Pierburg 2E3 on a VW Vanagon
Please refer to this link for a schematic diagram of the pierburg 2E3 carb. I was too busy learning it to take any pictures. :-)
Excuses out of the way, this is perhaps the most annoying part of any fix for the DIY mechanic. The Pierburg 2E3 carburetor is a marvel of confusion and complexity that has led most people to switching to more ‘reliable’ carbs such as Webbers. Well the Pierburg 2E3 is not the worst of instruments, with a little patience and lots of knowledge you could get it working like a charm.
Common problems caused by the carb are poor idling (too high or completely non-existent), very poor running during a cold start, fouling of spark plugs due to too rich a mixture or other problems due to too lean a mixture and of course the worst of them all poor fuel efficiency. I shall attempt to guide you on what to do to try and iron out some of these issues assuming everything else that the carb is dependent on such as distributor and engine timing are working well.
Solutions to common problems
Vacuum leaks are common and these occur at gasket points and vacuum lines. Determine a vacuum leak by spraying some carb cleaner on the base of the carburetor where it meets the intake manifold and if there is a change in engine sound then there is a vacuum leak there. Also spray between the upper and lower part of the carburetor and listen for change in engine sound. Examine the vacuum lines especially the one to the distributor and ensure the line is not split or punctured. This simple test will solve common idling problems however idling problems could also take on larger proportions. Caution: Ensure you have a fire extinguisher at hand when you spray carb cleaner on a hot engine. There could be a fire incident
Most common problems will also be solved with a good cleaning of the carb using carburetor cleaner. Spray the carburetor jets and linkages occasionally and they will run problem free. Frequent fuel filter replacements will also do your carb a world of good.
Cold starting/Choke problems
This is the Pierburg 2E3’s Achilles heel. It has a choke mechanism that has always been misunderstood but this is the theory;
A choke is meant to actually ‘choke’ or starve the carburetor of air when the engine is cold so that the richer mixture is ignited easier. As the engine warms up a bi-metallic strip uncoils as it senses the increasing engine temperature. This sensing of engine temperature happens with the help of coolant that is ran through part of the carburetor’s choke mechanism. The choke works hand in hand with a mechanism called fast idle cam that if well set, keeps idle speed high and reduces it with increasing engine temperature. There is an additional component that helps heat up the bi-metallic strip using electrical energy from the battery. This usually helps open up the choke faster than the water would. From my experience, it is not very important here in the tropics since we hardly have very low temperatures and furthermore, it keeps failing. I’ve totally disabled it in my van and I am running just fine.
The aim is to set the choke (butterfly) gap such that when the engine is at its coldest it leaves a gap along the barrel that is only small enough to accommodate a 3mm drill-bit and the fast idle cam can cause idle speed to rise to 2000 +/- 200 rpm.
- Remove the choke body to reveal the bi-metallic strip
- Open the throttle and position the fast idle cam screw on the highest step of the cam by turning it
- Push the pullrod on the choke pull-down diaphragm the furthest it could go and check the gap left when the bi-metallic strip is turned to the ‘start’ position. Turn the screw that manages the pullrod in or out accordingly until pushing the pullrod furthest in will lead to a 3mm gap between the choke butterfly plate and the barrel, when the bi-metallic strip is turned to its ‘start’ position.
- Refit the choke body ensuring that it remains on the ‘start’ position when coldest.
- The position of the choke body can always be adjusted depending on seasons so that there is always optimum cold start engine speeds
- Position the fast idle cam screw by turning it in or out to the second step of the fast idle cam and check that the fast idle speed is between the specified 2000 +/- 200 rpm for fast idle. Adjust as neccessary
- Ensure the engine is running at optimum operating temperature
- Various engines have various idle speeds but they usually range between 750 and 950 rpm
- Set your engine to run at the recommended rpm by turning the idle speed control screw
- Turn the mixture screw in until the engine begins to stumble and then turn it out again until the engine begins to stumble as well. Somewhere in there will be the optimum mixture setting. This will be verifiable over time with the process mentioned above
- Sometimes turning the mixture screw has no effect on the running of the engine or idle speed cannot go lower than a certain point. If that is the case, check the carburettor barrels to ensure they are clear of any foreign matter and if not then the engine timing is off. I have assumed you have determined that there is no vacuum leak at this point