Engine running rich

[Don C]

One other thing you have to keep in mind, is altitude. Most out of the box carburetors are set for sea level. My experience with Edelbrock carburetors (Northern Nevada - 4,000+ feet elevation) is that they seem to be more sensitive to elevation changes and will likely run rich at higher elevations.

Good tutorial on carburetors, droptop73, concise and accurate...

 

[hyena429]

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.

I will dissagree with that....A normal fuel pressure is 6.5 lbs. per square inch. High fuel pressure "usually due to a fuel pump that's defective or worn" can cause carburetor flooding...carburetor for the most part is a air and fuel regulator..Delivering gas is not its only job.....Fuel pressure can effect it...But should be the same......A fuel pump has alot to do with how lean or rich the carb is runing too...So if you put a carburator that is too big for your car...It will not get more fuel...It will get less!!

Of course carb doesn't match the cam lift and heads.. its going to run a bit rich or lean...Its sucking more gas than air..or other way around...Same with a bad fuel pump...Will deliver too much or too less of gas..It all has to match from one end too the other...cam..manifold..carb...pistons...fuel delivery."or pump"..Any out of order will make you run rich or lean.

 

[mchandford]

Alright, finally got out to the car.



This was what the choke plate did when I lifted the throttle at the carb with the engine cold. It didn't really snap shut, but closed entirely. Of course it is about 25 degrees outside right now.



Here is where the housing was set at by me. Note: when I got the car PO lived about 1000 ft lower elevation than me and the housing was set 2 notches rich. I put it back to center.



Took this one so you guys could tell me if anything looked 'off.' it looks fine to me and I wanted to make sure the spring was catching the post (?) correctly on the inside.



In order to get even a slight gap in the choke plate when cold...



the housing was set to almost under the housing screw.

I left it there for now, until I get a little more input from you guys. I think it will end up about halfway between there and center when said and done.

And I took this for grins.

 

[TommyK]

It is OK if the choke plate is completely closed when the engine isn't running. The choke pull off when functioning properly will open the plate about 1/4" immediately after the engine starts. If the choke plate doesn't open about 1/4" IMMEDIATELY after the engine starts adjust the choke pull off not the choke cap. The choke cap adjusts the rate at which the choke plate opens. The choke pull off adjusts the amount the choke plate opens IMMEDIATELY after the engine starts running.

 

[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.

I will dissagree with that..

Disagree all you want, the ONLY job the fuel pump has in a carbureted system is to keep the float bowls full, it's as simple as that.

Bach to the OPs dilemma. Have you re-adjusted the idle mixture screws from your prior settings? A good starting point is 1-1/2 turns from being lightly seated (some screws turn in to lean the mixture and some turn out). Is the engine running rich all the time or just at idle or cruise? Depending on what conditions the rich run is on will make a difference in what carb circuit you look at. If at idle you would look at the idle circuit. If at light throttle cruise you would look at the idle circuit. If rich at highway speeds look at the main circuit. The same with WOT. A key point to remember is the choke valve is in there to increase the pressure differential between the venturi and atmospheric pressure on the fuel in the bowl. This provides a slightly richer mixture to the engine. This is why you hold the throttle 1/2 open when cranking.

I am not terribly familiar with Edelbrock/Carter carbs but they all work on the same principles. Fuel and air are just regulated differently.

 

[mchandford]

It is OK if the choke plate is completely closed when the engine isn't running. The choke pull off when functioning properly will open the plate about 1/4" immediately after the engine starts. If the choke plate doesn't open about 1/4" IMMEDIATELY after the engine starts adjust the choke pull off not the choke cap. The choke cap adjusts the rate at which the choke plate opens. The choke pull off adjusts the amount the choke plate opens IMMEDIATELY after the engine starts running.

OK, that brings up another question for me then. How would I adjust the choke pull off? I have been searching for it since you posted that and can't find anything on the edelbrock site, or otherwise.

I did find a site that described a little more of the jets/rods. i also went back to the car, took the top off the carb and looked around a bit. just for learning's sake. I learned that the jets are a lot easier than I thought they would be. The rods I had messed with a little before, just removed, cleaned a bit and put back in. I also had not opened the carb up since I got the car. I had the whole thing out during my engine mishap last march, but just set it aside and then put it back later.

So my thought is this. I am getting a 1406 tuning kit just as soon as I can, but what does everyone think of switching the main jets with the secondary jets to see if that leans out the car at idle, and lower rpms? Then when I get the kit I can change the secondary jet back out with either another of the same size, or other appropriate size. According to the owners manual, the secondary jet (.095) with the primary metering rod (7547) will give me the #12 setting, 12% lean in cruise and 6% lean in power mode.



This is the front driver spark plug. It looks pretty good in the picture, but was very black when I was looking at it. Now, I had just gotten done pumping the accelerator a few times when I was playing with the carb, but there was still some fuel on the plug. I also noticed that the plug started to thread out before I had the ratchet on it. I was able to twist it out by hand. I did not check the other plugs, but that will be on my list of things to do before I put the car back on the road.



This is the inside. I think before too long I am going to pull the carb body again and give it a good clean and flush.



Someone mentioned the 'butterflies' earlier. This is the secondary circuit in the back correct? is this the butterfly that would be stuck open?

Thanks guys for all your help. I like that my questions at least stir up a little conversation.

 

[hyena429]

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.

I will dissagree with that..

Disagree all you want, the ONLY job the fuel pump has in a carbureted system is to keep the float bowls full, it's as simple as that.

I will...Reason they build fuel pressure regulators for people having this issue with a high or low flow carb.... usualy happens more to fuel injected systems with too powerfull of a pump..But a messed up fuel pump will make your car lean out...or flood out!! Believe me or not...Thats up too you...lol...It will not fill the bowl up fast enough..Your car will lean out..it will over power your needle valve...Car floods out...You can dissagree all you want..But that is a fact.

 

[droptop73]

How much are you able to drive the car presently? It may be best to wait until the weather breaks and you can get the car fully warmed up and under the normal loads. I would highly recommend working through the carb systematically. Get the idle mixture correct then work on the main circuit at highway speeds (transition will likely take care of itself) finally tune the choke since it normally does not have much effect on drivability.

 

[Mister 4x4]

I too have a 1406 on mine, albeit brand new and has yet to be fired up for the first time. Edelbrocks are the easiest carbs (IMHO) to initially set-up and keep running properly. That being said, if you're not the original owner of this car with the current set-up, you might consider setting everything on the carb back to the initial factory [Edelbrock] set-up and go from there.

All that being said, once my engine (and car) is broken in after I finally get it back on the road, I will be saving up for an EFI system (Edelbrock E-Street, of course) since I've become spoiled with the no-hassle EFI on my current daily driver.

 

[mchandford]

Ok, back to this again. I was at the car again, trying out a different tactic. I adjusted the timing. Initially I put the vacuum gage on the vacuum connection on the left side of the carb. When I fired up the car I had no vacuum there. So I connected it to the right side (with blue cap in picture). The one I have not been using. This gave me my 15 in vacuum.



After playing with the idle, air screws and distributor I got about 17.5. but my idle is still around 900. My next thing to check is the spark plugs and see what they look like and what the gaps are. I have been seeing a lot of people referencing about .54 for spark gap. Is this correct? I'm not sure what they were when I put them in. I guess I could check the dizzy and see if anything is amiss in there, but it is electronic so I wouldn't expect to find anything.

A couple of questions though. 17.5 seems low for vacuum. I am at about 2000 ft elevation, so that takes away 2 inches right? that would still only make it 19.5. I am wondering if this is somehow connected to my running rich and creating a lot of 'bad' exhaust. I also noticed that there was a lot of black soot in the water coming out the tailpipe. Someone mentioned this as a symptom, but I don't remember for what. i think just not burning all the fuel, which I already know.

Thanks again everyone.

 

[droptop73]

A plug gap of .030" is a good place to start for a stock ignition system. My Cleveland is running about 18hg of vacuum at idle as well, I do not think your readings are out of line. Water from the exhaust is normally just condensation from running in cold weather. The soot is carbon from the combustion process, possibly excessive from rich running.

 

[mchandford]

A plug gap of .030" is a good place to start for a stock ignition system. My Cleveland is running about 18hg of vacuum at idle as well, I do not think your readings are out of line. Water from the exhaust is normally just condensation from running in cold weather. The soot is carbon from the combustion process, possibly excessive from rich running.

Good to hear about the vacuum. I thought someone had said it was low. maybe not for this engine.

And thank you about the soot. i was pretty sure that was all it was. Wanted to confirm.

Any thoughts on the vacuum ports? From what I am reading elsewhere I need to be using manifold and not ported. I haven't tried this on a cruise yet, but it sounds like it should help me idle better.

 

[mchandford]

So trying to find a little more info about my idle speed. I think it may still be in the carburetor. Someone mentioned butterflies in the carb, and the choke pull off. Well my choke plate does not hold "hard open" with spring tension on it fully when warm. With the car warmed up I still have an 1/8th of movement with the choke plate. Dumb question: is the choke plate mechanically attached to this butterfly and could this be giving me a high idle/rich condition?

What are some other causes of not being able to lower my idle?

 

[Don C]

Yes, the choke is connected to a fast idle cam that controls the throttle opening when the choke is activated. See figure 11 on page 8:

http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf

 

[mchandford]

A bit of an update. I went back to the unit, started Sheila, let her warm up, then I turned the distributor counter clockwise, which should be retard correct? either way I turned it that way until it stumbled, then came back clockwise a touch, I was able to get the rpms down to about 900. Here is the exciting part though. When I went back to the idle air screws and as I was turning them all the way in the idle changed significantly. it went up, which i think makes sense because it is taking away air from the mixture. then as i turned them back out again 1 and 3/4 turns, the idle went back down a bit and the car seemed to run pretty good. The idle is still at 900 but i guess that is better than 1000. I pulled the drivers side plugs and they are all black and covered in carbon. I will be replacing them but need to figure out what is going on first.



Here is the plug after i pulled it.

and after i brush it off.



I also checked the spark plug gap. i think I remember someone saying .035 was a good stock starting point. The plug that I checked was at .045. What is the cause and effect of changing the gap? Would a larger gap cause a rich condition? Thank you for your guys' help again.

 

[hyena429]

Well i think more gap makes the fuel burn better..."On weaker or stock ignitions, opening up the gap CAN increase the spark kernel size, thereby creating a more efficient burn. The problem lies in that any added gap creates more strain on the other ignition parts. " what i read about gap.

She is runing realy rich..I wonder if your carbs idle circit is screwed up..You have a freind with a carb on the shelf you can test?...Im thinking something wrong with your carb in delivering fuel....cause if i remmeber right you got quite a strong build for that carb..."which i was thinking it was too small anyways for it"

 

[mchandford]

Well i think more gap makes the fuel burn better..."On weaker or stock ignitions, opening up the gap CAN increase the spark kernel size, thereby creating a more efficient burn. The problem lies in that any added gap creates more strain on the other ignition parts. " what i read about gap.

She is runing realy rich..I wonder if your carbs idle circit is screwed up..You have a freind with a carb on the shelf you can test?...Im thinking something wrong with your carb in delivering fuel....cause if i remmeber right you got quite a strong build for that carb..."which i was thinking it was too small anyways for it"

You know, I have had mixed signals about the carb size. You and several others have said it is too small. But others have said they are running a 600 on the 351 and no problems. I will see if I can borrow one from someone and see how it goes.

Speaking of the idle circuit. I think I may have made an improvement by retarding the timing today, but won't know until I clean plugs and test.

So do you think I should stick with the spark gap I have? These are autolite 25's BTW, was thinking of trying the 26's and see how they do.

Someone else posted that they were using a gap of .060?! that seems like a lot, but what do I know. I am running electronic ignition as well so maybe the wider gap is ok and I just need to work on the idle.

 

[droptop73]

The plugs look very rich. There are several things that can make it look rich. First is actually being too rich. There are a few things to look for to find the cause of the rich run. First is improper settings on the carb, mixture screws or jetting. Second is parts failure like a blown power valve on a Holley. Another and easily overlooked cause is blocked air bleeds.

Secondly, it could be ignition related. Poor spark energy, too cold of a spark plug and too wide a spark plug gap can make a plug look rich.

My take on the plug shown is an overfueling situation. The soot on the plug looks to dry for it to be oil. Since the idle picked up when you closed the idle screws it sounds like a failed power valve.

 

[woodsnake]

Just idling will also cause the plugs to look rich, as you are not putting a load on the engine. It sounds like all of your diagnosis are being done in the garage, is that right?

 

[mchandford]

yes it has really just sat in the garage for quite a while. Not too many good runs with it. I am hoping the weathers stays decent for tomorrow. I am going to try checking the needle spring on the carb and see if changing it to a lighter spring helps.

I do not have a holley, so I don't think the power valve is the concern. It is an edelbrock. i guess there still could be something up with the 'pump'.

If I can get it out on the road tomorrow I will let you guys know what the plugs look like afterwards. i do still think there is something up with the carb. My next plan is to take the whole thing off and rebuild. Or at least get some air and blow out all the passageways. The thing sat for quite a while and has not been rebuilt. It all looked pretty clean when I took the top off but it only takes a little bit of crud to cause a problem.

Droptop, you mentioned spark plug gap and cold/hot plugs. I am running a 25 right now, and the inside drivers side (is that #8?) plug i pulled and photographed was gapped at .045. i think I may get 26s tomorrow and try them at .35 as i think is stock.