Zenith Carbs

pcar9119 · 04-10-2009, 12:25 PM

I'm building a set of zenith carbs for my 3.0 and I'm not to hot on buying anything more from Motormeister. Does anyone know of anybody else who sells jet kits for Zenith 40's other than Motormeister. Everyone I talk too say once you build the Zeniths, they are actually better carbs than the Webers. That is waiting to been seen, but I want to stay with the Zeniths for right now. Thanks...

TVRLOTUSTR3 · 04-11-2009, 04:52 AM

I Don't have kits, but I have a few Zenith jets. I do not know what you will need for your 3.0
What size chokes do you have? What cams are you using? Any head work done (porting)?

You can use Weber chokes with a spacer, buy a few Zenith jets, a jet reamer and a inovative CO meter.

I would ream out a set of Zenith jets to the recommended Weber sizes for your engine as a starting point. Hook up a CO meter and go from there

I have done this on a 2.4, ported with E cams. I also think Zenith is a good carb, but tuning parts are rare.

pcar9119 · 04-11-2009, 07:35 AM

Thanks, You stated exactly were I'm starting. I bought a jet reamer kit last night, and going from there. I have stock cams, and big port heads. I was told 160 mains, and 50 air. Does that sound right to you?

TVRLOTUSTR3 · 01:24 PM

What size chokes (venturi) are you using? I think you would need 36mm. I would start with 150 or 155 mains and 55- 60 Idle. I hope you have a CO meter!

911Etarga · 04-12-2009, 11:55 AM

Doesn't altitude make a difference in Jet size too?? Mt Zeniths had 60 idle's when they were rebuilt at sea level (MM.........), but I live at 3000 ft above sea level so it ran really rich. I put 50's in, and it is better. Not perfect, but better.

??

timc · 04-12-2009, 06:38 PM

Wonderful carbs, make sure, but I think the 40's may be to small for the 3.0. I used them on 2.2's and a 2.4, and felt I was pushing it on the 2.4. I actually found one of the "sports" kit that was made for the Z40's to make them work on the 2.4, which had jets and larger venturis, been 20ys since I messed with them, but I think I went from 32ish to 36ish venturis to make them work on the 2.4. Incredible throttle response.

4G1 · 04-12-2009, 09:28 PM

I'm doing the same thing with my 2.7. I had a set of 32mm venturi made for $120, pelican sells weber vents that will work with a 1.5mm spacer and MM sells the same vents for almost twice the price. Do a search, I think it was "quite boom" that wrote a great thread on the Zeniths. I think its beiker engineering that can answer all of your zenith questions and provide you with the proper jets.

pcar9119 · 04-13-2009, 08:42 AM

Thanks guys. 40's are actually perfect for a 3.0 application. I'm using 34 mm venturis, and this should be perfect. I appreciate the info on these companies. I bought a reamer kit this weekend, but still looking for jet guys. I'll let evryone know when they are complete, and how the buld was. I actuallt machined my own venturis, so if anyone is interested, i can do them fairly cheap...

timc · 04-13-2009, 09:44 AM

Quote:

Originally Posted by pcar9119

Thanks guys. 40's are actually perfect for a 3.0 application.

That's great, as they are really nice carbs when setup and working correctly. Good luck. I may have some old jets laying around, If I can find them I'll send them to you for spares.

send me an email to timc1018@hotmail.

Tim

TVRLOTUSTR3 · 04-13-2009, 10:31 AM

Most guys run 34-36 in a 2.7. I would think you would want to be on the 36 side.

I have been told, but don't know for a fact that the VW Solex carbs use the same jets.

4G1 · 04-13-2009, 11:20 AM

TVRLOTUS, I think it might be the 356 Solex carbs, I spoke to a friend that works for VW, stumped him with the solex question. I think the jets from the 356 carbs are the same dimension as the later solex models.

pcar9119 · 04-13-2009, 01:33 PM

Weber suggests that the throttle bore should be 25% larger than your venturi size. Buy using the equation, Using the formula Porsche 911 Performance Handbook., The venturi size should be 34mm. This means the throttle bores should be between 37.4 and 42.5. Which means for the 3.0 SC the 40 tin or ida is the best compromise. With a 46 you going to have a alot of reduction in the mertering signal wich will give you large flats spots in the bottm end .

TVRLOTUSTR3 · 04-14-2009, 03:00 AM

I will bet you that you will have great throttle response at low RPM. But will run out of steam about 6,000 RPM with 34mm chokes in a 3.0 liter.

pcar9119 · 04-15-2009, 12:50 PM

Time will tell. I think I would rather Have the low end throttle response anyway. I don't plan on driving in wide open throttle very often. Even on some track days you really don't drive at wide open throttle but a little bit. I can't wait to gewt the conversion done so. I am so curious to see the difference from that cruddy old CIS to this tuned carb...

nabilious · 04-25-2009, 07:59 PM

subscribed.

4G1 · 05-13-2009, 09:29 AM

Sudscribed
Any updates?

ddubois · 05-26-2009, 02:49 PM

Did you ever find an alternate to MM for Zenith jets? I'm in the process of rebuilding my Zeniths for a stock 71 911T and I'm trying to figure out what to do with the jets since I live at 6,000 ft. The carbs are off a car the spent it's entire life at sea level.
Anybody have any advice for re-jetting for altitude?

Thanks,

john walker's workshop · 05-26-2009, 04:35 PM

vw solex jets are the same. except the all important emulsion tube, which doesn't have any upgrades that i ever found. works ok in a 2.2, but like on webers, it would need to be changed to one that gave decent transition. so good luck. you don't just drill the holes bigger on them. a gas soaked sponge in a box would probably run the engine somewhat also. why bother with anything that doesn't give you the full range of performance?

pcar9119 · 05-28-2009, 12:24 PM

The carbs are done and are awesome. I just machined my own vents and remmed my own jets. It wasn't hard at all. If anyone is interested in Zenith vents, I saved my program in my cnc at work, I might starting making some if people are interested. Carbs work awesome. I am way happier with the carbs than the CIS. Thanks for the posts guys..

pcar9119 · 05-28-2009, 12:29 PM

The 3.0 doesn't make any power really over 5900rpm anyway, the only benifit for reving the engine that hard is to make sure your in the power when reach shift into the next gear, but that same power is on right at midrange in any gear, so reving the engine that far is just saying you can anyway. My engine stops pulling hard at about 6200rpm, when i shift it's right where it needs to be for the next ratio. If this was a rotary engine I would be concerned with revving the engine all the was to red line all the time, but theses engines don't require you to do that.