My truck will idle at 600 rpm but I have no power off the line unless I idle at 1000.

[Hazieview]

So I’m confused. I can idle my truck down to 600 rpm and it idles fine. You can really hear the cam at the lower rpm. However, if I stomp the throttle the truck bogs down real bad before it takes off. It won’t even spin the tires. If I idle it up to 1000 rpm and I mash the throttle it will spin all day long. Also, at 1000 rpm, at idle, I can feel my truck wanting to roll when stopped so I have to keep my foot on the break. I have a 1500 stall.

I’m just curious on how RPM affects hard acceleration off idle.

My cam specs.
280°/290° Advertised Cam Duration
214°/224° Cam Duration @ .050"
.473/.497 Gross Valve Lift
Initial timing is at 18 degrees. Advance is at 35.


Any explanation? Thanks guys.

[geezer#99]

At what rpm is your initial of 18 measured at?
Is your balancer/timing tab accurate?

[Hazieview]

Good question! I actually unhooked my vacuum advance and reset my timing. I’m now at 12 degrees at an idle speed of 900 rpm and 35 at 3500 rpm.

[geezer#99]

Get your idle down closer to 700 and then set your initial.
At 900 you could be just into the mechanical timing.
Set your initial at 14 to start with.

Always plug off your vac advance to set initial.

[garyd1961]

Sounds to me like you need a bigger stall, 1500 and a big cam just doesn't go together.

[jamyers]

Accelerator pump, probably not giving enough of a shot to get from idle into the main circuits

[garyd1961]

Originally Posted by jamyers

Accelerator pump, probably not giving enough of a shot to get from idle into the main circuits

If the accelerator pump ain't working at 600 rpm it's not going to be working at 1000 either. Put a bigger stall converter in it and it will idle at 600 but rev up past 1000 when you hit hit the gas. Your cam has no power in the 600 range.

[GASoline71]

More pump shot nedded. When you set the idle higher your carb enters into the transition from off idle to the primary metering circuit. So you're pulling more fuel. Which is the job of the accelerator pump so you can stay at a lower RPM.

And I second the stall needs to be at a higher RPM. 1,500 is barely over stock.

Gary

[Hazieview]

Good info guys thanks for replying. My camshaft rpm range is from 1500 to 5500 rpm. I was thinking a 1500 stall should be fine for this cam.

It use to burn the tires down with no problems not too long ago. I put a new accelerator pump in it and set it to the hole that will give the biggest shot... Still don’t know what’s going on. I’m really hoping I don’t need a bigger stall. I’m going to idle it up to 900 rpms and see what happens.

[Hazieview]

I swear it seems like the accelerator pump but I replaced it with a bran new one.

So I ended up idling the truck up to 900 rpm with the truck in park. I slammed on the throttle and got a tiny backfire out of the carburetor. I fled town to 600 rpm and the backfire went away. Took it for a test drive and it still bogs down when I stomp the throttle but it gradually speeds up and takes off. It never dies. Just a weird bog. So instead of spinning the tires it just bogs down. I’ve had the exact same problem with a bad accelerator pump but I just changed that so now I’m stumped.

[Wrenchbender Ret]

Try raising the float levels a little.
George

[kwmech]

Which carburetor are you running?

[garyd1961]

Just because the advertised stall is 1500 doesn't mean that is what it will be. It depends on a lot of other factors what the actual stall is.

[Hazieview]

I’m running an Edelbrock 600 cfm. It’s undersized by about 50 cfm but it has been getting it done.

I don’t understand why stall would all of the sudden be a problem. I use to smoke the tires through all three gears with no problem at all. Right now it will spin the tires on a dirt road but if I put it on pavement it bogs.

[garyd1961]

U

Originally Posted by Hazieview

I’m running an Edelbrock 600 cfm. It’s undersized by about 50 cfm but it has been getting it done.

I don’t understand why stall would all of the sudden be a problem. I use to smoke the tires through all three gears with no problem at all. Right now it will spin the tires on a dirt road but if I put it on pavement it bogs.

I didn't see that in any of your other posts. From what I read I thought your problem started when you idled it down to 600 but it ran fine when idled up to 1000+. Popping through the carburator is timing off, bad carb, bad cam, or vacuum leak. I would check for vacuum leaks first.
Also what does the inside of your distributor cap and rotor button look like. When was the last time they were changed.

[jamyers]

Sure sounds like an issue going from the idle circuit, through the transition slots, into the main venturis - generally caused by an Accelerator Pump issue.

You might try dialing back the pump shot...

Or, open the carb up and make sure there's no trash in the transition slot passages, that would cause a stumble going from idle to the mains...

[Hazieview]

I wonder if it did get some kind of trash in the Carb. It just doesn’t make any since. I had this same issue before. I simply changed the accelerator pump and the issue was fixed. Now I have a bran new accelerator pump but the problem is still there.

I have an HEI distributor custom made by DUI. I’m going to change out my plugs and wires any way so I’ll see what happens after that. If I can’t figure it out I’m going to buy a new carburetor and just tear down my old carburetor to see if it has issues.

[cadillac_al]

How much vacuum is that cam making? It kind sounds like a vacuum leak to me. A vacuum leak will make the engine die down when you put it in gear and want to creep.

[Dead Parrot]

If I have read the thread correctly, the build as is used to work great and has recently stopped being great. If so, I don't see the choice of parts being too far off.

Which carb? If it is one of the Eddy 1400 variants, the power pistons are prone to getting gummed up. Try loosening the covers and cleaning both the pistons and cylinders. I have a 1405 on a stock 350 setup and when the power pistons start sticking, it will bog on a hard acceleration.

Other things to check:
The timing curve. Possible the mechanical is sticking and not coming in like it used to.
Transmission fluid level.
Fuel lines and filter.

[mattfranklin]

I don't know Edelbrock carbs, but I know a little about Holleys. Holley carburetors have a larger volume accelerator pump available for theirs, also more than a dozen different accelerator pump cam profiles. Maybe Edelbrock has similar accessories for their carbs?

[mooseboy84]

I can't speak about the cam specs and torque converter, but the reason you are having the issue is the accelerator pump. A lot of people hate on Edlebrock carbs, but they're fine for the most part. However, it is a known issue about the idle off circuit and lag on acceleration. You need a new accelerator pump.

Get a #1468. Its an accelerator pump with a much heavier spring and gives a good shot. I have 1406 and even adjusting all the way rich, it didn't really change until I got the 1468 accelerator pump, that will help tremendously.

http://jgronoj.weebly.com/hesitation-or-bog.html

Also, you should install a pressure regulator, I think I got a summit model for $50. That helped with the extreme gas smell by limiting the pressure to 6psi.