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Author Topic: Slight bog on acceleration  (Read 3493 times)

Offline DT1

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Slight bog on acceleration
« on: January 16, 2011, 08:32:59 AM »
Hi everyone,
I just rebuilt my Quadrajet and installed it on my freshly rebuilt Chevy 350, 8.5:1 Compression, 87 octane fuel.  I'm noticing a couple of problems. I have a slight bog or hesitation that wasn't there before rebuilding.  I used one of Cliff's kits and also used his book as a guide.  I know I can probably fix it by advancing my timing which is at 8 Deg BTDC but anymore advance causes a slight ping at low speed and hardly any load.  I pretty sure this is caused by the vacuum advance module allowing the distributor to advance too much at low RPM.  I'm going to buy an adjustable module to see if I can tighten it up a bit but I'm just wondering if I should chase the problem at the carburetor too.  Any suggestions will help
Thanks
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Offline omaha

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Re: Slight bog on acceleration
« Reply #1 on: January 16, 2011, 11:04:06 AM »
Is the engine broken in  yet?  Idle set with a vacuum gauge? Ported vacuum source to the dizzy?
Just throwin things out there. I wouldnt think an 8.5 to 1 engine would ping.
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Offline DT1

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Re: Slight bog on acceleration
« Reply #2 on: January 16, 2011, 12:57:51 PM »
Quote from: omaha on January 16, 2011, 11:04:06 AM
Is the engine broken in  yet?  Idle set with a vacuum gauge? Ported vacuum source to the dizzy?
Just throwin things out there. I wouldnt think an 8.5 to 1 engine would ping.

The engine has 1,100 miles on it and I used a vacuum gauge to adjust the idle.  It is a ported advance but I haven't checked how many inches it takes to advance yet.  It has never pinged before and it only make sense that the advance module is causing the problem.  It seams that the pinging only occurs just when the the throttle plate moves past the advance port.  I like the ported vacuum and I think that if I get an adjustable module, I can increase the the vacuum required to open it. 
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Offline Cliff Ruggles

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Re: Slight bog on acceleration
« Reply #3 on: January 17, 2011, 05:52:14 AM »
No need to buy an "adjustable" vacuum advance.  The stock ones are easily modified.  I MIG weld the slot here, and file the opening with a small round file.

You can also make a limiter to go under the screw that attaches it to the housing, or drill/tap the unit and use a washer under the screw.....whatever works.

1/8th travel is apprx 10 degrees at the crankshaft, nearly as I can remember?.....Cliff
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