1st Start Up On Webers... Tuning ??

[P Moore]

Looking so some advice here....
Has not been started in about 4 years

So I'm just after converting over from CIS to Webers (thanks to speedo!)

My next step was to start tuning these Carbs but looking for some advice here 1st...
I have recorded a short clip of the car starting up for the 1st time and maybe you guys can tell if its running too rich or lean and maybe a few steps from there....
Porsche 911 1st Start up - Webers - YouTube

Cheers,

[1QuickS]

Lots of spitting up through the intakes...lean.

Best to start from the beginning with clean everything and then follow this procedure: http://http://www.performanceoriented.com/technical.htm#Installation

[Uncle Enzo]

Ive got more or less the same set up. I agree with the 1QUICK and they might need to be sync'd as well. Once you get those babies tuned there is no turning back. The sound at WOT is pure sex.

[Trackrash]

Sounds to be too lean, however plugged idle jets can do the same thing.

Keep in mind that your ignition, timing, valve adjustments, and the motor's condition will affect its running.

What are the details of the motor? What are the details on the Webers? Venturi size, jets, and model # of the carbs.

[Steam Driver]

Oh yes, the definitely will need to be synched, that can be a source of the popping also (definitely a lean mixture will cause it). Here's how I used to do it with the Webers on my 914-6 when putting them on after disassembly and cleaning. (Note: This assumes jetting, etc. are all OK for the engine in question)

1. Carbs on engine, cross shaft between the carbs disconnected. On new installations you would need to eyeball down into the carbs and see if the butterflies are in more or less the same position, i.e. openings. When I rebuilt I didn't disturb the setting of the idle adjustment screw so that would be more or less correct.

2. Initial Settings: Make sure fuel pressure is correct, then set float level with the float gauge. Same thing with the accelerator pump discharge; set it. On the latter I found that the factory specs were 'way too much (again, for my particular car) and adjusted that down to something like .38cc/stroke (it's been a long time, that may have not been the number). Screw the idle mixture screws all the way in and then back them out about 1.5 turns. Close the little needle valves (air correction? Balance? I forget the term and don't have my books handy) at the top of each carb throat all the way. (These are the little bitty things with the locknut on them, top center of each throat)

On the accelerator pump discharge thing. If you romp down on it and you get an initial hesitation and it immediately clears and goes if you lift your foot a little, the pumps are lean. If on the other hand it bogs and continues to bog if you lift your foot, then clears after a few seconds on it's own with the foot still down, it's rich. What you want is an immediate and continuous response, foot on the floor.

3. Start car. First thing to do is to use your Uni-Syn (or whatever) tool to get the carbs more or less in synch from side to side and an idle speed of about 1200 or so. (Not too high here or you will get into the intermediate circuit) Then do an initial twiddling of the idle mixture screws. This should get you a more or less stable idle.

4. Now go back with the Uni-Syn and check each throat of each carb to see if the carb is pulling evenly. If not adjust all three throats on a given carb to pull the same, using the one pulling the most as the base; i.e. open the appropriate correction screws to make the low ones match the high one. Do this for both sides.

5. Now go back and using the idle mixture stop screws adjust the carbs to be pulling the same, and the idle speed again (probably need it)

While all this is going on you will probably have to "clear" the engine with bursts of throttle. Do this by just pushing manually operating the carbs together as much as you can; no need to hook up the linkage for this; just "blip" it with both hands.

6. Dress up the idle mixtures to get the smoothest running.

7. Recheck side to side synchronization.

If you're happy with the idle and synch, hook up the throttle cross-shaft. You may or may not have to adjust the length of the drop links. Keep checking the synchronization as you do this; some adjustment of the linkage will likely be required.

8. Just for kicks recheck/retwiddle the idle mixture screws. Also on my car I always found it better to be on the rich side here for overall performance.

9. Put whatever else needs to be reinstalled back on the car and go drive.

That's how I remember it. This worked for me for 18 year and probably six carb cleanings on the 914-6

[dfhtrhjn]

Here's the trick I use for the idle mixture on each cylinder. (part 6 from Steam Driver's instructions)

Once running warm.
1) Turn the screw in on one cylinder until you hear it turn off.
2) Then begin unscrewing it until your idle is at its fastest only adjusting that one screw. You'll have to give it bursts of gas to clear it, and at each setting you think you have right, give it 5 seconds of medium gas, then let go to see where it idles.
3) Repeat with each cylinder to optimize them individually.
4) readjust the idle
5) mark each mixture screw with a black dry erase pen
6) repeat 1-5 to refine the mixture even more (getting the smoothest peppiest response).
7) I use a black permanent pen to mark the final setting on the screw, I also count how many turns out each mixture screw is. e.g. 2.5 etc.

The idea is that your engine will run smoothest with the optimal settings.

Note on your final settings: If you idle circuit screw is less than .5 turns out from closed, then the idle circuit jet is too large. If you screw or more than 3.5 turns out then the jet is probably too small.

[P Moore]

Originally Posted by Steam Driver

Oh yes, the definitely will need to be synched, that can be a source of the popping also (definitely a lean mixture will cause it). Here's how I used to do it with the Webers on my 914-6 when putting them on after disassembly and cleaning. (Note: This assumes jetting, etc. are all OK for the engine in question)

1. Carbs on engine, cross shaft between the carbs disconnected. On new installations you would need to eyeball down into the carbs and see if the butterflies are in more or less the same position, i.e. openings. When I rebuilt I didn't disturb the setting of the idle adjustment screw so that would be more or less correct.

2. Initial Settings: Make sure fuel pressure is correct, then set float level with the float gauge. Same thing with the accelerator pump discharge; set it. On the latter I found that the factory specs were 'way too much (again, for my particular car) and adjusted that down to something like .38cc/stroke (it's been a long time, that may have not been the number). Screw the idle mixture screws all the way in and then back them out about 1.5 turns. Close the little needle valves (air correction? Balance? I forget the term and don't have my books handy) at the top of each carb throat all the way. (These are the little bitty things with the locknut on them, top center of each throat)

Close the Air correction screws ALL the way & then start the engine ??
At what point to these start to get opened up again ?

[Steam Driver]

They may not. You use that to correct the imbalance between the three throats of that particular carburetor. So the one on the throat pulling the most with them all closed will stay that way; closed. The other two are opened up as required to match those throats with the highest one. At that point you lock them down and forget them until the next time the carbs are diasassmbled and cleaned.

Good point about the idle adjustment above, particularly that about the final positions of the screws. I forgot to mention in my point #6 that the mixture adjustment may take several passes and the "clearing burst" to get it right.

[P Moore]

Slowly getting there... it gets warm in that engine !! plus no eyebrows !!

One problem I'm having is at times when I give it a quick burst it takes time for it to return to idle......

[Steam Driver]

Hmmm. If butterflies are snapping closed and it's doing that I think that may be a jetting issue, but don't take that to the bank. Maybe someone with more knowledge on that than I will comment. You might try searching this forum "Slow return to idle" or something l ike that and see what you get.

[1QuickS]

Strong recommendation to start at the beginning and methodically setup the carbs and adjust idling with linkage disconnected. Then adjust linkage at 3K RPM. Slow return to idle may be one bank being fundamentally "ahead" of the other for air balance. See the link for the procedure I offered earlier but basically:

1. check fuel delivery pressure to be 3.0 to 3.5 psi
2. disconnect drop links from carbs
3. let idle speed adjustment screws just touch the throttle lever arms and then open them 3/4 turn
4. close idle air bleed screws
5. close and then open idle mixture screws two turns
6. get fuel pump running and check float levels (static for now but you will want to do so later once engine is running)
7. check that accelerator jets are squirting
8. adjust drop links so they easily slip onto the ball studs on the throttle lever arms; you will later disconnect them during idle adjustments but it is handy to have both carbs actuated during the initial starting
9. give two full squirts into each bank of carbs (manually operating throttle levers)
10. try starting
11. once idling can be stabilized you need to use STE air flow meter to balance air flows with idle air screws; be sure to disconnect drop lings during this part of the tuning
12. after air flows are set then perform "Lean Best" idle mixture adjustments with mixture screws; make 1/4 turn adjustments starting with mixture screws nearly closed and opening them until peak engine RPM is realized and then open another 1/8 turn. After each screw adjustment let the engine settle for about 5 seconds before you decide if RPMs increase or decrease; blipping the throttles is something I don't find the need for.
13. if mixture screws are open past 3 1/2 turns or less than one turn then idle jets are probably too small (3.5+ turns) or too big (less than one turn)
14. once you have performed the "Lean Best" procedure you will find the engine RPMs will increase which will affect mixture screw settings which will require repetition of the whole procedure. I find that a STE reading of 4 1/2 indicates you have achieved Lean Best, higher readings indicate a rich idling condition.
15. Strong recommendation to use a STE; I have used Unisyn, mercury sticks and a Gunson carb balancing tool and the STE is the best and easiest.

Remember that your engine displacement and cam selection will drive the configuration of your Webers. Also, if there are wear related issues with the Webers then these will confound you during tuning.

[P Moore]

Many thanks for your help Paul...
Ill get back to the car in a week or so.. I have also sent the dizzy off to Barry Hershon, but in the meantime I was going to get myself the Colortune - do you think this will a great help when sorting out the mixture ?

Ever use 3 or 6 colortunes in one go ! ??

[1QuickS]

I was using 6 Colortunes when I was test running both sets of carbs at one time. I now have a test engine with three cylinders so I need only three. Colortunes are indispensable for my work as they show idle mixture while the engine is running and they allow a quick and accurate idle mixture adjustment. I have learned that any change in idle air flow will affect idle mixtures so the iterative process of adjusting six mixtures and six idle air flows is a bit painful when using the Lean Best mixture adjustment method.

A single Colortune is rather painful as well...got to keep shuffling it from cylinder to cylinder. I did this for years until I started servicing Webers and decided I needed a quicker method to perform my testing.

Colortunes have some additional advantages for observing mixture response with small throttle angle openings past idle position but beyond that you need to perform on the road testing and then to use an AFR meter if available.

Colortunes also provide an excellent troubleshooting aid. Spark and mixture are visible immediately and if the firing is erratic then you have all the info to know what issue to chase.

[rbogh901]

Originally Posted by 1QuickS

I was using 6 Colortunes when I was test running both sets of carbs at one time. I now have a test engine with three cylinders so I need only three. Colortunes are indispensable for my work as they show idle mixture while the engine is running and they allow a quick and accurate idle mixture adjustment. I have learned that any change in idle air flow will affect idle mixtures so the iterative process of adjusting six mixtures and six idle air flows is a bit painful when using the Lean Best mixture adjustment method.

A single Colortune is rather painful as well...got to keep shuffling it from cylinder to cylinder. I did this for years until I started servicing Webers and decided I needed a quicker method to perform my testing.

Colortunes have some additional advantages for observing mixture response with small throttle angle openings past idle position but beyond that you need to perform on the road testing and then to use an AFR meter if available.

Colortunes also provide an excellent troubleshooting aid. Spark and mixture are visible immediately and if the firing is erratic then you have all the info to know what issue to chase.

How reasonable is it to tune with just one? It's my understanding they will not tolerate higher RPMs. Is 1500-2000 RPM tolerable? Maybe we can do a group buy and get a price break.

[kostya.lyt]

Lots of great info.

I found that I had to enrich the mixture quite a bit more than on double-throat Webers (IDF or IDA) on VW motors. First, I was getting a ton of popping out of the carbs.

[1QuickS]

I tuned with one Colortune for years but it is tedious. They will sustain higher RPMs but not under power and probably better to just run the engine up and then drop back to idle; besides, opening the throttles with the car parked does not replicate driving conditions so using Colortunes for elevated RPMs has limited usefulness.
They have limited use in my opinion but are wonderful as a tuning aid...eliminates guesswork in setting/diagnosing idle mixture/issues.