low vacuum 383

[67 ragtop]

I have a thread open about vapor lock but this is different.
My 67 Sport Fury convertible with a 383 2 bbl only has 8 inches of vacuum . Timing is set at 8 degrees vacuum is steady at 7-8 inches depending on the vacuum gauge. compression is 160- 165 across all cylinders. idle is set at 700 RPM . the idle is smooth but sounds like it may have a small cam in i,t as there is a slight lope heard in the exhaust. I have used propane but could not find a leak, plugged the brake diaphragm hose and no change. I just rebuilt the Carter BBD 11/2 inch.
My neighbor and I who have both been either term backyard mechanics or actual mechanics are trying to figure this out. it runs beautifully but the vacuum is low. I am enclosing a video of her idling. If I didn't know better I would think she has a cam but who puts a cam in a 2bbl unless it is for class racing.
I couldn't post a video I guess it isn't allowed.

 

[CBODY67]

Intake manifold vac at idle is one thing. What is it at 2000rpm? What about if you advance the timing to 10 degrees BTDC or so? Miles on the motor? Hard to start?

 

[67 ragtop]

Intake manifold vac at idle is one thing. What is it at 2000rpm? What about if you advance the timing to 10 degrees BTDC or so? Miles on the motor? Hard to start?

I didn't look at it at 2000 RPM. I will check tomorrow. It was hard to start when cold until I got the choke pull off right, warm it always started immediately. I believe at 10 btdc it was at 12 inches. I will recheck tomorrow. Miles on the motor I don't know odometer says 6000 so probably 106,000 but could be 206,000 . I do know that the vacuum advance canister leaks but I did not have it connected during the test. I have a new canister coming this week.
The car drives great. I did not check the damper to see if the timing mark had shifted.
Thanks for the reply. I had already decided to up the timing to 10 degrees as that is where I had had it at prior to rebuilding the carb, and my neighbor helping me. He wasn't concerned about the low vacuum since the car idled and drove so well after we had adjusted the rebuilt carb.

 

[CBODY67]

Of course, with the vac advance on ported vacuum, that part is not advancing anything at idle, so it's all what the base timing is. At 2000rpm, though, it's fully operational and hopefully will be in the 18+" Hg at that speed. The base + centrifugal + vac advance should be in the range of 50 degrees BTDC or a bit more. That should increase the vac a good bit.

Personally, I have never had good luck using a vac gauge, from back in the late 1960s when I bought one to play with. I never could get anything we had (including a '66 Newport 383 2bbl) and our then-new '69 Chevy C-10 350 4bbl pickup to get over about 17" Hg at idle. Everybody claimed they should be over 18", but I never could get close to that, much less 20". Of course, I could get those vac levels on coast-down from highway speeds. BTAIM

Hopefully, things can get figured out,
CBODY67

 

[Ripinator]

I have a thread open about vapor lock but this is different.
My 67 Sport Fury convertible with a 383 2 bbl only has 8 inches of vacuum . Timing is set at 8 degrees vacuum is steady at 7-8 inches depending on the vacuum gauge. compression is 160- 165 across all cylinders. idle is set at 700 RPM . the idle is smooth but sounds like it may have a small cam in i,t as there is a slight lope heard in the exhaust. I have used propane but could not find a leak, plugged the brake diaphragm hose and no change. I just rebuilt the Carter BBD 11/2 inch.
My neighbor and I who have both been either term backyard mechanics or actual mechanics are trying to figure this out. it runs beautifully but the vacuum is low. I am enclosing a video of her idling. If I didn't know better I would think she has a cam but who puts a cam in a 2bbl unless it is for class racing.
I couldn't post a video I guess it isn't allowed.

Sounds like you have a vacuum leak somewhere. . .

 

[cbarge]

Are you reading a factory console vacuum guage?
If so it may not be 100% accurate. Check vacuum line feeding it for leaks
If not, Where are you hooking up your vacuum guage?
Need a constant vacuum source. Typically a tee at back of intake with booster hose.
Just for process of elimination, spray WD40 around the intake/ carb when running to see if the idle increases.
If so vacuum leak.
Factory A/C? Check vacuum pods at blend doors and main vacuum line from engine to HVAC controls for leaks
Next suggestion is crank the timing up while reading vacuum guage to get more vacuum.
You may need to turn idle down then recheck vacuum reading.
A factory 383 should get 18-20 inches of vacuum at 12 degrees BTDC with an 800 rpm idle with todays corn fed gas pumps.
Note where the timing is and road test for ping.
You did a compression test, but did you do a leakdown test to check for burnt valves?
Sometimes a burnt valve may not show up in a compression test when cranking the engine.
You said carb was rebuilt, but it is possible on of the 2 idle circuits picked up dirt, creating a lean condition, which can create a lopey idle.
Sorry for throwing a lot at you, but hope it helps.

 

[67 ragtop]

Sounds like you have a vacuum leak somewhere. . .

I think so too. I upped the advance to 10 degree and I now have 12 inches of vacuum. I also need to shorten my upper radiator hose because the vacuum advance can is pushing on it when set to 10 degrees. It slants in toward the carb before it tuns .

 

[sprice]

I think so too. I upped the advance to 10 degree and I now have 12 inches of vacuum. I also need to shorten my upper radiator hose because the vacuum advance can is pushing on it when set to 10 degrees. It slants in toward the carb before it tuns .

Could you not move the number one cylinder (and then others of course) plug wire to left or right? This should change the clocking of the distributor without needing to change the rad hose.

 

[Boydsdodge]

I really think you need to set it with more initial advance. You my end up with 16 deg initial and 18 inch vacuum. Then if you can get to a distributor machine you can do a recurve.
You don't even need a machine, you can get the recurve plates from How to limit mechanical advance in a mopar distributor, tuning for street, strip or all out racing, cure that rich stinky idle, win races
I use the plates when setting up distributors. Gotta order some more.

 

[cbarge]

I really think you need to set it with more initial advance. You my end up with 16 deg initial and 18 inch vacuum. Then if you can get to a distributor machine you can do a recurve.
You don't even need a machine, you can get the recurve plates from How to limit mechanical advance in a mopar distributor, tuning for street, strip or all out racing, cure that rich stinky idle, win races
I use the plates when setting up distributors. Gotta order some more.
View attachment 652574

With todays gas a recurve is a must to make the engine more effecient

 

[Boydsdodge]

Find the initial that the engine likes, then send it off to @halifaxhops for a curve. Watch Tall Johnsfun shop for plenty of info on the whys and hows of timing setup.

 

[ynst]

Vacuum hose rotted away or fallen off in the heater control system, probably under the dash?
Bad power brake booster?
Cheap vacuum gauge?

 

[67 ragtop]

Vacuum hose rotted away or fallen off in the heater control system, probably under the dash?
Bad power brake booster?
Cheap vacuum gauge?

Vacuum can is leaking a little I tried to order a new one but was sent one for a Chevy. Rock auto is the only one who lists one for the 383 they list 2 but one is not in stock and the other one is the one NAPA ordered which does not mount to my distributor and standard lists it as for a Chevy 350 . Will the can off of a 440 work? The only cans I can find for the 383 are for the Electronic distributors and the arms are wrong.
Moving my initial to 12 degrees boosted the vacuum to 15 . I am about to take the tach off of my Ranchero ( temporarily) so I can set total centrifugal timing to 36 degrees and total with vacuum to 40 to 45 degrees.
I am used to playing with Mallory dual point distributers on my Ranchero and that is the way I set them. Normally with 22 initial all in at 2800 RPM and fourteen degrees advance The Mallory is so tunable This car I meant to be a cruiser and it doesn't have a Comp 292H cam in it and 750 cfm double pumper .

 

[cbarge]

Vacuum advance for a 440 will fit but may have a different advance curve.

 

[Boydsdodge]

Contact @halifaxhops
Or if all else fails get one of these. More Information for CARDONE 843817

 

[3C's & a D?]

Vacuum Advance Mechanism

 

[MoPar~Man]

What is a "Vacuum can" ? Do you mean diaphram?

How are you not getting spark knock at 10 - 12 BTDC ? What octane gas are you running?

Buy another vac guage (one that can read engine vac and fuel PSI in case you need it). Prices are like $20 on amazon. Connect it with supplied (ie - SHORT) length tube to the correct port on the carb.

With compression numbers as high as you say - I would expect much better vacuum. And why is warm idle speed so high? Should be aiming for 550 rpm. And people wonder why their cars overheat in stop-and-go parade traffic like the Woodward dream cruise.

How are the plugs looking? Maybe weak spark, too rich or lean? Electronic or points ignition?

 

[CBODY67]

Base initial timing for any B/RB motor used to be 10-12.5 degrees BTDC, before emissions got to be an issue. I normally ran our '66 Newport 383 2bbl at 15 degrees initial for ages. For some reason, the 383 2bbls have an advance curve that hits all the numbers. With total of about 36 degrees BTDC at just over 4000rpm, yet the 10.0CR motors were more like 31 degrees total. In those times, I was normally using premium fuel as the car never did like regular.

On that 383 2bbl, one time the mpg dropped to 10mpg from about 14mpg average. The vac advance diaphram had failed. I could not tell a whole lot of difference in the way the motor ran, as things evolved, but the new vac advance unit picked it back up on town driving and put the mpg back to where they had been.

Vac advance units are different for electronic ignition distributors, as the arm is shaped differently. Seems like Standard Ignition Products used to have some listings? In Rock Auto, when you click on the "INFO" icon in the parts listings, that brings up the appropriate page for the part. Then click on the manufacturer's icon in the upper lh part of the screen and it will take you to that company's online catalog.

KEY thing to remember is that if the main companies which sell rebuilt distributors can still sell products, then somebody has to be making parts for them to build their products. The aluminum-body items are different from the cast iron body distributors (i.e., Prestolite, which also built single-point distributors).

Just some thoughts,
CBODY67

 

[67 ragtop]

What is a "Vacuum can" ? Do you mean diaphram?

How are you not getting spark knock at 10 - 12 BTDC ? What octane gas are you running?

Buy another vac guage (one that can read engine vac and fuel PSI in case you need it). Prices are like $20 on amazon. Connect it with supplied (ie - SHORT) length tube to the correct port on the carb.

With compression numbers as high as you say - I would expect much better vacuum. And why is warm idle speed so high? Should be aiming for 550 rpm. And people wonder why their cars overheat in stop-and-go parade traffic like the Woodward dream cruise.

How are the plugs looking? Maybe weak spark, too rich or lean? Electronic or points ignition?

Yes vacuum can was what we called it back in the 1960's/70's. 12 1/2 degrees btdc is factory spec for the 383 2 bbl in 1967 unless you had the California emission package 'C.A.P]where it went to TDC adv for the 2bbl and 4bbl for std trans and 5 btdc for Automatic trans. [which is where I got my original timing specs from google. and went from manifold vac advance to ported . I have 3 vacuum gauges already and they all read the same after I fixed the small leak in the one I borrowed from my brother before I found mine'. As for the idle speed the service manual states 550 for C.A.P. engines 700-750 for non C.A.P not to drop more than 50 RPM when put into gear and it should be smooth transition. I originally was using the 550 as that is what google had said.
I need the tach to set total advance/ and to follow the specs in the manual for the timing curve. Now that I have located where the distributer curves are in the manual and I don't have a distributor machine,
I am running 87 octane. Pertronix ignition and flamethrower coil. I, like you expected more vacuum hence the post. As for the overheating at low speeds. Ford actually had a thermal switch to go from ported to manifold vacuum when engine temp went over 212 degrees to advance timing and increase engine speed. This was in 1968 after emission regs went into place. The early years of emission controls caused a lot of different ideas to be tried.
Thanks for the interest I appreciate it.
Also this has gotten me to delve deep into the service manual because I couldn't find where the timing specs and idle speed ere located. They are not altogether in the same location for example ignition specs are on 8-102 which also gives the centrifugal and vacuum curves, the general engine specs for a 383 are on 9-99 which gives the timing specs , idle speeds are in a totally different section.
On further checking you are correct idle speed is supposed to be 500 to 550. I got the 700 from my Old motors manual.

 

[67 ragtop]

Vacuum Advance Mechanism

Thanks I appreciate it. I called Mancini racing and that one won't work on a single point distributer. it is for electronic ignition. Which is what I am finding every where. I may go with the Cardone distributer or a Summit racing distributor. Proform Parts 66993 Proform Electronic Distributors | Summit Racing , Summit Racing SUM-851014 Summit Racing™ Electronic Mopar Distributors | Summit Racing/ The cardone I can fit my Pertronix into it and use my flamethrower coil with the other two I can't use my flamethrower coil because its resistance is to low.

I really think you need to set it with more initial advance. You my end up with 16 deg initial and 18 inch vacuum. Then if you can get to a distributor machine you can do a recurve.
You don't even need a machine, you can get the recurve plates from How to limit mechanical advance in a mopar distributor, tuning for street, strip or all out racing, cure that rich stinky idle, win races
I use the plates when setting up distributors. Gotta order some more.
View attachment 652574

Thanks to the link for the FBO plate. I have been looking for it since hearing about it several places on you tube.
I wish I had a distributer machine. When i lived in CA. I used a friends machine.