Engine running rich

[mchandford]

So I am having an issue with the car. Since I got the car it seems the exhaust is very rich. I currently have a 351C with Edelbrock Performer intake, Crower Baja Beast Cam, and most importantly (i think) an Edelbrock 1406, which I had previously thought was 650 CFM but apparently is only 600. The idle is set at about 900, which was where the carb manual said to put it. I currently have the choke adjustment at about 1 notch lean. Looking for some thoughts on adjustments and/or getting a bigger carb. I know a bigger carb will get more air, but will it also try to get more fuel. That would basically give me the same problem on a bigger scale. I did adjust the idle mixture screws to what i felt was the best vacuum/idle. Maybe this is where I went wrong however. I did have to run my own power for the electric choke because previous owner had it connected to ground side of alternator (?). It seems the choke is not coming all the way open when warmed up, but only just barely. I am not sure if that means that one of the linkages is off, or if the heater is not functioning properly. Thanks in advance for the inputs.

 

[MotoArts]

Firstly, 900 R's sounds way way too much.

If an automatic, it probably strains against the brakes when in gear at a stop.

I'd imagine somewhere around 600 RPM for that cam should suffice.

Generally, it is the cam's determination, not the carb, as to where the idle should be.

Personally, I don't set a choke by recommendation. I initially adjust the spring housing just so the flapper barely touches the carb body when ice cold. If it "snaps" shut, it's too tight. Adjusted this way it will open fully, and early. If jetted properly, throttle stumble should be at a minimum when cold or the first few minutes of operation.

If it's too cold blooded, go a tad tighter on the spring (towards "rich"). I'd rather have my cold engine a bit lean than (choking-the-plugs-out/washing the cylinders with fuel) rich.

The flapper should be vertical as possible when warm (spring should be holding it hard open). You should literally be able to watch the flapper open slowly as the spring heats up over the course of a few minutes from cold startup.

That carb should be a perfect match for your cam and intake. Throttle response should be real nice. No need for anything bigger in your application.

Is the engine rich only at idle, or all over the rev/temperature range? Have you checked the color of the plugs after a good run? Although it sounds like your problem is choke related, **DO NOT** perform any other adjustments in jetting, spring or metering rod changes until you are satisfied that the choke is functioning properly. You'll need to isolate the real problem first...

 

[marks73]

Verify one before moving on to the next. Good advice!

 

[mchandford]

OK, so your suggestion is to first check that choke housing? As I said i have it one notch to the lean. I will get out there again soon and check the choke position when 'ice cold' as you said. I think it may be too tight. Would that be in the choke housing or in a linkage, which is what I am concerned about. Still trying to figure out how to make those little adjustments. I had an autolite 2100 on my 72 f250 that I had finally dialed in...then I sold the truck. Thanks for the help, I will get to this check as soon as I can.

 

[Don C]

The owner's manual:

http://www.edelbrock.com/automotive_new/misc/tech_center/install/1000/1404_manual.pdf

And the rebuild instructions should help:

http://www.edelbrock.com/automotive_new/misc/tech_center/install/1000/1477.pdf

 

[MotoArts]

Yes, basically.

Inside the black choke spring housing (what Edelbrock is calling the "choke cap") is simply a flat coiled spring. As it gets heated, and expands and opens the flapper (they call it choke valve).

They list setting it kinda bass ackwards than how I explained it, but achieves the same thing.

Between pages 14 and 16 in the owners manual, they get pretty detailed on the adjustment.

Again, I'd simply start with the spring adjustment and see how it works for you. I'll also venture a guess that all those other settings are close and rod bending and such probably (hopefully) will not be needed, unless someone else has fiddled there before.

Key is to get it off of "closed choke" asap... Find the balance to keep it from gagging on raw fuel, yet still be drivable within a reasonable amount of time from startup.

 

[VegasFastback]

Another thing for richness is to make sure the butterflies aren't open enough to be into the transition circuit on the carb. Being that the engine is idling at 900 RPM at idle instead of 600 RPM you may have them set too far open. The tell for this is the car will diesel or backfire when you turn it off.

 

[Jeff73Mach1]

You may need to change the metering rods. Have you determined from exhaust gas how rich it is after it warms up or when it is under load? Have you done a good hard run, shut it down and pulled the plugs?

 

[mchandford]

I didn't get around to visiting the car yesterday like I had hoped, but hopefully tomorrow morning.

1. Pull the plugs and inspect,

2. Adjust the choke housing

Not going to be able to run the car too much on the road this is North Idaho in December. Can I just get the engine revved for a few minutes or will it not give me the same indications?

 

[MotoArts]

No.

Not even close.

As long as it's running on all 8 cylinders, pass on the plug check for now.

To do it properly requires a good, solid hot run.

Do the choke adjustment and get back to us. I think you'll be seeing a good result

 

[mchandford]

Another question that I was having is: would the car sitting in the storage unit face in cause it to maybe not get as much 'good' air and therefore run rich? because I noticed this too when it was in the garage at my old place. just a thought, will be getting to the car tomorrow. I will take a picture of a couple of the plugs tomorrow and look at that choke adjustment.

To be clear the only thing I am checking is the choke housing setting? making sure that the choke plate is just open when fully cold.

Thanks everyone for the ideas, this is why I wanted to be active in a forum like this.

 

[MotoArts]

Nah, it could be in a coal mine and still run OK.

Choke, yes.

When you first get there, do NOT start the engine. First, take the air cleaner off and observe the plate as you activate the throttle linkage once (at the carb) by hand. If it "snaps" hard shut, it's too tight.

By the directions that Edelbrock has, it should have that little clearance...

If it's too loose, it might start OK but want to die very shortly after.

Tip: Don't overtighten those screws on the choke spring housing either. Do them just snug enough to hold that black cap from turning when finding your desired setting. No need to gorilla them "tight". After you get the setting, just a fingertip/wrist power twist is all ya need (so they won't back out).

 

[hyena429]

So I am having an issue with the car. Since I got the car it seems the exhaust is very rich. I currently have a 351C with Edelbrock Performer intake, Crower Baja Beast Cam, and most importantly (i think) an Edelbrock 1406, which I had previously thought was 650 CFM but apparently is only 600. The idle is set at about 900, which was where the carb manual said to put it. I currently have the choke adjustment at about 1 notch lean. Looking for some thoughts on adjustments and/or getting a bigger carb. I know a bigger carb will get more air, but will it also try to get more fuel. That would basically give me the same problem on a bigger scale. I did adjust the idle mixture screws to what i felt was the best vacuum/idle. Maybe this is where I went wrong however. I did have to run my own power for the electric choke because previous owner had it connected to ground side of alternator (?). It seems the choke is not coming all the way open when warmed up, but only just barely. I am not sure if that means that one of the linkages is off, or if the heater is not functioning properly. Thanks in advance for the inputs.

Well not really..Yes a bigger carb will lean you out...Fuel pump only pushes so much gas into your carb..The air mix cfm is the most importaint....You will never get it too run right with a carb too big or too small....the stock 351 4v cleveland carb is 716 cfm's..edelbrock 600 i put on my car barly worked with stock cam...Any bigger cam and mods you should move up too a holley 750 or edelbrock 750.....You wont use any more or gas...You will use less....You know anyone with a bigger carb you can test out?

Leaning out is a good indication your carb is too small...It cant suck enough air too mix with the gas.. motor is tring to suck more...and sence it cant get enough air...It will take gas instead....A good way too check too...When its runing..does is it keeping your butter flies open a hair? And wont idle low?...Usualy a good indication your carb is too small.its starving for air and needs to keep the rpm's up high too get enough air to breath.....Its the first thing i would look at...Cause most edelbrocks dont need much tuning...Your cam lift? Anything above 480 lift...You should be looking into carb changes...stock boss and cobrajets back in the day got no less than 716 cfm carbs and above.

 

[Tnfastbk]

A little rich will always be better than a little lean

 

[mchandford]

Nah, it could be in a coal mine and still run OK.

Choke, yes.

When you first get there, do NOT start the engine. First, take the air cleaner off and observe the plate as you activate the throttle linkage once (at the carb) by hand. If it "snaps" hard shut, it's too tight.

By the directions that Edelbrock has, it should have that little clearance...

If it's too loose, it might start OK but want to die very shortly after.

Tip: Don't overtighten those screws on the choke spring housing either. Do them just snug enough to hold that black cap from turning when finding your desired setting. No need to gorilla them "tight". After you get the setting, just a fingertip/wrist power twist is all ya need (so they won't back out).

Roger, I can do that pretty easy. Not today, we had to do some running around. The wife bought me a security system for the stang and it was from a dealer I didn't want to go through, so we refunded it and now I get to take the funds to the right place and buy the one I want. Just going with a 2 way for now.

Back to the carb. The wife works tomorrow so I can run out there first thing and check the carb. I think just from memory that the choke does 'snap' shut when cold. I will get back to you guys with an update when I am done.

So I am having an issue with the car. Since I got the car it seems the exhaust is very rich. I currently have a 351C with Edelbrock Performer intake, Crower Baja Beast Cam, and most importantly (i think) an Edelbrock 1406, which I had previously thought was 650 CFM but apparently is only 600. The idle is set at about 900, which was where the carb manual said to put it. I currently have the choke adjustment at about 1 notch lean. Looking for some thoughts on adjustments and/or getting a bigger carb. I know a bigger carb will get more air, but will it also try to get more fuel. That would basically give me the same problem on a bigger scale. I did adjust the idle mixture screws to what i felt was the best vacuum/idle. Maybe this is where I went wrong however. I did have to run my own power for the electric choke because previous owner had it connected to ground side of alternator (?). It seems the choke is not coming all the way open when warmed up, but only just barely. I am not sure if that means that one of the linkages is off, or if the heater is not functioning properly. Thanks in advance for the inputs.

Well not really..Yes a bigger carb will lean you out...Fuel pump only pushes so much gas into your carb..The air mix cfm is the most importaint....You will never get it too run right with a carb too big or too small....the stock 351 4v cleveland carb is 716 cfm's..edelbrock 600 i put on my car barly worked with stock cam...Any bigger cam and mods you should move up too a holley 750 or edelbrock 750.....You wont use any more or gas...You will use less....You know anyone with a bigger carb you can test out?

Leaning out is a good indication your carb is too small...It cant suck enough air too mix with the gas.. motor is tring to suck more...and sence it cant get enough air...It will take gas instead....A good way too check too...When its runing..does is it keeping your butter flies open a hair? And wont idle low?...Usualy a good indication your carb is too small.its starving for air and needs to keep the rpm's up high too get enough air to breath.....Its the first thing i would look at...Cause most edelbrocks dont need much tuning...Your cam lift? Anything above 480 lift...You should be looking into carb changes...stock boss and cobrajets back in the day got no less than 716 cfm carbs and above.

I got a little confused by your post at first. At first you were saying that a bigger carb would lean the mixture out. Then in the second half you were saying that being lean is an indication of a too small carb. I think there you meant too rich. I don't have another carb just yet, but I will ask around. i like my edelbrock so far, but I think the 750 will be a good upgrade. The carb seems to be in fine shape, but from what everyone else has said the 600 may be just a little too small. I am going to start with a few adjustments and see if we can get it in the zone first. I do have the idle a little higher than some were saying should be necessary, and maybe that is why.

 

[hyena429]

oppss sorry...I meant flooding out...lol..i should of re read what i typed better But yes...Bigger the carb...The leaner it will run...mechincal fuel pump will deliver the same pressure no matter the carb size...jets can slow or speed up fuel delivery a bit......The carb only lets in so much air to mix. ...716 cfm is the stock carb..600cfm edelbrock i ran...seemed to run a bit rich on my stock cam...And yes it is better to be rich than lean...But!! You shouldnt have to be either..lol...750 holley is what im putting on mine...but im going with a 5.30 lift...So i will have to jet it up a little im sure....But even with a stock boss cam size...I would not run something as small as a 600cfm edelbrock.

Mine was a pretty much stock 351 4v cleveland...And she ran rich and not as fast when i switched out my old 4300d...I could tell a diffrence...It was a good carb thou...I like the edelbrock carbs...simple and easy....But the 600 cfm version is something i would stick more on a stock 2v cleveland....And i wished i didnt switch from my 4300d ...I thought the hesitation was from a old worn out carb....Nope...More issues than that down below...But the carb gave me less go..and more smelly rich gas smell...lol

 

[marks73]

If you've been reading c9zx's post on heads and flow rates you can see where your heads can and need to breath from a cfm standpoint to reach peak performance. Naturally everything is a balancing act. Cam, heads carb, timing, vacuum. It takes time and experience (a ton of patience helps as well) but the more you play with it and learn your engine (no 2 are alike no matter what) the more you can get out of it. They're very resiliant so don't think your going to do a lot of damage by making minor changes. The closer you get to peak the more minor the changes.

 

[droptop73]

WOW it looks like we need a tutorial on how carburetors work. First the fuel pump does not have anything to do with a carb running rich or lean, it's only job is to supply fuel to the carb. In my experience teaching carb theory is easiest to understand by looking at pressure differentials in the carb. The venturi speeds up air flowing through the carburetor causing a low pressure area at the venturi this is the most important fact in carb operation (look up the Bernoulli principle, remember air is a "fluid"). The smaller the restriction the more the air speeds. Notice how the booster is located right at the venturi the fuel flows to the booster via the main jets which determine how much fuel flows through to the airstream. A small carburetor will tend to have more "signal" at the venturi due to the venturi sizing. This could cause a carb to want to run rich. A side benefit to a smaller carb should be better throttle response. A large carb will tend to have less "signal" at low throttle angles. Fuel will flow from higher pressure areas to low pressure areas, there is atmospheric pressure on the fuel in the bowl and less than atmospheric pressure at the venturi, this is what causes the fuel to flowthe fuel moves through the main jet to the emulsion tubes where it is pre atomized with air and then moves through the main nozzle to the booster and into the airstream where it becomes fully atomized. Beyond these parameters there are the idle circuits function and air bleeds along with how they affect the emlsion of the fuel and how that affects fuel mixture. there is WAY more to how a carb performs than just picking one from a catalog. One of the biggest problems is selecting the proper carb which has more to do with intended use than engine size. Please try the calculator at hte following link, you may be surprized with your carb requirements if the inputs are honest. The recommended CFM for my engine based on 75% VE and a dual plane intake used up to 5500 RPM is 503 to 628CFM.

http://www.wallaceracing.com/intakecfm.php

 

[marks73]

using a 351 at 90% VE for a roller cam @6500 Red line equated to 713-891 cfm

using a 351 at 80% VE for a flat tappet hydraulic @6500 Red line equated to 634-792 cfm

of course the more radical the cam the larger the cfm requirements so you can see where this is headed