| Author |
Message |
JRV (Jrvall)
Member
Username: Jrvall
Post Number: 260
Registered: 11-2002
| | Posted on Tuesday, December 03, 2002 - 7:16 am: | |
To set idle properly you need at least 2 gas readings..CO & HC, without reading HC you simply end up using good cylinders to mask weak ones. HC is unburned hydro-carbons, a good running motor is 200ppm or less. all the way down to 60ppm, a nice, crisp perfect running bank should be 300 and below...CO tells you how rich a port/bank is running, but HC tells you what the cylinders are doing with the fuel, burning it or just passing it thru.
I read the other thread about lean running with colortune, i disagree with those conclusions. To properly balance a set of carbs can take 4-6 hours the first time thru, depending on different factors, of which there are many, timing, linkage, contamination, air leaks, etc.. Constanly rechecking intake air volume while making mixture adjustments while at the same time allowing the engine to cool from time to time. Intake runners will overheat after long periods of steady idleing throwing off the desired results, additionaly, as the weak cylinders are brought online the first strong cylinders will need to be reduced as their load has reduced. So it is neccesary to run through the entire engine several times gently pulling all the cylinders closer to each other with each pass. As the engine starts to run cleaner and crisper the idle will increase, neccesitating reducing the air intake volume(idle speed) which in turn richens up the mixture to some degree. So even a gas analyzer is not a one pass operation. However if the time is invested learning how to carefully massage and tweek the engine to a near perfect harmonious balance, the tune will last much longer as will plugs and rings/valves/guides.
It is also neccesary to monitor timing as idle speed picks up and adjust as neccesary. |
Hans E. Hansen (4re_gt4)
Member
Username: 4re_gt4
Post Number: 642
Registered: 4-2002
| | Posted on Tuesday, December 03, 2002 - 12:58 am: | |
As for me, I'm only interested in setting up for idle mixture. I'm reasonably confident as to running mixture, as I had exhaust analyzed on a dyno. Running mixture is fine, idle stinks. I'm fine on main jets, slightly lean on air correction jets (i.e. full throttle, hi rpm a little lean), and maybe just a touch rich on idle jets. But those idle mixture screws....... It runs smooth, but stinks. |
'75 308 GT4 (Peter)
Intermediate Member
Username: Peter
Post Number: 2240
Registered: 12-2000
| | Posted on Monday, December 02, 2002 - 10:59 pm: | |
Colourtune does make exhaust-gas analysers, but from the looks of it, they only measure CO.
http://www.gunson.co.uk/acatalog/Gunson_Catalogue_Exhaust_Gas_Analysers_Mixture_Control_5.html
I've seen one or two on Ebay, for prices marginally less than advertised at the Gunson site.
I've asked this question before on FC:
http://server.ferrarichat.com/~ferrari/ferrarichat.com/discus/messages/112/153963.html?1035119518
The concensus was to use either the Colourtune plugs, or the lean-cut method. That's fine and I will for now, but I'm still keeping my eyes open on Ebay though for a (multi-gas) analyser... |
Paul Newman (Newman)
Member
Username: Newman
Post Number: 753
Registered: 12-2001
| | Posted on Monday, December 02, 2002 - 8:44 pm: | |
Robert, my old carbed 308 doesnt stink me out of the car. I dont smell anything driving or idling in traffic. It is pretty rich from behind in the driveway but thats about it. |
JRV (Jrvall)
Member
Username: Jrvall
Post Number: 254
Registered: 11-2002
| | Posted on Monday, December 02, 2002 - 8:23 pm: | |
If you could find an old 2 gas analyzer (CO & HC) that still works, that would serve you just fine. Hmmmmm... where to find one though ?
I tuned carbs for years with a color tune & tach...but even as good as I am, even I can't get as low and nice as with even a 2 gas analyzer. The reason is, intially while tuning, the engines run smoother when they are too rich....about 5% CO....so the tendency is always to err on the fat side. Also without a gas analyzer you can't see HC's which is extremely important to perfect running on every cylnder. Knowing the HC count prevents letting one strong cylnder mask a weak or missing cylnder.
There are small portable EG analyzers these days but they're expensive $6K-$8K for a cheap one. Keep an eye on ebay and places used shop equip might be liquidated...it won't be long before even 4 gas analyzers will be selling cheap as the 5-6 gas analyzers are phased in. MY EG analyzer is one of the best most frequently used tools in my shop. You cannot properly tune an engine without one imo. |
Hans E. Hansen (4re_gt4)
Member
Username: 4re_gt4
Post Number: 635
Registered: 4-2002
| | Posted on Monday, December 02, 2002 - 7:47 pm: | |
Is there such a thing as an inexpensive home-use exhaust gas analyzer? I realize such an instrument wouldn't be lab accurate, but it would be of some use if it were reasonably close. |
JRV (Jrvall)
Member
Username: Jrvall
Post Number: 252
Registered: 11-2002
| | Posted on Monday, December 02, 2002 - 7:16 pm: | |
You might not be able to get rid of the fumes completely at a standstill...however if the engine is running rich (High CO %) and missing (high HC's PPM)(even though you might now hear it, it can miss) the smell of fumes is very stout. Solution = have exhaust gas checked on a 4-5 gas analyzer and carbs tweeked to where they should be...CO 2.5-3.5 % HC's 250-400(400 absolute max)PPM. The odor will be greatly reduced, the motor will start and run crisp and the plugs will last. Not to mention you will no longer be washing lubrication from rings & valve stems. |
Paul (Pcelenta)
Junior Member
Username: Pcelenta
Post Number: 222
Registered: 7-2002
| | Posted on Monday, December 02, 2002 - 3:11 pm: | |
my wife gives me the same. on our '78 gts we get it pretty bad and our clothes smell of exhaust too...(which doesn't score well with the wife) and I'm running an electronic ignition with slightly hotter plugs (bp5s)...I don't know of any solutions other than avoiding getting stuck in traffic (impossible here in NYC) |
Robert W. Garven Jr. (Robertgarven)
Junior Member
Username: Robertgarven
Post Number: 86
Registered: 2-2002
| | Posted on Monday, December 02, 2002 - 2:47 pm: | |
Friends,
I cannot find any exhaust leaks on my 75 gt4 but must admit when I am in traffic or stopped at a light the fumes almost kill my passenger. Even though I love the car I must admit it is allot and sometimes I even feel lightheaded. On my last FNA trip I drove behind a Daytona which seemed to be about the same. Do any of you carb car guys,gals have a simillar problem. I am running 1 set of points, stock ignition and unhooked air pumps. My wife almost refuses to ride in it any more. When moving it is fine. I think that we are so spoiled by cleaner new cars that any 70's emission vehicle really stands out. I am wondering if there are any timing solutions?
Rob
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