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How To Solve
Air Leaks

Tags: Air Leaks
Author: Thomas R.

I've been working on Puch mopeds for a long 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. Let's show you how in this post.

Why this post?

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.

Because in a lot of cases, fixing Air Leaks solves a lot of problems, it should always be one of the first thing to check!

What and is it bad?

Air leaks are spots that are not correctly sealed and are literally sucking extra air. The only source of air should come from the air filter and nowhere else.

On the short term I would say that air leaks are not necessarily bad. On the longer term, it can and will cause severe damage because of overheating. One day your engine will just stop running, and then it might be already to late.

So basically, if your moped sucks to much air, your cylinder will get too warm and you'll damage it.

HOW DO I KNOW THAT MY MOPED HAS AIR LEAKES? 


    When your moped got one of the following symptoms, you should check for vacuum leaks:

  • 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.
  • 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.
  • 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.

WHERE TO CHECK FOR AIR LEAKS? 

    Check the following spots:

  • Check your cylinder: both the cylinder head and cylinder foot
  • The manifold (see movie below)
  • The inlet (where the manifold meets the cylinder)
  • The outlet (where the exhausts meets the cylinder)
  • On the carburator itself

HOW TO NOTICE AN AIR LEAK?  

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.

In the following video you'll notice that we definitely got an air leak between the manifold and the carburator. Time to solve that issue!

spotting the airleak.

HOW TO SOLVE THE AIR LEAK 

  • If it's on the cylinder, inlet, outlet or carburator : change the 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
  • Try 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 looks, you can also use 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're using an imitation carburator, I advice you to consider buying a original one (imitation is almost never good... certainly not the Bing imitations).

common problems and solutions

Here we will discuss some common issues and how to solve them. If you have an issue that needs to be solved, send us an email to thomas@puch-mopeds.com