What should my vacuum reading be?

[Dino]

Before I start changing cam and who knows what else, I'd like to get my car back up and running and all that is left to do, for now, is tune the carb.  With my specs, what vacuum readings should I have?

'71 440 HP with purple cam Duration 280/280, Lift .474/.474
http://www.summitracing.com/parts/dcc-4452992ae/overview/

Supposedly TRW pistons with 10:1+ compression but that's not confirmed.

Thermoquad 6545S on Edelbrock (non-rpm) performer intake.  Unknown brand of uncoated headers.

[Chryco Psycho]

approx 10-12" at idle , 7-10 in gear if auto

[Dino]

approx 10-12" at idle , 7-10 in gear if auto

Great!  I'll go play and see what I find.  Is it ok to stick the gauge tube where the a/c control tube goes?  On the back of the intake.

[A383Wing]

you want a more "centralized" port to get a good even reading. The one on the intake is more over one runner. Try to find a constant vacuum source from a vacuum hose nipple on the carb.....one that is below throttle plates

Bryan

[Dino]

you want a more "centralized" port to get a good even reading. The one on the intake is more over one runner. Try to find a constant vacuum source from a vacuum hose nipple on the carb.....one that is below throttle plates

Bryan

Can I use the one the choke pulloff is hooked to?

[flyinlow]

Choke pull off port is OK./ The port that goes to the air cleaner snorkel door is OK.  What is an AC port? 

Do not use the Ported vacuum port for the distributor, the EGR port (very small on front if installed ,coming out of the phenolic section), Evap. Canister bowl vent (large hose on top of the air horn) or the Evap canister purge (med. hose on front of the throttle valve body.)

[flyinlow]

Ports ID

http://www.carbkitsource.com/carbs/tech/Carter/pages/tqguide-Vaanth.html

[Dino]

Thanks gents!  Flyinlow I don't have all the smog stuff, this was a truck carb.  Sorry for the confusion, with a/c I meant the small nipple where the a/c control vacuum hooks onto.  It's on the back of the manifold next to the brake booster port.

I hooked up the gauge on the carb itself, where the choke pull off connects and get a reading of 9 at idle, the cam makes the idle go between 8.5 and 9.  I'm kinda lost playing with the idle screws and don't see much happen on gauge or by rpm unless I close them.  The car still runs real nice but it's not happy without a choke and takes it sweet time warming up.  Flooring it so it kicks down to 2 is still spot on but shifting into 3rd makes it unhappy.  I haven't played with the metering rod yet either and I don't think I should mess with the carb until everything else checks out.  I think a new exhaust is in order for one.  I also hear a much more prominent 'vacuum' sound under the hood and from behind the dash.  Not sure if that's the carb or if I have a leak.  I also suspect my heater fan kicks in from time to time, with the controls out of the car.  Spooky   

Oh, I thought that vacuum went down as rpm went up?  I sure hope not because my rpm goes up quite a bit!

[A383Wing]

vacuum will rise as RPM goes up without a load. You probably won't see much of a change with the mixture screws because of the cam you have.

yer gonna have to probably play with metering rods & jets as well, 8.5-9" of vacuum is a little lower than I would like to see for a street car

[cdr]

you might have a vacume leak at the base gasket

[flyinlow]

At light throttle vacuum will go up as rpm increases and peak about your engines peak torque rpm. It will be temporarily higher during closed throttle deceleration when the car is pushing the engine.
The plastic fantastic (TQ) is a decent street carb for mild built engines. Mine sits on top of a Holley Street Dominator Intake with no intake heat, and a mechanical choke. Only use the choke in the winter for a couple minutes. The idle circuit will only get so rich on a TQ. Mine idles best about 13:1 A/F ratio. about 2 1/2 turns out. You can turn them as far out as you want and it will not get richer than 12:1. The bigger TQ's where rated at 850cfm. Most of the air flow is thru the big secondaries. You will hear it at WOT.

[Dino]

Thanks guys, this is really helpful.   

The idle screws are out 2 1/2 turns, that seemed to work nicely and I'm glad to hear the cam is involved so it wasn't me.   

How can I check for a vacuum leak?  I'm not sure how to go about doing that.

I tell ya, I was not always sure I would get the TQ running again, especially since I had never even opened up a carb and having beat up linkages.  Without fine tuning this car already runs so much better than it has in who knows how long. 

I'm going to get some new mufflers and add an H pipe.  I'll also play with the metering rods a bit, I guess it can't hurt.  Besides metering rods and jets or a possible leak, is there anything else that could be responsible for the low vacuum?  Now keep in mind, my idle is so low it's a wonder it doesn't stall on me.  It's way low, does that bring vacuum down to 9?

[Canadian1968]

Sorry to high jack this thread slightly . I have 440 stock except for a Holley 750 CDMA carb. I am getting 20" of vacuume at idle . The cam will make that much of a difference??

[A383Wing]

yea, it will...I had the purple shaft in my 66 back in the 80's....it lasted maybe 6 months...no vacuum, and not very streetable for a daily driver with a 4spd..

Dino, you may be able to bump yer timing up a bit to get more vacuum...I would like to see yours around 14" or so if possible

Bryan

[cdr]

Sorry to high jack this thread slightly . I have 440 stock except for a Holley 750 CDMA carb. I am getting 20" of vacuume at idle . The cam will make that much of a difference??

yes it can









yes dino a real low idle will make the vacuum lower,also is this your intake?

[flyinlow]

What is low? 800 - 900 rpm in park seams to work . Engine is happy, power brakes are happy and the transmission can live with it. 

[flyinlow]

A way to check for vacuum leaks is with a can of carb cleaner. Use the plastic tube to spay around the base of the carb with a warmed up engine idling. listen for rpm increases and a smoother running engine. Also check the intake to head gasket . Don't spray in the throttle bores, that always increases rpm.
Lose carb mounting bolts, or the 10 carb thru screws not snug can cause leaks.  TQ use a specific base gasket. A Quadra Jet gasket looks similar ,but will leak.

Main jets, secondary jets and Main metering rods are not in use at idle and should have no effect on idle vacuum.

Vacuum  leaks, ignition timing, idle speed and idle mixture screws will effect idle vacuum.  That MP cam from what I have heard is know for lower idle vacuum, but that's what you have ,so tune what you have for the best results.

[Dino]

Ok I'll start with setting the idle a bit higher and record the numbers.  I'll have to take it to the shop to do the timing, I have no clue what to do.  Cdr that does look like the intake I have.  The base gasket I'm using is a grey 1/4" thick felt type that came with the rebuild kit..

I mentioned the metering rods because of the wot trouble.  But I'm still not sure what is causing this.  I don't understand why the car moves as swift as it does at wot in second but sounds like it's going to die when It shifts to third.  Why would it do that?  Obviously it can climb in speed and rpm real fast so why change when it shifts  I wonder what it does when I bring it up to high speed slowly?  It's academic unless the let me borrow the airport runway but would be nice to know nonetheless....
I would think the accelerator pump works as it reacts instantly when I mash the pedal.  I can understand that the load changes going from 2nd to 3rd but I guess I just don't understand mechanics enough to find the link.

Can it have anything at all to do with the transmission?  Can my linkage be out of synch? 

I can't say what rpm the idle is at without a tach but a quarter turn less on the idle screw and it dies.  It's as quiet as I've ever heard the and gives a nice slow chugga chugga.   
One of my mufflers also rattles which I had never heard before.  Seems the low idle frequency is playing ping pong ball with the muffler against the frame.

I have a can of carb cleaner so I'll go play a bit with that!  I have to admit, after a day of work, and school, it's fun to tinker with this carb and guess what!  The horrendous fuel smell is pretty much gone.  All I smell is a tiny amount of normal, non cat exhaust.  When I really stomp on the throttle I may get a whiff of gas so hopefully I can get rid of that but it's really not that bad.
Oh and I'm ordering a fuel sending unit as well.  Any tips on where to buy fuel lines?  Being this was a sb car, I think I have a single 5/16 line so I''ll need a 3/8" line and a 1/4" return line and whatever connects fuel pump to canister to carb.  I think I saw a pump to TQ hard line on ebay so I'm gonna look for that.

[flyinlow]

Probably not the trans if was working fine before. Incorrect kick down linkage adjustment can cause no kick down, early or late shifts, rpm flaring during 2-3 shifts and eventually premature trans failure if driven hard without sufficient throttle pressure. Switching carbs or intake can mess up the adjustment. Basic adjustment has the  kick down linkage all the way forward at curb idle (no choke) and all the way rearward at WOT. Always check that if you hold the kickdown linkage fully rearward ,that the carb can still return to idle on it's own in case the kick down linkage sticks you will not have the carb at WOT. That's why there is a slot in the link.
You could be running out of gas about the time you hit 3rd gear: dirty fuel filter, restricted fuel line, dirty pick up sock in the tank, plugged vent in gas cap and of course the dreaded worn out BB Mopar push rod.

3/8 metal fuel line would be a good choice .

Carter carbs like high fuel flow but not high pressure. over 6-7 psi can cause flooding.

[flyinlow]

push rod

http://www.dodgecharger.com/forum/index.php/topic,82973.0.html

[Dino]

It looks like my linkage is set up just as you describe so I guess I did that part right.

Before I swapped the carb I was able to floor it through all gears without having this issue.  It wouldn't run great with the old carb but it still pulled through third fine. 

That said, maybe it's a good idea to replace the pump when I replace all the fuel lines, sending unit and install the vapor cannister. 

I drove it into work this morning, it's very responsive but it takes a long ass time to warm up without that choke.  What type of mechanical choke are you running flyinlow?

[71 SE3834V]

Dino, you can always run by here and I can put a tach & timing light on it. Downriver cruise is the 29th (hint, hint).

[flyinlow]

.  What type of mechanical choke are you running flyinlow?

Home made. Jegs cable and soldered a lever to the choke linkage.

[Dino]

Dino, you can always run by here and I can put a tach & timing light on it. Downriver cruise is the 29th (hint, hint).

It looks like my car will be done running for this year.  There's too many things that need to be done to the car.  I'm going to have to try this timing light thing on my own so wish me luck!

[71 SE3834V]

Dino, you can always run by here and I can put a tach & timing light on it. Downriver cruise is the 29th (hint, hint).

It looks like my car will be done running for this year.  There's too many things that need to be done to the car.  I'm going to have to try this timing light thing on my own so wish me luck!

Yeah, I'm kinda in the same boat since I found out how much slop I had in the timing chain. Don't wanna risk jumping a tooth or worse so back into storage it went until fall when I'll have more time to deal w/it. Fortunately I have a back up cruiser so the summer is not all lost but it too needs work (brake line). It's always something.

Alot of times it's easier to work w/someone to learn something new as opposed to "learning" it yourself so when the time comes, if you want, the offer is still open about the timing light/tach issue.