1406 Question

[chickenwing]

Finally got my truck out of paint! Drove her home with no front/rear glass. Rain was threatening... On the drive home there was a consistent hesitatation of idle, on part throttle acceleration. Step in it a bit more she smoothed out fine. Read every thing I could find on the search. Most of the stuff seemed to be "running too rich" posts. Re-read carb owners manual.

Truck has following: 10"? Air filter, 1406, 3/4"-1"? wood spacer, performer manifold. New Goodwrench crate motor with stock cam, HEI, accel wires, forget plugs but they are Delcos gapped to .045, cheapie flowtech headers, 700R4 with 3:73 diff.. Nice smooth idle @750 timed to 8 btdc. cheapie Autozone electric fuel pump supposedly rated 4-5psi.

As mentioned everything is brand new. Have not tried to tune anything beyond timing and idle. I found this tid-bit in the carb owners manual: CALIBRATING THE PUMP

If you encounter any hesitations or stumbles that do not seem to be related to the basic metering or have not responded to changes in the basic metering, move the pump drive link to one of the holes closer to the carburetor body. This will increase the stroke length of the plunger and result in more pump delivery.

Am I heading in the right direction here? I gotta concentrate on the glass first to get her road-worthy, but the carb is running a close 2nd.

any input appreciated. Oh, pics soon when rain lets up!
Rich

[sactoC10]

Wow, good questions. Let me get out of the way for the answers...

[lukecp]

What kind of stumble are we talking about? A rich stumble or a lean stumble? A rich stumble is more of a bog, while a lean is more of a hole in the power, and pops through the carb due to the lean condition. The accelerator pump could be your problem. If you think its running rich, move the lever down to get a smaller shot, and up to get a richer shot. I had a lean stumble on mine and moving it up helped out a little bit.

Also, if it runs fine and moderate throttle but not part throttle, check into the metering rods. You can get them in pairs for about $6 each from any auto parts store, and is a better buy then the kit IMO. I'd stick with whatever size the lower part of the metering rod you have now is, and go either larger or smaller on the top to fix your lean or rich condition.

Your owner's manual has a chart in the back which shows positions and rod/jet numbers to tune your 1406. If you have a 350 any more hopped up than stock it may need to go richer. I installed a stock 1406 on my 350 with a RV cam, headers, and allumium intake and it was too lean. I put in some richer metering rods (both in the cruise and power positions) and got it running great, along with upgrading the secondary jets from .095" to .098" for a larger shot of fuel when the 4bbl opens.

[chickenwing]

Yellow72, Thanks for the reply. I'm not exactly a tuning guru... Based on your description I have a rich stumble. Truck kinda bogs down on a slow easy acceleration from a stop and evens itself out around 3rd gear. NEVER pops through carb. If I get on it, the secondaries kick right in and she launches off fine. I think I will play with the pump first. Sounds easy enough. If that does not work I'll put it back where it was and start fiddlin with the metering rods. I think I can chart out the metering rods on the diagram ok. I just need to figure out which way to go. Mo gas or less gas.
Any further input from anyone appreciated.


Jeff, I saw your carb post a while back.... I take it you never figured it out? Will keep you in tune. ONE day we will tag up again. Doesn't look like it will be soon though. PHEASANT SEASON is here!!!!!

[dwaite72lnghrn]

Did you set the idle mixture screws or just set the idle with the idle screw on the driverside of the carb?
It sounds like the idle mixture is running rich or your float is off.

[incoma]

I had the same problems with my 1406 when I bought it years ago. I bought the tune kit from Edelbrock and used a full array of jets and rods until I found the right combination. It became a quest or crusade to find the right combination. I also find that my idle mixture screws are EXTREMELY sensitive with this carb. I also use the pump hole closest to the pump to help smooth that out. If you disconnect the wire from the pump and try to move it by hand, its tough to get started, but if you get it started its smooth. I'll be tuning mine this weekend. I should have my truck running again this weekend.

[chickenwing]

Dwaite, I have not played with the idle mix screws yet. I achieved a nice smooth idle with just timing ad the idle screw. Ok. Will do that first then. Instructions call for set 1 side for max idle then the other trimming for max idle. Once this is achieved it says to lean it out to drop it 20 RPM. I've got a digital tach and this is real hard to do!!!! How can I adjust the idle mix screws with a vacume gauge?
Any input appreciated.
Rich

[lukecp]

Its easy with a vacuum guage....just plug it into a vaccum port on the carb you aren't currently using that gives you vaccum at idle, set the idle RPM using the air screw, then fiddle with the mixutre screws, evenly on each side, until you get the highest vacuum reading. I'm sure there is a more scientific way to get the idle mixture set with a vacuum guage, but i had great luck just messing with the screws until i had a really high vacuum reading. Gave the truck a glass-smooth idle.

[chickenwing]

Yellow72, Been reading up on the manual. Under the cruise mode section it says that if there are any flat spots on light acceleration a lean condition probably exists. Sounds like I could potentially fix it by adjusting the pump. After reading though, the book calls for you to go to metering first. Chart calls for a .073"x.047" rod to go 1 step richer on the lean step, leaving high step alone.

I'll make sure to adjust my carb properly first and then go this route.
Rich

[lukecp]

Sounds like a good place to start, after properly adusting the idle, with the metering rods. Another thing you might want to try if swapping the metering rods dosen't give you the results you want would be some heavier step up springs, to pull the metering rods out of the lean cruise setting and into the richer power setting sooner. The PN#'s should be listed in the manual.

[dwaite72lnghrn]

I set the mixture sort of like yellow72. Warm the engine up, turn it off turn the mixture screws in slowly and softly (do not run them in tight) counting the #of turns (in case you need to go back to a point where you know it runs). Once they are in back both out 1 3/4 turns. Start the engine with the vacuum gauge in the drivers side vacuum port(full vacuum) Tach on also. adjust one side mixture screw till you get max vacuum, then the other side to get max vacuum. Keep an eye on the tach and watch for it to stop climbing( there is a point that no matter how far out you twist the tach will stop climbing it seems) you are looking for 20" of vacuum on that engine because it is stock (big cam might not get above 12"). if the RPM's get above 900-1000 adjust the idle screw on the side so your idle is around 750rpm.
The 2 mixture screws when you are done should have been turned out about the same amount of times (within 3/4 of a turn). You can have them out to far to start and cause a rich condition or to far in and get lean at idle or cruise which can cause the stumble when you start or accelerate.
Check your exhaust pipe to see if it is running black (rich) or grey (Lean) unless you have a cat on it then it will have to be real rich for it to be black as the cat burns most gas and they will look grey all the time..

[chickenwing]

I was talkin to a bud about my impending rod change. He went over and looked at it and promptly pulled my vacume advance hose from the timed port and put it on the constant vacume port. Big differance off the start immediately!! Still kinda boggy. He also suggested I time it to 12 before instead of 8. I'll do this first before the rod change. Will keep on updating.

[Super Duck]

one easy thing. have you checked for vacume leaks?