Edlebrock 1405 carb surge

[Charlie Brown]

I have an Edlebrock 1405 600 cfm carb with auto choke. Fast idle works as it should. Issue - when engine is cold and I'm in cruise mode, the engine is surging. At operating temperature, it runs perfect. Carb currently has .98 jets in primary circuit and metering rods 1446 ( .068 x .042). Phoned Edlebrock, but that was a waste of time. Waited 45 minutes for a tech and then he told me to move the position of the accelerator pump lever - this issue is not under load but in a cruise situation when cold. Would increasing the primary jets to next size up (.100) help? Or should I be adjusting something on the electric choke? Thanks, Charlie

 

[ykf7b0]

Do you have a fuel pressure regulator installed?

 

[ruffcut]

You might try opening the choke about 2 notches on the adjustment. Upping the jet size will just make it richer.

 

[Charlie Brown]

Do you have a fuel pressure regulator installed?

I do. Currently set at 5.5 lbs.

 

[lewtot184]

i like .101 jets with 70x47 rods in my 600's. you could have a timing issue too. if you're using a vacuum advance there may be too much advance at high vacuum cruise.

 

[Charlie Brown]

i like .101 jets with 70x47 rods in my 600's. you could have a timing issue too. if you're using a vacuum advance there may be too much advance at high vacuum cruise.

The vacuum advance on my distributor is adjustable via an allen key (Mopar electronic kit). Would adjusting this help?

 

[JG71B]

The vacuum advance on my distributor is adjustable via an allen key (Mopar electronic kit). Would adjusting this help?

Curious...do you have the light weight distributor springs in that? Also does that allen key adjustment affect how much actual advance or actually when the advance starts engaging by cruise vacuum?

 

[Charlie Brown]

Curious...do you have the light weight distributor springs in that? Also does that allen key adjustment affect how much actual advance or actually when the advance starts engaging by cruise vacuum?

No light weight springs. As I understand it, the adjustable vac advance affects the total advance (while under no load) and not when it starts engaging.

 

[moparwacko]

You didn't mention how the plugs are reading, or if this is something new.

I find most 1405/06 are rich out of the box for a stock set up. I just built a 1406 for a mild 360. 92 pri, 95 sec, and 70/47 rods, yellow springs. Very good results.

Carb setting recommendations are like opinions......a good tuner needs the car in front of him to listen, smell, and feel what's going on.

Good luck, and only change one thing at a time.

 

[Geoff 2]

You are experiencing the problem that electric chokes have.......
They 'switch off' after a predetermined time, not when the engine no longer needs the choke.
- make sure your exh xover is not carbon blocked. This causes the intake to take longer to warmup, engine runs lean which is what is causing the surging.
- you might be able to adjust the choke to 'hang' on a bit longer.
- the best fix is to convert it manual choke. Then YOU control choke on/off.
- do NOT change rods/jets because it runs perfectly at operating temp.
- congrats on buying a great carb

 

[YY1]

What engine is this on?

You should be able to adjust the choke "time on" a bit.

 

[Rebelrouser]

I have an Edlebrock 1405 600 cfm carb with auto choke. Fast idle works as it should. Issue - when engine is cold and I'm in cruise mode, the engine is surging. At operating temperature, it runs perfect. Carb currently has .98 jets in primary circuit and metering rods 1446 ( .068 x .042). Phoned Edlebrock, but that was a waste of time. Waited 45 minutes for a tech and then he told me to move the position of the accelerator pump lever - this issue is not under load but in a cruise situation when cold. Would increasing the primary jets to next size up (.100) help? Or should I be adjusting something on the electric choke? Thanks, Charlie

You could try a couple things. First take the springs out under the metering rod pistons. Replace them with a stronger spring, or just stretch the spring and make it stronger, this will allow the rich step on the metering rod to come in quicker. I like to idle the engine and carefully slide the metering rod cover over and play with the throttle, I want the piston to rise as I play with the throttle. And while you can change the jets, a few numbers richer, a metering rod change is a lot easier and quickly done.

 

[Charlie Brown]

You are experiencing the problem that electric chokes have.......
They 'switch off' after a predetermined time, not when the engine no longer needs the choke.
- make sure your exh xover is not carbon blocked. This causes the intake to take longer to warmup, engine runs lean which is what is causing the surging.
- you might be able to adjust the choke to 'hang' on a bit longer.
- the best fix is to convert it manual choke. Then YOU control choke on/off.
- do NOT change rods/jets because it runs perfectly at operating temp.
- congrats on buying a great carb

Your analysis of the electric choke "switching off" before engine reaches operating temp seems reasonable. My crossover has been blocked off on purpose. I previously had a vapor lock issue and this was one of the things I did to help solve the problem. I'll try to adjust the choke to "hang on" a bit longer. Thanks.

 

[Charlie Brown]

You didn't mention how the plugs are reading, or if this is something new.

I find most 1405/06 are rich out of the box for a stock set up. I just built a 1406 for a mild 360. 92 pri, 95 sec, and 70/47 rods, yellow springs. Very good results.

Carb setting recommendations are like opinions......a good tuner needs the car in front of him to listen, smell, and feel what's going on.

Good luck, and only change one thing at a time.

Plugs read nice. Jets are actually 2 steps leaner (.98) than factory (.100). Engine in question is a 413 Chrysler 300H with dual 1405 Eddies on a Edlebrock aluminum intake. Linkage is set up for progressive action and not in tandem.

 

[Charlie Brown]

What engine is this on?

You should be able to adjust the choke "time on" a bit.

I think this is the first thing I'll tackle. Thanks.

 

[lewtot184]

The vacuum advance on my distributor is adjustable via an allen key (Mopar electronic kit). Would adjusting this help?

it could help. i know i mess with them a lot. counterclockwise brings the advance in later.

 

[lewtot184]

Plugs read nice. Jets are actually 2 steps leaner (.98) than factory (.100). Engine in question is a 413 Chrysler 300H with dual 1405 Eddies on a Edlebrock aluminum intake. Linkage is set up for progressive action and not in tandem.

i use .101 jets and 70x47 rods with orange springs with my ch28 intake. i do go after the idle jets. i open them up to .035". mine runs and burns great. i have done a bunch of ignition tuning also.

 

[Geoff 2]

Charlie,
'It runs perfect' [ at operating temp ], your description.
YOU DO NOT NEED BIGGER JETS, DIFFERENT MET RODS OR A CHANGE IN SPRINGS.
Your problem is as described in my post #10. Also, with cruising on a cold engine I imagine you are keeping the speed down until the engine has warmed up.
Light throttle cruise is on the idle cct [ the transfer slots ], not the main jets, so
richening the main cct will just make it rich at operating temp.

 

[Geoff 2]

Another compromise fix, which I do often, with street engines, is to use a steel plate to block the exh xover. I drill a 1/2" hole in the plate so that the intake gets some heat. Liquid petrol does not burn, it needs to be in vapour form & heat coverts it to vapour.

 

[Charlie Brown]

Charlie,
'It runs perfect' [ at operating temp ], your description.
YOU DO NOT NEED BIGGER JETS, DIFFERENT MET RODS OR A CHANGE IN SPRINGS.
Your problem is as described in my post #10. Also, with cruising on a cold engine I imagine you are keeping the speed down until the engine has warmed up.
Light throttle cruise is on the idle cct [ the transfer slots ], not the main jets, so
richening the main cct will just make it rich at operating temp.

You are correct to assume that I use light throttle until engine reaches operating temp. I'm inclined to keep off the throttle until then for fear of engine damage.