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Looking for some idle problem assistance?
https://slantsix.org/forum/viewtopic.php?t=18419		 Page 1 of 1
Author:  lindross [ Thu Jul 06, 2006 5:59 am ]
Post subject:  Looking for some idle problem assistance?
We're running a 0.040"-over 225 with an Offenhauser single 4bbl intake in our 18 Dodge bucket, the Krylon Special. I don't know what tranny off the top of my head, but could get that info if needed.

The car runs and idles well, except in drive. When you pull up to a stop light, the car will "kick down" to almost 300RPM and try to die on ya unless you put it in neutral? Jim's (of Linder Tech) been thru this on several different occasions and I believe this one has him stumped for the time being. Any ideas on what we might be overlooking? Could this be transmission related?
Author:  Charrlie_S [ Thu Jul 06, 2006 6:23 am ]
Post subject: 
Take a look at your ign timing. See if the amount of advance changes, between what you have in neutral, and just before it stalls, in gear. If the timing decreases as the rpm drops that is your problem. You will then need to determine whether it is centrifical or vacumn. At closed throttle there should be no vac advance.
Also what is your neutral idle RPM, and Vacumn?
Author:  lindross [ Thu Jul 06, 2006 6:26 am ]
Post subject: 
Quote:
Take a look at your ign timing. See if the amount of advance changes, between what you have in neutral, and just before it stalls, in gear. If the timing decreases as the rpm drops that is your problem. You will then need to determine whether it is centrifical or vacumn. At closed throttle there should be no vac advance.
Also what is your neutral idle RPM, and Vacumn?
Not sure on the Vacuum, but neutral idle is usually around 800-900 RPM if memory serves me correctly.
Author:  Sam Powell [ Thu Jul 06, 2006 7:01 am ]
Post subject: 
I think Charlie is right. Chances are two things, your centrifigal advance is coming on way early, so your initial timing has centrifigal advance already in it. As rpm drops when you put it into gear, , timing drops too, thus dropping rpm further and dropping timing further yet. As it begins to die the vacuum drops off, and then the timing is reduced further yet, killing it off. A stiffer centrifigal spring, and more initial timing should solve your problem.
Author:  lindross [ Thu Jul 06, 2006 11:38 am ]
Post subject: 
Thanks for the suggestions guys, we'll take a look this weekend or early next week and let ya know. 8)
Author:  sixinthehead [ Thu Jul 06, 2006 11:55 am ]
Post subject: 
I've had engines with vacuum leaks want to stall at idle under load. Check the intake gasket sealing carefully in case the manifold isn't true or has come loose.
What do you mean by "kick down" when coming to a stop?
Has it always done this or did it develop after something was changed or?




Maybe you'll have to bring it over and leave it with me for a while :wink: 8)
Author:  lindross [ Thu Jul 06, 2006 4:27 pm ]
Post subject: 
Quote:
I've had engines with vacuum leaks want to stall at idle under load. Check the intake gasket sealing carefully in case the manifold isn't true or has come loose.
What do you mean by "kick down" when coming to a stop?
Has it always done this or did it develop after something was changed or?




Maybe you'll have to bring it over and leave it with me for a while :wink: 8)
By kick down I meant that when coming to a stop the car would be idleing normally and then just seemingly drop in RPM's. So it would be idling happy around say 800 RPM, then just drop down to approx 300 RPM and want to sputter and die. Yeah, it's been a small problem with the car for some time. You would think that the engine is getting loaded down, or something is getting cut off at idle in drive??
Author:  Sam Powell [ Fri Jul 07, 2006 6:38 am ]
Post subject: 
It is certainly possible that there are other things besides a timing issue going on. If the timing is stable, another 'glitch' or tuning problem might go un-noticed, or be seen as only a small blip in the idle. You could have a vacuum leak, or maybe dirt in the carb bowel that gets into the idle circuit. But the thing about that idle circuit is that it is highly dependent on vacuum to be stable as well. If the idle drops, and it is accompanied by a drop in timing, then the idle mixture will see a change as sell, further compounding things. Make sure your vacuum advance is tapped into a ported vacuum port, and not manifold vacuum. If it is on manifold vacuum, then things really can get dicy in a hury when the engines falter or misses, as about 12 crank degress of timing can go away all of a sudden. Hook a vacuum gauge up to the port that your advance is hooked up to, and see if it has vacuum at idle. If it does, then try to find a port above the throttle plates.
Sam
Author:  lindross [ Fri Jul 07, 2006 8:05 am ]
Post subject: 
Thanks Sam, we'll beat on the old man and make sure we've looked at that too.
Author:  SlantSixDan [ Fri Jul 07, 2006 8:14 am ]
Post subject: 
I like the timing theory. What distributor are you running, specifically?
Author:  lindross [ Fri Jul 07, 2006 11:19 am ]
Post subject: 
Quote:
I like the timing theory. What distributor are you running, specifically?
Don't know off the top of my head. I'll get back with you on that one.
Author:  SlantSixDan [ Fri Jul 07, 2006 11:25 am ]
Post subject: 
Kinda wondering if you're running the MP P3690789 electronic ignition conversion kit, which came with a distributor having a drag race advance "curve" (all mechanical advance gets dumped in all at once...has only one spring, and it's very lightweight!) If the advance weights are sticking in the "flung out" position, then at idle they snap back to their retracted position, that would indeed cause the symptom you describe. Not the only thing that would cause it, though. Can you duplicate the condition without driving the car, i.e., by revving the engine with the car parked? If so, you can put a timing light on it and watch what the timing's doing.

When did the 4bbl replace the previous 2x1?
Author:  lindross [ Mon Jul 10, 2006 6:17 am ]
Post subject: 
Looks like you guys were right on it. Jim and myself hooked up a smart scope and looked at the ignition timing and vacuum pressure. Timing and vacuum were all over the place. We put in a new distributor that removed the vacuum advance and replaced a bad coil and the car starts and runs like a top.

Next on the menu is to look at the carb as the ol gal seems to not be getting enough fuel to let her run under acceleration.

Thanks for your input guys!
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