I am having some issues with my 1406 carb. The carb was new about 2 years ago and was put on when I had the engine built( these are on going problems since the install). I believe I am running rich, however when I press the throttle between 3/4 - WOT I get a bog/hesitation and then the car takes off. The exhaust smells moderately of gas but I am not blowing black smoke out of the tailpipes (except on start up). I have not changed anything on the carb as far as jets, rods, springs etc... The Acc. pump is set to deliver the max shot. I have adjusted the idle mixture screws using a vacuum gauge. I verified the floats to be at 7/16".

My set up is :

355
CR: 9:1
cam: xr276 -224/230 duration @ 50 .502/.510
Dart S/R heads
Edelbrock performer RPM air gap manifold
spark plugs NGK YR-5
MSD street fire HEI
Fuel pressure is set at 4.75 PSI

I think my vacuum reading is right on 12" @ 900 rpm( that is the highest I could get when setting the idle screws. Comp had a very similar build and got a similar vacuum reading.

http://www.compcams.com/Technical/Dy...6HR-10_001.asp

I attached pictures of the plugs below the one on the top is the driver side and the one on the bottom is the passenger side. In each picture the plug on the right is the plug closest to the firewall.

 

The 1406 is designed to run a little leaner than the 1405. You can start with changing the rod up or down a step.

Does it have the stock jets?

What Air Filter?

Sounds like you are going a bit lean when the secondaries open.

What is your timing situation? Are you using Vac advance?

 

The carb is exactly as it came out of the box nothing has been changed out.

I don't recall what I set my timing at it is I believe it is 16* initial. The engine builder recommended between 38 - 42 total timing. If you look at my cam and compression ratio I suspect that is the reason for the excessive timing. The engine was supposed to be 9.5:1 but the engine builder had his own ideas. I have adjusted the timing previously and it did not seem to help this problem.

Air cleaner NON- drop base K&N open element 14x3

Vac advance is hooked up to timed vacuum.

It appears to be lean when I give it throttle but by the look of the plugs it seems to have a rich condition.

 

Warning! I'm not a fuel system expert... However, I do have a 1406 on the standard Performer intake on a mostly stock, new 350 replacement motor. No problems whatsoever.

Observations: Edelbrock doesn't really recommend a 1405/1406 on the Air Gap manifold. They recommend a 750 CFM carb for the Air Gap.

Your plugs are "loading up". That can be caused by several things, but the most common is running way too rich at low speeds, but will "burn off" if run at well above idle speeds. My experience with "loading" plugs is that they will usually give a hesitation if WOT is suddenly applied.

You say the pump is set to give max surge when punching it. That will also give a waaay rich condition resulting in a hesitation...and "loading" plugs.

My recommendation: Before doing anything else, change the plugs. If that doesn't cure the problem, adjust the accelerator pump and drop your initial timing down a couple of degrees.

Make sure the choke is kicking out as it should and isn't set too rich. Within a few seconds of engine start, blip the throttle to disengage the choke.

If you have a nice sounding lumpy cam, don't let it sit and idle for several minutes to impress the little kids. That can load the plugs super fast.

But change the plugs first and go from there. Once plugs have been fuel fouled, they will usually cause further trouble.

 

I am on my second set of plugs first were NGK 5673-7. I switched to a hotter plug NGK YR5. I had the same issues with the other plugs. I will probably get some NGK UR5 plugs or Autolite 13. I have previously had the ACC. pump set to the mid setting and still have the same problems.

I have messed with the ignition timing and to be honest it seemed to like a lot of timing. The best dyno numbers were achieved with 42* total. Timing is set at 38* total now from what I recall. I just didn't feel comfortable with it there, even though the builder said it would be fine with 93 octane gas.

from what I had read reducing the timing would amplify my plug problem. I even had a mechanic ( after he looked at it) tell me to not run any vac advance (which was a very unpopular opinion from most of the people I talked to.)

The 1406 is supposed to be calibrated lean out of the box so I don't know why I am getting this rich condition.

I also noticed that when idling I have a slight to moderate raw fuel odor, but according to my vacuum gauge the idle screws are set so it is pulling max vac.

I am at sea level so altitude should not be a factor.


I have read the edelbrock manual and am wondering if I need to start changing jets and rods???

 

1405-6 are fine on the air gap, they are not really any different than the RPM performer. I have run plenty of 600s on them without issues.

Did your builder rejet your carb?.

Have you tried the leanest accelerator pump setting?


You can try to disconnect the vac advance if you want to.

 

Probably going to have to tune the carb, but get the distributor and timing set right before you touch the carb.
But keep in mind these carbs are notorious for bogging on accel and sometimes even with the pump shot maxed out they can't be fixed.

 

Ok, I went back through everything I wrote and verified it today.

Everything with the exception of my timing was accurate. My intial timing is 24* BTDC the total advance is 42*. I have an MSD Street fire distributor in stock form no changes have been made to the springs. I am not getting any knock.

I know my timing seems very high. I pulled the plugs and verified that my balancer was accurate using a piston stop.

I moved the accelerator pump to each of the positions, the car accelerates best when it is in the top position ( max fuel squirt). It appears JaBoT was correct about the lean condition upon acceleration.

I also checked for vac leaks by running propane around the intake manifold and did not find any leak.

Car seems to run good with the exception of the flat spot under heavier acceleration. I would also like to stop fouling these plugs.

According to the Edelbrock manual they recommend richening up the "power mode" by decreasing the main jet from .098 to .095 and changing the metering rod from 075x047 to 070x037 ( pages 13, 22 and 23).

http://www.edelbrock.com/automotive_...ers_manual.pdf

 

If you think it is running rich I would start by leaning out cruise until it lean surges on light passing on the highway, then go back up a couple sizes. That will give you the leanest possible cruise and also give better fuel economy. Make sure your vacuum advance is hooked up. The extra timing is very important to burning a lean cruise mixture.
Then tune power mode after that. For wot you either need a wideband afr gauge or use mph down the track.
Also if the distributor didn't come with extra springs get msd PN 8428 and use the light springs. It will give more timing down low which should help the low compression over camed engine.

 

Ok I will give it a try. Thanks for all the help and suggestions.

 

The first phase is complete. I got it running smoothly during cruise, power mode ( part throttle acc.) and WOT. It seems I no longer have any flat spots during acceleration.

I changed the following:

Primary jets went from .098 to .095

Metering Rods went from 075x047 to 075x037

After these changes I didn't notice much of a difference maybe a slight improvement on acceleration part throttle but a stumble was still present.

I read on a MOPAR board that if you take your idle vacuum and divide by 2 that is the spring you should be using. My vacuum was 12" so divide by two it is 6" since there was no 6" inch spring in the kit I had , I stepped up from the stock 4" spring to the orange 5" spring. I went out for a test drive and it was smooth across the entire band.

I still don't know if I am rich or lean but now it's a matter of some fine tuning. I may try 073 x 37 rods or 073 x 042 rods.

 

Great way to go.