weber carbs

[Boydskyking]

I have a 1980 911 which I just finished rebuilding the engine. I ended uo making it a Short stroke 3.2 with the 98mm P@c set. Also changed the cams. I have bought two webers with manifolds and gear to put on the engine. Am in the process of rebuilding them and need to know what is a good starting point for all the jets and emusion tubes. I have no idea where to start. If I have a starting point I feel I can work the rest out. I would like for one of you experts to give me on information on the carbs

[zedsn]

Why don't you pick up a book on weber carbs and go from there.

[wayner]

i'm no expert but here is what I have.

I have a 3.0 mild compression but high flowing ported and cammed engine on 46mm webers.

When I got it jetting was 60 idles, 160 mains.
In warm weather it had a bad stumble at 5k rpm
after some jetting runs I ended up with 65 idles, 145 mains.

I don't know what else are in them but thats a start.

You have more displacement so you'd probably be at least at 160 mains??
Paul will probably chime in with some good advice

Post what your results are as you figure this out. I'm going up to 3.2 ss as well and could use the info.

P.S.
Which P&C set did you go with?
What is the compression on the 98mms?

[l_turn9]

What size webers did you go with? 40? 46? 50? Also is it a CIS heads engine? If so, you should consider PMO manifolds as the spacers and gaskets will not seal the opening used for the Fuel Injector Squirter. The gasket will start to leak causing a vacuum leak which can damage the intake valves. the links page on my website has instructions for synch'g Webers & starting places for selecting jets and venturi's. I don't have much info custom engines like your but you might learn something.. youroil.net - check the Links page.

[Jack Stands]

I'd agree that getting a book on Webers and using their formulas will give you a starting point. Also, reading the information on the Performance Oriented website may give you some guidance as well.

Eventually, setting them up on a Dyno is the ultimate answer to really dial them in.

[1QuickS]

Cams? Need to know if Webers are 40mm or 46mm throttle bore size.

Application? Street? Street performance? Driver events?

[gamin]

If you want to know how to set up your webers, contact Paul Abbott at PerformanceOriented.com. He is THE authority on webers. He can take your webers and make them perfect.

[Boydskyking]

after taking your advise I have the following 3.2 ss engine with s cams that have been alter to give more lowend torque' The carb had as follows 35mm ventures,main jet 145,emulsion tube F-3,air correction jet 160, idle jet 55. It runs like it is very lean(poping thru carbs, Hard to start etc.
Any feed back is greatly used with respect

[l_turn9]

The jets are pretty close - popping like you describe is often a vacuum leak. Get a can of Carb cleaner and spray around the engine (when running) and if the rpm spies when spraying the carb cleaner it indicates a vacuum leak. Paul Abbott is a great source for carb set-up.

LarryT

[1QuickS]

55 idle jets too small for a 3.2; try 60 idle jets.

IDTP Webers are troublesome as well, the others are fine.

If "Lean Best" idle mixtures are set & air flows have been checked/balanced and you have idle popping through intakes then try opening mixture screws 1/2 turn to see if that helps low speed driving. If so then idle jets too small. This test assumes that the mixture screws are less than 3 turns open at idle. If they are more open then that then opening them much more will not have any change in mixture since they are pretty much all the way open at that time.

[Boydskyking]

thanks Paul. I ran my engine to warmed it up good and adjusted the mixture screws and still have popping back thru the carbs not all the time but intermiting. I checked for air leaks like Larry T said to do but found no leaks. I will try 60 idle jets

[Jose_JGC]

I had some pops out of the carbs in my 1970 911T and it turned out to be weak ignition spark.
Jose

[Boydskyking]

How did you fix the popping in your 911T

[Boydskyking]

Paul
I changed out the idle jets from 55 to 60 which corrected the popping which was great. I was wonder where do I get this tool which you call the color tuning tool to set the mixture by turning the idle mixture screws and observing the color of the burn.

[1QuickS]

Google "Gunson Colortune"

[Targa Time]

I have a 3.2 SS that I have spent the last couple of years dialing in (yeah, I know thats a long time but thats what happens when you lack talent)

Anyway this is what I ended up with.

46mm PMO
38mm vents
160 mains jets
55 idle jets
130 idle airs
190 air comps
F11 tubes

I also just installed the new profile accelerator pump cams and are very happy with them.
Good luck with your build. Once you get it sorted out I'm sure you will love it.

[Jose_JGC]

On my 1970 911T the pops out of the carbs stopped after I discovered a bad contact in a fuse that provides power to the ignition coil.
In trying to get rid of the pops, I did a tune-up (rebuilt dizy, new plugs and wires), cleaned the fuel tank, replaced the fuel hoses, the filter and rebuilt+tuned the carbs. The pops out of the carbs were reduced but still continued.
One day the engine wouldn't start, it turned and I could hear the humm noise from the fuel pump, I happen to open the trunk tap on the fuse box and the engine started easily after that.
With further investigation, I found that I could easily rotate a fuse that is powering the ignition coil. I then did a main fuse box cleanup/maintenance and the pops out of the carbs ended.

I am not saying this is exactly your situation, but I would not rule out a weak/inconstant ignition spark as the cause of the pops out of the carbs.

Jose

[Jose_JGC]

Are your carbs float level correct? Are both left and right carbs balanced and all 6 throats with the same air flow? Are all 6 idle mixture good?

In the following thread John (rw7810) gives the best Weber/Zenith/PMO carbs setup I have ever came across. 71 T still backfires
Jose