IDLE SPEED DROPPING

[mbandit]

WE HAVE OUR 440 IDLING NICELY AT ABOUT 1150 RPM, WHEN THE CAR IS SHIFTED INTO GEAR THE IDLE DROPS ENOUGH TO JUST ABOUT STALL THE ENGINE WHEN COLD.  EVEN WHEN ITS HOT IT'S NOT IDLING FAST ENOUGH WHEN IN GEAR.  ANY IDEAS WHAT THE PROBLEM IS?

MEL (needs to get this fixed so he can take the Charger to Bayton this weekend).

[cudaken]

 Details would help.

When did this problem start? What if anything was changed that may have caused the problem.
What kind of car, and engine.
What cam does it have?
Is the Choke wide open when warm?
Are you setting the idle when warm, or cold?


I was having the same problem with my 68 Road Runner and 750 Holley. We advances the timing to around 12 BTDC and played with the idle scew's on the front bowl. Car still drop's around 400 RPM's when I but it in gear but has a good idle in gear. Car has a MP 292/292/509/509 cam and has a nasty lop to it.


                    Cuda Ken

[mbandit]

69 Charger, 727 professionally rebuilt, Transgo shift kit and cooler, new torque converter 2500/2800 stall, 355 posi rear. 440 9.2 CR ported 906 heads with 80cc combustion chambers, Mopar 280/280 cam, 1.6 roller rockers, 770 Holley, street dom manifiold, Hooker headers, etc etc.  Everything is new.  Idles at 1150 with the engine warm (choke off).  I had one suggestion that there may be some restriction in the trans cooler or the lines too it.  Those componants are all new and look fine, there are no shift problems.  Timing is 26 static and 36 full advance.  Runs great but the idle thing ain't right.

Mel

[Ghoste]

26 initial seems like a lot of advance?

[mbandit]

Yeah, it should be more like 16 - 18, starts fine and gets off the line fast enough though, not sure if thats a problem, or the problem...

[cudaken]

 It not in the trans.

So everything is new and guessing you are just now starting to play with it.

Till Ron or Neil tells shut up, I would still play with the timing and idel screw's on the Holley. Have you checked for vacuum leaks from ports and intake? On the distributor, is it a vaumme advances? 280 Cam is a down grade of the old 284/284/484/484 Cam I ran in the Runner before I went with the 509 cam. Will not like a vacuume adavances distributor. 1.6 Rockers will hurt more and lower vacumme.

If it is a vacuume dist, check to see if there is a leak in the diaphragm. Pull the line that goes to the Carb and shuck on it, then put your toughen on the line. If you lose vacuume either the hose is bad or diaphragm.

Onces again, if the Dist is vacuume, did you shoot the timming with the dist unhooked and carb plugged?

                      Cuda Ken

[mbandit]

KEN,

NO VAC ADVANCE AT ALL, WE DITCHED IT, IT FLUCTUATES TOO MUCH, WE REPLACED ONE OF THE MECH ADVANCE SPRINGS WITH  A LIGHTER ONE.

MEL

[cudaken]

 Mel, are you mad at me? What little I know about computers, upper cased letters mean you are yelling at me.

Guessing you are not mad at me. Have you checked the ports and intake for a leak?

How many if any miles are on the engine? Was the idle messed up on start up or after a few miles? Have you retighten the intake? After 50 miles you should retighten all bolts you can get your hands on.

Well, got to go, and better luck than I. Got to pull the $7,000.00 440 with 85 miles on it.

                      Cuda Ken

[Chryco Psycho]

you have a low stall conveter in the car , replace it with a 2200 stall & the problem will go away , the car will respond a lot better too

[mbandit]

What stall speed was that again?  The engine did this with the previous mild cam in there too,l explain to me why this happens.  I don't see how the stall speed loads up the enging just by engaging drive.

Tx,

Mel

[cudaken]

 Neil, I ran the 284/284/484/484 cam with a stock 68 Road Runner converter, and did not have a problem with idle.

                               Cuda Ken

[firefighter3931]

What stall speed was that again?   The engine did this with the previous mild cam in there too,l explain to me why this happens.   I don't see how the stall speed loads up the enging just by engaging drive.

Tx,

Mel

Mel,

If the converter is a stock 12in then it will lock up ~1500 rpm and it will drag the motor down at idle...which causes problems when trying to tune a hotter than stock combo. A bigger cam with longer duration will require a higher idle speed so in essence the engine is fighting the converter.

The factory roadrunner converter that Ken is talking about has a higher stall to go with the longer duration Roadrunner factory cam. This is why it would be easer to tune with a bigger cam like the 284.

Ron

[cudaken]

new torque converter 2500/2800 stall,

Ron, I wouuld think a 2500 stall should handle the cam he has. Now what the 1.6 rocker arm's would do to vacuum I have no idea. The 509 cam is also being used with the Runner's stock converter.

                                Cuda Ken

[firefighter3931]

new torque converter 2500/2800 stall,

Ron, I wouuld think a 2500 stall should handle the cam he has. Now what the 1.6 rocker arm's would do to vacuum I have no idea. The 509 cam is also being used with the Runner's stock converter.

                                               Cuda Ken

Yep, you are correct Ken....didn't see that about the 2500 stall. The 1.6's won't affect the idle vaccum appreciably. The 280 cam is fairly large with 238*@.050 so it can be difficult to tune with a vac secondary carb. The long overlap hurts signal to the primary boosters which can cause tuning issues.

The problem most like lies with the carb. If it's idling at 1150 in neutral, then it's running on the main circuit and not the idle circuit. When the car is put in gear it drops beck down to the idle circuit and wants to stall because there isn't enough air getting in. The converter is putting a load on the engine pulling the idle speed down. This is a common problem with vac secondary carbs and longer duration cams. The fuel metering on a vac sec carb is designed for a cam with less overlap. If the engine had a DP carb with 4 corner idle then it would be easier to tune. Since it doesn't, the carb needs to be tweaked so that it's running (at idle) on the idle circuit and not the main circuit. One way to tell if it's on the main circuit is to try adjusting the idle mixture screws with the engine running....if closing/opening the screws has no effect on idle speed/quality.....you are running off the main circuit.  

This is accomplished by drilling holes in the primary throttle blades. Start off real small and work your way up until the idle cleans up. It may take a few tries but better to start off small and work your way up.

Set the base timing to 18* would be my recommendation and move on to the carb for some tweaking.

Ron

[69fuchs]

The distribtor needs to be curved on a machine.   The springs are letting the weights go shut, retarding the timing when you get below 1100 rpm.   When the timing retards, you loose engine rpms, and the engine dies.   I would first make sure that you don't have a vacuum leak somewhere....because a vac leak can cause those same symptoms.

[firefighter3931]

The distribtor needs to be curved on a machine.   The springs are letting the weights go shut, retarding the timing when you get below 1100 rpm.   When the timing retards, you loose engine rpms, and the engine dies.   I would first make sure that you don't have a vacuum leak somewhere....because a vac leak can cause those same symptoms.

I wouldn't necessarily agree with that statement. Re-curving a distributor isn't rocket science....just a little common sense. Mel is using one heavy and one light spring and this combination works well from my experience. Sometimes the plates need to be welded up to limit mechanical advance when dialing in more initial. The speed of the curve is adjusted by spring weight/tension. Two light springs would bring the advance on ~ 1100 rpm but with the heavy/light it shouldn't start moving untill ~ 1500 or so. Fwiw, i usually delete the heavy spring and replace it with a light spring....keeping the medium spring.

I agree that there could be a vacuum leak: have you checked for that Mel ? How much vacuum is it making at the 1100 rpm idle and in gear ?

Ron

[cudaken]

 Boy, drill holes in the thottel blades, that bring back memories. Think around 1977 or so, so they still used that trick.

Ron, I do not know is carb, but my Runner has a stock 1310 (might be wrong on the number) 750 Holley and I can idle off the idle circuit with no holes in the blades. When in netural, I aso hit 1150 RPM's.

I bet I know what is problem is!

Mbandit, with the Charger in gear, have you adjusited the idle scew's? Like I said, in netural, I idle at 1150 RPM's, but in gear around 700 RPM's. Had to set the idle screws with friend in the Runner in gear while I played with the idle circuit.

Just as Ron said at that high of RPM's you are not on the idle circuit but in gear you are!

  As a collective, we sort of have a brain.


              Next question Cuda Ken

PS, sure hope that is the problem, full of my self right now.

[mbandit]

OK we worked on it again this morning.  I think Ron's on the right track.

We re-gasketed the base of the carb and the idle (still 1200 rpm) is a little smoother now.  We set the mixture screws again but it doesn't seem to alter things very much.  I'm clueless with Holley's, more used to Mikuni's and such where if I mess with the screws it eventually kills the motor.  Surely the Holley should work like that too?  The other thing I tried was backing down the idle speed.  I'm theorizing that the engine should idle down to maybe 600 rpm before it really gets the shakes but if I get much below 1000 it stumbles and wants to die - just like it does when it's put into gear.  That leads me to believe either the idle circuit is not working or its not running on that circuit.

Bear in mind that the engine did the same thing with a much milder cam in it, so its not the cam.  Vacuum is 9" right now, no evidence of any leaks.  I do need to do the right thing and back the timing down before we go any further.  The only other worry is that there's too much pressure in the transmission.  We checked the lines to the cooler but everything looks OK, in any case the trans has 250 miles on it and I figure it would have gone bang by now if the pressure was an issue.  Do you concur?

[firefighter3931]

Mel, have you checked the indexing on the balancer ? If it's an original (old) unit, the outer ring might have slipped making the factory mark obsolete for timing purposes. I would suggest you check the indexing to verify that the mark is lined up right at tdc. Trying to tune an engine with the wrong reference point is frustrating. Here's an explanation of the indexing procedure if you're unfamiliar with it:

http://1970chargerregistry.com/70messageboard/viewtopic.php?t=1885

Ron

[mbandit]

I'll try that too.  Ron/Ken - at what revs is the carb oof the idle circuit and into the main circuit?

[cudaken]

 At 700 RPM's with the Bigger 509 cam mine is on the idle circuit. My Holley book is 20 years old and will not list your carb or I would look it up. Did you try to adjust the carb idle circuit in gear? I was having the same problem with mine with the 509 cam.

One old trick is to set your timing to the max vacuume, that should be where your engine should be  happy.

You know, with the same carb and 2 driffrent cam's, it just might be a bad Carb. Have any friend's close to you that you can try there's? I all so learned one thing, just because it is new does not mean it cannot be bad.

Where do you live?

                                      Cuda Ken

[Chryco Psycho]

usually between 1200 -1400 the carb will switch over to the main circuit depending on th esize of carb & engine

[mbandit]

Ken,

I'm in the Houston area, I really need to borrow a Holley to prove the point or put mine on another engine.

[cudaken]

 Bananabeast lives down by you, his 440 is out of his Charger as well. I would try PM him and see where he lives, never know might just be on the other side town. If you want to ship your's up to me and can see if I can get it to idle on my Road Runner with the 509 Cam.


                             Cuda Ken

[mbandit]

According to his profile he's in San Antonio.  I'm west of Houston but that still makes it 1 1/2 hours away.  Anyone out there from Houston?
HMCC member?

[Nacho-RT74]

I'm on similar deal, with a pure stock car. but I'll start a different thread

[mbandit]

tell me more....

[firefighter3931]

usually between 1200 -1400 the carb will switch over to the main circuit depending on th esize of carb & engine

But in this case it appears that at 1150rpm idle speed it's running on the main circuit. The idle mixture screws don't have any effect on idle quaity according to Mel.

Ron

[cudaken]

 Mell, I just send you a PM, if you don't want to take me up with the offer, that is fine. But as soon as I sent the PM I started to wonder if you have checked this.

What PSI do you have at the carb at idle?

Have you adjusted the float level?

I don't think that is it, but seems all the other bases have been covred.

At this point, I still think the Carb is the problem.

                                        Cuda Ken.

[Chryco Psycho]

idle bleeds could be too large to get response with low vacuum

[mbandit]

Troy Hawkes of the Houston Mopar Connection Club loaned me a carb. THANK YOU, THANK YOU, TROY!

The motor started up 5th turn of the key and practically purred.  I'm over the moon!  This car has been kicking my ass for over 2 years now; at last we are nearly done.  We we rebuild my Holley and figure out what was wrong, get back with the diagnosis soon.

[cudaken]

 Mbandit, glad to hear you know what the problem was and hope to hear you sing the praise of your Mopar.


                           Cuda Ken

[mbandit]

Well we know where the problem is, just need to figure out the specifics.