Too rich or too lean? What does this spark plug tell you?

[Letsurf]

So I've been troubleshooting like a mad man to find the power issue with my 86.5 d21. So many issues there that I will likely create a whole post on it eventually. I put new plugs in and ran around town for about 30 minutes and wondering what this plug color means. It has dry black soot around the base of the threads. So much that you could probably write a sentence with it. The ceramic and electrodes look clean. Would 30 minutes be enough to see the full black plug that is indicative of a rich mixture? Why would it be black at the base but not on the rest?

 

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In this second image you can see that line where I wiped the black char off. 

 

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[Ooph!]

My 2cents is it looks a little fuel rich because of the dry soot but with either a hot plug or not enough time because it's a little too clean on the porcelain.

If it were mine I'd wipe off most but not all of the anti-sieze, I use it but very sparingly on plugs.

I've read it can contaminate the tip and it may also be an electrical isolator (weak spark) and may insulate the heat (hot plug).

Good Hunting

[Letsurf]

My 2cents is it looks a little fuel rich because of the dry soot but with either a hot plug or not enough time because it's a little too clean on the porcelain.

If it were mine I'd wipe off most but not all of the anti-sieze, I use it but very sparingly on plugs.

I've read it can contaminate the tip and it may also be an electrical isolator (weak spark) and may insulate the heat (hot plug).

Good Hunting

 

I may have found the issue. So I had read that when tuning the weber 32/34 that the idle speed screw was to be set less than 1.5 turns. I thought this was for tuning purposes only. So after tuning I would turn it in about 2 turns to get enough idle speed to drive. Turns out that if you run it with more than 1.5 turns in then it messes everything. Looks like I need a bigger carb so going to go with 38-dges. 

[Lockleaf]

You most definately do NOT need a larger carb to run a z24. If you can't run the engine with the correct settings, it means you need to change jetting. So tune the carb.

[Letsurf]

You most definately do NOT need a larger carb to run a z24. If you can't run the engine with the correct settings, it means you need to change jetting. So tune the carb.

 

I changed the jets to the following and it helped performance quite a bit but still doesn't seem optimal:

 

Main jet: 150/180

Air Corr: 150/180

Idle jet: 65/60

 

It has a Z24i with larger ports on the intake and I was told by redline that the 38-dges would be much better for that engine. Do you think it would increase performance? 

[Lockleaf]

Increase? Yes. Necessary? No, it's not. It will give you more power, but because it's a synchronous carb, it will FEEL more powerful than it actually is. Carb tuning is more art than science. You've gotten closer than it was, but if it needs more, then it needs more. Jets are cheaper than a whole other carb. And if fuel mileage is a concern of any kind, the 38 will not help you.

[Letsurf]

Increase? Yes. Necessary? No, it's not. It will give you more power, but because it's a synchronous carb, it will FEEL more powerful than it actually is. Carb tuning is more art than science. You've gotten closer than it was, but if it needs more, then it needs more. Jets are cheaper than a whole other carb. And if fuel mileage is a concern of any kind, the 38 will not help you.

 

I will probably go for it. It's a project truck and literally everything under the hood is new. So much blood sweat and tears what's another $250 lol. 

[Lockleaf]

You will need to tune the 38 once it's on, but the extra fuel it delivers will hide more sins.

[Letsurf]

You will need to tune the 38 once it's on, but the extra fuel it delivers will hide more sins.

 

I put on the 38-dges and it has a lot more power now but it's bogging when I hit the accelerator too fast. Also, when I go down the street then do a rolling stop and take off it will almost die then shoot forward with power. I tried jetting from 135 all the way to 160 mains and all different idle speeds and can't get it to stop this cutting out when accelerating too fast.

[Lockleaf]

Does the 38 run an accelerator pump? Might need adjusted or replaced with a larger one?

[Letsurf]

Does the 38 run an accelerator pump? Might need adjusted or replaced with a larger one?

 

Yes it does but I don't think it can be changed.

[datzenmike]

The 38/38 is a synchronous carb... both barrels open at the same time so you have to change how you drive it. It's intended for much larger displacement engines like a six cylinder or small V8. Your tiny 2.4 can't use that much carb if you stab it open suddenly. Try 1/3 and then roll into it as it accelerates. Like learning the use of a clutch... once learned, you don't even notice it later.

[Letsurf]

The 38/38 is a synchronous carb... both barrels open at the same time so you have to change how you drive it. It's intended for much larger displacement engines like a six cylinder or small V8. Your tiny 2.4 can't use that much carb if you stab it open suddenly. Try 1/3 and then roll into it as it accelerates. Like learning the use of a clutch... once learned, you don't even notice it later.

 

So would I be better off just going back to the 32/36 then? 

[Letsurf]

The 38/38 is a synchronous carb... both barrels open at the same time so you have to change how you drive it. It's intended for much larger displacement engines like a six cylinder or small V8. Your tiny 2.4 can't use that much carb if you stab it open suddenly. Try 1/3 and then roll into it as it accelerates. Like learning the use of a clutch... once learned, you don't even notice it later.

 

I think this could be a velocity issue due to the large plenum on the intake. Is that possible? If so would putting the original intake instead of the z24i intake solve the issue? 

[datzenmike]

Intake is not a factor in this.

 

Carb is just too big to drive by stuffing the throttle suddenly. Try 1/3 and as you pick up speed and get going add the rest. The 38/38 will have the best top end power but shitty low speed and mileage.

 

The 32/36 is not only smaller, the secondary only begins to open when the primary is above 1/2 throttle. Even the 32/36 has a slight bog if hit too fast. The 32/36 will be a more drivable carb 

[Lockleaf]

If they happen to be correct and the plenum velocity really does cause that significant an issue, then yes, swapping to a carb z24 manifold would be beneficial to you. Its a theory worth testing out, both manifolds back to back.

[Letsurf]

If they happen to be correct and the plenum velocity really does cause that significant an issue, then yes, swapping to a carb z24 manifold would be beneficial to you. Its a theory worth testing out, both manifolds back to back.

 

I guess a question to ask is would the 38 amplify the issue. The 32/36 did not have that issue so is it possible the 38 made the issue with the large plenum and velocity worse. 

[racerx]

32/36 is better fit.  38/38 is too big. Unless you have a built L20 or something or change the jets but then that will defeat the purpose of having a 38/38 synchro carb.

[Draker]

I've had this issue on a L16 and L20 with the 32/36 with recommended jetting. It was a used untested carb.. I swapped to side drafts.

[Letsurf]

I've had this issue on a L16 and L20 with the 32/36 with recommended jetting. It was a used untested carb.. I swapped to side drafts.

 

this is a brand new carb and I have tried every jetting variation I can find with no fix. Maybe it's just a faulty carb. I keep getting conflicting answers. Some say this carb is perfect for that truck and have even used it on 1.6L Suzuki Samurai's and 1,300 cc minicoopers. Others are saying it's way too much lol. I have 21 in hg vacuum at the intake manifold, new coils, holy red top fuel pump with regulator at 3lb, the engine is rebuilt and bored .50. 

[Letsurf]

Something else to note. I have the idle speed screw completely out and the butterflies are closed and sealed and the engine still runs. How is that possible? 

[datzenmike]

 What you describe... it can't. So you are missing something. Air has to be getting in and so is gas. Is it flooding? Shut off and take the top off the weber....gas at correct height? Float OK inlet needle not stuck or jammed?

 

 

32/36 and 38/38 will both run and work... BUT the 38/38 will not have the drive ability of the smaller carb. It will make good power but be harder to live with at lower speeds and have poorer mileage. The 32/36 will behave better at low speeds and part throttle, give better mileage but not have as much top end. There is no right and wrong to this choice it's just that there are differences.

 

Generally it's better to have a smaller carb and wish it were larger than to have a large carb and wish it were smaller. If larger carbs were really practical, we would all put 4 barrels on, but we don't. There's a reason for this. 

[Letsurf]

 What you describe... it can't. So you are missing something. Air has to be getting in and so is gas. Is it flooding? Shut off and take the top off the weber....gas at correct height? Float OK inlet needle not stuck or jammed?

 

 

32/36 and 38/38 will both run and work... BUT the 38/38 will not have the drive ability of the smaller carb. It will make good power but be harder to live with at lower speeds and have poorer mileage. The 32/36 will behave better at low speeds and part throttle, give better mileage but not have as much top end. There is no right and wrong to this choice it's just that there are differences.

 

Generally it's better to have a smaller carb and wish it were larger than to have a large carb and wish it were smaller. If larger carbs were really practical, we would all put 4 barrels on, but we don't. There's a reason for this. 

 

I checked the float level and it was exactly 18mm as it should be. Also the needle came out and the little ball bearing moved freely. Not sure how to check the gas level with the top off. I also checked for vacuum leaks and couldn't find any. Maybe it's a faulty pcv valve or something letting air in? 

[datzenmike]

The PCV valve is a metered and accounted for air leak. So as long as it's there it's fine.

 

A vacuum leak would tend to cause a lean mixture and a drop in idle speed.... unless you are running too rich and there is excess gas that just needs more air... then a leak might raise the idle. Check any hoses connected to the intake that would have manifold vacuum. Don't forget the brake booster hose. Look for loose or cracked hoses. Maybe pinch them with pliers and see if the idle stabilizes. 

[Letsurf]

The PCV valve is a metered and accounted for air leak. So as long as it's there it's fine.

 

A vacuum leak would tend to cause a lean mixture and a drop in idle speed.... unless you are running too rich and there is excess gas that just needs more air... then a leak might raise the idle. Check any hoses connected to the intake that would have manifold vacuum. Don't forget the brake booster hose. Look for loose or cracked hoses. Maybe pinch them with pliers and see if the idle stabilizes. 

 

I checked all the possible connections and also took the 1 way valve that goes to the break booster and checked it. Replaced the PCV valve. Is it possible the carb is faulty? I mean if the butterflies are closed is there another route air could flow?