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Old 07-31-2012, 07:48 PM
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350 sbc fine tuning

Ok guys got a Chevy 350 small block....had issues getting this thing timed and still may not be timed right because it starts and runs great EXCEPT when driving this thing has a small putter and not accelerating like it used to .....where am I falling short? Is it in timing or in the carb adjustments?
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Old 07-31-2012, 09:11 PM
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What do you have the timing set at? Has the carb been tuned since the timing was changed? Need more information. Ignition and carbs often diagnose with the same problems which can make it difficult which is why we need all the info you can give us.
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Old 07-31-2012, 09:54 PM
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Originally Posted by DoubleVision View Post
What do you have the timing set at? Has the carb been tuned since the timing was changed? Need more information. Ignition and carbs often diagnose with the same problems which can make it difficult which is why we need all the info you can give us.
True dat!..
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Old 07-31-2012, 10:12 PM
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I got initial timing set at about 14 -16 ...running hei dist with vac canister .....now it's brand new and I can't tell you what it's adding to initial timing ..I did turn both adjustment screws on the carb clockwise until tight then I backed them out about two turns ....I've come a long way guys seems like fine tuning all that's left ....I d hate to have to go to the shop now ...please offer any suggestions and ask the necessary questions ....ima confess now ...I'm not a mechanic but I do know the basics and then some
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Old 08-01-2012, 06:55 AM
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what kind of carb.& what cfm is the carb.Is your vac.advance adjustable?Do you have a vac.gauge
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Old 08-01-2012, 07:11 AM
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It's a Holley carb on it ...it was on there when I got the car ....the vac canister can be adjusted as far as I now by using an Allen wrench ...I don't have a vac gauge ....would that prove worthy in fine tuning this thing?
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Old 08-01-2012, 07:36 AM
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If you had an Eddy carb.I could of gave you some advice but to be honest Ive never had a holly.It just seems Eddys always end up in my garage.Yes you need a good vac.gauge.Youll end up like me doing endless searchs for anything that might be an answer.Youll just have to devote so time to it.But dont be like me an filp flop between carb. changes an timing adjustments,get one of them right then work on the other.Youll find all the info.youll every need on here.
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Old 08-02-2012, 05:39 PM
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Thanks dog water ....now where is my Holley pros at ...I'm in trouble over here
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Old 08-02-2012, 06:06 PM
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350 sbc fine tune

Like dogwater said you have to have a vacuum gauge to check engine vacuum at idle. The screws you adjusted will be adjusted until you get the highest reading. Get the numbers off the carb and look it up on the internet to find out what you have. Look closely at night at spark plugs wires, may have been too close to headers. Pull one wire at a time and reconnect to see if each cyclinder stumbles. Take carb spray and spray along intake flanges and base of carb checking for vacuum leaks.
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Old 08-02-2012, 06:35 PM
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With vacuum advance disconnected and plugged, set the base timing at 12 degrees before top dead center.
Reconnect vacuum advance, make sure it's connected to a manifold vacuum source on the carb which is a source that pulls vacuum full time, including at idle. When you connect it to a manifold source right away it's going to idle up, so Idle it down to around 700 rpm. Now recheck the timing, it should be 18 to 24 degrees before top dead center. Test drive. If you detect ping, adjust 2 degrees out of the vacuum advance until detonation is no longer detected. Next with the car at idle you'll want to reset the idle mixture screws. When you run just 12 degrees base timing at idle with nothing else then what happens is the idle is raised so high it's off the idle circuits on the carb and it's forced to pull fuel from the main boosters.
Why use vac advance at idle? First off this is how GM did it. Next is because idle and off idle mixtures are lean. Lean mixtures burn slower than do richer ones which is why more timing advance is needed. While you could just not use vac advance at all and just move your distributor to the desired setting of 18 to 24 degrees the side effect will be the hot start syndrome where you go to start it after it's warm and it just drags over instead of spinning over.
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Old 08-04-2012, 02:20 PM
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Ok guys I just made a gruesome discovery ....haven't corrected it yet as I don't know why or how it happened and wanted some pro input ......so I'm under hood about to make adjustments with engine running at idle when I notice one of my 4 bolts that hold down the carb is spinning ...I pull the screw out to look for damage as maybe screw broke or just back out ...at this time I'm not sure but could thus be causing the popping coming from carb when I accelerate? Not a back fire pop but just a pop pop pop and only when I throttle up ...sounds decent sitting at idle ...ima put screw back but I'm concerned on how it backed out
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Old 08-04-2012, 04:31 PM
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Lol gruesome! Check the manifold for stripped threads, common on aluminum manifolds. Or maybe it just wasnt tight enough to begin with.
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