Idle problem need help

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M

Mark Benson

1975DodgeDartSwinger318
Joined
Feb 23, 2007
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Location
Langley,S.C.
Just rebuilt my 318 and have a question. First off when I set my idle to 750-800 rpms in park and then put it in gear it drops to 400-500 rpms and runs like crap. Tried setting it at 750 rpm in drive and when I put it in park it idles around 1500 rpm. I am positive there are no vacumme leaks. Initial timing is at 10 deg. btdc. Any advice would be appreciated.
 
The torque converter is a stock replacement from advanced auto parts and the camshaft is the smaller summit cam part# SUM-6900. Carb is a Edelbrock performer 600 cfm also.
 
You have something wrong, Your engine/cam combo should idle at 750 RPM with no problem. Did you degree the cam when installed?

Sounds like a vacuum leak. Disconnect and plug everything at the source, that comes off the intake or carb that is vacuum related.

If you have a vacuum advance distributor, time the engine with the hose disconnected at the distributor and plugged. Check that you aren't getting mechanical advance right away.

You might try bumping the initial up a but as well.
 
I did not degree the cam. I am absolutly positive it is NOT a vacuum leak as I have checked all possible vacuum leak areas. The distibutor is a Mopar performance w/ adjustable advanced curve by the way and I timed it w/ the vacuum hose disconnected and pluged.
 
are the idle mix screws set to highest vacuum then turned in a 1/4 turn?
 
Dose it run good at idle ? What's your vacume reading at idle ? any black smoke ? thats a big drop in rpms that small cam's not the problem if not a vacumeleak or carb problem is the coil good? what do the plugs look like
 
Runs great at idle. Has 20-21 in. of vacuum and has some but VERY little black smoke when I punch the gas. Spark plugs are sooty black too. Coil is pretty old will change it out tomorrow at work
 
Is fuel dripping in from the carb booster?

Too much fuel pressure, sunk float, garbage in needle and seat, float adjustment required...

Also,

Use the vacuum gauge to set your initial timing. Advance until you reach the highest level, then back out 1" of vacuum by retarding timing. That's what the engine wants and easiest way to find a good starting point.
 
I have already set my timing up w/ the vacuum gauge and got a max of 21in of vacuum. The carb is not leaking plus the carb I have on mine now came off my brothers dart and it ran flawlessly on his engine. I'm not sure what kind of fuel pressure I have. I will get one sometime this week though.
 
Did some testing today. I replaced my coil, ECU, carb, ballast resistor and tried another distributor. Still I am having the same problem. Plus when I start to drive it stumbles. Fuel pressure is at 7 psi at idle and even when it starts to stumble. The spark plugs are now cleaner after I did all this parts changing. I'm running out of places to start. Would appreciate some more tips from you guys if you will. Thanks.
 
Have you tried disconnecting everything vacuum related from the manifold and carb and plugging off the source.

If you tried a different carb that was working fine on another car and it doesn't work on yours, I'd kind of rule a carb issue out.

Does the car blow any smoke at idle?
 
I did plug all possible vacuum sources and it does not smoke at all at idle. Tried spraying carb cleaner around any and all vacuum sources too and no change in idle.
 
Just a quick thought on this, kind of inline with what others have said already.

With the dizzy vacuum capped, does it still drop/increase the idle as posted earlier? Which port on the carb do you have the dizzy advance hooked up to? On the Edelbrocks it should be the passenger side port, which is the timed port.

Just a thought,

valentek
69 B5 408 FB
 
I do have the hose on the passenger side of the carb. When I disconnect the vacuum hose and plug it, the rpms still drop.
 
Maybe the advance diaphragm on the distributor is no good
 
With all vac caps plugged, can you remove the oil breather or oil filer cap, spray a little card cleaner in the valve cover? I have seen intake leaks act like this too. Does not sound electrical. Has to be a carb issue, idle circuit, or vac leak most likely... ug..

PCV not stuck you checked that right? Power brakes booster etc.. Sounds very lean at idle or vac leak. Could be a tight convertor, not very likely ...At a steady 2500 RPM in N what is the vacuam? Is exhaust your heater intake bypass frozen stuck, most times they stick open though.
 
I will check my PCV vavle and try everything you said djwhog tomorrow and keep ya'll updated. Are you refering to the flap on the pass. side exhaust manifold. If so I had it cut out and the holes welded up by the way.
 
If you plugged off everything to the carb/manifold, then it's not the pcv valve because that would have been removed from the equation.
 
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