Q: Why does my bug bog when I step on the gas? When I try
to take off from a light, it just sits there and coughs. If I take
off easy, it’s OK. If I slip the clutch a lot and rev the motor up,
I can work through it. My clutch is smelling like burnt toast
and my passengers think I am a spaz. I had it tuned, every-
thing was replaced. Help!
A: Bogging is not only irritating, it can make crossing the street
downright dangerous. That slipping clutch trick can also turn into
a “lottery jackpot” for your technician. He might think of it as job
security. You start off with one problem, ignore it, and then it
takes a bigger bite out of your wallet. Bummer! If the person who
tuned it does not have a working knowledge of air cooled VW’s,
find someone who does. I’ll try to explain it in the simplest terms
with a few helpful hints thrown in here and there.
Strong acceleration requires a number of related systems to work
together. Think of engine power as a three legged stool. If you
lose any one of the legs, the stool falls down. The legs of our stool
are fuel, air, and spark. With so many possibilities this can get
complicated, but hang in there.
The first “leg” we need is air. Engine vacuum must be strong to
suck a proper air/fuel mixture into the cylinders for combustion.
This involves the basic compression of the engine, correct valve
adjustment and tight cylinder heads. On ’71 and newer cars,
vacuum leaks at the intake boots upset the fuel mixture by adding
air to the intake without the benefit of first mixing that air with
fuel. On many carburetors that I see on vintage VW’s, the base
is warped from being tightened down too much, causing a similar
problem with unmixed air.
The second “leg” is spark. The ignition system needs to produce
a hot spark and the spark has to occur at the right time (ignition
timing) to fire the fuel/air mix. One tip: Use original equipment Bosch
components on your VW and you can’t go wrong. I don’t claim that
Bosch is the best and that everything else is trash, it’s just that
over the years, so many cars have come to me with aftermarket
and cheap Taiwanese parts, I just don’t trust em’. As Gene Berg
so aptly pronounces: “Buy the best and cry once”.
Even Bosch parts wear out over the years. Some of the most
common ignition/timing problems we find are: sticky vacuum
advance/retard units, leaking vacuum advance units and sticky
or stuck “breaker plates” (the points are mounted on the breaker
plate). These conditions all relate to the timing of the engine
when it is accelerating or conversely, BOGGING. You can set
the timing perfectly at idle but if it does not advance or retard
correctly, the car will stumble.
Why not replace your old worn or damaged distributor with a 009
distributor? Seems like a great idea! There are a number of reasons
why it may not be for you. If you are interested in originality and
bog free performance, the 009 is no cure all. If you have a 68 or
newer car with the original carb, other modifications to the fuel
system will be needed to make it work right. If your mechanic knows
how to make it work though, it is a darn good idea. Since a vacuum
advance/retard unit for the later bugs can cost as much as the
entire distributor it might be the best idea. Be aware it is not a
simple bolt on.
Fuel is the third “leg”. Your fuel may be old or contaminated. How
is the quality of your fuel? If it smells funky it probably is. Add some
fresh fuel and a can of drygas. It might really help. You also need
to take into account the octane and lead content of the fuel that
was available when your car was built. To compensate, additives
or modifications to the ignition timing might be needed.
I suggest that you replace your fuel filter every spring…whether
you think it needs it, or not! If you do not have a filter, put one on.
Think of it as “spring cleaning” for the fuel system. See if the normal
yellow color of the filter media turns rusty red after driving. If so,
the fuel tank itself may be corroding internally. Tip: The cheap
aftermarket “recycled parts place” tanks are so cheap that they
begin to corrode in a year. If you have a good original tank and it
needs repair consider a process called “Gas Tank Renu”. It costs
more, but NEVER needs to be done again, and carries a lifetime
VW carbs are no mystery to experienced VW technicians. In fact,
all you have to do is look under the hood of an old Honda Civic to
appreciate why we VW techs love VW carbs. As simple as they are,
though, they can get out of whack. Over the years they get crusty
and worn. The carburetor plays a pivotal role in acceleration.
On older cars, the quantity of fuel usually wasn’t the problem,
since they were set up “rich” (meaning too much fuel) right out
of the box. On the later VWs, which were set up with emission
controls for good fuel economy and clean air, things were a lot
tighter. On 68 and newer vehicles, bogging is especially a problem.
“How much fuel is enough?” This is a tough question to answer,
since we non-engineer types really have no way of knowing. To
understand how the carb works, open the repair manual and read
all about it. Some good questions include: Does the car have the
right carb on it? Does it have the right jets? I have found thousands
of different combinations over the years and, typically, there is only
one way that it came from the factory. As far as referencing what
carb and jets are the right ones, the original reference books, called
“Without guesswork”, were published by VW. If you find one, buy it,
if you have one, treasure it. Unfortunately the manuals I have seen
such as Bentley or Haynes are written for technicians, not do it
yourselfers. A good reference for all VW lovers is “VW Beetle, Car
of the Century” by J.T. Garwood. When it comes to working on the
carb itself, give it a try. Bosch makes a rebuild kit that is very good;
part number CTK 83. You probably can’t hurt it and a thorough
cleaning can only help. Failing that, I suggest that you leave
the trouble shooting to a professional.
I get a lot of questions about squirt nozzles. The squirt ozzle lives
downinside the carb throat. If you remove the air filter and look
down into thecarb you can see it. With your safety glasses ON
and the engine OFF, check to see if it is aiming down the throat
and giving a forceful squirt as you push on the throttle lever. If it
is not, or there is a delay before it begins to squirt, that could be
your problem. Linkage parts that workedwell when they were new
may need to be modified or repaired to work well on a vintage car.
I have even found squirt nozzles totally gone, yet the car still ran.
When the nozzle is missing, the fuel tries to squirt UP instead of
down. Guess where the nozzle went?
For the owners of vintage fuel injected cars, (that sounds like a
contradiction in terms doesn’t it?) bogging takes on a whole new
meaning when it blows up your air flow meter’s air flap. With fuel
injected cars, the basic adjustments are critical. The mixture on
later cars is already lean and the slightest air leak in the intake
system will lean the mixture out further and drive you nuts when
trying to eliminate a bog. There is one trick that seems to work
well on all these models: (no, I don’t mean rip the fuel injection
off!!!) After eliminating all the basics, try advancing the timing by
5 degrees. It makes a world of difference. You cannot adjust the
fuel mixture correctly without an exhaust gas analyzer, but you
can screw it up. The “CO” can be safely set one percent richer
than specifications for good results, but if it is found to be grossly
out of spec, suspect vacuum leaks, air box damage, or tampering.
If your F.I. beetle bogs and backfires, stop driving it or you will
dramatically increase the repair costs.
In closing, be careful when working around the carburetor. Especially
that bit about looking down into the throat of it. Gasoline is not
only hazardous to your health, it burns pretty well too. Since I
can’t watch you working on your own car…let me emphasize that
you observe safety precautions. If you feel that it is getting too
complicated, give me a call. Until next ime, Happy Motoring.