progressive weber, running like crap
Scott
It's having significant acceleration issue. Any time I accelerate the
engine nearly stalls. I've tried rapid accelerations from 1000 RPM to
4000 RPM in 500 RPM increments and experienced the problem, although
it's most pronounced the lower the RPM is. The engine has a Bosch 009
distributor. Timing is set for 30 degrees at full advance on the 009.
I've rebuilt the carburetor and given it a thorough cleaning, and I've
substituted it with another progressive weber that had very little use
on it. Same problem, both carbs.
The motor sat for about two years with minimal use. I could have swore
two years ago I did not have these severe drivability problems. Prior
to that I ran the same carb for about 4 years with no issues that I
can recall. I just don't remember it performing like this.
Also, both carbs seem to run well if the choke is stuck mostly closed.
Problems only occur with the choke open. I've fiddled with the mixture
screw to no effect. I've verified the jetting on both carbs is
correct. I've verified the accelerator pumps are throwing a good shot
of gas into it. I've checked for vacuum leaks.
I'm a bit stumped as to where to proceed from here. Any tips would be
helpful!
Robert
Since both carbs give the same results, I doubt it is the carbs. If
the engine sat for two years, maybe it is fuel pump related.
Jan Andersson
Check to make sure the distributor advance mechanism moves ok.
Those carbs are next to impossible to tune for the VW engine, with the
manifolds that are readily available. They need a totally different
intake design. One you would have to fabricate yourself. And you'd still
have too long intakes for that carb design.
They need to be jetted too rich for them to work acceptably throughout
the rpm range. And the distributor curve needs to be tweaked, as it does
with every 009 out of the box. ;)
Scott
Can you explain a bit how to check it? Last time I checked timing, I
verified that it was advancing, but I didn't pay particular attention
to the advance curve. Looking inside of it, it looks like I'd have to
do a bit of disassembly to get into the mechanism.
The thing that gets me is that I believe this carb, distributor, and
engine were all working together acceptably well at one point. There
was always a bit of a flat spot, but nothing like what I'm
experiencing now.
Thanks for the advice,
Scott
Randy
How old is the gas in it ?
All cylinders firing ?
What's the timing set at ?
Jan Andersson
If the timing advances when you rev it up, the basics are ok... still,
with the engine off, pop the distributor cap off and turn the rotor by
hand. It should turn (a little, like less than 1/8 of a turn) one way
against spring tension, and snap back when released.
You can oil the shaft from the top and spray lube the weights too
through the points mounting plate. Don't get ANYTHING on the points
themselves.
Scott
> All cylinders firing ?
> What's the timing set at ?
I drained all the gas and replaced with new before starting. As far as
I can tell all 4 cylinders are firing (manifolds/exhausts equally
warm, plugs show similar color). Timing should be in the neighborhood
of 30 degrees maximum advance (it's been about 2 weeks since I last
checked it). Certainly not more than 30 degrees, if anything a little
less. I'll have to double-check to be sure.
> If the timing advances when you rev it up, the basics are ok... still,
> with the engine off, pop the distributor cap off and turn the rotor by
> hand. It should turn (a little, like less than 1/8 of a turn) one way
> against spring tension, and snap back when released.
Thanks for the tip, I'll check this.
One bit of information -- I'm *not* using manifold heat with this
setup. The very first engine I used a progressive with may have had
it, but this particular buggy never has (it has an off-road tri-mill
type exhaust). After reading some of the information at aircooled.net,
I'm finding the manifold heat sounds like it may have been more
important than I'd ever given it credit. I'm still certain that I had
the engine running acceptably (albeit with a bit of an annoying flat
spot) without heat and with the current jetting, so there's got to be
something additional going on. As it stands now, it's flat out
undriveable.
Scott
hal...@gmail.com
> It's having significant acceleration issue. Any time I accelerate the
> engine nearly stalls. I've tried rapid accelerations from 1000 RPM to
What kind of intake manifold are you using? Does it have heat riser
pipes? If so, are they clear, and is the header drilled to send
exhaust through them?
Without adequate manifold heat your Weber will ice up. BT, DT, got the
t-shirt. Intake icing causes all kinds of odd driveability problems,
especially if the humidity is high.
I never had much luck with my progressive weber. In my case the
biggest problem was my intake manifold was a total piece of shit. And
I had a -009 distributor, which was strike #2. That was enough to make
my bug a semi-drivable pile of manure.
Things got a whole hell of a lot better when I junked the Weber and
went back to a stock intake, stock 34pict-3 carb, stock exhaust
system, and a vacuum advance distributor. In my case, it was the
difference between night and day once the work was done.
Good luck with it,
Chris
AircooledJohn
http://www.thesamba.com/vw/forum/viewtopic.php?t=393346&highlight=progressive
http://www.thesamba.com/vw/forum/viewtopic.php?t=293837
this is a lot of GREAT info for you to read to get you up to speed.
John
Aircooled.Net Inc.
362 West 6100 South, Unit A
Murray, UT 84107