Question on bogging - Pontiac GTO Forum
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post #1 of 4 (permalink) Old 10-20-2017, 12:21 AM Thread Starter
 
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Question on bogging

Hey ya'll -

I'm trying to figure out where to tune....what to look at. 68 with 400 - not sure of the engine internals. Edlebrock performer intake, Holley 650.

If I mash down the gas, the engine will bog a little, sputter, then catch up and go. When that happens, it will eventually "catch up" and get going. But if I feather the gas just right, it'll burn the tires up.

The throttle response is great if you do it just right, but it seems to me that you shouldn't have to know the car like the back of your hand in order to let it rip, right?

How "should" the throttle response be in this context? Does this sound like a timing issue? Running rich? I'm betting someone else has had a similar performance experience and can point me in the right direction....

Thoughts?
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post #2 of 4 (permalink) Old 10-20-2017, 07:43 AM
 
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You can get a lean stumble, or a rich stumble ...if it is the carb. Vacumn secondaries also can cause that but at speed. Is this a s tumble off idle? Or at lower speeds?.....or is this a stumble from light throttle cruise to higher speeds?

One easy thing to check is the accelerator pump gap,...it is a screw on the left front bottom of the carb and the gap must be set right, thefloats in the carb must be right as well and the accelerator pump and the transfer slot and mixture right.

Look on the Holley web and watch their video's on setting float and acc pump gap. Mixture etc. start there.

Good luck
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post #3 of 4 (permalink) Old 10-20-2017, 09:37 AM Thread Starter
 
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Hey Lemansguy - Thanks for those points - I'm off to learn about setting the ACP...

This only happens from idle or very low speed. If I'm already at speed, it does just fine.

BUT...something else that I hadn't thought was related, but now I'm rethinking... I have noticed that it doesn't so much like to kick down. Car has TH400. I'f I'm already in 3, and go wide open, most of the time it does not kick down to 2. In "normal" acceleration, if I am going pretty slow like just after the shift to 3, if I go wide open it will drop back down to 2. But once I get a bit into third gear, it almost never kicks down. Normal, something in kickdown linkage, or related to my bogs?

Thanks again!!
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post #4 of 4 (permalink) Old 10-22-2017, 05:40 PM Thread Starter
 
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Well, I fixed the bogging.... Timing, timing, timing! Well, I did tweak on the carb too, but only on the idle. Basically, I went from 32 degrees of total timing to 36 degrees and it made a HUGE difference. After I adjusted the timing, my idle had jumped up, so I played with that a bit.

It started out at 9 degrees initial, and 32 total and went to 15/36. Then, I tweaked the idle until I got around 750 (769 on timing light).

Now - I cant get it to bog. Where before it would squeal a wheel, now it'll do a full on Paul Newman-white-cloud-of-death burn out. In addition to the crazy improved throttle response, just regular driving is all smoothed out. It sounds smoother, feels smoother and accelerates better in normal driving conditions.

And here I thought it drove pretty good before, just with the little bog problem. The timing change made a huge difference.

There's a thread in Gen Discussion that is related - I'll post details of the process and some pics there...

I do have some carb issues to deal with....that'll be for another weekend.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

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