1406 problems and how I fixed them
I am not going to act like I know everything because I am very new to carburated motors. I purchased a 1406 from edelbrock and ran into problems with flooding and acceleration stumble. Being new to this I set off to forums and google to find a straight forward or step by step action and it was hard to find or was centuries old and couldn't post in them. One thing I did find is that the problems I was having are extremely easy to fix. With suggestions from gear heads on this site and gear heads around me I was able to compile a systematic approach to solving, especially new, edelbrock problems. Please do not say how much better other carbs are because that is not relevant to this topic. However, if something I say is wrong or you want to add please do so. The very first thing to mention is this carb will not run well, if at all, with stock fuel pressure. 3-6 psi needs to be achieved whether it be with an after market fuel pump(e.g. edelbrock 1721) or a regulator. Most likely a regulator will be required no matter what, even though edelbrock will not say so. Either way a fuel pressure gauge needs to be installed and read 3-6 psi or you WILL have a flooding condition! Even though edelbrock carbs are very simple it takes time to tune them properly. After each adjustment take a test drive to see how it effects how the motor runs. If you change 3 things and then the motor runs like crap, then you are back at square one and it will take even longer. Be patient, it will pay off!
- There are 3 circuits on any carb. Idle circuit which is controlled by idle mixture screw on the front of the carb. Floats can also be included in this circuit because a flooding condition by floats is easily identified at idle. The spark/timing side of the circuit is initial timing. The cruise circuit is controlled by the primary jets and rods. Vacuum advance can be included in this circuit, but on the spark/timing side of the circuit. Usually above idle-3000rpm give or take. Last is the power circuit which includes all jets and rods (primary and secondary). On the spark/timing side of this circuit is mechanical/centrifugal advance, controlled by springs weights and bushings inside dizzy. Power circuit is usually above 3000 rpm("all in"), give or take. It is clear that spark and fuel work together in each circuit to make things go boom.
- First and most important is make sure your timing is dialed in. My gramps always said 99% of carb problems are timing. If your motor will start, then timing needs to be the first thing before the carb is even touched. Spray carb cleaner or brake cleaner(not starter fluid!) at vacuum connections and intake to make sure you do not have leaks or timing will likely be inconsistent/inaccurate. Attached is a write up by Lars Grimsrud that explains Timing better than most anything out there. Especially helpful to those at high altitudes since he is from Lafeyette CO.
- Second, which if the carb is new and you followed directions should be done before carb is installed, and that is checking float levels are at 7/16 which is factory setting. Check needle and seats to make sure they are clear of dirt. Although it is tempting don't change the jets while you are in there. The carb should run relatively well with stock jets, rods and springs. These carbs are simple, if your flooding at idle and your timing is set correctly then it is either fuel pressure, floats or seats and needles. Jets, rods, springs and pumps only come into play once throttle is open. Note: I found 5/16 float at 5000 ft. to be one of the only changes that needed to be made from stock.
- If you experience excessive flooding after checking and confirming the float measurement, and you know that fuel pressure is between 3-6 psi, then open the carb back up. Remove the float and shake it. If there is fluid in the float, it becomes more of a sink and must be replaced. I experienced this with a brand new carb.:spank: Contact edelbrock and they will send one. If you are impatient like me pepboys carried floats needles and seats near me.
-Now that the motor is purring, even though it may be rich or lean, take it for a cruise around the block. More likely than not, if you have a stock/mild built 350, you are going to experience hesitation/stumble when you press on the gas from idle. This is the accelerator pump going down to far when the throttle is pressed, causing an off idle flooding condition. Luckily this is easy to fix. Go back to the garage, or bring needle nose with you and remove the clip on the front of the drivers side accelerator pump linkage. Move it up to the hole on the top, nearest the pump/towards the hood, then reinstall clip. Drive again to see if this corrected the problem.
-Edelbrock provides a description of how to adjust idle mixture screws that is somewhat accurate. However, hooking up a low speed tach(optional) and a vacuum gauge(not optional), you can get idle mixture screws dialed in more accurately. Vacuum gauges are cheap! Hook up your vacuum gauge to somewhere that has full vacuum, I use power brake connection. Put a mark so you know how many revolutions you have made with each strew Now turn one idle mixture screw down(clockwise) until motor seems like it wants to bog out. now turn counter clockwise until you achieve highest vacuum. You will need to adjust idle screw as you go to maintain desired idle. Now go to the other side and follow the same steps. The trick here is that both screws need to be at the same setting, the mark you make will help you make sure of this. Now, go back and forth, making slight adjustments, until you get highest possible vacuum at your desired RPM. Take note of the vacuum as it will help for the next setting. Take the car for a drive see how she runs. This is a dumbed down version. here is a website that goes into detail how to perform this task: Setting Idle Mixture The Right Way
- Even at 5500 ft here in Denver, the stock jets, rods and springs enable my mildly built 350 to run pretty darn good. However, edelbrock produces a calibration kit #1487 that has some jets rods and springs if you are running rich or lean. I will attach the manual which has a chart of which setting may be best for you. It also explains the different steps on rods. The 1406 is set from the factory lean for fuel economy, at sea level. After experimenting with the kit, I found the stock jets and a step up in springs was the best setting. A rule of thumb for springs is to take 50% of vacuum at idle and start there. If you have 16"hg at vacuum then start at 8"hg spring. Some will say add or subract 1 from 50% but this is just a starting point. Take it for a test drive with a couple different springs and see which one feels the best.
- The last thing I will say is similar to the first. Timing is key. If your spark isn't right then you will need have accurate fuel. Before changing ANYTHING on the carb get initial timing dialed in. Follow the article by Lars to get mechanical and vacuum at a good starting point. Do not change anything on any circuit until the respective timing is set on that circuit. The most accurate way to get Air/Fuel ratio is to have a wide band sensor and gauge installed. Then you can see in real time, for each circuit, when you are running rich or lean. If the 200 dollar investment is too much then save your money and you won't regret it! In the meantime you can pull your plugs to obtain somewhat of an idea. If plug is tan you are right where you need to be. If plug is white you are lean. If plug is black you are rich. Those are general guidelines, but I can not stress how important and how much easier a sensor and gauge is!
If old timers or anyone thinks I missed or mis-spoke please speak up. Like I said I will not act like a pro, just sharing my experience so that it may help someone. Also anyone that has had other woes with 1406 carb please mention those.
That is some pretty good info and seems you have picked up quite a bit working on your truck but one thing though when using a vacuum gauge to get highest vacuum on setting idle mixture screws on engines with bigger cams and more overlap they require a richer mixture and for instance on my 350 with a lunati voodoo hydraulic roller cam with 272/280 219/227 @ 50 515/530 lift with a 112 lsa I get around 17 to 18 inches in park and setting the mixture screws for highest vacuum leaves it to lean and that happens a lot on more performance oriented builds. I usually get it to the highest vacuum and then give it a 1/4 of a turn richer and it pretty much is spot on. If I don't have my gauge out I use the old edelbrock method and turn it slowly in and then when it starts to stumble I back it out a 1/4 or a turn when I am in a pinch and man it works every time. Edelbrock's are pretty simple to tune it just takes time like you have discovered and when one learns how each circuit works etc it makes tuning a lot easier. Good write up.
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