I have a 1406 carb on my 289/with a c4. My engine is sluggish in city driving at about 25 mph. It seems to bog until it has about half throttle. I have already changed out the mettering rods for a richer mix, but I think that the problem may be with the rod springs. Reading in the manual, it shows me colors for the springs on the metering rods vs the vacuum. My question is: Is the vacuum to be measured at idle or at mid-range engine speed?? Thanks, John

 

What is your rear ratio?

 

John

Give us the rest of your engine vitals again. I forgot what you're running. Camshaft and the gear info Danlee asked for are real important. You've got the right carb IMO to make this work on the street. Looked at the spark plugs since you tuned on the carb?

 

Hi guys, if you recall, the tuning of this carb has been going on for a while. A few months back my plugs were showing snow- white color. So that told me that I was too lean. I installed new metering rods (1 step richer) after asking advise from the column. Since then the plugs are a light tan color. My truck has a 289/c4 combo from a 67 Mustang. Stock cam. Also, a 9" rear with 3.00 gears. Accelleration is good from any speed. Idle is good. The only thing that bothers me is cruising through the neighborhood at about 20-25 mph. It runs kinda slugish and boggy I wish I was better at describing this. So I'm thinking I have too stiff of spring on the metering rods. What do you think? Signed: Stiff Spring in Antelope (John):-staun

 

John what gear dose the c4 want at 20-25 and what rpm is the 289 spinning. High gear + low rpm + tall rear end gear = No torque and lots of bog. Try cruising in 2nd gear. The plugs say you,ve got the carb tuned right. Good luck, Rich.

 

A 1406 is a 600 CFM carb. That is a lot of carb for a 289, add to that a 3.00:1 rear ratio and low speed and you have a metering problem. Do you have a carb spacer? A 1 inch or 2 inch spacer may help. There are spacers made which are supposed to improve the flow through the carb.

 

You also might want to check the accelerator pump on the carb. I replaced mine because my Carter 625cfm carb was sluggish feeding fuel off the line. So, maybe yours would benefit from a new accelerator pump?

Just a thought...

 

I do not have a carb spacer. I will keep that in mind though. The c-4 wants to shift into 3rd just putting around the neighborhood. You are right about the idea of staying in 2nd. It does run a lot better with the revs up a little. I am still going to check the metering rod spring color against the vacuum just to confirm that it is correct. After my initial question, it seems to me that I should be checking the vacuum with the carb operating in the midrange not the idle. Is that right? If the spring is correct then it will raise the metering rod at the appropriate time. Otherwise the flow is too low. That's what I keep thinking is happening. Or, have I missed the boat somewhere. Hey Daryl, did the accellerator pump help Butch get some extra rubber burning?? I know at one point you were wanting more.Thanks guys, John

 

John

It sounds to me like you got it pretty close actually. My 1406 pretty much worked right out of the box on my 302, although I think I am just a bit rich and will play with it when it warms up for best fuel mileage.

I assume you have studied your tuning section in the Edelbrock manual for the next step? Don't be afraid to call Edelbrock. Sorry if I sound like I'm bailing out on you, but carb problems are so hard to diagnose without being there. What you describe sounds like you are going just a little lean when you are cruising not too far out of the idle circuit. It doesn't sound like something you would cure with a carb spacer. But I'm not there driving your truck either. Can you keep the truck at that speed for a considerable distance, then pull over and inspect a couple spark plugs? Do you think you are running too rich or lean? Wasn;t sure from your posts.

 

You probably want to adjust the shift points in the tranny to keep it in 2nd longer.

 

Hi Dewayne, In answer to your question, I think I am probably a little lean. And I agree that I am very close to right on. And it may even be that I am as good as I can be. I'm checking the vacuum versis the spring code this weekend. Then I should know for sure. And Danlee, just to show you what a neophyte I am, I did not know that the shift points in a c-4 could be adjusted! So, in summery, it sounds like I'm very close to right on and if I can't make it any better, I do like the idea of just keeping it in 2nd. That monster 289 sounds a lot meaner when it's running a little faster. Thanks a lot, John

 

John, not sure if this will be of any help, but I had a similar problem in an old Jeep I used to have. It had a turbo buick 231 V6 with a Quadrajet carb. That carb had a part throttle valve which was adjustable. I could not run the rig on light throttle settings. Had to excelerate or slow down. Tweaked the PTV adjustment and day vs night difference. This may be completely unrelated to your problem but ????
Hope it helps.
Good luck

 

I know that the shift points can be adjusted on some trannys. I don't know if the C4 is one of those. It probably means removal of the tranny in any case.
The other thing is the vacuum modulator. I assume that you do have it hooked up to manifold vacuum, and it is working correctly.

Do you have a tach? What is your RPM at 25 MPH in high gear?

If you do not pull enough air through a carb the fuel will not flow or vaporize correctly. The larger the carb primary venturis the more air is required to make the carb work properly. If your RPM is low and you have a small cubic inch motor this could with the carb that you have.

There are several possible solutions, most have been mentioned already. One is to go to a smaller carb. Edelbrock recommends the 500 CFM carb for 302 cubic inch and smaller engines.

The second solution is to use a signal amplifier device. Summit Racing sells a Swirl Torque device that is supposed to improve low end performance. I used one on my 400 with a 750 CfM carb. I am not sure how much benefit it was, but I had no trouble at low RPMs.

The third solution is raising the RPMs at low speed via gear changes. That could be a tranny change or rear ratio change.

 

John

I'd do some more tweaking in small steps. I suspect l'll be a Edelbrock Performer guru in a few months after I screw my own up. That's how it always seems to go. What Danlee suggests is certainly not incorrect, but I suspect you want to try to tweak this carb out if you can. A bit more rear end gear would be nice for your power to weight combo. Not that small blocks aren't real powerful. A 600 CFM carb may not be the perfect size for a 289. but it's been done successfully many times before.

You're C-4 probably has a set screw if you remove the vacuum hose and insert a small screw driver. Thats only good for a couple miles per hour on the shift point though.

Check one more time to absolutely rule out any vacuum leaks at cruise. PCV valve, any and all vacuum lines. Carb base gasket. Just a minor leak can put you over the edge into a slightly lean condition. I assume you do NOT have an EGR equipped manifold. If you do it is highly possible it is causing/adding to the problem. Due to a failure to seal or getting incorrect vacuum. If you do have one, make a temporary block off plate from sheetmetal or a soda can.

Are you pinging when accelerating lightly in the problem cruise range? Sure sign you are lean. You said bog earlier I associated with too rich.

So does it go shabwaaaaaaaaaaaa and then vroooooooooooom or aaaaaaaaaahhh aahh aaah aaaaaaaaahhhhh and just lay there embarassing you like a Chevy 305 in a 1978 Impala station wagon.

 

I know that I am not allowed to solict on this forum, but I am going to put my 2" Swirl-Torque carb spacer up for sale in the classified section. If you are interested you should look there for a good buy.

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