Weber 38 jet sizes for 2.0
Andrew Poulton
have not been confident enough to do it. But since the standard 32/36 packed
up I was left with no choice. So I swapped the jets which were ok from the
old one to the 38 and in it went. To my surprise it idles very nicely, makes
a nice noise and goes like stink, especially up hills in high gear. It has
made a real difference. HOWEVER!...
It is an absolute dog to drive at low revs - cough cough jump jump splutter
splutter. I'm guessing the jets are still wrong and the carb is throwing in
more petrol than the engine can deal with at low revs. Does this sound the
right diagnosis? Anyone got any suggestions? How can I fix it? Awaiting fuel
consupmtion figures with dread!
Cheers,
Andy
Pete Lucas
This isn't just a jetting problem, it's because basically
the 38DGAS Weber opens both chokes together (whereas the
old 32/36 opens the smaller choke first, the larger one only
coming into play at large throttle openings).
With both chokes opening together, the air-velocity through
the carb. at low revs is so low that it doesn't actually pull
any fuel through the main jet assembly - so you get this
"stumble" effect just off idle.
No real easy fix - unless you can alter the laws of Physics -
the 32/36 Weber is fine for up to 140 horsepower anyway
so i dont know why you're bothering with a 38 on what sounds
like a stock engine.
//PJML//
Dave Baker
>From: Pete Lucas pj...@ua.nsw.ac.uk
>Date: 22/08/00 09:28 GMT Daylight Time
>Message-id: <39A239C9...@ua.nsw.ac.uk>
Plus the 38 has a much larger power enrichment valve which will flood a 2 litre
unless you solder it up or replace it with the 2 litre parts.
Dave Baker at Puma Race Engines (London - England). Web page at
http://members.aol.com/pumaracing/index.htm contains technical & tuning
articles on various engines.
Alan Eardley
In article <20000822145836...@ng-cu1.aol.com>, pumar...@aol.com
says...
>>Andrew Poulton wrote:
>>> It is an absolute dog to drive at low revs - cough cough jump jump splutter
>>> splutter. I'm guessing the jets are still wrong and the carb is throwing in
>>> more petrol than the engine can deal with at low revs.
Dave Baker replied:
>>This isn't just a jetting problem, it's because basically
>>the 38DGAS Weber opens both chokes together (whereas the
>>old 32/36 opens the smaller choke first, the larger one only
>>coming into play at large throttle openings).
>>With both chokes opening together, the air-velocity through
>>the carb. at low revs is so low that it doesn't actually pull
>>any fuel through the main jet assembly - so you get this
>>"stumble" effect just off idle.
>>No real easy fix - unless you can alter the laws of Physics -
>>the 32/36 Weber is fine for up to 140 horsepower anyway
>>so i dont know why you're bothering with a 38 on what sounds
>>like a stock engine.
Alan Eardley adds:
All true - though a smaller venturi might help to improve air velocity at low
revs. Just to try and get it as good as you can without going to this trouble,
try this. If the stumble is at full throttle, its the accelerator pump that's
too big and all the points above apply. If it stumbles with a gradual increase
in throttle, it may be that the transition from the idle circuit to the power
circuit is poor. In this case, adjust the idle screws carefully (one on the
rectangular base of each barrel) at tickover. Screw them in gently as far as
they will go, open them one and a half turns (I'm guessing here) and then start
the engine. Adjust both in and out in small increments until a fast, smooth
idle is produced. Then set the final idle speed with the throttle stop screw.
However, I agree with Puma - a 38DG is too much carb for a stock 2 litre.
Alan