Weber 38/38 DGAV

[tcrock]

Is there a jet/tubes set up that works best on a stock

8.3:1 M10

The motor is fresh and runs great with a 32/36.

But with the 38 it runs crazy in the upper rpm's

and has a flat spot around 3200-3500.It idles fine at

900 gets out of the hole fine and after 3200 goes like hell.

Right now there are 145 and 185 jets in it I'm not sure about

the emulsion tubes.The idle screws are out @1 turn.

Thanks for any help

[Guest Anonymous]

Have you tried searching the archives? This subject has been addressed several times including the past 4-5 days.

[dubois]

I may be wrong but I think that is the nature of the beast. It is exactly the same as my old 72 with 38/38. I think if you change jets, you will just shift the flat spot, or run too rich somewhere. Maybe a carb expert can chime in.

[esty]

i bought a new 38/38 from a board member a year or so ago...no idea how it's set up, didn't do anything but bolt it on and have never had any issues in any range

i've had on 3 of my o2's and they all run super with it

do i have a fluke?

[devo1]

My guess is you are lean at some point in the operation of the carb.

In my limited self taught experience based on twin 38/38 on a CS is that the idle circuit effects 0-2500rpm, mains 2500 - 4500rpm and air jets to redline. The range of effects overlaps the jets but in general its a starting point on where to makes changes. Change on thing at a time. A fuel air ratio meter is also very helpful.

Generally the 38/38 stumble occurs at the transition from idle circuit to mains at around 2500rpm. That symptom can mean that your idles are to small and you have a lean condition that cause you to rely on the mixture screw to minimize. Mixture screw less 1 turn, idle screw less then 3/4 and engine idle speed should be fine at 750rpm.

Your problem sounds different given the flat spot is around 3200rpm but you have great performance above 5000 which is typically where the 38 drops off. Guessing this is where you are lean. Try increasing the main jet by one half size. If it improves but still exists go up another half size. etc etc

If this is working and you are pretty happy with the results then increase the air jet one size and see if there is an improvement. If it gets better then increase another size. Etc etc etc

[TobyB]

searchy searchy searchy...

your 'transition' jets are lean. We're not 100% sure, but bigger than 50

seems to be a general consensus...

and you have to searchy to find out what I mean by transition jets...

t

[Green2k2]

searchy searchy searchy...

...

Wha?

http://journals.sfu.ca/dcpapers/2005/paper30.pdf