My E9 update Carbs and wheels

[Mattiee7]

Hi,

I have got my later alpina wheels to fit with some 25mm front spacers and extended studs.

I have after much thought decided to replace my zeniths rather than rebuild them with a straight forward weber kit from Korman including electric choke and adapter plate for the original air cleaners.

I am getting it fully set up on the rolling road so will be able to post the comparison bhp.

These are straight zenith replacements as just want it run better.

Regards
Matt

 

[Mattiee7]

New webers installed better driving up on torque and low down power but down on high end power. Redline kit supplied by Korman.

 

[sreams]

The right part of your dyno chart is chopped off, so the scale for mixture isn't being shown... but it does look like the Zeniths were running leaner at high RPM. It is likely your Webers have secondary main jets that are too large.

The going consensus on this site has been to run 140/140 main jets with Weber 32/36 carbs installed on M30s, but believe it or not, I found 140/110 to be suited best to my stock M30B35. A 140 secondary was far, far too rich.

 

[Mattiee7]

The webers are the hatched lines so I think what you'll saying is the other way round?? My main jet is a 140.

 

[sreams]

The webers are the hatched lines so I think what you'll saying is the other way round?? My main jet is a 140.

I can't tell because I can't see the scale for mixture. It is chopped out of the image. I can't tell which line is richer and which is leaner, because I don't know in what direction the scale goes.

Your Webers each have two main jets (total of four). Primary main and Secondary main for each carb.

 

[Mattiee7]

How's this?

 

[sreams]

It looks like your Zeniths were consistently delivering a 12:1 ratio throughout the RPM range at WOT, while the Webers go a bit leaner (about 12.5:1) above 4000rpm. You might actually try smaller secondary air corrector jets on the Webers. This should richen up the mixture at high rpm. Weber recommends changing these by three sizes at a time, so take a look at the number on the air correctors and subtract 15. So, if you currently have 160 air correctors, change them to 145s.

I run a wideband O2 sensor and gauge while driving to tune carbs without a dyno. I've found it useful to do multiple runs at 2/3 throttle (primary butterfly open, secondary closed) to tune the primary jets first before moving on to WOT and the secondaries.

 

[Stevehose]

Why would he want to go richer than 12.5, seems ideal under WOT.

It looks like your Zeniths were consistently delivering a 12:1 ratio throughout the RPM range at WOT, while the Webers go a bit leaner (about 12.5:1) above 4000rpm. You might actually try smaller secondary air corrector jets on the Webers. This should richen up the mixture at high rpm. Weber recommends changing these by three sizes at a time, so take a look at the number on the air correctors and subtract 15. So, if you currently have 160 air correctors, change them to 145s.

I run a wideband O2 sensor and gauge while driving to tune carbs without a dyno. I've found it useful to do multiple runs at 2/3 throttle (primary butterfly open, secondary closed) to tune the primary jets first before moving on to WOT and the secondaries.

 

[Mike Goble]

12.5:1 is pretty good...

 

[sreams]

Sure... But the Zeniths were making more power at 12:1. One possibility is that the sensor was not calibrated correctly. My suggestion was based on the hp results, not directly on the lambda numbers.

Another possibility is that the Webers being smaller is the limiting factor, but I doubt that. I'm making nearly 170rwhp with the same carbs on an M30B35.

 

[couttsdesign]

It looks like you could (and should) lower your car at least 2 inches.....nevertheless a beautiful car. I think Verona coupes look FANTASTIC!

 

[aearch]

la jolla has a sale on all springs 400.00

 

[Gransin]

la jolla has a sale on all springs 400.00

Last I checked they wanted $275 for shipping to EU, so the total of $675 + import tax is quite expensive for 4 springs.