Help! 454 bog/die on accel

[rich weyand]

When you buy the step-up springs, you get all five sets in one package. Vacuum pulls the pistons down against the spring pressure. Stiffer springs will push the pistons up (and richen the mixture) sooner on throttle application. Go to the max step-up.

I talked to an engine tuner buddy tonight. I asked him about your situation, and his diagnosis is that you are way lean. Backfire through the carb is the giveaway to him. Having the engine heat up quickly and having a hard time cooling it is another sign.

When you pop the throttle plate and air rushes in, the mixture goes way leans and the fire goes out.

Fiddling with the accelerator pump can address that somewhat, but not if you are tuned too lean.

Do you have any idea what your mixture is? What jets and rods are in the carb?

[Dylan86]

Originally Posted by rich weyand

When you buy the step-up springs, you get all five sets in one package. Vacuum pulls the pistons down against the spring pressure. Stiffer springs will push the pistons up (and richen the mixture) sooner on throttle application. Go to the max step-up.

I talked to an engine tuner buddy tonight. I asked him about your situation, and his diagnosis is that you are way lean. Backfire through the carb is the giveaway to him. Having the engine heat up quickly and having a hard time cooling it is another sign.

When you pop the throttle plate and air rushes in, the mixture goes way leans and the fire goes out.

Fiddling with the accelerator pump can address that somewhat, but not if you are tuned too lean.

Do you have any idea what your mixture is? What jets and rods are in the carb?

This is very very useful and it's what I have been thinking all along. I'm just unsure of the correct carb adjustments to completely fix this concern. I'm running an edelbrock 1407. All jets and sizes are out of the box. Nothing's changed yet. This link is the manual with all the specs http://www.edelbrock.com/automotive/...ers-manual.pdf

The Max step up is the blue springs?

[geezer#99]

So!
6 and 12 or 12 and 12?

[Dylan86]

Originally Posted by geezer#99

So!
6 and 12 or 12 and 12?

6 and 12

[rich weyand]

No, blue is the minimum, 3#. You want the maximum, 8#, which is plain metal. This will kick in the power circuit (richer mixture) soonest as the throttle is opened.

For tuning my Edelbrock, I got an air/fuel ratio meter (AFR meter). This allows you to see the AFR as you drive, and how lean or rich you are. They're not free, but it really lets you get the mixture nailed down.

Amazon.com: NGK AFX Powerdex AFX Air-Fuel Ratio...

[Dylan86]

Why does everywhere I look say to switch to the blue spring?

[rich weyand]

Originally Posted by Dylan86

Why does everywhere I look say to switch to the blue spring?

Dunno, other than that it is easy to get turned around on vacuum and how the system works. So here's the long explanation.

The springs are rated in pounds, from 3 (blue) to 8 (bare metal). The bigger the number, the stronger the spring. The way they work is: manifold vacuum from the underside of the throttle plate pulls a piston down against the spring. If the vacuum is strong enough, it overcomes the spring, the piston moves down, and with it the metering rod moves down. The end of the metering rod is narrower than the middle, so as the rod moves down, it blocks more of the jet and the mixture leans out.

The vacuum can overcome a weaker spring easier, so the piston will spend more time in the down (lean) position if the spring is weaker (3# blue) than if the spring is stronger (8# bare metal). At idle the engine pulls a lot of vacuum and the pistons are down. As you open the throttle plate, the vacuum decreases until the spring wins. The stronger spring will win sooner, where the weaker spring will keep the needles in the lean position longer.

I run the 8# springs on my 350. I have bogging problems at mid-range throttle settings with the weaker springs.

[Dylan86]

Originally Posted by rich weyand

Dunno, other than that it is easy to get turned around on vacuum and how the system works. So here's the long explanation.

The springs are rated in pounds, from 3 (blue) to 8 (bare metal). The bigger the number, the stronger the spring. The way they work is: manifold vacuum from the underside of the throttle plate pulls a piston down against the spring. If the vacuum is strong enough, it overcomes the spring, the piston moves down, and with it the metering rod moves down. The end of the metering rod is narrower than the middle, so as the rod moves down, it blocks more of the jet and the mixture leans out.

The vacuum can overcome a weaker spring easier, so the piston will spend more time in the down (lean) position if the spring is weaker (3# blue) than if the spring is stronger (8# bare metal). At idle the engine pulls a lot of vacuum and the pistons are down. As you open the throttle plate, the vacuum decreases until the spring wins. The stronger spring will win sooner, where the weaker spring will keep the needles in the lean position longer.

I run the 8# springs on my 350. I have bogging problems at mid-range throttle settings with the weaker springs.

Thank you. Makes allot of sense! Carbs are new territory for me. Do you think this will stop the backfire through the carb also?

[rich weyand]

Originally Posted by Dylan86

Thank you. Makes allot of sense! Carbs are new territory for me. Do you think this will stop the backfire through the carb also?

Probably not. I think your basic tune is off in the power circuit. You probably need bigger jets, though you may just need to go down in diameter on the rods. You won't know for sure what is going on without some kind of AFR meter.

One thing that may help is a heat insulator between the carb and the manifold.

Read this thread:
http://www.hotrodders.com/forum/edel...gs-199736.html

[LynnJr]

Dylan
You set the idle mixture with a vacuum gage attached and adjust until you get your highest reading.The throttle plates need to be closed so if you set the idle up lower it back down.
Once you find your maximum vacuum you divide it by 2 and put the proper spring in it.You pick the spring by halving the vacuum reading.
If your plugs are gas fouled you want the secondaries to kick in sooner.

[Dylan86]

I ordered the spring kit. Richer metering rodd and bigger accel pump squirter. I'll play around with those and see if I get an improvement. Anyone know how to replace the accelerator pump jet/squirter?

[rich weyand]

Originally Posted by Dylan86

I ordered the spring kit. Richer metering rodd and bigger accel pump squirter. I'll play around with those and see if I get an improvement. Anyone know how to replace the accelerator pump jet/squirter?

How did you know which rods to get? There's about fifty of them.

The accel pump jets are screwed to the underside of the top of the carb, so you need to order the gaskets, too, for putting the carb back together. They come in a five-pack.

While you are in there, make sure to adjust the floats. They will not be right.

[LynnJr]

Originally Posted by rich weyand

How did you know which rods to get? There's about fifty of them.

The accel pump jets are screwed to the underside of the top of the carb, so you need to order the gaskets, too, for putting the carb back together. They come in a five-pack.

While you are in there, make sure to adjust the floats. They will not be right.

And adjusting the floats was not mentioned earlier as well?

[rich weyand]

Yeah, keep us posted. I'll help out if I can: I can take that carb apart in my sleep.

You really, REALLY should consider springing for the NGK A/FR meter, though. You'll be able to dial it in exactly, which will save the purchase price on gas in the first year.

[LynnJr]

Dylan despite what you might read here Edelbrock knows how to tune there own carb.They want you to measure your vacuum so you get the right spring for your engine.If your engine has 16 pounds of vacuum the 8 spring is what they want you to use.
On free flowing heads creating more vacuum I have been building engines since most of the posters here were in diapers and I have never heard that before.Most engines built with free flowing heads have very large duration camshafts in them to take advantage of the extra flow and have very little vacuum at idle.
That is exactly why big cams cause problems with power brakes.
I would do a google search for Edelbrock carb bogs on acceleration and read 50-75 posts on what actually fixed the issue.
You can do the same thing on You Tube.
Good Luck with your motor.

[Dylan86]

I don't really care if it's edelbrocks info or a guys personal experience I'm just wanting it to run right. I got my springs in I tried the spring according to half my vacuum and it still bogged then threw the 8" springs in and it fixed my bog. So I guess personal experience won this round....Just now need the jet to fix the lean under heavy acceleration.

[rich weyand]

OK, here's what's going on. LynnJr is right in that Edelbrock says the springs should be half the vacuum. (I've been saying the springs in pounds (#) instead of inches, because that's how springs are normally rated, but Edelbrock labels them in inches, to correspond to inches of vacuum.) And that's probably close for most applications. BUT: you and I suspect you are running way lean. The pistons up is the richer position, and you can run an engine way rich and it will still run, but way lean and the fire goes out, as you have seen.

Thus my recommendation: put in the biggest springs and see what that does. Now, once you get the cruise circuit tuned, you may be able to back off a size, see what that does. If it's still OK, do it again. When you get a bog, back up one.

So, LynnJr is trying to hit the sweet spot right off. I am saying go to the heaviest spring first and see what you have. You can always back off -- move the onset of the richer power circuit down the throttle pedal -- and walk to the correct setting by testing. Engines are all so different, they breathe so differently because of the cams, that testing is more valuable than instructions written for the generic case.

I'm curious as to what vacuum reading you get at idle. It may be the case now with the 8" springs that you are *always* in the power circuit -- that the vacuum is low enough that the springs always win, and, given how lean you are, that is helping a lot.

In my case, I think I am pulling about 18 inches of vacuum at idle with my marine cam. I actually had to stretch the 8" springs to get my power circuit to kick in soon enough.

You are still going to be shooting in the dark without getting an A/FR meter on that beast. Do you know anybody around your parts who has one you can borrow?

[rich weyand]

Dylan, another question. When you say "Just now need the jet to fix the lean under heavy acceleration", do you mean when the secondaries start to come in? On the Edelbrock, you can feel it mechanically in the throttle pedal when you pick up the secondaries. Is it running right until then, and going lean when you hit the secondaries? Or is it still going lean before you hit the secondaries?

[Dylan86]

Originally Posted by rich weyand

Dylan, another question. When you say "Just now need the jet to fix the lean under heavy acceleration", do you mean when the secondaries start to come in? On the Edelbrock, you can feel it mechanically in the throttle pedal when you pick up the secondaries. Is it running right until then, and going lean when you hit the secondaries? Or is it still going lean before you hit the secondaries?

I'm not 100% sure to be honest if it's before or after... I don't feel a change through the pedal. All I know is when your giving it more throttle (above quarter throttle accel) it seams to still act lean and feel underpowered like a hesitation. But the bog causing me to not be able to accel unless babying it is gone. I'm running 12-13 inches at idle. And no I have to order a meter and it's over a week away... I also retimed a bit more advanced 35° total. And used the upper vacuum port for my advance. It seems to like that more also.

[rich weyand]

Interesting that it likes ported vacuum. A lean mixture burns slower, so you would think it would like the advance at idle. 35-36* of total advance sounds right to this SBC guy, but I don't know if that sounds right or not for a BB.

At least it sounds like you have it now so it's driveable. Getting the meter on it will give you the answers to a lot of questions, that's for sure!

BTW, for the meter, the bung for the O2 sensor has to be welded/brazed into the exhaust. My recommendation is to weld it into the exhaust pipe a few inches behind the header flange. The sensor has to be at least a bit above horizontal, in the upper half of the pipe, so it doesn't catch water and debris. I had a muffler shop install mine. They cut a 6" length out of the exhaust pipe, drilled the hole, brazed in the bung, cleaned up the threads with a tap, then brazed the section of exhaust pipe back in.

When putting the meter in, I screw the O2 sensor in first. I drop that end of the wire harness down the front of the firewall, and go under the truck and plug in the O2 sensor. Then I hook the wire harness around the drivers side windshield wiper shaft and run it in through the vent window. I put the meter in the recess in the dash with a piece of foam around it to hold it in place (I don't have A/C, so I have that little storage recess) and I plug the meter into the cigar lighter. They say to hard wire it, but it's not a permanent install and the cigar lighter works fine for occasional testing.

[Dylan86]

The trucks not lean at idle. In fact it's a bit rich. So the lower advance seems to be good. And ya I'm going to need to get that meter/ sensor to properly tune this in.