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Sluggish off the line! HELP!

5286 Views 7 Replies 5 Participants Last post by  itsa65
ok, I have a 1968 Rebuilt 289ci with 302 heads, an edelbrock performer 289 intake with an edelbrock 600cfm 4brl carb, stock dizzy with new insides (still points). I changed my plugs which were really fouled, set my spark wires accord to chilton (two were in the wrong order). Im sitting at 15in of vacuum steady, carb vacuum tuned to highest vacuum possible. Im sitting at 8BTDC on my timing(max I can go before I get ping). it idles and starts up A LOT better with the new plugs and correct spark pattern, but from a dead stop, if I gas it hard it bogs down for about 5-8 seconds then picks up, its really bothering me because when I had the stock 2brl on there I NEVER had that problem, someone please point me in the right direction.

Thank you
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Check the vacuum advance module on your distributor. Sounds like it could be blown. Also check points gap.
you really should switch to a Mallory Unilite dizzy, well worth the money, those points dizzys always have problems...the bog is probably the carb, you might have a pro take a look at it
What camshaft do you have? IF the stock cam then you may have a vacuum leak, 15hg is not high enough for stock. What is your rear axle ratio? What was the benefit to the 302 heads? What year are the 302 heads? If it is not backfiring through the carb when you punch it, then it is probably too rich on mixture, you need to check the float level, idle mixture screw and air bleed, accelerator pump settings. Vacuum advance should be connected to ported vacuum (this means there is not vacuum at idle), correctly connected and operating, vacuum advance will have little to do with hard acceleration. Is your dist a dual diaphragm unit, if it is, one side advances the timing the other retards it, this is for emission? Post your results. Good Luck.
I had the motor and trans rebuilt in 04, stock cam, rear axle is 3.00, the guys that rebuilt it asked if I wanted 289 or 302, I asked for 289, I did have a vacuum leak and pulled the manifold off to fix it and pulled my vavle cover while at it and discovered 302 heads, so I havent looked at the crank yet but assuming its 289 with 302 heads, Ive found a couple other people thats happened to, some say they breathe better, not sure what up with that. while the manifold was off I took the carb apart and checked floats, needles and cleaned it all out. I put the manifold back on yesterday morning, used "the right stuff" gasket maker in the valleys, started it that night and checked vacuum still steady at 15in, I sprayed carb cleaner everywhere trying to find a leak and no change at all in idle. my dizzy is the original (new insides, had a shop adjust points gap) dual advance, retard is plugged (before I got it) and the advance is on the carb where there is no vacuum at idle. how do I know if my advance is busted? if I pull the line off while running and suck on it the motor picks up.
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An older guy from work that used build them back in the day (real older guy) siad I should set my idle at 950-1000 and it should be about 550 in gear, that seems a little high to me but Im no expert. chilton says 550 curb idle but not sure exactly what curb idle means. and I have been considering changing the whole ignition system, just waiting on some funds

thanks for the help guys I appreciate it!
That's way to high of idle speed for an stock automatic, it should be somewhere around 450-550 in drive, which would probably be around 550-650 out of gear. The way you tested the vacuum advance is how I check them, so it is okay. Have you adjusted the carb, the ones with air bleeds are a little tricky, you have to go back and forth between the air bleed and the idle mixture screws. Do you have vacuum secondaries, if not you can't floor it at idle you can only punch it far enough so the secondaries don't open until the rpms are around 2500 rpms. I wouldn't change the ignition system yet. Many give points and condensor a bad rap, I run points and condensor in my 65 fb 289 271hp which is modified and I turn it pretty high, no miss fire, in fact we've been stranded by more electronic ignitions failures than any of the cars with points and condensor. You could have a vacuum leak on the pcv connection or a bad pcv valve (it should rattle when the engine is off, and cause about a 200rpm drop if you plug it with a finger at idle), power brake connections if you have it. IF the heads are 71 or newer they will be lower compression heads, fyi. IF the car is out of gear and you punch it, does it rev up okay or does it bog down. IF you are driving (not at idle) and you punch it, does it take off or does it bog down. Post your results. Good Luck.
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Even if your mixture is properly adjusted, you might not be getting enough fuel when you punch it -- this is probably the cause of it bogging down and may be the accelerator pump. I have the same carb. Here is what Edelbrock says in the owners manual (available online on the Eddy site):

If you encounter any hesitations or stumbles that do not seem to be related to the basic metering or have not responded to changes in the basic metering, move the pump drive link to one of the holes closer to the carburetor body. This will increase the stroke length of the plunger and result in more pump delivery.​

Good luck.
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