Carb Adjustment - again -sorry

Bernd · Post by **Bernd** » Mon May 14, 2007 4:09 am

Sorry for another carb adjustment question, but I hope for your expertise:

After having bought a CO tester that actually works (e-bay, loger story...

), I tried to adjust the carbs (+synchronize of course) on my 712 last weekend. All adjustment screws 2 turns out gave around 4% CO, idle at 990 to 1000 rpm, carbs synchronized well.
If I know slowly increase idle to about 1100 to 1200 rpm with the hand throttle and hold it steady there, the CO reading drops to about 1.5%, even lower with higher revs????

Is this normal or do I have an air (vacuum) leak?

The spark plugs on cylinders 1 and 2 are beautifully brown, on 3 and 4 they are more to the white...

Any Ideas?

Greetings from Innsbruck

Bernd

lindenengineering · Post by **lindenengineering** » Mon May 14, 2007 8:42 am

Ah Bernd, my favourite subject.
Burning fuel efficiency and getting the best from a litre of fuel.

You did'nt post the HC's and oxygen (O2) from your analyser. Since there is a direct correlation between CO and HC's you need to adjust the idle mixture to get the best figures possible. The O2 count should always be taken into account to finalise the settings.

Taking a stab at what you have posted 4% isn't too bad, I normally see anything from 3.00% CO to 4.25"ish" at 6500 feet here in Colorado. The HC's being something like 250 to 350 ppm for the average. Oxygen being the final "determiner" and I like to get 9.0000 something on that reading.

To give you an example I set up a Pinz on Saturday which had an initial of 7.56CO% at idle and a HC of 2.35ppm, with 7.2 CO2 A polluter!
I adjusted it down after doing some carburetor repairs plus adjustment to 2.35% CO and HC went up to 3.64% and O2 was 9.3%.

Judging from your figures at "revs" the engine appears to be running just right at 1.5% something but again without an HC count it's hard to be specific. Do make sure your timing is correct, an over advanced engine will push the HC's up and make adjustment difficult to get good readings.
A good method to gauge manifold depression is to connect a vaccum guage to the manifold, a steady 15" mercury should be achievable.

Best of luck, come back with some more parts of the puzzle and I can be more specific. A gas analyser is the best engine diagnostic tool there is.
You may question why the higher disparity at idle that is normal for the Steyr engine. Basically it is a very inefficient beast in this day and age.

In my case the customer reported to me on Saturday evening a 50% decrease in fuel consumption initial 10.3 mpg after a quick fix 15.3 on a flat out run north.
Customer happy.
Dennis

Bernd · Post by **Bernd** » Mon May 14, 2007 9:14 am

Thanks Dennis for your quick and as always substantiated reply. Unfortunately, my old Souriau engine analyzer just gives a CO reading, I know HC and so on would be nice, well Captain Wallet wasn´t so fond of more sophisticated equipment for a weekend mechanic like me...

I´m glad to hear, that in short, a drop in CO when revving the engine is quite normal (my VW Bus didn´t show this), so I will watch the spark plugs, a Carburator rebuild is on its way, when I can get hold of a sealing kit (mailed the supplier two times, obviously doesn´t need my money...)

Greetings to Colorado

Bernd

lindenengineering · Post by **lindenengineering** » Mon May 14, 2007 7:36 pm

Bernd

I suspect the difference in plug colours from "front twins 1&2" as opposed to "rear twins 3&4" is probably due to carburetor wear on the spindles giving some mixture dilution or you have/had a carburetor imbalance that was causing one unit to "lead" the other.

In any case the old fashioned way to determine mixture strength is to find a straight piece of road run flat out then "kill" the engine, coast to a stop, and remove the plugs and read the colour(s).

We used to do this in the early 70's with Jaguar 4.2 S types belonging to the local police; they used these for high speed pursuit, and equally they were also popular with the villains for high speed getaways!
Good fun to test and just like Pinzgauers would need frequent tuning to get the things over 132mph. In that respect nothing changes with these old vehicles.
Best regards
Dennis

todds112 · Post by **todds112** » Mon May 14, 2007 8:05 pm

I need to rebuild my carbs. I could not get them to sync-up until the idle speed was pretty high. With the rear carb throttle plate just cracked and the mixture screws at 1 turn out, it read 12 on the meter. The front at the same settings was 4! Adjusting out the front one to get it to 12, really makes the idle high.

Which carb would this indicate is the worse off?

lindenengineering · Post by **lindenengineering** » Mon May 14, 2007 9:57 pm

Todd
A tip. Disconnect both linkages at the carburetors. Then screw in the slow running screw (NOT MIXTURE SCREWS) until the engine will run albeit roughly. Then put your tester onto each throat and set it to 9.75 on the balancer scale. The engine should idle smoothly at this stage since they are both working in unison.
Now fit the rearmost carburetor link. There should be some spring return resistance felt. Recheck the setting, adjust the rear carb if necessary (on the slow running SCREW; now offer up the link for the front carburetor. You may need to screw in or out the forward carb link ball end to allow the carburetor to accept the ball joint without increasing the revolutions one iota!
Example too short a link will increase the rear carb, too long will increase the front unit.
Have go & best of luck.
Dennis

Roman · Post by **Roman** » Tue May 15, 2007 2:54 pm

I am also fiddling with my carbs now and would wish if someone can explain to me what is happening.

The trouble is that the engine starts quite easily when cold, runs smooth for some time and then stops for no obvious reason.
The ignition is set with strobe light to 2 mm BTDC.
Both carbs are synchronized to the detail with an air flow meter.

Now to question 1:
When I am looking into the carbs during idling it is visible that the fuel droplets are coming from the small cylinders and are falling down on to throttle flap. It is happening on 3 cylinders, but not on the cylinder 2 (second pass of the first carb from the front). If I add some throttle, the cylinder 2 also starts to have fuel. Is this normal, or is this indicative for some problem.

My question 2:
When the engine is stopped, the small cylinders within the carbs passages are continuing to weep droplets of fuel for some time and are covering with fuel the closed throttle flaps - all but number 2.
Is this weeping normal? It seems odd to me. What it indicates?

I tried to explain the best I could. Hope that it is clear enough.
I would be very glad if I could get some explanation, since I am very unhappy when something bothers my pinzi.

lindenengineering · Post by **lindenengineering** » Tue May 15, 2007 10:10 pm

Roman
First check to see if the blank plugs are still in place in the top carburetor covers. To see these observe the venturi balance tube running across the throat of each carburetor and then glance down the side to see the dished plugs blanking off the internal drilling in the tube. They are staked in place and can fall out if your engine likes to spit back.

With these plug(s) missing the carburetor will behave very strangely indeed.

The droplets of fuel cascading down the venturi(s) are a sign of a flooding carburetor(s) and there have been some observed instances on very well worn units that fuel gets drawn up by manifold depression from the bowl bypassing the accelerator pump pistons. So check these for good sealing in their respective bores.
Best of luck
Dennis

Roman · Post by **Roman** » Tue May 15, 2007 11:41 pm

Thank you very much Dennis.

If I understood properly - the plugs shall be inside the venturis. There are actually a certain copper plugs.

The engine has 50 Tkm and I don't know if this is worn or not.

For now I'l try with another carbs for which I know that are quite good.

lindenengineering · Post by **lindenengineering** » Wed May 16, 2007 8:13 am

Roman
The plugs are dished disc like and are observed on the outside of the top cover next to the accelerator pump arm, and equally on the opposite side.

The float level valve is prone to leaking and this causes the bowl lwvwl to rise causing the flood symptoms. Sometimes shimming can eliminate the problem. In the interests of labor cost I usually throw two new ones in and test.
Best of luck
Dennis

Roman · Post by **Roman** » Thu May 17, 2007 5:41 am

Dennis
Now it is clear. I have carbs removed but the plugs are in place. I guess that you are right about the fuel level.
I ordered the carb rebuild set from Munich, but was advised to be patient.

For now I'am about to took carbs from my old 710M, which I have allready 2 years in the bodywork restoration process (chasis and bodywork separated allready 1 year, but never have time to work on it).

I guess that I shall not tear the perfect working engine, but I am in hurry to be ready for our military oldtimer rallye in saturday.

Carbs on the 710MK were sealed on place by red sealing compound. I don't think it is regular.

Roman

Roman · Post by **Roman** » Thu May 17, 2007 2:31 pm

Just for information.
With replaced carbs, pinzi now runs sweet like never before.

best wishes to all.

Roman