Timing - BTC, ATC and carb

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Aug 22, 2004
San Antonio, Texas
Please check my thoughts and add to them...refers to a 70 460 Ford engine. Timing advanced to far, carb was set up to run right. Timing is retarded to get the pinging out. Pinging gone, timing is now set to factory spec of 10 BTC. Now it bogs down on acceleration. I'm thinking I need to go one(two?) step leaner on the metering rods in the Edelbrock 1406 to fix the bogging down. That sound right? Any other pointers/suggestions?
It bogs from a dead stop? On an Edelbrock carb, changing the pump arm location can make a big difference. What hole is yours currently in? I think they come out of the box in the middle, try moving it to the upper hole, like the picture shows. A bog off idle, is usually a lean condition.
Mine is already in that position. Bog is a lean condition? So that means by retarding the timing back to factory specs I now need to put MORE gas in? Makes no sense to me...please explain.
If it didn't bog with the timing advanced, but it does when retarded, you may need to recurve the distributer advance with lighter springs, or limit total advance in the distributor and run more 'timing lead'
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It kind of hard to offer advice when you still haven't said WHEN IT BOGS! Pump arm is irrelevant if it bogs at speed.
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Originally Posted By: sasilverbullet
Mark - from a crawl, stomp on gas, get bogging.
Since it's as easy as it gets, I just start by trying different settings on the pump arm. If it's all the way one way, try the other way. It made a big difference to me in the past.
A stumble on acceleration is a lean condition. Is it squirting a good amnount of fuel out of the squirters when you move the throttle with the engine off? You can buy different springs for the acceleration piston to add more or less fuel and different squirters also. Often on these Edelbrock carbs the acceleration piston gets a tear or shrinks. That car should have 10-1 compression. It's designed for high 90's octain which isn't available today so it's never going to run as well as it did in 1970 unless you go buy race gas. Todays 91 octain is = to 1970's regular.
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^^^ pretty good post until you commented on fuel quality. Simply not true, octane is simply measured differently now. To the OP, watch the throat of the carb as you move the linkage from idle stop. At the SLIGHTEST movement there should be fuel squirted. If not you may get a stumble. That big motor needs a large sustained squirt as it comes up off idle. You may also have the timing off, retarded timing may cause a bog off idle. Forget the springs as they aren't playing a part at slow engine speeds.
Originally Posted By: Chris142
Todays 91 octain is = to 1970's regular.
I think that's correct. Leaded regular back then which I think was rated by RON was probably equivalent to about 89-91 AKI today and premium leaded about 95-98 equivalent today. Octane had to be higher because compression ratios were much higher before the switch to unleaded a year or two later. I don't think a 1970 model with 11-12:1 CR would run good with today's 93, but a 10:1 CR probably would run OK on today's premium. But you still have the pesky problem of no lead and ethanol. Anyway I think the accelerator pump shot needs enrichment.
On the timing - I just retarded it till the pinging went away, which happened to be 10 BTC, the factory setting. I have the calibration kit from Edelbrock for the 1406. Right now I'm two metering rods richer than stock and I'm running the pink springs, yellow was stock. question - Does retarded timing require more fuel to accelerate properly?
Originally Posted By: SteveSRT8
Forget the springs as they aren't playing a part at slow engine speeds.
I'm not talking about the Springs that go with the metering rods and inside the metering pistons. On the upper side of the Accelerator piston is a spring and the amount of stiffeness this spring has also determines how long of a squirt as well as when. A stiff spring is more sooner and a light weight spring is less later.
Originally Posted By: sasilverbullet
On the timing - I just retarded it till the pinging went away, which happened to be 10 BTC, the factory setting.
Vacuum hose disconnected?
Yes, vacuum hose disconnected when checking timing. Ok on the spring - the carb is only 6 months old so the spring/seal should still be ok. Will double check though. question - Does retarded timing require more fuel to accelerate properly?
Before you do ANYTHING else, make sure that a) your vacuum advance is disconnected when you set the basic timing, and b) you connect it to ported vacuum when you do re-connect it. There are applications where non-ported vacuum (manifold vacuum) is OK for vacuum advance, but not in most applications. And the symptom of manifold vacuum being used where it shouldn't be is... (wait for it!)... huge bog on acceleration. If you don't have a ported vacuum port on that carb (or don't know where it is) just go for a test drive with the vacuum advance disconnected and the vacuum port plugged. I'll bet you a virtual beer that the bog goes away.
Originally Posted By: sasilverbullet
Just looked - it's connected to ported vacuum.
Drat. In that case, the next thing I'd do is determine for sure if its a lean bog or a rich bog. My bet is lean, because it takes a metric poopload of fuel to make an engine (especially a big block) actually bog down due to being over-rich. A lean bog is also much more abrupt and can be accompanied by a backfire, whereas a rich bog isn't even so much of a bog as it is a slow ramping up of power with some shuddering and black smoking. If its lean, then step one is to fiddle with the accelerator pump shot- make it bigger and faster by adjusting the linkage as someone else mentioned. After that, before you change the metering rods I would go to stiffer metering rod SPRINGS, which will put the rods on the rich step sooner.
Ah. then go the OTHER way on the accelerator pump. Make the shot slower and smaller (move the pump end further from the fulcrum and/or the throttle end closer to the fulcrum).
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