help with new 383 stroker issue

[88Stanger]

Originally Posted by Mike C

Having messed with multi-carb setups on 240z and motorcycles, usually a backfire out the carb is a lean condition. Needs more accelerator pump shot, faster pump cam timing or just to be enriched. A 600 cfm carb is probably set up WAY lean for a cammed 383. See if moving the stock pump cam to a the second position makes a difference (I'm assuming a Holley carb but if not check how to adjust accelerator pump voluem/timing on the Edelbrock.) Go up several sizes in the shooter and see if that doesn't improve things.

If it runs fine at idle and at cruise speed, it seems to be a transition thing which is either idle circuit too lean or pump shot too small etc. Increase your idle mixture richness as well. Sometimes that improves the transition between part throttle and full throttle and will cover the "hole" or backfire that's created when you stomp on it.

On Webers of Del'Ortos, the "idle" circuit controls mixture until around 3000 rpm when the mains come in. So it's imperative that you get that right or you have all sorts of driveability issues.

i hear ya on this, and you make a good point. I have tried Fitech fuel inj system, even increased the pump setting alot, and then tried the carb that i know is good.

[geezer#99]

What's your idle rpm?

[88Stanger]

Originally Posted by geezer#99

What's your idle rpm?

idle RPM from 1200 down to 800.

[randy500]

Did you check with vacuume gauge yet? Quicker and easier test than leakdown and more informative at this point.
If smooth gauge reading then find the vacuum leak which is causing the lean condition.

[88Stanger]

Originally Posted by randy500

Did you check with vacuume gauge yet? Quicker and easier test than leakdown and more informative at this point.
If smooth gauge reading then find the vacuum leak which is causing the lean condition.

I have a brand new vacuum gauge that i set up and was hoping to see something that would give me some direction, but it was only moving about 1/2 in if any but smooth really, low maybe 13in of vacuum is all. I seen nothing that would say what is crazy or wrong.

[88Stanger]

you guys are awesome, i really appreciate your time and ideas. I have a couple things to look at, but all in all, i see the engine coming out again soon.

[88Stanger]

to be honest, getting a new cam with more duration is ok with me and getting a 2400 stall instead of my stock stall. i would then take the existing roller cam i have now and install it into a good fresh 355 i have for sale or use in another possible toy. just a note. Removed and installed motor in the truck enough times to almost do it in my sleep.

[geezer#99]

So to sum it up, you've got a cold intake that creates a lean condition and no initial timing.
With your idle that high you're well into the mechanical timing so your initial is likely closer to 4-6 degrees.
It backfires or coughs because it's lean and retarded.
You can't easily change the intake but can bump your timing up to 20 initial to start with.
Then you can slow the idle down to 750 and more accurately set your initial.
And when you set your valves don't do the twist of the pushrods, just wiggle the slack out of them then go a 1/4 turn more.

[88Stanger]

I am honestly thinking that the issue may be as some of you have said, a valve is sticking or not working correctly. Even though the heads are brand new Edelbrock aluminum RPM heads, they could be bad. After sleeping on it, I think I'll pull them off, tear them all down and inspect them,rebuild and off needed I can use my buddies iron race heads to see what happens. If same issue with them or I find a problem with new heads, answer found. If not and it does the same with iron heads and no issues with aluminium heads, then I'm to believe it's a cam issue at this point I think. Maybe time to look at different brand cam at that point, just a thought.

[geezer#99]

Your valves aren't sticking, your heads are fine, swapping heads won't change anything except the size of your wallet!
Just do the free things first!
Put a bunch of timing in it, get your idle down where it belongs and then drive it.

What do you have for a timing light?

[88Stanger]

Originally Posted by geezer#99

Your valves aren't sticking, your heads are fine, swapping heads won't change anything except the size of your wallet!
Just do the free things first!
Put a bunch of timing in it, get your idle down where it belongs and then drive it.

What do you have for a timing light?

i have an adjustable timing light, new.

Ok, ill do a whole lot of timing in it. Then ill try to swap the 5 and 7 wires. my issue is that when it is running it will not run enough to drive it, or at least it did not earlier. who knows, after adding timing, who knows.

the head swap will only cost me head and intake gaskets as i already have a set to try.

[Marine-58]

I totally agree with Geezer, do the free things first.

From what Aussie said earlier,

"I have also seen cams boxed wrong and you end up with a 4/7 swapped firing order cam"

It is worth a try to just swap those 2 plug wires. Someone else had mentioned getting 5 and 7 reversed. Depending on how the plug wires are ran, it is easy to make a mistake tracing them from the plug to the cap.

[mattfranklin]

What Geezer said. Adding more timing is free and fast, at least as a check. Takes three minutes.

[geezer#99]

Remember to plug off the vac advance line.
And your increased timing will speed up your idle.
Get the idle back down under 800 and put your vac gauge on and adjust your mix screws.
Be conservative, start with an extra six degrees and then go from there.

[88Stanger]

Originally Posted by geezer#99

Remember to plug off the vac advance line.
And your increased timing will speed up your idle.
Get the idle back down under 800 and put your vac gauge on and adjust your mix screws.
Be conservative, start with an extra six degrees and then go from there.

Ok. I do know to remove the vacuum from the distributor.
I'll give your thoughts a try

[AussieinNC]

Wondering how you are progressing with the 383 issue....

Havent seen an update today...

Hope you are doing ok...

[88Stanger]

Originally Posted by AussieinNC

Wondering how you are progressing with the 383 issue....

Havent seen an update today...

Hope you are doing ok...

Thanks for asking.
Tried timing, still no go.
Try more this weekend. Really frustrating so far. I k pw God willing I'll figure it out, especially with your guys and gals help.

[KQQL IT]

Afr meter time.
My 400 wanted a bunch of accelerator pump cam.

[geezer#99]

Originally Posted by 88Stanger

Thanks for asking.
Tried timing, still no go.
Try more this weekend. Really frustrating so far. I k pw God willing I'll figure it out, especially with your guys and gals help.

So how many more degrees initial did you try?