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Old 06-24-2011, 11:32 AM   #1 (permalink)
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Default Off Idle Bog - Could it be timing?

I have a Ford Racing 306 with a new Holley 600 cfm carb. When I come off idle with light acceleration, the car bogs down before it catches. It seems to run fine at idle, cruise and when accelerating. I adjusted the accelerator pump spring from one extreme to the other and everything in between. It changed the nature of the bog but did not eliminate it.
Around the same time as I put the carb on the car I reset the initial timing to 12 degrees. Since I canít find the problem in the carb, Iím beginning to wonder if my problem could be in the timing. Before I go fooling around with the timing, I wanted to get some advice from you all. So, can bad timing cause the car to bog down when coming off idle? Thanks
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Old 06-24-2011, 11:56 AM   #2 (permalink)
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It's possible, have you tried advancing it some and trying it out? I would think 12 initial is enough, what converter are you running? There is a method for adjusting the Holley accelerator pump, that spring/bolt is there to set clearance, you're not going to alter the pump shot significantly with that method. You may need more fuel from that circuit initially, there is a kit with several different pump cams, and you may also need to increase the shooter size. Which model of 600 are you running?
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Old 06-24-2011, 12:01 PM   #3 (permalink)
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I bet the accel pump needs to be replaced. Diaphram may have a hole in it. If it does, adjusting the arm position will not make any difference.

Dave
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Old 06-24-2011, 12:29 PM   #4 (permalink)
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The carb is a new 80457S model with less than 50 miles on it. I'm running a 2200 stall converter with an AOD. I haven't fooled with the timing because I have a long history of trying to fix one problem by creating another. That's why I'm asking if timing can cause the same bogging symptoms. It's upsetting to think the Accelerator pump is bad on a brand new carb but I know stranger things have happened.
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Old 06-24-2011, 01:06 PM   #5 (permalink)
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I bought a reman 80457S from Holley (ebay) and it had a myriad of problems, one of which was a leaking accel diaphram. I, too, have a slight bog off idle if accelerating moderately hard. Granny driving doesn't produce the bog. Fixing the leaky diaphram didn't cure it.

It was also suggested to me to increase timing, although I'm currently at 13 degrees. Haven't tried it yet because I don't have access to the car right now but I'm curious to know if it'll fix your problem. If it doesn't fix the problem, be sure to put the timing back to where it was; that way, a 'second' problem won't arise. Change variables one at at time.
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Old 06-24-2011, 01:24 PM   #6 (permalink)
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Originally Posted by GTA6T7 View Post
I have a Ford Racing 306 with a new Holley 600 cfm carb. When I come off idle with light acceleration, the car bogs down before it catches. It seems to run fine at idle, cruise and when accelerating. I adjusted the accelerator pump spring from one extreme to the other and everything in between. It changed the nature of the bog but did not eliminate it.
Around the same time as I put the carb on the car I reset the initial timing to 12 degrees. Since I can’t find the problem in the carb, I’m beginning to wonder if my problem could be in the timing. Before I go fooling around with the timing, I wanted to get some advice from you all. So, can bad timing cause the car to bog down when coming off idle? Thanks
I had a bog like that with my newly rebuilt Pony Carb. I called them and they insisted that the bog is caused by retarded timing & that the best way to time it is with a vacuum guage instead of a light. I advanced the timing with my vaccum guage until just below where it started knocking & it pretty much cured the bog. I do seem to get it every so often again, but not like I did before.
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Old 06-24-2011, 01:35 PM   #7 (permalink)
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Quote:
Originally Posted by GTA6T7 View Post
I have a Ford Racing 306 with a new Holley 600 cfm carb. When I come off idle with light acceleration, the car bogs down before it catches. It seems to run fine at idle, cruise and when accelerating. I adjusted the accelerator pump spring from one extreme to the other and everything in between. It changed the nature of the bog but did not eliminate it.
Around the same time as I put the carb on the car I reset the initial timing to 12 degrees. Since I canít find the problem in the carb, Iím beginning to wonder if my problem could be in the timing. Before I go fooling around with the timing, I wanted to get some advice from you all. So, can bad timing cause the car to bog down when coming off idle? Thanks
I'm not totally familiar with that model Holley but,

Typically on the side of the carb, at the linkage, there is a cam shaped device with 3 holes in it...they are usually set @ #1 hole, try the #2 hole as this will advance the pump/diaphram & meteroring system faster.
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Old 06-24-2011, 02:04 PM   #8 (permalink)
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I'd hazard a guess to say there is not any defect in the accelerator pump system. The carb is most likely calibrated for an engine milder than the one you have, and as such the system will need fine tuning with a different accelerator pump cam and/or pump shooter. I'd try 2 degrees more timing, and see where that gets you. If there is a minimal improvement then I'd start by putting it back to 12 and get the acclerator pump assortment from Holley and go with one that offers more shot. Now that I think about it, you might even look at the pump cam you have now, most have a couple mounting holes, try it in a different one than is being used now. If you have a friend with some carb stuff you can also try a bigger shooter, don't know what they come with but even if you bought a new one they arent that pricey, probably has a 28 on it, maybe try or borrow a 31. I'm talking of course like you know what all the pieces are, if you don't please ask, no disrespect intended if you already know.
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Old 06-24-2011, 02:45 PM   #9 (permalink)
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What rear end gears do you have? My car, 302 weiand intake, Holley 600 carb, headers, mild cam does the same thing. Runs like a scalded dog but not off the line.
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Old 06-24-2011, 06:50 PM   #10 (permalink)
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What rear end gears do you have? My car, 302 weiand intake, Holley 600 carb, headers, mild cam does the same thing. Runs like a scalded dog but not off the line.
I'm running 3:55 gears with an AOD.
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Old 06-24-2011, 07:20 PM   #11 (permalink)
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i had same problem. My MSD dizzy was advancing timing degrees at idle and couldnt get timing to set right. When we finally figure out what was going on swaped in a new dizzy set the timing and everything was all good. I too though it might of been the accelerate pump but i did everything i could to try to adjust the carb but still same thing happened.
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Old 06-24-2011, 08:28 PM   #12 (permalink)
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Thumbup I think it's fixed

Well it wasn't the carb after all. I spent the last hour fooling with the timing to see if that affected the bog. I used a vacuum gauge to find the highest vacuum I could achieve and then set it back a couple of inches. The engine was purring like a kitten and I immediately noticed the bog was gone. It was so responsive to the go pedal I laid a little rubber when I gave it half throttle from a stop. My good fortune didnít last. Unfortunately my off idle bod got replaced by a bad miss at cruising speed. So I stopped on the side of the road with my trusty Ĺ inch wrench and backed off the distributor. I then drove it a little and adjusted it again. I did this three times before I found the setting where neither the bog nor high speed miss was obviously present. I guess itís fixed. I wish I could drive the car with more advance because it idled as smooth as silk and ran great out of the hole. :-) Thanks guys for all you help.
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Old 06-24-2011, 09:51 PM   #13 (permalink)
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Quote:
Originally Posted by GTA6T7 View Post
I have a Ford Racing 306 with a new Holley 600 cfm carb. When I come off idle with light acceleration, the car bogs down before it catches. It seems to run fine at idle, cruise and when accelerating. I adjusted the accelerator pump spring from one extreme to the other and everything in between. It changed the nature of the bog but did not eliminate it.
Around the same time as I put the carb on the car I reset the initial timing to 12 degrees. Since I canít find the problem in the carb, Iím beginning to wonder if my problem could be in the timing. Before I go fooling around with the timing, I wanted to get some advice from you all. So, can bad timing cause the car to bog down when coming off idle? Thanks

Never adjust the spring. Never.
I hope You can get it back to where you started.
The cc's of the squirters, the accelerator pump cams, throttle linkage and vac. secondary diaphragm can all be adjusted.
With the throttle fully open, you need to be able to have the clearance of a match book cover. Use a feeler gauge.
If you don't the pump arm will bottom out the diaphragm and you WILL tear a hole in it then.
Get a book on Holley carbs, it will pay you back 10 fold. You too can be a Holley god like me.
Don't forget the Power Valve too.
It prevents hesitation between the Idle circuit and cruse circuit,
just what you running in to.
Tell me you engine vacuum once the base timing is set and I will hook U up.

Best Regards,
joe the holley boy
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Old 06-25-2011, 02:37 AM   #14 (permalink)
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I think you need to have your distributor recurved. What are you running? Set it to where it runs good on the road, forget about the idle. Then park it, and with a timing light rev the engine to about 2500 (or whatever your freeway cruise speed is) and see what the timing is . Re-adjust it to where it idles good and revs good coming out of the hole, and take the reading at idle. Say it idles best at 14 degrees. And the rpm of the highway reading was 34. Take the distributor to a specialist and give him that info. Or if you have a Mallory or MSD you can do it yourself.
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Old 06-25-2011, 05:21 AM   #15 (permalink)
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Well it wasn't the carb after all. I spent the last hour fooling with the timing to see if that affected the bog. I used a vacuum gauge to find the highest vacuum I could achieve and then set it back a couple of inches. The engine was purring like a kitten and I immediately noticed the bog was gone. It was so responsive to the go pedal I laid a little rubber when I gave it half throttle from a stop. My good fortune didnít last. Unfortunately my off idle bod got replaced by a bad miss at cruising speed. So I stopped on the side of the road with my trusty Ĺ inch wrench and backed off the distributor. I then drove it a little and adjusted it again. I did this three times before I found the setting where neither the bog nor high speed miss was obviously present. I guess itís fixed. I wish I could drive the car with more advance because it idled as smooth as silk and ran great out of the hole. :-) Thanks guys for all you help.
Like my father used to always tell me, 90% of the time, the problem is in the ignition. I'm glad the vacuum guage approach worked for you. The miss on the other hand is a defective part, either a plug, wire or the cap is defective (even if new).
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