Engine Idle Drops A Lot in D

-
74Dart318

74Dart318

Well-Known Member
Joined
Mar 20, 2009
Messages
505
Reaction score
148
Location
az
Hey guys,

I have been researching this and it seems like I might need a larger stall converter for the issue. I wanted to see what all the FABO experts think :)

Car: 1974 Dodge Dart Swinger
Engine: 318 Bored .030 with KB pistons
~9:1 compression
Indy LAX heads
TTI shortys, full exhaust
Eddy air gap, Eddy 650 with elec choke
Comp Cams XE268H (Duration @ 0.006": 268° / 280°; Max Lift w/ 1.5RR: .477" / .480"; Lobe Separation: 110°; Intake Centerline: 106°)
Trans: Rebuilt 727, shift kit, stock converter
Rear-end: 8.25, SG, 3.21 Gears

Initial timing set around 10° which I will probably need to check again now that it has full exhaust. I have the orange box installed currently with a Rev-N-Nator I haven't put on yet. Also running a Summit distributor and MSD Blaster 2 coil.

Not sure what else to list that will help. Thanks in advance!
 
check your AFR. I was lean on a carb and it did the same thing. Just try opening the meter screws 1/4 turn each and see if there is any effect, then you can turn them back if nothing.
 
Need not much convertor, but yes a true 2600-2800 stall would help.
This where quality will show, need not a 700 converter, but spend at least 400.00, even a turbo action 'Tight' 3000 would do it.
 
Last edited:
Thanks guys.

I should also mention I'm running 1500 for P and like 700 rpm in D
 
Sounds like we have the same build in our 318's. 10* seems a bit low. 18* initial and all in at 40* and 3500 rpm is where mine developed the most power on the dyno with no detonation and 9.8 compression, premium E10. I had the same issue with the stock converter. running the vcan to allow 24* at idle helped alot. A 2800 loose converter in the 904 was the fix. it absorbed the lope at idle and allowed me to idle in gear at 800 rpm and the stalling out issues were gone. It's a screaming high revving beauty but develops it's power high in the rpm range and is why I'm putting in a forged 408 stroker now with brians (IMM Racing) worked indy heads to develop the power lower in rpm. found a place that sells 93 clear ethanol free locally...I'll be running that in a few weeks after I finish up the fitech efi installation.
 
Got the same cam in a 360 in 73 Duster except I am using a MP race electronic distributor with full advance ......Initial timing is 35 degrees....no vacuum advance...Idles easy at 800 rpm in gear...
 
Normally the drop would be 100-200 RPM on a mild engine like that. I think my (similar) 340 idles at 800, and in D it drops to 650. "Stock" converter, same cam , 780 vacuum Holley. However, my initial timing is 18°, with a total of about 35°. That really seems to help.
 
Thanks everyone for the help so far and suggestions. I played with the timing a little yesterday.

With the orange box it was still following this large rpm drop pattern.

So I swapped in the rev-n-nator to see what it would do. Without changing anything it made a big difference. Now it is closer to 1000 rpm in P and ~650 rpm in D. I think I can continue to advance some more as well.

I was trying to check total timing and might set it based off of that instead of initial timing.

Should the total timing be set and checked at 3500 rpm?
 
Don't worry about the total timing until you figure out what it wants for initial. If you increase the initial advance and the rpm's increase, the engine wants it. Where did you end up for initial? It should be around 20, maybe more. Once you put more initial timing in it, limit the total to around 35 and play with the curve.
 
mopowers said:
Don't worry about the total timing until you figure out what it wants for initial. If you increase the initial advance and the rpm's increase, the engine wants it. Where did you end up for initial? It should be around 20, maybe more. Once you put more initial timing in it, limit the total to around 35 and play with the curve.
Click to expand...

This is great. I haven't done this really much before on my own. I was worried that something wasn't quite right.

I would increase initial timing and rpm would increase as well. I wasn't sure if that was good or not. So I will look at it again tonight and continue to add timing. I am guessing I will get to a noticeable point where adding timing will negatively effect rpm and how the engine is running, right?
 
74Dart318 said:
This is great. I haven't done this really much before on my own. I was worried that something wasn't quite right.

I would increase initial timing and rpm would increase as well. I wasn't sure if that was good or not. So I will look at it again tonight and continue to add timing. I am guessing I will get to a noticeable point where adding timing will negatively effect rpm and how the engine is running, right?
Click to expand...

If you give it more ign advance at idle and rpms increase, lower the idle speed at the carb and try to give it a little more. You can use a vacuum gauge as a tool too to see where you get the most vacuum. Usually, you'll get to a point where, the starter will kick back when you go to start it if you have too much initial advance in it. That's usually the limiting factor. Don't be surprised if you end up with 24* initial (without vacuum adv hooked up). Just remember to dial back the mechanical advance in the distributor so you have around 35* total (without vacuum adv. hooked up) before you put a heavy load on the engine.
 
Your 800rpm drop is indicating trouble. For some reason your engine is down on idle-torque. It could be in the idle-timing, or in the low-speed circuit, or a lack of idle-vacuum,or in the TC.
I can usually make a combo like that idle in gear at 650 with 12to 14* of idle-timing. Keep at it; you'll get there.
But I gotta tell you, that cam will not like that 1750rpm type convertor at the factory compression ratio.At a true 9/1Scr, I would suggest a minimum 2800. With your 3.21s I might go with a little more yet.Yeah Ima thinking 3000.
So make it easy on yourself and slap a TC in first, then carry on. You're on the right track .
I would recommend a cranking compression test. A 9/1 318+.030 should make over 145psi. The more pressure you have, the lower the stall can be, for a DD.
 
Any sign of a vacuum leak? Vacuum leak will allow air to bypass the throttle blades and not pull as much fuel threw the venturri, and will raise idle speed. Then, most folks tune idle mix (more fuel) and speed (less idle throttle blade) to throw more fuel at it to idle right, blind to the vacuum leak. You can't get a lower idle because there is too much bypass air leaking by the carb. When you drop it into gear, less and less available vacuum = less fuel, less and less idle speed.

Just my 2c on issues I see a lot which turn out to be a simple air leak.
 
Thanks everyone for the input.

I finally worked on it again last night. I found a trans line leak and finally got new lines last night and fixed that issue.

I increased initial timing and it is right around 20° and 1000 rpm in P. It seems pretty happy here. In D it is dropping to about 600-650 rpm.

Before it was almost dying at 700-800 rpm now it seems to run pretty smooth at 650 rpm in D.

I was going to try and use the vacuum gauge to work on further tuning tonight. I have not done this before, any suggestions?

Also, I have the Edelbrock AVS thunder that has a secondary flap and the torx screw is stripped (this is a refurb carb). So I need to figure out a way to adjust that also.
 
Did you make sure the vacuum advance is disconnected?

That's still a huge RPM drop for that cam. It probably wants more initial timing.
 
mopowers said:
Did you make sure the vacuum advance is disconnected?

That's still a huge RPM drop for that cam. It probably wants more initial timing.
Click to expand...

I can play with it some more tonight. I did have the vacuum advance disconnected. Actually just hooked it up after driving last night for the first time since rebuild.

I think you mentioned limiting total timing. Is this only done by actually modifying the distributor?
 
Yeah there's still a problem, you need to get back to basics;

1) compression test
2) Leakdown test
3) idle manifold vacuum reading.At 700/750rpm in Neutral and with about 16* idle-timing. Why those numbers? Cuz that is closer to normal settings. If you give me a number like 18 inches at 1000rpm with 20 degrees, well that number is artificially high and is next to meaningless, as a diagnostic aid. .
 
Give us your vacuum readings. Something is not right that more initial advance is not going to fix; this cam and stock TC should have a 100-150 RPM drop tops.

It may be that you are being fooled on the initial timing and it is actually mechnically advanced some in P; the mechanical advance springs may be too light and adding some timing to be 20* at 1000 RPM, and then when the idle start to drop in gear, the mechanical advance springs pull back timing, causing the idle to drop even more. Do you have the history on this distributor?

Also, tell us what PCV valve you have with the vacuum readings. The wrong PCV can help cause this problem.
 
I'll guess a vacuum leak somewhere. No way should that cam with 20* of timing require a 1K idle and a 400 rpm drop.

Is it dropping timing in gear. Might want to check that.
 
nm9stheham said:
Give us your vacuum readings. Something is not right that more initial advance is not going to fix; this cam and stock TC should have a 100-150 RPM drop tops.

It may be that you are being fooled on the initial timing and it is actually mechnically advanced some in P; the mechanical advance springs may be too light and adding some timing to be 20* at 1000 RPM, and then when the idle start to drop in gear, the mechanical advance springs pull back timing, causing the idle to drop even more. Do you have the history on this distributor?

Also, tell us what PCV valve you have with the vacuum readings. The wrong PCV can help cause this problem.
Click to expand...

I used this PCV valve
https://www.summitracing.com/parts/frm-fv163dp
 
You got the timing set. Now slow down the idle speed to 800 or so in nuetral, and set the mixture so it's not lean at idle. It's dropping that far becuase the carb is not set right. Slow it down, add some fuel, and it will be fine.
 
You must log in or register to reply here.
-

Back
Top