Weber 38/38s

[Jellobmw]

So last year I replaced the 32/36 dual webers with a pair of 38/38s.

Dramatic improvement in power, but with that came poor fuel consumption and one big flat spot from 2k to 4k.

My local mechanic (Ralph's Foreign Auto here in the Burlington area) did some tweaking based on guidance from Jim Rowe at Metric Mechanic, and there is some improvement, but still not acceptable.

His recommendation was to ship the carbs off to Metric Mechanic who can rework them to run properly.

Any thoughts or recommendations?

It is properly timed, has a Crane electronic ignition and a fuel regulator (2.5psi).

And if anyone is interested, those 32/36's are available.

 

[decoupe]

38/38

Before you do that, read and follow the instructions on this Weber tuning guide. I have the same set up and no flat spot. Mileage is about 20-22mpg at highway cruise but not great in the city.

The flat spot is most likely due to the idle jet being at least one size too small and the idle circuit is what you drive on up to 2500rpm unless you are really stepping on the throttle. Be patient and work through the idle and then the mains though they probably aren't too far wrong.

http://www.redlineweber.com/html/Tech/38_dgas_tunning.htm

 

[Percy]

Weber 38/38 jetting

There have been a few posts on this subject. See for example: http://www.e9coupe.com/forum/viewtopic.php?t=1221 and
http://www.e9coupe.com/forum/viewtopic.php?t=450 There are others.

It might be helpful if you posted your current jetting information, engine displacement and modifications (if any e.g. different camshaft), altitude and typical driving pattern. Other E9'ers and E3'ers have no doubt discovered a jetting middle ground from which you can resolve your problem. Pierce manifolds might offer some baseline info on its website too.

Good luck. Remember, if you discover that jetting "sweet spot", sharing it might prove helpful to someone else in the future. :wink:

 

[TodB]

38s

Hi Jeff,

I have the 38s also. I went from triple 40s to the dual 38s. My low compression 3.3L couldn't keep up with the 40s. Although I miss the intake noise from the 40s, the increase in power going to the 38s was dramatic and worth it.

I don't think you have to send the carbs to Jim but rather fiddle a bit with the jetting and set up. Mario finally got mine right last year and I think he swapped out the idle jet (I am not at home now so I cannot check). I did not have flat spots but I did have issues going off/on gas (a bit of a bucking bronco at times) which is all gone.

You should also check that your linkage is correct and not binding at all.