Carb stumble on a SBF

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Carb stumble on a SBF

Post  jbozzelle on May 28th 2012, 8:05 pm

Guys,

I need help trying to figure out a stumble my brother's SBF has. I currently has my old 850Dp on it. It has a stumble during part throttle and I can't figure it out. It'll stumble to the point of killing the engine. I can't figure out of it's a rich or lean stumble though... Plugs look rich though...

Any things to try?

I've already disconnected the secondaries and it seems to have gotten a bit better. It has a 1:1 secondary linkage on it. I also richened up the primary idle circuit and it seems to have gotten a bit better as well.

What should I do next? richen or lean the pump shot cam? Squirter?

I know the 850 is a bit big for just 357 inched but it's all we have to use on it for now.

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Re: Carb stumble on a SBF

Post  69F100 on May 28th 2012, 8:47 pm

have you tryed moving the timing if you unhook the secondaries sound like the timing to me
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Re: Carb stumble on a SBF

Post  QtrWarrior on May 28th 2012, 8:54 pm

John,

On my dirt car motor...we found that if he hit the throttle before the motor was at least 160*, we had a similiar thing happen...
Anything over 170* or so and it was fine...

Maybe not in your case..but ya never know...
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Re: Carb stumble on a SBF

Post  fordman50 on May 28th 2012, 8:58 pm

I had this when my float level was too low once... could be a lot of things... dizzy advancing ?

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Re: Carb stumble on a SBF

Post  whatbumper on May 28th 2012, 10:18 pm

More pump shot to cure stumble and probably less jet if the carbs rich. Could be power valve that needs too much vacuum. Lots of variables here.

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Re: Carb stumble on a SBF

Post  whitefield on May 28th 2012, 10:21 pm

whatbumper wrote:More pump shot to cure stumble and probably less jet if the carbs rich. Could be power valve that needs too much vacuum. Lots of variables here.

X2

Check the pump spring adjust ment and make sure your squirters are clean
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Re: Carb stumble on a SBF

Post  powerstrokeace on May 28th 2012, 11:37 pm

You didn't say if it had a power valve. I would put a low one in 6.5-4.5 and maybe jump up in squirter size 2-4 numbers.

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Re: Carb stumble on a SBF

Post  jbozzelle on May 29th 2012, 3:11 pm

No power valves and I stuck the jets a box stock 650 would come with in it. And it's still a bit rich for some reason. I did go back through my notes and I did change the timing at the track. That's when the problem started too so that's the first place I'm going to look at.

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Re: Carb stumble on a SBF

Post  powerstrokeace on May 29th 2012, 8:29 pm

jbozzelle wrote:No power valves and I stuck the jets a box stock 650 would come with in it. And it's still a bit rich for some reason. I did go back through my notes and I did change the timing at the track. That's when the problem started too so that's the first place I'm going to look at.

If you remove the power valve you need to jet the primary up 6-10 numbers (depending on combo) to off set that. So your way lean.

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Re: Carb stumble on a SBF

Post  jbozzelle on May 29th 2012, 9:31 pm

I'll have to pull it apart and what I did.

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Re: Carb stumble on a SBF

Post  powerstrokeace on May 29th 2012, 9:40 pm

I had a killer carb (650dp) on my small block worked great. Then i decided to change the cam,heads,intake. Found a killer deal on a Quick fuel 750 and sold the 650. Boy what a mistake as now I'm lost on what to do to get this thing to run right on the low end. Now the bigger dilemma. Looking to have a E85 carb built and have no idea what to tell the guy about the carb. Mad

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