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Hello I'm new to the forums, after being brought to Hotrodders many times googling around questions on tuning my Edelbrock 1406 I thought I'd make my own thread.

I drive a 1980 Camaro it's got a Chevrolet 305 with a camshaft upgrade, I was told it was an "RV" camshaft. I'm not certain on any specifications on it. I've been chasing the 'perfect' tune for maximum power and drivability as I daily drive this car.

The issues
I get run-on when turning the car off in park sometimes but not every time
At WOT or hard acceleration the engine bogs hard again sometimes, but not every time.
It's also got a bit of a stumble at about 10% throttle, after that it smooths out.

My timing is 10 degrees BTDC and tuning the air/fuel mixture screws on the front of the carburetor I'm getting 20 - 20.5 hg on my vacuum gage.

I'm idling in park at about 1000-1050rpm with the idle-speed screw turned completely out, in drive I idle at about 650-700rpm. I'm connected to ported vacuum in regards to the vacuum canister on the distributor, is this normal considering the different cam? The car runs pretty good but I feel it could run better.. it sounds like it's idling fast not quite that 'muscle car' rumble.

Any tips/recommendations on anything I can do to chase this issues away or help improve the overall performance of my car is greatly appreciated, thanks!
 

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True Hotrodder
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Most RV cams are meant for low rpm and high torque, probably moves the car pretty good initially then dies out. Fine tuning the 1406 requires that you have some tuning parts for it - if not, you can spin the screws any direction you want and you're only going to get but so much out of it. Throttle tip-in stumble is indicating that you need additional pump shot. Looking at a picture of one, I see that there are 3 pump shot holes - you could try working with those. And you might want to experiment with increases in the idle timing - a few additional degrees there might help you out.
 

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From Canada, eh!
Where in Canada?
Your location can effect your tune of the carb and your timing.
 

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A thousand RPM idle sounds like a lot as does 20 some inches of vacuum. One possibility is the cam is not very radical and the engine is tuned wrong for it. The other is the cam is on the rad side of RV and wants more compression than the engine has and as a separate but related issue is it wants more idle advance. Whether it prefers more of that in the base setting or will be happy if it comes from vacuum is something you’ll have to play with, that includes some back and forth as to whether it likes more base and a delay of vacuum on the timed port, whether it likes more base with vacuum on the full time port against leaving the base where it is and fiddling the timed or full time vacuum port. Keep notes, it’s easy to loose track of what you did and what results you got.

Generally the best solution is the least curb and mixture screw with the most advance that provides the best idle vacuum. So you have to walk all of this back and forth, which can be a real exercise in PIA. Run a compression test before doing the timing if there are cylinders that are down it makes solving these other issues more difficult. We’ll save wiped cam lobes for another day.

Bogie
 

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Edelbrock part throttle bog can often be fixed by changing step-up springs. The springs determine how fast the rods move from cruise to power position. Stock springs are probably 5”, which means it goes power mode when vacuum drops to 5”. Tuning kits have 6”, 7” and 8” springs, and by using a higher rated spring you get power mode sooner when you accelerate, which helps get rid of a bog.

I would also try more base timing. 12-16 BTDC is fine as long as you don’t get detonation during light acceleration from cruise. Also check your mechanical advance, and don’t let base + mechanical go higher than about 34-36.

Bruce
 

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1949 Ford Coupe RESURRECTION
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I've posted similar recommendations before and have gotten a bit of pushback from some of my dear friends here, but here I go again. I'm not just guessing, as this is what I did to get my carb perfectly tuned the first time and she runs as well as if she was fuel injected. No stumbling, flat spots, etc...

Purchase a wide band fuel/air ratio sensor/meter kit. Google it. Lots available from 40 to 150 bucks. You or a friend or a muffler shop can weld the bung in your header drop pipe. Make a note of all ratios from idle, soft acceleration, harder acceleration, and WOT. Download the tuning manual from Edelbrock website. Compare your readings to the charts for rods and jets and get a selection of rods and jets closest to your estimate of what you think it needs. You might get it right on the money like I did on the first combination! Good luck and keep us posted. Bogie is always right, by the way.
 

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Discussion Starter #7
Most RV cams are meant for low rpm and high torque, probably moves the car pretty good initially then dies out. Fine tuning the 1406 requires that you have some tuning parts for it - if not, you can spin the screws any direction you want and you're only going to get but so much out of it. Throttle tip-in stumble is indicating that you need additional pump shot. Looking at a picture of one, I see that there are 3 pump shot holes - you could try working with those. And you might want to experiment with increases in the idle timing - a few additional degrees there might help you out.
Thanks for the reply! I'm still experimenting with the pump shot holes, it's been in the top hole the entire life of the car and moving it around didn't seem to resolve anything. I'll have to look into some tuning parts & play with a few additional degrees in timing I think. I'll be getting a timing light this week and post how things turn out.
 

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Discussion Starter #8
From Canada, eh!
Where in Canada?
Your location can effect your tune of the carb and your timing.
Indeed! I'm from British Columbia, Vancouver Island Area. It's definitely getting colder and I did notice an increase in rpm when the cold hit.
 

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Small Island.
Not sure if there’s room for both of us!
I’m north of Qualicum Beach near Bowser.
Where exactly are you.
 

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Kinda like a neighbour!
You want some help tuning your 305 I’m here. Retired. Here all the time.
My mug shot is on this link. On their Facebook page. I gave some tools to a young guy. I’m the old guy in the hat.


 

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Try manifold vacuum. This will allow you to backoff the idle screw which will stop the run-on.
or you can add more mechanical with the distributor but be careful of total mechanical advance.
The drop from park to drive should not be as great as you have.
 

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1949 Ford Coupe RESURRECTION
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55_327, that's what I alluded to in my previous post, but an OXY sensor/gauge is needed for the guidance as to which way to go...
 

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Just an FYI...

The 1406 is designed for better mileage, whereas the 1405 is the "performance" model of the two 600cfm models.
It isn't a matter of the same carb with different chokes. They are actually different bodies, so changing the jetting doesn't make a 1406 the same as a 1405.
This is according to Edelbrock's documentation... which of course you wouldn't even know until you've bought the carburetor, if you happen to read the documentation completely... and I'm not even sure if that info is provided with the carburetor.

As for the off-idle stumble, as mentioned it could be an accelerator pump issue, or it could be a step-up spring issue.
I'd try stronger step-up springs first, as that's the easiest change to make. You don't have to take the top off the carb.
I had a stumble on my 327 with an L79 cam. I had messed with the acc. pump and that didn't fix it. Recently I changed to the "Silver" step-up springs and the stumble went away.
Since you mentioned that you have alot of vacuum, I'd try the Silver springs, which are stronger than the stock Orange springs.

If you look at the instructions in the Edelbrock rebuild kit for these carbs, they specify which hole the linkage should go in, depending on the model. I don't recall changing that being one of the steps in the calibration guide, so I'd suggest leaving that where it should be for your model until you've gone through the steps in the calibration guide.
Change the springs to stronger ones, see if that helps, and then go through the calibration guide procedure to get everything fine-tuned.

Oh, and also as mentioned by someone, make sure your dizzy vacuum is hooked up to the port on the driver's side of the carb. The one on the passenger side is "timed port", which is for smog equipped vehicles apparently. That may actually solve your problem altogether.

Can't say what the deal is with that high idle. I'd suspect a vacuum leak, but you're reporting high vacuum, so...

Best of Luck
 

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55_327, that's what I alluded to in my previous post, but an OXY sensor/gauge is needed for the guidance as to which way to go...
Sorry I missed your earlier comment. I've had pretty good success over the years tuning those carbs based on the charts, throttle response, and altitude -- everywhere from 5,000-10,000 ft in Colorado to 600 ft and less in Texas. Should have bought a wideband sensor years ago, but I think EFI is in my future.
 

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Off idle stumble is often the result of too much curb idle open adjustment. Most often seen with big cams but also associated with insufficient base advance.

What is going on with too much curb idle opening is that the throttle blades are in a position that exposes the transition fuel feed ports. When this happens there is a fuel supply gap between idle and main metering because the transition circuit is now feeding at idle and there is a physical gap between when the combination of throttle position, manifold vacuum, and airflow. Both the idle and shortly thereafter transition circuits depend on manifold vacuum to operate where main metering depends upon air flow. The main metering is also vacuum sensitive but that vacuum is formed in and by the venturi air flow and is proportional to air flow. Where manifold vacuum is inversely proportional to airflow so the closed or nearly closed throttle results in little air flow which causes a high vacuum on the idle ports and to a lesser degree the transition ports.

When both the idle and transition ports are feeding fuel at idle, the mixture tends to be rich while the screw adjustment has little if any effect. This is an indicator of maladjustment between the idle throttle position and probably too little base advance for the cam timing and compression.

In the latter of the above in general factory compression ratios are inadequate for large cams, especially those with narrow LSA’s at or under 110 degrees.

Bogie
 
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