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If your GL1000 carb top looks like this, I guess you will notice that it's broken !!

But now I want you to look at the second picture.

This top has been cracked for quite a while, the cause has probably been backfires over time. The plastic button acts as a stop for the piston (stupid idea in the first place!). A backfire will cause the piston to shoot up hard, impacting the plastic button.

Even more stupid is the bevel on the top of the piston rod, reducing the area of impact to a thin ring. A flat top would have spread the force over a wider area and perhaps prevented the damage.

Click the second picture to get a bigger image and you will see that I have highlighted three areas which look clean. Between  clean areas, the plastic is discoloured. This where it had been cracked for sometime; only those three small clean areas were actually holding it together.

It wasn't until I broke the main part out that this became so visible. Initially, when I was polishing the cap, I got the dirty polish on the button and tried to clean it off.

There were two very thin black lines around sections of the raised part of the button that would not clean and on futher inspection, seemed to be inside the plastic.

Although I had looked at the buttons, I guess I didn't look hard enough. Those lines could only mean that the cap was compromised by cracks, quite severely in this case.

These cracks would have cause air leaks and so would have affected the vacuum necessary inside the cap for the carb to operate correctly. One symptom of that could be the apparent sticking of the piston during operation, as the vacuum would have been insufficient to lift it.

Usually the poor owner would then be pulling his carbs off, polishing the cap guide and piston pin to eliminate the 'stickiness', re-mounting the carbs and getting exactly the same result!

As I can now replace these buttons ( see the replacement service HERE) I broke out the main sections to see just how badly it had been cracked. It turned out that this was a perfect candidate for total replacement. If you look at the picture (click for large image) you can see the clean sections where I broke the top out (red arrow points to them).  The areas inside the black lines were already broken.

Sometimes a tiny crack can be covered over with epoxy and our Beauty Buttons used to cover the repair, but that would not have been the answer in this case.

So if you have a running problem which is down to carb trouble, or when you are doing your carb rebuilds, close inspection of the caps is imperative.

What if you suspect a crack but don't want to break it out to make sure?

Not everyone has access to a vacuum pump but most of you can get to an air line. Screw the cap down onto a piece of wood that has a hole so that you can blow into the cap.

DON'T GO PUTTING 125 PSI INTO IT, UNLESS YOU REALLY WANT TO HAVE TO REPLACE THE BUTTON!

Just a little air, enough to feel if there is a leak. Some soapy water around the button would help to show this. Then you can look at your fixing options.