Timing Questions

[Kuruton]

Hello again!

I've got another probably dumb question or two. I am running electronic ignition with mechanical and adjustable vacuum advance on a 440 and an Edelbrock 1411. I have my vacuum advance running from the carb's "timed vacuum" port to the distributor (rather than "manifold vacuum"). I had previously set my timing to about 15 at idle with the vacuum disconnected but hadn't read up much other than that. I've been having some pinging in certain rpm ranges (with 91-93 octane) and figured I'd give it another look. I noticed that at idle I was sitting at probably 35-40 degrees of advance with the vacuum connected which left me a bit confused. I was under the impression that the timed advance doesnt pull a vacuum until higher in the rev range? I can adjust the vacuum advance screw super far out and get it back to 15, but I imagine I'm basically just cutting off all vacuum advance at that point? Any insight would be super helpful! Also worth noting is that I have the performer rpm intake with the vacuum port plugged.

 

[Challenger RTA]

More info on build. There are some builders here that can answer that. What's your compression? That's what comes to mind. Don't go off that. I could be dead wrong.

 

[Ricks72Chlgr440]

If you're using timed vacuum you should not get any vacuum at idle. Could be your idle is too high because the engine wants more base timing. If the engine is pinging at higher RPM'S then you should change the advance springs and likely put in an FBO limiter plate to keep the timing from advancing too far.

 

[Xcudame]

What RPM is it idling at now? Give more particulars on your total build. Camshaft, engine compression (gauge - not ratio). Like Rick said, you my need to tayler your mechanical advance to fit your combo.

 

[Kuruton]

As far as I know and can tell it's a stock late 70s RB 440. I ran a compression test yesterday and these were the numbers:

1: 132
2: 140
3: 135
4: 129
5: 134
6: 127
7: 135
8: 125

I have it idling around 800 at the moment, and if I were to re-adjust the vacuum advance on the cap, it would idle higher. I'll definitely look into how to adjust my mechanical advance and that limiter plate today. The thing that still confuses me us why I'm pulling vacuum through that port at idle?

 

[Ricks72Chlgr440]

As far as I know and can tell it's a stock late 70s RB 440. I ran a compression test yesterday and these were the numbers:

1: 132
2: 140
3: 135
4: 129
5: 134
6: 127
7: 135
8: 125

I have it idling around 800 at the moment, and if I were to re-adjust the vacuum advance on the cap, it would idle higher. I'll definitely look into how to adjust my mechanical advance and that limiter plate today. The thing that still confuses me us why I'm pulling vacuum through that port at idle?

The Edelbrock carb has two vacuum ports. Does the one you're not using have vacuum at idle?

 

[Kuruton]

The Edelbrock carb has two vacuum ports. Does the one you're not using have vacuum at idle?

I'll check that, when you're looking at rhe face of the carb, I'm using the left one, which shhhoooouuuuld be the timing advance but I can definitely check the other one. Is there a world where a bad gasket could have both pull vacuum?

 

[Xcudame]

The "ported" vacuum is right above the throttle blades in the venturi. The port should set a little higher on the right (left side your perspective looking at the carb). See photo below.

 

[Kuruton]

The "ported" vacuum is right above the throttle blades in the venturi. The port should set a little higher on the right (left side your perspective looking at the carb). See photo below.

View attachment 117592

Thanks! Yeah as far as I can tell, I should be hooked up right. Here's a pic

Also, the pcv Is hooked up to that front middle port and brake booster to the back.

 

[Xcudame]

You got the correct port. Try dropping the RPM at idle a little bit. In gear, the idle should be in the 650 to 700 RPM range. You could be just opening the throttle blades enough to expose the ported vacuum. Why does the throttle cable look disconnected? And one carb mounting bolt is missing?

 

[Kuruton]

You got the correct port. Try dropping the RPM at idle a little bit. In gear, the idle should be in the 650 to 700 RPM range. You could be just opening the throttle blades enough to expose the ported vacuum. Why does the throttle cable look disconnected? And one carb mounting bolt is missing?

Okay, I will definitely look into my carb settings as well.

Haha good eye! it's just an old picture while I was disassembling and reassembling things. I did actually ruin the threads on the intake on that front right outside hole, so I had to move that stud to the inside hole in the end.

 

[Challenger RTA]

By chance do you have a vacuum gauge. Check it see what you have at that port. Just incases there is some thing amuck.

 

[Kuruton]

By chance do you have a vacuum gauge. Check it see what you have at that port. Just incases there is some thing amuck.

I do not, but I can grab one. Have any recommendations of something quick that would work from like Amazon or something?

I don't know what's normal but I did notice quite a bit of vacuum on that port as well as my pcv while idle

 

[moparleo]

The best thing that you can do to help us help you, is to give us as much info on this engine as possible.
Stock short block ? cam ? intake manifold ? ignition ? etc..
A picture of your entire engine would be a plus to see the setup.
You gave us some compression numbers. How exactly did you measure it ?
Normal procedure is warm engine, spark plugs removed, throttle blades held wide open ( as simple as a screw driver wedged down the throttle bores).
Crank the engine no more than 4 complete revolutions. Do exact same number for each cylinder.
You need proper tools to do any type of service/testing/repairs.
Factory Service Manual ?
Need more than a hammer to build a house.
Resource Library – MyMopar

 

[Kuruton]

The best thing that you can do to help us help you, is to give us as much info on this engine as possible.
Stock short block ? cam ? intake manifold ? ignition ? etc..
A picture of your entire engine would be a plus to see the setup.
You gave us some compression numbers. How exactly did you measure it ?
Normal procedure is warm engine, spark plugs removed, throttle blades held wide open ( as simple as a screw driver wedged down the throttle bores).
Crank the engine no more than 4 complete revolutions. Do exact same number for each cylinder.
You need proper tools to do any type of service/testing/repairs.
Factory Service Manual ?
Need more than a hammer to build a house.
Resource Library – MyMopar

It is as far as I know a completely stock '78 RB 440 and all I have done to it that is relevant is added the Edelbrock performer non-EGR intake and installed a new distributor [This one], along with swapping the cap to the male type [here]. It has the Edelbrock 1411 carb with no spacer. Fuel is always 91-93 or 87 with octane booster. Valve covers have one baffled opening on each side. Drivers side has a one way valve acting as a PCV that pulls air from the carb into the crankcase and passenger side is a vent. Carb has all stock needles but has springs changed to be slightly richer on the higher end. Spark plugs are NGK XR5 3332 gapped to .035. Mechanical fuel pump with regulator set to 6psi.

I measured compression with all spark plugs removed, battery hooked up to charger/jumpstart unit to maintain voltage, 8 total cranks for every cylinder but nothing done to keep throttle blades open.

I have timing at 15 according to the balancer with no vacuum hooked up and with the vacuum hooked into the timed vacuum port on the carb, it jumps up to probably around 35ish (hard to say because the gauge only goes to 20 and Im not sure how accurate it is.) I could add some ticks to extend it though. And then if I pull the throttle cable with the vacuum advance turned way down, to where it still idles at 15, it maxes somewhere around probably 40, thats not doing any math, just looking at the line on the balancer.

 

[moparleo]

A stock 78 440, Had to come from truck/motor home.
The CR specs for for a 71 440 was 9.7 : 1 (Last year for automobiles and HP) and the factory specs for compression test was 110 PSI so your readings are very high for a low compression 440.
New distributor? What exactly did you install ? That can make all the difference in the world.
Best plugs for stock heads/ cam , would be a stock type plug . Champion Copper was factory.
Auto-lite std and platinum are also excellent choices.
Avoid gimmicky stuff like muti- groove, electrode, U-channel etc...

 

[Kuruton]

A stock 78 440, Had to come from truck/motor home.
The CR specs for for a 71 440 was 9.7 : 1 (Last year for automobiles and HP) and the factory specs for compression test was 110 PSI so your readings are very high for a low compression 440.
New distributor? What exactly did you install ? That can make all the difference in the world.
Best plugs for stock heads/ cam , would be a stock type plug . Champion Copper was factory. RJ12YC
Auto-lite std and platinum are also excellent choices.
Avoid gimmicky stuff like muti- groove, electrode, U-channel etc...


View attachment 117608

Based on the casting number, I know it's a 75-78 motor home engine. I don't quite remember where I read that it's likely a 78 specifically so that could be wrong. Would that compression lead you to believe that it isn't stock then?

 

[mrmopar340]

Did you verify the timing marks on the harmonic balancer to see if timing marks are correct? We always try to verify those before we do any timing work. If that is off by even a little bit it changes the timing quite a bit.

 

[Ricks72Chlgr440]

Based on the casting number, I know it's a 75-78 motor home engine. I don't quite remember where I read that it's likely a 78 specifically so that could be wrong. Would that compression lead you to believe that it isn't stock then?

View attachment 117610

If there is a lot of carbon & junk built up on the pistons & combustion chamber that can certainly raise the compression. That could also account for the pinging.

 

[Xcudame]

By the way, the link for the distributor took me to a Mopar small block. That must have been a mistake as a small block distributor wouldn't bolt up. Hopefully you got this one:
DODGE Summit Racing SUM-851005-1 Summit Racing™ Billet Electronic Mopar Distributors | Summit Racing

Timing should be set with the vacuum advance port capped off. Shoot for 32-34 degrees total. If your at 15 degrees by rotating the distributor plus the 22-24 mechanical advance of the distributor, you're between 37-39 degrees and that's too much and it's going to ping! Try 10-12 degrees before on the timing mark.