Slant Six Forum :: Transmission vs. Engine, The battle rages on!

I'm thinking an idle airflow issue caused by improper throttle plate position with respect to idle transfer ports and â€” depending on specific carburetor model â€” other wall ports, and/or by excessive airflow past the throttle shaft/bushing area (worn shaft/bushing). The California '71s specced really late base timing, if I'm not mistaken. Something like TDC, maybe even 2Â½Â° or 5Â° ATDC? As a result the carburetor was calibrated with the transfer slots relatively high up in the throat so the throttle could be opened up relatively wide and achieve a normal idle speed despite the late timing. What're you running for a base timing setting?

Disregard that decal; with the CA stuff no longer hooked up and the recurved distributor it no longer applies. Shoot for an idle speed of about 700 in Neutral, which should give 650 or so in Drive. If you can't achieve that close of a Neutral/Drive idle speed relationship, we can probably home in on why.

Another thing to check is the PCV valve. If it's the wrong one, you can wind up with strange idle speed problems...

Author:	THOR [ Wed Sep 17, 2008 11:44 pm ]
Post subject:	Transmission vs. Engine, The battle rages on!
Alrighty, well I've got some questions concerning the way my transmission acts, the story told by the engine's reaction to it. Keep in mind, I have a MP 2200 stall converter (it flashes to 2k, so I assume it is rated slightly higher due to V8 vs. SL6). This all stemmed from the fact that my alternator is weak, and needs to be rebuilt. Factory spec for idle speed on my car (California Emissions - 1971) says that idle speed IN GEAR should be 750 RPM. If I set my car (setting curb idle screw to achieve this) to run @ 750 RPM in gear, it jumps to around 1250-1300 RPM while in N or P. This doesn't seem normal. I am not all that familiar with the A904, but this just seems wierd. If I lower the engine RPM in P or N to 1000 RPM, where it sounds "au natural", I drop it in gear, and w/lights off, it idles around 550, and with the lights on, it drops to about 450. If the RPMS are any lower than 1000 RPM, the alternator basically quits "putting out" and my ALTERNATOR gauge goes heavily into the "D" or Disharge. Even slowing to go around corners, the alternator gauge dips heavily. I have been in my fair share of other A-bodies, with much heavier mods done to the engine and trans, and they do not have this problem. This alternator issue is what sparked my interest in finding the factory spec, so that my stereo doesnt shut off when I come to a stop light. Also, with the blinkers on, pretty much all of my lights dim a bit when they lights activate, I attribute this to the weak alternator. Then I discovered the funkyness of the engine/trans. Can anyone help? ~THOR~

Author:	68barracuda [ Thu Sep 18, 2008 3:11 am ]
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UHHMMMM D-A-A-A-A-NNNNNNNNNNN HELP

Author:	Dart270 [ Thu Sep 18, 2008 5:33 am ]
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Engine should not drop down that much going into gear. Sounds like a timing advance problem or a vacuum leak or poor idle mixture. Most likely a vac leak from your description. A typical drop would be 850-950 in N, then 750 in gear. Lou

Author:	SlantSixDan [ Thu Sep 18, 2008 6:05 am ]
Post subject:
I agree with Lou, except that with your trans setup you should be seeing even less of an RPM drop than he says. 800 in Neutral should give you 750 in gear. A few questions: 1. Where'd you find the idle spec you're using? 2. Are the CA emission components still present and hooked up on your car? 3. Please remind us what distributor and carburetor you're using (be specific as to type, condition, modifications, etc.), and mention whatever other modifications you've made. 4. How (exactly) is your vacuum advance hooked up?

Author:	Dart270 [ Thu Sep 18, 2008 8:54 am ]
Post subject:
A really good thing to try is a valve lash adjustment also. If valves are even a little too tight, it will do what you describe. Lou

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Transmission vs. Engine, The battle rages on! https://slantsix.org/forum/viewtopic.php?t=31172	Page 1 of 2

Author:	THOR [ Thu Sep 18, 2008 7:45 pm ]
Post subject:
Quote: I agree with Lou, except that with your trans setup you should be seeing even less of an RPM drop than he says. 800 in Neutral should give you 750 in gear. A few questions: 1. Where'd you find the idle spec you're using? 2. Are the CA emission components still present and hooked up on your car? 3. Please remind us what distributor and carburetor you're using (be specific as to type, condition, modifications, etc.), and mention whatever other modifications you've made. 4. How (exactly) is your vacuum advance hooked up? 1. Directly off the little green sticker on the inner fender, thats also how I found the CA emissions info. 2. No. The only thing that is attatched, is the fuel tank vent into the valve cover breather. 3. Pre-'73 Holley 1920. All choke equipment has been removed, and it is running a #56 jet, with no lean surge at any speed. The dizzy is an EI unit that Duster Idiot built. He installed a new vacuum pod and set the springs on it for stock performance. 4. Vacuum runs directly from 1920 port to vauum pod on carby. It does not have vacuum at idle, and is the only other port on the carburetor. Duster Idiot and I have tried to solve this problem before, and utilized carb cleaner to find vacuum leaks... there were none. Valves have been lashed within the last month or so, and I run them a little loose myself, Intakes: .011, and exhausts: .022. ~THOR~

Author:	DusterIdiot [ Thu Sep 18, 2008 8:13 pm ]
Post subject:	Hmmm...
Quote: The dizzy is an EI unit that Duster Idiot built. He installed a new vacuum pod and set the springs on it for stock performance. the unit is a 1973/74 EI with stocker springs, and a 10R vacc. pod instead of the 8.5R vacc pod... His car is experiencing the same thing that happened to the beater Valiant A-904 before it finally tanked...big rpm drop from park/n to drive... -D.Idiot

Author:	THOR [ Thu Sep 18, 2008 8:28 pm ]
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That kinda worries me, because it seems that my old 904 (ceej has it now) did it off and on, and then it tanked. In fact, I remember us testing this because the old transmission did the same thing! Oh crap..... ~THOR~

Author:	SlantSixDan [ Thu Sep 18, 2008 8:40 pm ]
Post subject:
I'm thinking an idle airflow issue caused by improper throttle plate position with respect to idle transfer ports and â€” depending on specific carburetor model â€” other wall ports, and/or by excessive airflow past the throttle shaft/bushing area (worn shaft/bushing). The California '71s specced really late base timing, if I'm not mistaken. Something like TDC, maybe even 2½Â° or 5Â° ATDC? As a result the carburetor was calibrated with the transfer slots relatively high up in the throat so the throttle could be opened up relatively wide and achieve a normal idle speed despite the late timing. What're you running for a base timing setting? Disregard that decal; with the CA stuff no longer hooked up and the recurved distributor it no longer applies. Shoot for an idle speed of about 700 in Neutral, which should give 650 or so in Drive. If you can't achieve that close of a Neutral/Drive idle speed relationship, we can probably home in on why. Another thing to check is the PCV valve. If it's the wrong one, you can wind up with strange idle speed problems...

Author:	THOR [ Thu Sep 18, 2008 11:27 pm ]
Post subject:
Quote: I'm thinking an idle airflow issue caused by improper throttle plate position with respect to idle transfer ports and â€” depending on specific carburetor model â€” other wall ports, and/or by excessive airflow past the throttle shaft/bushing area (worn shaft/bushing). The California '71s specced really late base timing, if I'm not mistaken. Something like TDC, maybe even 2Â½Â° or 5Â° ATDC? As a result the carburetor was calibrated with the transfer slots relatively high up in the throat so the throttle could be opened up relatively wide and achieve a normal idle speed despite the late timing. What're you running for a base timing setting? Disregard that decal; with the CA stuff no longer hooked up and the recurved distributor it no longer applies. Shoot for an idle speed of about 700 in Neutral, which should give 650 or so in Drive. If you can't achieve that close of a Neutral/Drive idle speed relationship, we can probably home in on why. Another thing to check is the PCV valve. If it's the wrong one, you can wind up with strange idle speed problems... I'll replace the PCV just for the heck of it, since its a platic POS and should probably be replaced anyways, its most likely original to the car. Far as the throttle shaft being loose, I have a few 1920 carcasses around, and I chose the tightest fitting one, there still may be a slight leak, but I have run carbys with much much looser fitting throttle shafts, and other other than a lean surge at various speeds, it ran the same way. I am not for sure if it is a '71 carb or not. It's not the original carb for the car, I know that much. I'll go get some numbers for you, and I will bow to your almightiness for the answer. If I calibrate the carb to run at 700 in gear, it will drop to 400 or maybe less. I should also note, that I've had this problem before, with a different trans, and a different carb. I dont have an accurate timing tab on my cover. I am using the cover, tab, and balancer off my 1966 Valiant, since my double pulley (non-removable 2nd pulley BTW) was always trying to walk off the end of the crank. I figured that if I had all 3 of these parts, it would line up, but I think that the key-slot on the crank is in a different position from the earlier '66-down cranks. My original cover had the timing tab broken off of it, and it was extremely dirty to boot, so I thought it would work... of course not... I will check it out for definite shortly... straps on shoes to go warm up the car... ~THOR~

Author:	sandy in BC [ Fri Sep 19, 2008 7:22 am ]
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So what in the 904/convertor is dragging that much in neutral? (side bar....I noticed the new 3500 stall convertor in the mudbogger spins down for quite a while after I shut down.....)

Author:	slantzilla [ Fri Sep 19, 2008 9:07 am ]
Post subject:
Broken sprag in the converter will make the engine lug at idle.

Author:	THOR [ Fri Sep 19, 2008 4:08 pm ]
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Ok, so I went out and drove around today doing some errands, I set the carb curb idle screw to 700 in P and N, and it drops to about 450 in gear. So, I am still confused.... ~THOR~

Author:	emsvitil [ Fri Sep 19, 2008 4:44 pm ]
Post subject:
The centrifugal advance starting too soon can do this...... When you put it in drive, the idle drops a little, but then the timing retards a little, causing the idle to drop more, timing retards some more,............ See when the timing starts to advance, you want the timing to start advancing after the rpm that you get in neutral.

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Author:	ceej [ Fri Sep 19, 2008 8:24 pm ]
Post subject:
Where is your cam timed? Let's find out. CJ