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#1
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Carter AFB issues
Ok, Here is the Specs of my combo:
I have put a near bone stock "76 400ci motor and tranny in my "72 duster. I did angle mill the heads to reach a 9.2.1 comp ratio. This was an original 4brl engine. I used a "69 383 intake. The bores were so clean that it only needed honing and standard rebuild. I had a MP 484 lift cam that I had in my vst inventory of spare parts(I ran this in a simular 440 years ago). I had a Demon 700 on car that ideled a little to rich, but did idel in gear, bareLY. The carb was too tall, so i changed to a Carter 1406(600). I have tried all variables of jets/rod/springs. It will idel well with decent signals from frt adjustment screws. The problem is. it will not idel in gear at all. This combo has a factory spec built 727 and the factory convertor that was ran with this combo. This vehicle will never see ther track and i know that is alot of cam for near stock engine, but like i said before, I've ran this in a 440/holley card without too many issues. Here is how is set now: yellow springs - idel vac is @ 10hg, when in gear drops to around 3hg. Put jets 98 frt, 95 rear - runs around 190 drgs. rods - .705-47 and pump shop on long stroke. No hesitation and mid to wot does appear good with level running and no stumbles. The downer - when you run RPM around 800 the carb rises and falls randomly. The Rpm drops from 10hg to around 5 to 6 hg when this happens. I've went from silver to yelow springs without helping the idel in gear issue and not really changing anything on reg idel circuit. Lost and need some help. |
#2
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This may sound silly, but isthe return spring strong and pulling the arm foward all he way? ouble check for leaks and that would include areound the two towers that hold the step up springs. There could be cracks there.
That cam doesn't rally generate alot of vacuum. What is the idle RPM range, not the Hg. |
#3
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When the drop occurs in vaccum, the RPM drops from 1100 to about 600.
Check for leaks and none have shown their face. I really think that possibly the stall is not enough for this cam. I can get the car to idle perfect with exception to the surge issue, but will not idle in gear. |
#4
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Let me add, the return is good and make solid contact with adjustment screw.
This cam did not make this much vaccum on the 440(around 8hg) and did have a 1800 stall, I would bet the stall on this factory combo is around 800 to 1000. The Rpm drop did not happen as often from 1100, but when you get down to 800 on the top side it cycled back to 600 and below, bump the throttle and would raise back up for minute and drop again. I pulled thr frt vaccum port plug and let it bleed a little to see what it would do. It picked up around 100 RPM, but could tell it was turning lean. This was with the yellow springs,havnt tried it with stiffer springs. Timing is around 38, adjusted it to make easy start and works perfectly. Thanks for your reply |
#5
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badmopars
Low idle vacuum equals low idle circuit syphon action which can cause poor idle characteristics. You could try drilling the idle syphon tubes 0.002 at a time untill the problem is resolved? |
#6
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All the ignition advance should be in at idle with no vacuum. About 34-5 is perfect. This may be your problem, Paul.
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#7
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Paul are you telling me that I should adjust the allen head in the distributor port to make all advance to come in at idle?
Now, explain to me how this going to help once it is put in gear and the vaccum drops even more. Im kinda slow thinkin today. Thanks |
#8
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When you put it into gear it may lower the RPM just enough to make the ignition retard which could stall the engine. Forget the vacuum reading, once you put it in gear the motor is going slower so it's only natural to loose some vacuum. The
jets/rods/springs have nothing to do with the idle circut, Paul. |
#9
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Ok, so I need to make the disytibutor more like a MP dist with quick springs and poss lighter weights. Get the dist to come in once the engine is busted off. Set the carb for best idle and mid range on the stands and total timeing in gear?
Am I right with your thinking or maybe you should spell it out for me if Im wrong. Thanks |
#10
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All the spring, rod and jetting work in the world will not help. You should be able to easily get this combination to idle down to about 650 rpm in gear.
AARRACER |
#11
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Do you know the carb very well?
There were some 1406's that had issues with passages not drilled correctly. I had two of those with off idle issues. |
#12
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I'm thinking this might be helped with small drilled holes in the butterflies.
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#13
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OK, I have had this carb since new and have ran it on two other vehicles without too many issues. Those cars did have higher stalls and approx lift/duration cams. I have thought about drilling holes in the butterflies, but this a last resort for me. I know that there shoud be a simple solution that I am over looking.
I am not sure how I can get the carb to idle at 650 rpm, maybe if it were larger carb which would lower the overall vac signal? |
#14
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Badmopars
It's the looser/higher stall converters that allowed you to run this carb on your other engines. But it still was'nt right? Rule of thumb, the smaller the carb, the smaller the idle syphon tubes. when you remove the top and then the boosters, there are two syphon tubes that go into the fuel well. One for the mains circuit and one for the idle circuit. If you buy some pin drills you can oversize the idle syphon tubes. This allows more fuel to be lifted into the idle circuit with the lower vacuum signal. Allowing full fuel supply and mixture control at very low vacuum. This information is readily available in some publications on Carter and Holley carbs. I never invented it, I just borrow it frequently. |
#15
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You have to shorten the amount of degrees in the advance mechanism. Some custom distributors come from the factory with way too much for this setup. A few hundred RPM drop could reduce your timing from 38 or whatever to 10 and cause the problem you are having, Paul.
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#16
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Well, I,ve had little time to mess with the car last week. Did ajust my base and can only get it down to 15* before it just flay stalls out. Adjusted the dash pot to put as much in on crankup and at 2000 rpm its about 30*. It take about 2800 rpm to be in full with this distributor and total ends up being around 41*.
With this said, this thing will idle in gear at around 600 rpm period. If I raise my timing the in park idle goes up, but in gear idle stays the same. Drilled 1/8 holes in butterflies and that didnt change a thing. Checked again to make sure no vac leaks and all is good. When time permits will jack with the car some more. Thanks for all of your advise. |
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