How to solve air leaks for Puch mopeds?

Red Puch Maxi - e50 engine
Picture by Thomas D. of the project ‘ The Red Puch Maxi N by Thomas D. ‘

About this troubleshoot post

I’ve been working on Puch mopeds for some time now and I strongly participate in groups where people ask for help. In the past years, it grabbed my attention that many people working on mopeds (Puch or others) asked us how to solve air leaks for Puch mopeds?

Air Leaks (also called vacuum leaks) should be one of the first things to check when your Puch moped is not running smoothly. People tend to think there is something wrong with the ignition, the timing, the spark plug, the piston, … But in a lot of cases, running issues can easily be resolved by removing air leaks.

In this post we want to show, why, where and how to resolve this issue.

What are air leaks and are they bad? 

One thing I know for sure is that a moped that suffers from air leaks is not good. Air leaks brings the ratio of ‘fuel-air’ in misbalance. So is this bad? On the short term I would say not immediately. On the longer term, it can cause severe damage because of overheating.

Fuel has several key roles. One is of course that fuel makes your moped run but on the other hand fuel also has a cooling function. So if you have to much air sucked in, your cylinder gets too warm.

So what are air leaks? Easily explained: places that are not correctly sealed and are literally sucking extra air. Where the only source of air should come from the air filter, additional air comes from other places.

How do I know that I suffer from air leakes? 

That’s a good question. When your moped got one of the following symptoms, you should check for vacuum leaks:

  1. Your moped won’t run stationary
    Too much air makes it hard for your moped to run stationary. You often have your stationary screw totally turned in.
  2. When your engine is warm, it stops when you arrive at red lights for example.
    When you stop driving, your engine just stops. In most cases you can turn your engine back on, but when you stop again, your engine quits.
  3. A stuttering sound when accelerating.
    This is not the famous bwoaaaap sound (4 stroking).  A bwoaaaap sound means it gets too much fuel. A stuttering sound means it needs more fuel or less air.  I will post a video of how stuttering really sounds shortly.

Where to check for air leaks? 

  1. Check your cylinder: both the cylinder head and cylinder foot
  2. The manifold (see movie hereunder)
  3. The inlet (where the manifold meets the cylinder)
  4. The outlet (where the exhausts meets the cylinder)
  5. On the carburator itself

How to check for air leaks? 

Now you know where to check for air leaks. But how can you know if you are suffering from air leaks?

That’s easy: grab some deodorant or brake cleaner (make sure it’s inflammable) and spray on the spots mentioned above. If you spray on a spot and you notice that your engine quits or reacts differently, that’s where the air leak is located.

On the following video for example, you’ll notice that we definitely got an air leak between the manifold and the carburator. Time to solve that issue!

How to solve air leaks for Puch Mopeds?

  • If it’s on the cylinder, inlet, outlet or carburator itself: add new gaskets.
  • If it’s on the manifold
    • Use an o-ring: put an o-ring in your carb where the manifold meets your carb. Make sure the o-ring has a good size. Push hard when you are installing the carb.
    • The coca cola can trick, you can also try to take a slice of a coca cola can and put it around the manifold. This means the manifold will be thicker and thus can solve the air leak issue. I haven’t done this myself yet, but several people did and apparently this works great (thanks for the advice Sander!).
    • If you don’t care about the look, you can also add some (heat-resistant) paste. For example I have used an exhaust fixing paste that hardens when the carb and manifold gets hotter. Not the best looking but definitely a good result.

In case you are having an imitation carburator and you are having a lot of air leaks from multiple spots, you can consider to buy an original carburator.

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I hope that with this Puch troubleshooter post I have helped you. If you have any question, I would be pleased to answer them. You can also join our Puch community ‘Make Puch Great Again Group’ on Facebook where you can ask for help to 800+ Puch people in our Puch community.

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