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#1
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idle not stable
Hi folks,
I am having trouble maintaining a stable idle. It acts like it is missing pretty frequently. When I put a timing light on it, the timing mark jumps around constantly by 3-4 degrees. I have a 440 with a Mopar Performance distributor. I am using the two brown springs. I am not using vacuum advance. Ignition is a Mopar Chrome box and an MSD Blaster II coil. Cam is a COMP XE274. Duration is 230/236 deg at 0.05". Lift is around 0.49". Carb is a Holley 770 CFM Street Avenger. Weiand DP intake. Hooker Headers. The engine is pretty much stock otherwise. The idle mixture is running just a tad on the rich side. Idle timing is about 18 deg at 1200 RPM and about 33 deg when all in and I verified that the timing doesn't start to advance until it is at about 1800 RPM. Any ideas what could be causing this to be so unstable? Even as I increase the RPMs, the timing mark moves around a bit, though a little less I think. Can the cam just have too much lope to give a stable idle at 1100 RPM? The specs say it is rated fro 1800-6000 RPM. Could something be loose or wrong with the distributor that I am missing? I'm lost. Any help sure would be appreciated. |
#2
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Richness
Could contribute to the idle. I think that cam should lope some, though. Try jetting down a bit, first. Then measure the reluctor gap with a non metallic gauge, and set gap at around 0.008", and see what happens.
Also, try blocking any other vacuum ports and see what happens. Could be a vacuum leak. |
#3
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idle
Thanks for the suggestions. I will check the reluctor gap and check for any unknown vacuum leaks. I do have strong vacuum at idle, about 15-20 inches but it also jumps around as the engine idle varies. When you say jet down, what do you mean? Should I lean out the idle mixture a bit? I don't think the primary jets are doing anything with the throttle plates closed at idle.
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#4
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Jets aren't your problem.
How many turns out are the idle screws? You should be able to almost close the throttle blades all the way before it'll die on you, especially @18*initial. |
#5
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idle screws
Hi thatwasfunny,
The idle screws are not much more than one turn out. Maybe up to 1.25 turns. A friend suggested that maybe my distributor weights are flopping around at idle because I am using such light springs and the mechanical advance doesn't start coming in until about 1800 RPM.... |
#6
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success
Hi folks,
I think I solved this problem. First, the reluctor gap was about 0.012" at the closest point and the two pieces were not parallel. So I gently bent the pickup coil mount to get it parallel and set it to 0.007". I also realized that my choice of two brown springs meant that the mechanical advance wasn't coming in until about 1800 RPM. I idle at about 1,200 RPM. I think with these springs, the distributor weights were a little loose at idle. So, I switched to the pink and orange spring which have about the same curve but come in much earlier. So now I think the distributor has just a little advance at idle, maybe 2 degrees, which means the springs and weights are tight at idle. Anyway, the timing mark is rock solid at about 20 degrees at idle now. Unfortunately it is too late to play with the timing much tonight so tomorrow I will set the timing and take her out to play. I also think I am a bit rich still at idle (burning eyes!) so I will play with that once I get the timing dialed in. Thanks for the helpful suggestions. |
#7
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Some times things get lost in translation, so that aside [for now] why are you idling around @ 1200rpm? you don't have enough cam to force that kind of idle rpm.
If you can't get it to 850rpm with the primary side, cause it dies, then have you by chance checked the position of your secondary throttle blades? |
#8
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still trouble
Hey Thatwasfunny,
I can idle lower than 1,200 but when I put the car in gear it drops to about 800-900. If I drop the idle any more, the car will die when I put it in gear. I think it is mainly because the ignition still has some trouble. Here is the latest. After the engine got hot today, the idle got erratic again. I tried a couple different sets of distributor springs, some that come in early (two gray springs), some late (pink and orange). None of these stabilized the idle. I also tried adjusting the idle mixture. It would certainly change the idle speed when I tweaked the idle screws. I have an O2 sensor and went from lean to rich but still the idle was unstable. I have one of those little lights that you hold near the spark plug wires to see if they are firing. I don't know how reliable this method is, but a few of them seemed to miss when the engine was missing too. I am thinking at this point that something is wrong in the ignition system. Maybe the distributor has something inside that is just not working right or maybe the chrome box is letting me down..... I am lost. I also wonder if I am using incorrect wires for my plugs or something stupid like that.... I will try swapping in my original electronic ignition box and then my old stock mopar distributor to see if that helps. Could my harmonic balancer be slipping? I am generally pretty good at this stuff, but this one has me stuck..... |
#9
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What are your timing readings at idle in neutral and then in gear? If it is dropping when put into gear, replace advance springs with stiffer ones and retest.
You want your initial timing to have the same reading in park and in gear at idle. |
#10
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tdaver
Maybe try getting your idle down to about 900 rpm in gear. The idle transfer slot should not show more than about 0.040" at the throttle plate. Get a vacuum reading and check to see if you then have the correct power valve installed. A power valve about 1" below your minimum vacuum reading at idle should be installed. I found with your type of cam a 4.5" pv may be in order. When you get to this point you should be able to stabilize your idle in neutral and in gear with maybe 25 - 50 rpm differential by using the mixture screws. |
#11
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That thing should idle nice at 800-850, and not stall in gear.
My 440 with 228 @ 50 and dual quads idles great at 850, and has a strong idle in gear with a stock converter. 1200 is way too high. As suggested I'd set the idle low and then check your timing, if the springs are too weak, you'll have issues. |
#12
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update
Hi folks,
Thanks for the suggestions. I did try several different springs in the distributor including some pretty stiff ones. The idle did get more stable with stiffer springs and some distributor tuning. However, there is still one glitch. About once every few seconds the engine seems to "miss". The timing mark will drop down a few degrees and then return immediately. It happens with either the stock or MP distributor. I tried new plug wires. I checked the plugs and they were all OK. I tried switching to back to my old stock electronics box instead of the chrome box and it still "missed". Also, I never got the idle to stay up when I put it in gear. Hello AARRACER!! The power valve is a 10.5" and my idle vacuum at about 900 RPM is about 13-15". Why do you suggest a 4.5" power valve? I have always had good vacuum at idle with this cam. |
#13
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Another thing you might want to look into is the amount of play there is in the blade at the end of the dist. and the oil pump shaft gear slot.You can peen the end of the dist. shaft so that it is tight in the gear.One more thing to try is putting a collar clamp on the end of the dist. so that the gear can't move up and down making your timing eratic.You can buy the collar clamps at any hardware store.Put the clamp on the shaft just tight enough that it still moves and place the dist. in the block.Remove the dist. and add about .010 for heat expansion,then lock-tite the clamp screws and tighten.Doing these mods has always helped me to have a very steady timing mark and better idle.Hope this is some help to you.
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#14
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If you have the orange box, it's not unusual for them to cause erratic timing.
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#15
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distributor
Hi,
I did notice that the spade at the end of the distributor seemed a bit loose in the gear slot. Since I have things taken apart, I will see if I can get a tighter fit. I am using the Chrome box. tdaver |
#16
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With the air filter off, look down the carb. It there any fuel dripping?
If so this is your issue. You will need to rich the idle transfer tubes. A lot of carbs any more come too lean so they can meet emmisions. I agree that set-up should idle real nice at 850rpm. |
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