RPM Drop From Nuetral to Gear

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mopowers

mopowers

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I seem to be having a heck of a time tuning the 340 in my Dart. It seems to run great in park, but as soon as I drop it in gear, RPMs drop from about 900 to about 500 and kills the engine. The only way I can get it to run in gear is to bump the idle past the transition slots in the carb which nullify the idle mixture screws.

I realize I need to address the timing first, but here's the basic combo: 340, torker intake (soon to be RPM airgap- will swap intakes this weekend), 750 Holley DP, convertor is likely stock but unknown, 727, 3.91s, 28" tire.

As for the cam- that's another unknown. I was told when I bought it, that it's a MP purple shaft, but I'm not sure which one. It's likely either the 280* or 284* hydraulic flat tappet. Do you think the stock convertor may be to tight for either of these cams?

This motor seems to love a ton of initial timing. I set it at 22* initial and it starts fine and wants more. Weird??? I set the timing in Park, but will check it in gear this weekend if I can get it to even run in gear. When I set the timing, it seems to bounce around at idle too. Is this a sign that the springs are too soft??? I'm using a MP orange box and new adjustable MP distrib. Not sure what springs are in it, but will have a look this weekend as well- they may have been changed by the previous owner.

So, what should be my plan of action?? I know I need to nail down the timing first, but how should I go about it if I can't even get it to idle in gear? I have extra butterfly throttle valves for my carb. Maybe drill a couple holes in them to help me get this thing to idle in gear??

Thanks for all the help guys. I realize I'm being really ignorant by asking these basic questions, so make fun all you want. :prayer: I just want to drive this thing.
 
Also, I had a 1406 edelbrock 600 carb on it too and it was acting the same way. Couldn't get it to idle in gear.
 
Put a vacuum gauge on it.....You may be opening the power valve when the rpm drops?
 
As for the cam- that's another unknown. I was told when I bought it, that it's a MP purple shaft, but I'm not sure which one. It's likely either the 280* or 284* hydraulic flat tappet. Do you think the stock convertor may be to tight for either of these cams?
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no doubt.. especially if its the 284/484 mp grind. that baby wants like a 3000 stall and a 3:91+ gear.
 
I can get the vacuum around 10-10.5 in park. Not sure what is is in gear because I haven't really been able to get it to idle in gear without opening the throttle waaayy open (past transition slots)

Power valve is 6.5 in pri, blocked in sec side.
 
I have a 750 DP as well, mine has 4 corner idle. I took off the carb and opened the secondary throttle plates some, so I could close the primaries a little. There is a small set screw in the baseplate. Are you running vacuum advance? If so plug it and see if it makes a difference.
 
Hi mopowers, motors with a lot of cam duration have this problem. Set timing in gear. Make sure you do it safely. FST73 makes a good point and so does oldmanmopar. You should be able to solve this one but it does need a gear. Our legal d/sa '69 Cuda 440 has a cam of 330d. of duration, the lift is limited to .450 by rules. It won't idle less than 2,400 rpm
 
mopowers,
I'm not an expert but here's my 2 cents:
1) does your dist have vacuum advance? If yes, running off manifold or ported? Is your 22* of timing without it?
2) Before drilling the throttle blades, have you tried opening up the secondary blades a hair so that you can draw a bit from the secondary circuit? You should be able to close the primary blades back once you do this.

(looks like qkuda beat me to it)
 
I'm with abodyjoe on this one I use that 484/284 cam a lot it was the stock hemi grind cam. If you don't have at least a 3000-3200 stall it will not idle in gear the hemi's had what was called the J converter and everyone I have had stalled around 3200. The only other thing is make sure you have not vacuum leaks around the intake if the heads have been milled or the block decked the intake gasket may not be sealing real good. one easy way to check that is pull the pcv valve out of the valve cover and get a propane cylinder with a torch head on it and some rubber hose put the hose in the valve cover and turn the gas on if the rpm's go up you have a vacuum leak do both sides of the engine just use the oil filler cap or breather hose on the other side. Good Luck
 
Also, a vacuum secondary carb will help but not at idle. You have enoough gear. DP carbs are too much for street
 
try this. (nobody in front of the car please)

left foot the brake, give it a little gas get the rpms up a bit and put it in drive.
if it still kills the engine you have a converter locking up (bad sprag?) or possibly a trans problem.

if you can keep it running that way, and not kill the engine, then your problem is 90% likely to be the carb. possibly timing/electrical but i'll bet cash it's the carb. even though you tested with another one, they both could be in need of rebuild/adjustment.

the other possibility is a valvetrain problem with an intake valve staying open, or a crack in your intake somewhere. your engine will not keep vacuum too well and will stall out in either case.
 
hemi446 said:
I'm with abodyjoe on this one I use that 484/284 cam a lot it was the stock hemi grind cam. If you don't have at least a 3000-3200 stall it will not idle in gear the hemi's had what was called the J converter and everyone I have had stalled around 3200. The only other thing is make sure you have not vacuum leaks around the intake if the heads have been milled or the block decked the intake gasket may not be sealing real good. one easy way to check that is pull the pcv valve out of the valve cover and get a propane cylinder with a torch head on it and some rubber hose put the hose in the valve cover and turn the gas on if the rpm's go up you have a vacuum leak do both sides of the engine just use the oil filler cap or breather hose on the other side. Good Luck
Click to expand...


the hemi grind is a 280/474. the 284/484 is even crazier of an idle..

even with the proper converter the carb will still need work. you really need to know exactly what you have inside that motor
 
1960's 426 max wedge... they would idle in drive and didnt have a high stall converter lol

'62 413 Maxie had .495 with 300 degrees duration

'63 426 Maxie had a .509 with 300 degrees duration
426-II/426-A had .520 with 300 degrees duration.

'64 426 Maxi had .520 with 300 degrees duration on the 11.0:1 motors and .520 with 320 degrees duration on the 12.5:1 motors.
 
Max wedges did have a stall from the factory...my denominator idlers in gear with them12 inches of vacuum ...you need a converter.....
 
qkcuda said:
I have a 750 DP as well, mine has 4 corner idle. I took off the carb and opened the secondary throttle plates some, so I could close the primaries a little. There is a small set screw in the baseplate. Are you running vacuum advance? If so plug it and see if it makes a difference.
Click to expand...

I turned the screw for the secondary throttle position over so I can adjust it from the top. I've got them open as far as I can and still be able to get a response out of the secondary idle mixture screws. If I open them any more, the idle mixture screws won't change anything. Butterflies on both pri and sec are open the same amount.

So far, the vacuum advance has been disconnected and plugged until I sort out the current issues.
 
383Scampman said:
Hi mopowers, motors with a lot of cam duration have this problem. Set timing in gear. Make sure you do it safely. FST73 makes a good point and so does oldmanmopar. You should be able to solve this one but it does need a gear. Our legal d/sa '69 Cuda 440 has a cam of 330d. of duration, the lift is limited to .450 by rules. It won't idle less than 2,400 rpm
Click to expand...

383Scampman said:
Also, a vacuum secondary carb will help but not at idle. You have enoough gear. DP carbs are too much for street
Click to expand...

Thanks for the input. I plan on putting the rear on jack stands when I start messing the the 'in-gear' timing.
 
moparlover said:
try this. (nobody in front of the car please)

left foot the brake, give it a little gas get the rpms up a bit and put it in drive.
if it still kills the engine you have a converter locking up (bad sprag?) or possibly a trans problem.

if you can keep it running that way, and not kill the engine, then your problem is 90% likely to be the carb. possibly timing/electrical but i'll bet cash it's the carb. even though you tested with another one, they both could be in need of rebuild/adjustment.

the other possibility is a valvetrain problem with an intake valve staying open, or a crack in your intake somewhere. your engine will not keep vacuum too well and will stall out in either case.
Click to expand...

I will try that next time I mess with it. I'm able to get it in gear, I just have to give it gas to keep it running.

The carb is freshly rebuilt to factory specs btw. Just an fyi.

Thanks for the input. I appreciate it.
 
abodyjoe said:
you really need to know exactly what you have inside that motor
Click to expand...

I'm assuming you mean camshaft? Is there an easy way to determine which one I have? I was thinking about loosening the rockers and measuring lobe life on a lifter when I change intakes, but won't the lifters bleed out enough to negate any reading I get with my dial indicator?

Thanks for the input Joe. I appreciate it!
 
If the idle speed increases when you give it more initial timing, it needs more initial timing.
 
RustyRatRod said:
If the idle speed increases when you give it more initial timing, it needs more initial timing.
Click to expand...

This thing seems to want as much initial advance as I can give it until the vacuum advance pod hits the coil and won't go anymore. that's around 24-25*. I guess I should move the coil or move the distributor gear a tooth over so I have room for more advance. I guess then I'll be able to see how much initial advance it'll really take.
 
mopowers said:
This thing seems to want as much initial advance as I can give it until the vacuum advance pod hits the coil and won't go anymore. that's around 24-25*. I guess I should move the coil or move the distributor gear a tooth over so I have room for more advance. I guess then I'll be able to see how much initial advance it'll really take.
Click to expand...

Or move the wires over one spot on the cap.
 
qkcuda said:
Or move the wires over one spot on the cap.
Click to expand...

^^^THIS^^^

How long does that take? 1 minute? Even I, me, the old beat up arthritic guy, can do that in a couple of minutes.

Mechanical advance sticking? Quick way to tell? Easy. Remove the cap and "spring" the rotor against the advance spring, clockwise. it should "snap" back with no delay, nice and free

Vacuum leak? I have no idea.........I'd be checking for that.

Carb float level? Is the carb "puking" fuel, that is visible droplets from the boosters? Usually this results in a "bacon popping sound" as the fuel drops down the carb. Cannot always hear this with a loud engine, or with exhaust leaks. LOOK down the throats when idling

WHAT do the idle screws do? Unscrewing them "more" have any effect? Do they have any effect at all?

Sometimes "really wild cams" do need more air. Holleys generally, have a sort of unobtrusive set screw that effectively adjusts "secondary idle," for lack of a better term. You can set that screw up a little more. to allow some air in the back barrels. This allows the fronts to close back down into the transition slots "Back in" the day, we used to sometimes drill the butterflies
 
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