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Idle drops when in drive

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Post by Joe73 on Wed Jul 19, 2017 6:32 am

Going from memory, because I never used timed port vacuum, is that they started using timed port in the later years having something to do with emissions.  Something to do with increasing exhaust temps for emissions reasons.
Here's a read on it. http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm

I'd stick with full manifold vacuum going to the vac advance and set it up that way.  If you have no change in your timing with the can either hooked up or not, then theres a vac can problem.  

My opinion is that most of these carbs we buy and use are not "race" bare bones carbs.  They are carbs designed to be used on emissions vehicles.  Emissions components started gaining momentum around 1968.  Carb companies are designing carbs for use on alot of different vehicles and the owners of these vehicles are doing what they want with them like us.  Carb companies are not going to tell anyone to go against federal law and change an emissions component.  Thats what we car guys do and the burden is on us.
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Post by SSTOOLMAN on Wed Jul 19, 2017 10:08 am

SonOfTheGrim wrote:So I've checked the timing and it is 11° and doesn't change with vacuum advance at idle. I have checked everything for vacuum leaks. I plugged the PCV and the nipple it was run to. No change at all to the idle dropping when in gear.

I have decided that what's happening is the transmission is trying to pull the car even at such low rpm as idle. When I put the car in gear it lurches and the rear wheels shift no matter how hard I hold the brake.
I am thinking the torque converter is the problem after all though I've never had a bad one to diagnose. Any input?
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Post by SSTOOLMAN on Wed Jul 19, 2017 10:20 am

My car did the same thing when I first got it. It has a turbo 400 with a shift kit.
Putting it into drive wasn't too bad but when I put it into reverse it clunked hard and pulled the motor down, I had to step hard on the brake to keep it from moving (does yours do this?)
When I switched motors I put in a B&M Holeshot 2400 RMP stall torque converter in,
it greatly improved the condition. I never had a car with a shift kit so I kind of chalked it you to that. If you put it in reverse and let off the brake will the rpms come up? I assumed my torque converter was no/low stall or going bad and I had the motor out so I switched it.
I don't know if this is your problem but its similar to mine.
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Post by SSTOOLMAN on Wed Jul 19, 2017 10:37 am

I once had a strange problem with a 73 impala, its probably not related but a good read. it was my winter beater back in 1983. One day leaving work I put it into drive it idled way down and sputtered to the point it back fired. It reverse it ran fine, I lived about a mile from work so I backed home. Long story short I found that my motor mounts were sloppy and when the car was in drive it shifted the motor enough it touched a worn bare wire by the starter, this grounded something in the distributor and made it run like crap, in reverse was fine. Try to figure that one out by yourself! LOL ! When your in the car you cant see the motor move in the mounts and when you shift into drive! I bent the wire away from the motor and called it good, never had a problem again!
I
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Post by SonOfTheGrim on Wed Jul 19, 2017 10:42 am

This is what I've decided too. I don't know what happens when a torque converter goes out but I'm thinking this is it.
Yes it definitely feels like I have to hold the brake extra hard to keep from rolling forward, in drive and reverse. The rpms don't rise if I release the brake though.

So you went to a 2400 stall? Does it seem to take more to get the car going? There isn't much info about them but from what I can discern the stock converters are around 1500 stall (I think) and I don't have enough performance to justify a hot rod stall.
I think for $100 I'll just get a new stock one and that way I'll know for sure. Problem is installing it, not buying it. But I have to do something because the car is becoming undrivable.

I could imagine the impala was a frustrating issue too. Electrical problems are so random it's hard to diagnose. Not that my issue is. That's why I rebuilt the distributor, because of a weird misfire after it got hot. Chased it from coil to module and finally down to the magnetic pickup and everything in between. Like I said my entire distributor is new except the shaft and housing. Really frustrating but I learned a lot!

Btw, what does a shift kit actually do?
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Post by SSTOOLMAN on Wed Jul 19, 2017 1:47 pm

I put in the 2400 stall for another reason also I put in a higher HP motor with a big cam. But now I am back to a normal cam motor and it works fine with both setups. It doesnt seam to take more to get it going at normal throttle. I will say I can do a effortless brake torque now, I think because the trans bites at a higher RPM. I would put the stock convertor in if I was you AND I would find a transmission shop that works on old school cars, have their best guy sit in the car and put it in gear and get a recommendation before you yank it out.
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Post by bracketchev1221 on Thu Jul 20, 2017 11:20 am

The higher stall converter puts less load on the engine at idle and doesn't pull the engine down as much in gear. You can get like an RV type converter that will raise stall minimally, maybe 18-2000 rpm. This will be mostly unnoticeable driving and may help your acceleration slightly.
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Post by SonOfTheGrim on Thu Jul 20, 2017 4:23 pm

I stopped by a transmission expert's shop yesterday and talked with him for half an hour and he said the torque converter was the problem and actually recommended me buy a stock one online to save money vs his cost. He's a good guy who's helped me out before and he knows his stuff. He said stock stall is 1300 to 1500.
Since my motor isn't much more than stock (if anything) there's no reason to think the stock converter won't work just fine. I'll report back when I get the new one in.
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Post by clanceman427 on Thu Jul 20, 2017 6:05 pm

SonOfTheGrim wrote:So I've checked the timing and it is 11° and doesn't change with vacuum advance at idle. I have checked everything for vacuum leaks. I plugged the PCV and the nipple it was run to. No change at all to the idle dropping when in gear.

I have decided that what's happening is the transmission is trying to pull the car even at such low rpm as idle. When I put the car in gear it lurches and the rear wheels shift no matter how hard I hold the brake.
I am thinking the torque converter is the problem after all though I've never had a bad one to diagnose. Any input?

I wouldn't replace the torque converter. You said you have another Isis with the fast shift to 2nd. Is it a th350 trans? Are you sure there is not a vacuum leak between the engine and the trans modulator? Check both the rubber line AND the metal line.
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Post by SonOfTheGrim on Thu Jul 20, 2017 6:16 pm

It is a th350. I have checked for vacuum leaks on both ends and everywhere in between several times. I've really done everything possible in an attempt to avoid dropping the trans but I honestly think that's the only thing left to do.
Honestly for $100 and a days work I'll know if it's the problem. If not I can sell the new one as slightly used and get some money back.
Not saying that the torque converter is the only problem but we'll see.
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Post by clanceman427 on Thu Jul 20, 2017 9:02 pm

Did you get to the bottom of why the idle speed doesn't change whether the vacuum advance is connected or disconnected?
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Post by SSTOOLMAN on Fri Jul 21, 2017 1:23 pm

SonOfTheGrim wrote:I stopped by a transmission expert's shop yesterday and talked with him for half an hour and he said the torque converter was the problem and actually recommended me buy a stock one online to save money vs his cost. He's a good guy who's helped me out before and he knows his stuff. He said stock stall is 1300 to 1500.
Since my motor isn't much more than stock (if anything) there's no reason to think the stock converter won't work just fine. I'll report back when I get the new one in.
I am curious, did he say why it is more prevalent in reverse than drive? it was way worse in reverse on my car.
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Post by SonOfTheGrim on Fri Jul 21, 2017 2:17 pm

I'll be looking into the timing after I swap the converter, which arrived today. Hoping tomorrow I can get it going.

Mine is the same in reverse or forward drive, and every drive gear. Since the only change from forward to reverse is inside the transmission I'd assume that was another problem, maybe on top of the converter. Maybe fluid not getting to the reverse valve?
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Post by SonOfTheGrim on Tue Jul 25, 2017 12:44 am

Got the converter in and it definitely helped the problem but it's still definitely there. Whatever the problem was with the torque converter, it had gotten so bad that putting it in gear killed the car immediately.
Meanwhile I found that my new carb was leaking from the baseplate so I had to take it off to tighten it. I also adjusted the secondaries which needed to be done.

So I'm still whittling at the idling problem but I always find more stuff to fix on this car.
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Post by BBMALIBU on Tue Jul 25, 2017 11:25 am

SonOfTheGrim wrote: Meanwhile I found that my new carb was leaking from the baseplate so I had to take it off to tighten it. I also adjusted the secondaries which needed to be done.

How does it run after these fixes?
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Post by clanceman427 on Tue Jul 25, 2017 12:09 pm

SonOfTheGrim wrote:.
Meanwhile I found that my new carb was leaking from the baseplate so I had to take it off to tighten it. I also adjusted the secondaries which needed to be done.

So I'm still whittling at the idling problem but I always find more stuff to fix on this car.

your new carb was leaking from the baseplate?? I found that my original quadrajet had the baseplate screws had backed out and got loose, causing a vacuum leak, but that was the original 42 year old at the time carb, on a car that hadn't run in several years and needed to be rebuilt.

What carb do you have and where did you buy it?
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Post by SonOfTheGrim on Tue Jul 25, 2017 2:45 pm

Yeah leaking from the baseplate does create a vacuum leak but this is a new-to-me Holley. I had the same idling and shifting problem with my old Edelbrock.
I took it off and used some gasket eliminator on both sides of the paper gasket. I'll put it back on this afternoon.

The engine originally had an Edelbrock 1406 600cfm but it was worn and old so I found a Holley 670 Street avenger on eBay. I think it was used with alcohol instead of gas because the inside was spotless but some of the gaskets and diaphragms had hardened. I took it completely apart replaced parts and it's worked great until the leak and the usual Holley flat off of idle. I need to adjust it to get rid of that.

BUT, the problem this thread is about has been with the engine and trans the whole time. Even back when it was in the El Camino it did this. I was hoping the Holley would make it better.
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Post by SonOfTheGrim on Wed Jul 26, 2017 11:56 am

Well I fixed the leak on the carb but now I've got a new problem. I believe it would be called a rolling idle?

I put the Holley back on yesterday, cranked the car very easily with just two turns over, the car ran for about 5 seconds then died. So I cranked it again and it started right up but tried to die so I feathered the gas to keep it going, then when I stopped it died.
So I turned the curb idle up so that it was idling higher to stay running. Then after running for a second the rpms started to drop down until about normal idle and rose back up again to the high idle I had set. It keeps doing this as long as I let it sit, up and down and up and down. Not fast, very steady as if someone is doing it with their foot. I adjusted the idle mixture and capped vacuum lines to find a problem but nothing. Gas is flowing through the filter and getting to the carb, the choke is fully open, and far as I can see the vacuum secondaries aren't moving. I capped the vac advance to eliminate it and no change. Maybe mechanical advance?

This is a problem I've had with modern cars with bad ecus or maf sensors but not with a carburetor. I'm stumped.
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Post by SSTOOLMAN on Thu Jul 27, 2017 10:30 am

Maybe a fuel pressure problem?? I know you said it has fuel in the filter but what if the pump pressure isn't consistent? just gasping for straws here. throw a pressure gage on the line that would rule out fuel problems before the Carb. I had a Quickfuel carb that didn't like too much pressure it ran like crap (bogged at take off, hard hot starts) until I figured out it had to be set at 6 psi, no more. I put a regulator on it and it took care of the problem.
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Post by clanceman427 on Thu Jul 27, 2017 5:58 pm

Are you sure the vac advance works? You can check it by applying a vacuum to the hose via a vacuum pump and verify that the arm of the vac advance moves. Some vac advance's have an adjustment inside the tube connection to limit or lock out any vacuum advance via an Allen wrench
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Post by SSTOOLMAN on Thu Aug 03, 2017 10:10 am

Just curious, did you get the problem solved?
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Post by SonOfTheGrim on Thu Aug 03, 2017 11:54 am

No I haven't solved it yet. I haven't been able to work on it in a few days. I ordered a jet kit so that I can fine tune the idle circuit on this Holley carb. I've also got my eye on a fuel regulator. But I'm not sure about that because isn't that the whole point of the bowl on a carb?
My other idea is the vacuum secondary being what's causing the rolling idle. That problem didn't occur until I adjusted the secondaries to barely open and I'm thinking maybe the diaphragm has gone bad? I don't know much about Holleys yet so please anyone enlighten me.

Anyway I'll be working on it some more today or tomorrow and maybe I'll have something positive to report.
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Post by Joe73 on Thu Aug 03, 2017 12:42 pm

Disconnect the arm on the secondaries so they do that effect anything. Fuel regulator adjusts fuel pressure. Do you have a big fuel pump or stock stuff?
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Post by SonOfTheGrim on Thu Aug 03, 2017 1:08 pm

I adjusted the secondaries to be just slightly open so as not to seal shut with vacuum, when last I touched the carb. I'll close them back up to eliminate that as a factor. The fuel pump is the stock pump that worked fine on the edelbrock, as far as I know.
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Post by thatfnthing on Thu Aug 03, 2017 3:50 pm

Admittedly my carb knowledge is rusty (and Q-Jet specific), but shouldn't the secondaries always be closed at idle?  Otherwise haven't you just given yourself a vacuum leak?
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