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B&M 250 on a 509 question

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Old 04-11-2007, 10:21 PM
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Default B&M 250 on a 509 question

I have obviosly a 250 on a 509 BBC. I was wondering 2 things 1, it has a rolling idle, is this normal or can i take care of this some how, Its not like an eratic idle from the came just up and down all the time until the throttle is lifted a bit, Also how to set the dual quads on it i think i have it dialed in pretty well but never hurts to ask for any pointers and and help is always appriciated thanks
Mike
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Old 04-11-2007, 10:49 PM
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Originally Posted by Sick Stinger View Post
I have obviosly a 250 on a 509 BBC. I was wondering 2 things 1, it has a rolling idle, is this normal or can i take care of this some how, Its not like an eratic idle from the came just up and down all the time until the throttle is lifted a bit, Also how to set the dual quads on it i think i have it dialed in pretty well but never hurts to ask for any pointers and and help is always appriciated thanks
Mike
Turn your idle mixture screws in a quarter turn at a time till it cleans up the surging. Make sure it doesnt stall when you drop it in gear
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Old 04-12-2007, 07:34 AM
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Blower "surge" is due to a richer idle mixture. Like JC said you do want to lean the idle mixture screws (clockwise) to tame the "surge". One of the most important things to do which most tuners miss is to sycronize the throttle plate positioning. If it is a four corner idle carb, The throttle plates must be open the same amount from seated! I would reccomend going an 1/8 at a time on the idle screws. Hope this helps.
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Old 04-12-2007, 11:16 AM
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my 2cents .i have a 454,with a 250tbs blower,running a 1050 4500 series carb and have the same problem too.if i run fat on the jetting...say98 squared,the idle is rolling bad,no matter where the idle screws are.if i lean out the jetting,say 92 squared,the idle is ok,but still rolling,and top speed drops off about 2-4 mph.hope this helps.
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Old 04-12-2007, 11:49 AM
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Get rid of the dual quads and get one good carb. and don't waste your money on a marine version. the curved emulsion tube will fight you on the high rpm tuning. just my .02 I'm a natural guy tho
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Old 04-12-2007, 01:07 PM
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JC and Dean are giving ya good advice.

What I do..

Take the carbs off and flipp them upside down and adjust the
Idle transfer slots so they form a square. They look like little
rectangular slots that are machined to allow air to pass between the venturi and the throttle plate.
Set these so they look like a square. What you want is the
butterflies to be as even as possible.
A blower surge is what you are describing. It is rich.. this
is what causes the roll. Turning the idle mixture screws in
will lean it out. But it should be done on the water.
If it is to lean it will stall when thrown in gear.

If it has to big of a roll it can actually go into the powervalve opening point. This will aggrivate the problem even worse.

Hope this helps
Gerry
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Old 04-12-2007, 01:27 PM
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How much initial and total timing are you running?
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Old 04-12-2007, 03:06 PM
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Hey knot i think you should come by and show me anyway i will give this a shot it did stall a few times out on the water i felt that it was due to a primary dripping fuel when at aidle and drowninf the motor causeing a flood condition to stall it. Also was very hard to restart cause and point flood came to mind. But seriosly i want to drop it back in say not this weekedn but next weekedn anyone who couold come down and willing to check it out n the water more then happy to have you aboard and if not i will do all every one said to get best idle and performance. I bough the boat doing this so i assume it has never been right
Mike
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Old 04-12-2007, 08:44 PM
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Mike anytime I can help!

If the primarys are dripping out of the booster then the float level is to high.

Depending on the carb model it will eithier have a brass plug
on the side of the bowl or a site glass.
I set them to just trickle out of the hole after you remove the plug.

The float level is set on the top of the bowl
loosen the philips screw then take a 5/8 wrench and turn
the nut very slowly maybe a 1/4 turn. If memory serves me
clockwise raises the level.

Or just bring that boat by the dealership and I will hook you
up.
Gerry
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Old 04-12-2007, 09:07 PM
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Hey gerry like i said not this weekedn but next you will have to come check it out happy for all the assistance i can get i wanna dial this B*tch in nice nice was told it did 85 solid, the engine builder who also tested the props, said he did a 93 but would run a 91 anyday. So to run it some where around there would make my summer. I was talking to ART (airtime) said you just had the skater painted i believe and was going ot check it out i was goiong ot go with him sometime. Anyway my father owns a shop in Fall River. Most of the time i keep it there and work on it so if you ever wanted to see it and stop by happy to go over it quick with you thanks again Gerry
Mike
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