge.
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Ned Lloyd
Senior Member
Username: ned_l

Post Number: 166
Registered: 08-2012
Posted on Saturday, May 26, 2018 - 09:24 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

I agree with JB.
That engine should tick along very nicely at 500 RPM, probably as low as 450.

That little copper tube runs from the bottom of the bowl to above the throttle plate in the throat. The purpose is to suck any gas out of the bowl if you flood the engine, and keep it from overflowing and dumping into the bilge.
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Eric Peggs
Advanced Member
Username: epeggs

Post Number: 36
Registered: 02-2017
Posted on Wednesday, May 30, 2018 - 10:36 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

Thank you guys for your responses!

I tore apart the carb blew air through every tube and orifice I could with my lungs. No restrictions at all when it comes to air flow through the carb. I am hoping this is a good thing.

What I did notice is that the throttle valve was not 100% closed at zero throttle. Which would mean the engine was getting more fuel and more air than needed for idle resulting in a higher RPM. Does this sound accurate? Would this be why the idle adjustment screw had no effect on the motor when adjusted?
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Eric Peggs
Advanced Member
Username: epeggs

Post Number: 37
Registered: 02-2017
Posted on Thursday, May 31, 2018 - 10:19 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

I stand corrected. I did not air test the idle orifice tube....it was clogged. Ran a drill bit through it at a very very low speed on the drill and cleaned everything very well with the carb cleaner again.

Got it to idle down to about 600 - 700 rpm. only issue now is throttle linkage and positioning. I would increase throttle and try to bring it back down to idle. would not go below 1000 rpm again. Id push on the throttle cable and it would idle down ....so more adjusting...but she idles down!!!!

once we get the throttle linkage adjustments i think it will go down even farther....

i'll keep you all posted. thanks for the help so far!!!
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Ned Lloyd
Senior Member
Username: ned_l

Post Number: 168
Registered: 08-2012
Posted on Tuesday, June 05, 2018 - 12:52 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

very good, it sounds like you are getting there.

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