distributor problem again
 

Once again my distributor problem is back. I seem to accelerate ok but
steady speed driving and the engine coughs and sputters. Disconnecting
the vacuum line to the distributor and the engine runs much better
(although not perfect... slight loss is power and acceleration). Does
anyone have a suggestion for a fix before I just buy a new distributor?

distributor problem again
 

Steven Rogers wrote:

> Once again my distributor problem is back. I seem to accelerate ok but
> steady speed driving and the engine coughs and sputters. Disconnecting
> the vacuum line to the distributor and the engine runs much better
> (although not perfect... slight loss is power and acceleration). Does
> anyone have a suggestion for a fix before I just buy a new distributor?

Does the vacuum advance diaphragm hold vacuum? Is its return
spring broken?

Does the advance unit's rod (connected to the distributor base
plate internally) move when you suck on the hose?

Does it hold its vacuum when you manage to block off the tube
with a finger while under vacuum?

Does the base plate return to its rest position when the vacuum
on the diaghragm is released?

The original diaghrapm will be well past its use-by date. The
base plate may be binding for whatever reason.

John

distributor problem again
 

Steven Rogers wrote:

> Once again my distributor problem is back. I seem to accelerate ok but
> steady speed driving and the engine coughs and sputters. Disconnecting
> the vacuum line to the distributor and the engine runs much better
> (although not perfect... slight loss is power and acceleration).

Another possibility:

While the distributor base plate should rotate in response to
changes in vacuum, it shouldn't move up and down.

On some Bosch distributors, the base plate is held down by a leaf
spring (retained by a screw). If this spring breaks the base
plate can move up instead of rotating, allowing the points to
stay closed so there's at best an intermittent spark.

Note that there will be greater vacuum at partial throttle than
while accelerating.

Again, you can check the movement of the base plate by sucking on
the vacuum hose with the engine stopped and the distributor cap
and rotor removed.

John

distributor problem again
 

> Note that there will be greater vacuum at partial throttle than
> while accelerating.
John

Explain?

distributor problem again
 

Bill wrote:

>> Note that there will be greater vacuum at partial throttle than
>> while accelerating.
> John
>
> Explain?

For a given RPM, the inlet manifold vacuum is greatest with the
throttle butterfly closed (foot off the pedal) and least with the
butterfly fully open (foot to the floor). That's because the
butterfly directly closes and opens the air path into the
manifold.

The vacuum tube to the distributor is taken from a point which
reflects manifold vacuum. To get maximum power and economy for a
given amount of fuel, you want maximum ignition timing advance
without the risk of pre-ignition/pinging/pinking. And that means
less advance at full throttle.

The alternative to vacuum advance is centrifugal advance, where
the degree of advance is governed by engine speed alone. In
that case, the advance curve is designed for full-throttle
operation, and economy at partial throttle suffers slightly.

VW industrial (stationary) engines were always fitted with
centrifugal-advance distributors, and these distributors were
much sought after by performance tuners whose modifications
were likely to upset the vacuum advance curve.

John

distributor problem again
 

On Mar 3, 12:09*pm, John Henderson > wrote:
> Bill wrote:
> >> Note that there will be greater vacuum at partial throttle than
> >> while accelerating.
> > *John
>
> > Explain?
>
> For a given RPM, the inlet manifold vacuum is greatest with the
> throttle butterfly closed (foot off the pedal) and least with the
> butterfly fully open (foot to the floor). *That's because the
> butterfly directly closes and opens the air path into the
> manifold
Understood, however since the vacuum advance port is above the
butterfly It's the transition from high vacuum (intake manifold ) to
atmospheric pressure which allows a momentary vacuum signal to the
advance port in the throttle bore. The key to remember is that it's
momentary, not sustained as would be the case using an actual intake
manifold take-off (i.e. like the vacuum brake port on a later bus.) On
a dual vacuum dist. the advance port is above the throttle and the
retard port below the throttle valve.
> The vacuum tube to the distributor is taken from a point which
> reflects manifold vacuum. *To get maximum power and economy for a
> given amount of fuel, you want maximum ignition timing advance
> without the risk of pre-ignition/pinging/pinking. *And that means
> less advance at full throttle.
>
> The alternative to vacuum advance is centrifugal advance, where
> the degree of advance is governed by engine speed alone. In
> that case, the advance curve is designed for full-throttle
> operation, and economy at partial throttle suffers slightly.

>
> VW industrial (stationary) engines were always fitted with
> centrifugal-advance distributors, and these distributors were
> much sought after by performance tuners whose modifications
> were likely to upset the vacuum advance curve.
> John

SA type distributors are best suited to the industrial motors which
tend to spend most of their time at constant RPM or competition
engines which are usually in the high rpm range. This is why the 009
is best suited to competition use and can't provide the initial
advance at low rpm need for smooth acceleration. Also, aggressive
camshafts often don't produce enough vacuum for SVDA type distributors
to properly function at low rpm.>

distributor problem again
 

Bill wrote:

> Understood, however since the vacuum advance port is above the
> butterfly It's the transition from high vacuum (intake manifold ) to
> atmospheric pressure which allows a momentary vacuum signal to the
> advance port in the throttle bore. The key to remember is that it's
> momentary, not sustained as would be the case using an actual intake
> manifold take-off (i.e. like the vacuum brake port on a later bus.) On
> a dual vacuum dist. the advance port is above the throttle and the
> retard port below the throttle valve.

It's been so long, I've forgotten some of the details, like the
exact plumbing details of the vacuum source. Thanks for the
reminder.

I do remember those dual (advance and retard) distributors. And
combinations with both vacuum and centrifugal advance.

> SA type distributors are best suited to the industrial motors which
> tend to spend most of their time at constant RPM or competition
> engines which are usually in the high rpm range. This is why the 009
> is best suited to competition use and can't provide the initial
> advance at low rpm need for smooth acceleration. Also, aggressive
> camshafts often don't produce enough vacuum for SVDA type distributors
> to properly function at low rpm.>

I used a distributor from a 126 industrial engine on my rally
beetle (1600 Mahle cylinders with domed pistons) back in about
1970.

John

distributor problem again
 

John:
Do you recall if the dist. from the Industrial engine was a version of
the 009 or did it give more overall advance?
Bill

distributor problem again
 

Bill wrote:

> Do you recall if the dist. from the Industrial engine was a version of
> the 009 or did it give more overall advance?

No idea sorry. I've not had a 009 myself. And my
brother-in-law thoughtfully threw out my 126-engine distributor
when he did one of his clean-ups and I was away :(

John