340 Idle problems

-
M

Maccoy

Member
Joined
Dec 5, 2004
Messages
16
Reaction score
0
Location
Oak Harbor, WA
Just got done replacing my Mopar adjustable rocker arms with some Comp Cams steel roller rockers (same 1.5 ratio). Did nothing at all to any adjustments, besides setting the valve lash, and now when shifting out of park to a drive gear, the idle drops off to where I have to give it gas to keep it going. Was fine prior to swap. Background on motor: 10.5/1 pistons; Ultradyne solid cam (251in & 255ex duration @.050, .570in & .581ex lift, 106 lobe separation); Mopar M1 single plane with BG Mighty Demon 750; Hooker 1 7/8 headers; 3" exhaust; Crane Hi6 ignition; Has a Dynamic 9.5" convertor of unknown stall. Purchased on Ebay a couple of years ago, and ran like a bat out of .... so I just wrote down all the settings and left them alone. Idles in park approx 1500, with timing mark @ 31BTDC. Cannot get timing to change when revving. Stays at 31 BTDC, but as I said it ran great through all RPM ranges prior to this part swap. Used to drop down to 1100 RPM when put into gear, which it still does, it just wont keep running now without getting some gas. Any help for this lost soul, whose simple part change has turned into the usual mess! :scratch:
 
Something screams out at me..1500 rpm is not idle. If it's true 10.5:1. you should be able to idle it down a bit..say, around 1K rpm. Your timing is also way off. You are supposed to have a curve..You dont..It's all in at idle..Thats a lot of your problem, IMO. I'd be running 18* initial, and another 10-12* centrifical. Total of 38-40, starting to comeup around 1500, and all in by 2800. You may need to mess with that dist a bit to get these, but I've found them to be good general settings for an agressive cam in a street compression engine.
 
moper said:
Something screams out at me..1500 rpm is not idle. If it's true 10.5:1. you should be able to idle it down a bit..say, around 1K rpm. Your timing is also way off. You are supposed to have a curve..You dont..It's all in at idle..Thats a lot of your problem, IMO. I'd be running 18* initial, and another 10-12* centrifical. Total of 38-40, starting to comeup around 1500, and all in by 2800. You may need to mess with that dist a bit to get these, but I've found them to be good general settings for an agressive cam in a street compression engine.
Click to expand...


i agree with moper something is wrong with the ignition, i have a similar engine but mine runs a solid roller cam with about [email protected] and it idles at a hair under 1000rpm and i dont have more than 12degrees btdc ignition timing.
i recomend that you check everything in the ignitiomn system, its always a good idea when something dosnt work as suposed
 
Humor me and try something.

Disconnect and plug the vacumn advance line at the distributor after you have the car running. Adjust your idle down to around 1000rpm or less. Make sure it idles good. Now check your timing. Write that reading down. Now grab your light again and run the motor up to about 3500 rpm. Read the timing there. Write it down. Now set the timing at 3500rpm to about 32degrees. This is called total advance. Let it come back to an idle. See if you can drop the idle rpm even more. If you can great. Check timing at idle and write this down again. Take good notes.

You should also check how much vacumn you have at idle at the port you are attaching the vacumn advance line too. (Make sure you have attached it at the right spot!!)

Reconnect the vacumn advance line. Check your timing at idle again...write it down. (are we developing a pattern here??)

Test drive. Listen closely for pinging under load (ie..pulling a hill in second). If no pinging heard you can probably go up another degree or two on the total advance.

Take two of these and call me in the morning....... :thumrigh:
 
Vacumn advance has been unused since I received the car, wasn't even hooked up. I never thought much about it figuring whoever built this engine knew what they were doing, as it ran so well. Seat slamming acceleration with the 4.30's and has cruised effortlessly to numerous car shows (although it is a very noisy 340 with the 3" flowmasters and downturns). I thought it odd that the timing at "idle" was so far advanced, but who was I to mess with something that seemed to work. So I checked all the present settings, wrote them down, and went about the enjoyment of driving my Mopar. Only this "simple upgrade to some roller rockers" has brought to light a problem. Now that I think about it, while cruising at 50ish before this problem, I remember the exhaust always popped! Not a miss sort of pop, just a rather regular popping sound. By the way it looks to be running a stock mopar electronic distributor with the Crane ignition box and LX92 coil. Thanx, for the responses!!
 
Ok I just kind of skimmed through all the posts but on the timing it sounds like your dizzy is locked down I’m going to do this to my Demon pretty soon when I get a little more radical with it. That is a typical thing to do when racing at least around here it is and alot of other people I talk to do it to. But on the rest of the problem with not running gear I’m not sure sorry I dident help much.
 
The car appears to have been built for the track rather than the street. I don't know what the "dizzy locked down" reference means. Sorry!
 
He means the distributor is set for full advance at idle. I would talk to Don at FBO and have him curve a distributor for you.
 
You must log in or register to reply here.
-

Back
Top