Help, White exhaust valve?!

[tk111]

Hi folks,

 

After my initial enthusiasm wore off about having succesfully removed my old exhaust system without any major damage I decided to have a closer inspection of the exhaust valves and ports.

 

1 of the valve's has a white powder coating?

 

Is this an issue with this cylinder not firing? or is it something more sinister?

 

 

 

 

 

Any suggestions would be highly appreciated.

 

Thanks

Terry

[SteveT]

Running too hot on that cylinder maybe?

[tk111]

Thanks Steve,

 

So from what I have read this could be caused by this cylinder running lean, need to read up about tuning the webers?!

 

I get an occasional miss (it sounds like a little cough) does this sound like it might be related?

[Uncle]

Webers coughing is not out of the ordinary at all. I would pull the plug and have a look to see if its the same colour. If so you are defiantly running lean. 

One the plus side Webers are very very easy to work on.

[tk111]

Thanks Martin,

 

That makes me feel better, hopefully the spark plug is the same.

 

Can't put it off any longer, the time has come for me to learn how to tune these puppies myself.

[Pauly]

Definitely running lean. I'd check the carbs & make sure they're all clean ect. You should get yourself a wide band o2 to see how the air fuel ratios are. 

[Uncle]

IF I recall correctly the B&B headers have bungs for the AFR probe just before the muffler. Would be a good investment if you are going to start tuning them.

[Babalouie]

Shame you're in Canberra, I could have a look.  I'm not too bad with Webers

[Uncle]

Want to buy some jets and chokes Bab's? I have some spare

[tk111]

I am liking the idea of putting a A/F meter in, there is a bung for a probe on one of the headers but not the other.

I would have thought it would be good practice to measure the mixture coming from both banks? 

 

Is it worth having a second bung welded in to the other headers for this?  

 

I suppose I would run a meter up in the console somewhere and look for a device that can do logging as well, would you guys agree with this approach?

 

Hmm, Babalouie it sounds like I might have to book a road trip to come and see you...

[Uncle]

Here you go..

 

http://www.ebay.com.au/sch/i.html?_odkw=aem+wideband&_osacat=0&LH_PrefLoc=1&_trksid=p2045573.m570.l1313.TR0.TRC0&_nkw=+wideband+kit&_sacat=0&_from=R40

 

2 Channel would be better than one but you could just do one side then the other.

[Pauly]

What would actually work better is if you had EGT sensors on every exhaust header pipe. then you'll know which cylinders are running hotter...

 

The problem with AFR sensor is that it's a combined reading of 3/6 cylinders. If this was EFI, no issue because all injectors should be equally flow matched. With carbs, well it's all mechanical and everything needs to be 100% clean for it to operate evenly. 

[Babalouie]

Here's a pretty simple check:

 

 

See those spring-loaded screws?  Those control the idle mixtures (but are still gradually in-play until about 3000rpm).

 

For one of the "good" cylinders, screw-in the mixture screw until it gently seats (not too hard, it's a tapered seat) and count the number of turns.  If it's correctly jetted, then it should be about 1 turn (plus or minus a quarter turn).  Then, for the "bad" cylinder, do the same.  If for some reason, instead of 1 turn, its more like a half-turn to seated, then that's your culprit right there. 

 

The more you unscrew it, the richer it'll be, so if say the good-cylinder is 1.25 turns from closed,  then adjust the bad-cylinder to this same setting and see how you go.  By rights, all the mixture screws should be at the same setting, but for the time being, let's assume it's generally correct, and we just have one screw possibly out of whack

 

If this experiment doesn't work, then we start looking at mismatched or blocked jets.

[tk111]

Thanks Babalouie, I will have a close look this weekend and see if this is the culprit. Great help with the photo also!

[Uncle]

This might also be of help.

 

[michel]

I am liking the idea of putting a A/F meter in, there is a bung for a probe on one of the headers but not the other.)

Terry is an A/F meter onE to add to the tool kitty? I'd find use for it at times others would too....

[Babalouie]

A/F probe is a nice tool for tuning carbs, I have a TechEdge one on my car

 

 

It plugs into a laptop and can make Excel charts and stuff, which is handy.

 

 

That said, once it's set up properly, you never need to use it ever again   As a maintenance aid, it's of limited use.

 

For example, see that pic of the carb above? You'll notice that the idle mixture screws are all at 9 and 3 o'clock.  So once you find your optimum setting, you can easily just check visually if one of the screws has shifted.  Not all carb idle screws will be perfectly matched like this, but even so you can just memorise the positions and check that way.

 

Also, an A/F probe is not really all that helpful in this case, where we have a problem with one cylinder only.