Hydrocarbons and AFR

[skimp930]

I recently got my adjustable fuel head and WUR and took it to a shop to get the fuel adjusted just right. They noticed hydocarbons was high around 1000 and CO was adjusted to 3.52 @ stock timing. They said since the hydrocarbons are high they could not get a good AFR reading, if I understood it correctly. Is that correct? Can I not adjust the AFR with high hydrocarbon? The shop, also managed to over fill the oil by about 2 quarts. I hear, by doing some search on this forum, overfilling oil can cause problems with tuning/adjusting afr. Is that right?

Thanks

[proffighter]

High HC readings means unburned fuel or simply said running fat. Oil of course can increase that too. Euro CIS readings are about:

CO: Less than 2.5%
CO2: Higher than 8%, ideal around 12% (higher number means better burning, but depending on cams, headers, etc... it can stay at the lower limit at idle)
HC: less than 400ppm's ideal below 100ppm's
(specs out of my emission document)

Here a diagramm for better understanding of emission mixture

[skimp930]

Thanks Roland for the info. Very helpful.

It appears some mechanics have no idea how to adjust the adjustable WUR or the adjustable fuel head. When I had WUR/Head converted to an adjustable unit, I was thinking I can just send the car the local Porsche mechanic and have them fine tune the fuel mixture. When I took the car to the mechanic, all they did was fine tune the fuel mixture on the air meter and didn't touch the fuel head or the WUR. I guess I am forced to learn how to adjust the units myself, which is a scary thought. Does anyone know a good mechanic in GA that knows how to adjust the fuel on the heads and WUR?

Thanks all

[RarlyL8]

What do you mean by "adjustable fuel head"? All fuel heads are adjustable. They are adjusted and set at the factory; the adjustment mechanism for each cylinder is part of the head so left in place. Where did you get an adjustable WUR and why does it not have instructions?
Unless your engine output > 375whp there is no need to alter the fuel head settings, only accurate AFR readings will determine if and how much.
The fuel head settings, fuel mixture screw, and WUR settings all play a tripple see-saw of fuel adjustment, altering any will affect all.
High HC can indiate low system pressure which can be caused by many things. Before adjusting anything you must verify system and control pressures are within spec. That is your baseline.

[alwaysflat6s]

Good info. I cry being reminded of what the factory specs are on these. In Calif they ream us on emissions while claiming that they never require emissions stricter than a vehicle was required when new.

Sorry... off subject rant.. but I feel better now.. snif.

[1986 930]

Originally Posted by skimp930

Thanks Roland for the info. Very helpful.

It appears some mechanics have no idea how to adjust the adjustable WUR or the adjustable fuel head. When I had WUR/Head converted to an adjustable unit, I was thinking I can just send the car the local Porsche mechanic and have them fine tune the fuel mixture. When I took the car to the mechanic, all they did was fine tune the fuel mixture on the air meter and didn't touch the fuel head or the WUR. I guess I am forced to learn how to adjust the units myself, which is a scary thought. Does anyone know a good mechanic in GA that knows how to adjust the fuel on the heads and WUR?

Thanks all

Huntsville Al is only a two hour drive from Atlanta. I think that you answered your own question!

RarlyL8 sells the BL WURs and is well known for making them work. If your little beast is drivable, time for a road trip.

It is a nice drive too!

[BlkBird]

skimp930 - ROAD TRIP!

I've been threatening to visit Brian for some time now. Maybe we can set up a convoy? Play some 70's radio tunes and head for banjo country?