uneven idle leading to cut off
 

Hi Y'all,
I have a idle problem. When I start my 69 beetle, it idles fine.
Accelerates with a little bogging but otherwise runs fine. When its at
operational temps the idle rpms rise and lower slowly and then eventually the
engine cuts off, especially at lights. Any ideas?
The engine is a standard 1600 DP with a 34 Pict carb, mechanical fuel pump
and a SVDA dizzy. Thanks!
David

On 16 Dec 2004 23:08:55 GMT, C7eca > wrote:

> Hi Y'all,
> I have a idle problem. When I start my 69 beetle, it idles fine.
> Accelerates with a little bogging but otherwise runs fine. When its at
> operational temps the idle rpms rise and lower slowly and then
> eventually the
> engine cuts off, especially at lights. Any ideas?
> The engine is a standard 1600 DP with a 34 Pict carb, mechanical
> fuel pump
> and a SVDA dizzy. Thanks!
> David

Those symptoms sound like carburator icing. What was the air temp at the
time?

Do you have working manifold heat and warm-air intake?

Max
--
http:/www.MaxWelton.net/

"When its at
operational temps the idle rpms rise and lower slowly and then
eventually the
engine cuts off, especially at lights. Any ideas?"

Check that the pre-heat tube isn't clogged, as this can cause carb
icing. You can test it by BRIEFLY touching the preheat tube once the
engine is warmed up. It should be hot enough to burn you on both sides,
if not you need to focus on repairing that problem first. Fixing it is
rather straightforward, remove the intake manifold and then use an old
clutch cable to clear it out. Chuck the threaded end of the cable into
a drill and cut the cable so it is slightly longer than half the length
of the intake. Use it as a roto-rooter type tool with the drill to
clear out the carbon. Work it from both sides and use compressed air as
needed to remove the chunks as you progress. If this is the problem
you'll be amazed at how much better your bug runs when you are done
with this job.

The other possibility is that the carburetor itself is in need of an
overhaul, or you may have an air leak around the throttle shaft. The
latter is fairly easy to test, get the car warmed up and while idling
spray some carb cleaner around the ends of the throttle shaft. If the
idle goes up you have an air leak. Fixing it requires the bushings in
the carb body to be replaced.

http://www.rimcovw.com/misc.htm

Looks like 40 bucks will get you a properly repaired carb casting that
you can overhaul and put back in service. Alternatively you could
purchase a new carburetor. If you don't find evidence of an air leak
around the throttle shaft you could just overhaul your existing carb.
The overhaul kit usually runs about 10 bucks.

Chris

"When its at
operational temps the idle rpms rise and lower slowly and then
eventually the
engine cuts off, especially at lights. Any ideas?"

Check that the pre-heat tube isn't clogged, as this can cause carb
icing. You can test it by BRIEFLY touching the preheat tube once the
engine is warmed up. It should be hot enough to burn you on both sides,
if not you need to focus on repairing that problem first. Fixing it is
rather straightforward, remove the intake manifold and then use an old
clutch cable to clear it out. Chuck the threaded end of the cable into
a drill and cut the cable so it is slightly longer than half the length
of the intake. Use it as a roto-rooter type tool with the drill to
clear out the carbon. Work it from both sides and use compressed air as
needed to remove the chunks as you progress. If this is the problem
you'll be amazed at how much better your bug runs when you are done
with this job.

The other possibility is that the carburetor itself is in need of an
overhaul, or you may have an air leak around the throttle shaft. The
latter is fairly easy to test, get the car warmed up and while idling
spray some carb cleaner around the ends of the throttle shaft. If the
idle goes up you have an air leak. Fixing it requires the bushings in
the carb body to be replaced.

http://www.rimcovw.com/misc.htm

Looks like 40 bucks will get you a properly repaired carb casting that
you can overhaul and put back in service. Alternatively you could
purchase a new carburetor. If you don't find evidence of an air leak
around the throttle shaft you could just overhaul your existing carb.
The overhaul kit usually runs about 10 bucks.

Chris

"When its at
operational temps the idle rpms rise and lower slowly and then
eventually the
engine cuts off, especially at lights. Any ideas?"

Check that the pre-heat tube isn't clogged, as this can cause carb
icing. You can test it by BRIEFLY touching the preheat tube once the
engine is warmed up. It should be hot enough to burn you on both sides,
if not you need to focus on repairing that problem first. Fixing it is
rather straightforward, remove the intake manifold and then use an old
clutch cable to clear it out. Chuck the threaded end of the cable into
a drill and cut the cable so it is slightly longer than half the length
of the intake. Use it as a roto-rooter type tool with the drill to
clear out the carbon. Work it from both sides and use compressed air as
needed to remove the chunks as you progress. If this is the problem
you'll be amazed at how much better your bug runs when you are done
with this job.

The other possibility is that the carburetor itself is in need of an
overhaul, or you may have an air leak around the throttle shaft. The
latter is fairly easy to test, get the car warmed up and while idling
spray some carb cleaner around the ends of the throttle shaft. If the
idle goes up you have an air leak. Fixing it requires the bushings in
the carb body to be replaced.

http://www.rimcovw.com/misc.htm

Looks like 40 bucks will get you a properly repaired carb casting that
you can overhaul and put back in service. Alternatively you could
purchase a new carburetor. If you don't find evidence of an air leak
around the throttle shaft you could just overhaul your existing carb.
The overhaul kit usually runs about 10 bucks.

Chris

C7eca wrote:
> Hi Y'all,
> I have a idle problem. When I start my 69 beetle, it idles fine.
> Accelerates with a little bogging but otherwise runs fine. When its
> at operational temps the idle rpms rise and lower slowly and then
> eventually the engine cuts off, especially at lights. Any ideas?
> The engine is a standard 1600 DP with a 34 Pict carb, mechanical
> fuel pump and a SVDA dizzy. Thanks!
> David

Are you familiar with the tuning procedures? Can we assume that
the ignition system is in good tune and timed properly? Is the carb
throttle plate stop, idle bypass screw, and idle mixture screw set up
properly?

If so, it's probably carb icing as already pointed out. Just below the
base of the carb, is it frosty? One easy way to verify that icing is
causing the problem is to idle it in your driveway with it acting up.
Direct a heat gun (or hair dryer) into the air intake and see if it
goes away. Then you'll know where to direct your efforts.


RT
--
E-mail=fullname-at-telus.net

C7eca wrote:
>
> Hi Y'all,
> I have a idle problem. When I start my 69 beetle, it idles fine.
> Accelerates with a little bogging but otherwise runs fine. When its at
> operational temps the idle rpms rise and lower slowly and then eventually the
> engine cuts off, especially at lights. Any ideas?
> The engine is a standard 1600 DP with a 34 Pict carb, mechanical fuel pump
> and a SVDA dizzy. Thanks!
> David


Air leak?

Jan

Thanks everyone! The weekend is coming up and I can do more diagnostic based
on your suggestions.

I had not checked the heat risers or the base of the carb for hot/cold.

The engine is tuned to spec. The temperature was 27 degrees with the humidity
around 15% when I first noticed this although its doing the same thing at
higher temps and humidity. The engine at each instance was cutting out at the
first light after coming off I-64 at 65mph. indicated.

David