Help! 454 bog/die on accel

[LynnJr]

Dylan
Sorry about that there are two caps held by a couple torx head screws and the springs are called step up springs.

[Dylan86]

Originally Posted by LynnJr

Dylan
Sorry about that there are two caps held by a couple torx head screws and the springs are called step up springs.

Thank you. I will order it and give it a shot. I'm just guessing now anyways haha

[geezer#99]

So you built the motor!!
Did you do all the assembly yourself?
Did you put the cam/lifters and timing chain in?

[Dylan86]

Originally Posted by geezer#99

So you built the motor!!
Did you do all the assembly yourself?
Did you put the cam/lifters and timing chain in?

I did everything yes.

[geezer#99]

I'd bet you got your timing gear off a couple teeth.
Did you align the dots at 6 and 12 or at 12 and 12?

[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 geezer#99

I'd bet you got your timing gear off a couple teeth.
Did you align the dots at 6 and 12 or at 12 and 12?

I have build over a dozen old chevy blocks. There is no chance it is wrong without any doubt.

[geezer#99]

So!
6 and 12 or 12 and 12?

[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?

[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 LynnJr

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.

Yup. Then you take it out and drive it and find you have a soft spot in the middle of the primaries, and you go back home and put the 8# springs in it. BTDT.

[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

Yup. Then you take it out and drive it and find you have a soft spot in the middle of the primaries, and you go back home and put the 8# springs in it. BTDT.

And Edelbrock who makes the carb is lying to all of its customers because that helps sales?

[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]

Originally Posted by LynnJr

And Edelbrock who makes the carb is lying to all of its customers because that helps sales?

If manufacturer's instructions were all complete and accurate and specific to our trucks, we wouldn't need forums to figure this stuff out. Manufacturers are 1) sometimes wrong (see adjacent thread about 350/290hp that GM says to run without vacuum advance, which is complete nonsense), 2) write their instructions generically to a wide variety of engines and vehicles, and 3) write their instruction to a wide variety of goals (mileage vs. performance etc). With heads that flow well, he's going to be pulling a lot of vacuum. The 8# springs may not even be enough. I had to stretch mine to get the transition right.

And adjusting the floats was not mentioned earlier as well?

Just a reminder while he's in there for the accel pump not to forget about the floats, along with some additional information: they don't come set right from the factory.

[Dylan86]

Thank you Rich you have been a huge help. I should be getting all my carb components in soon. I'll update you on how it goes.

[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.