💧 Haynes’ World: What’s Causing These Leaks?

From: Haynes - Thursday Dec 28,2023 07:30 pm

Haynes’ World is a regular feature that takes a look at what the staff at Haynes are doing with their vehicles. This time, two of Martynn’s bikes have issues.

Motorcycles: MZ Baghira 660, Yamaha V-Max 1200
Owner: Martynn Randall, Technical Editor

We’re all probably aware that the increase in the proportion of ethanol in our petrol probably isn’t good news for older vehicles, but I think this is the first time that I’ve come across fuel system issues that could be caused by it – or it could be just old age (not mine – the parts!).

I’m always on the lookout for new projects, and am lucky enough to be able to indulge my appetite for older motorbikes. But internal combustion engines don’t like to be left standing for extended periods without being run.

So when the first project (an MZ Baghira 660 from the late 1990s) didn’t tick over properly, and was hesitant under acceleration, I immediately pulled apart the carbs and expected to find the usual blocked jets/air holes/etc.

However, everything inside the Baghira's carbs looked good. So I put them back on the bike and started to look at the ignition system, and checked the valve clearances and the compression.

Everything seemed to be fine. So, I started it up again and, thinking there might be an air leak between the carburettors and the cylinder head, squirted GT85 maintenance spray around the inlet manifold.

Sure enough, spraying between the manifold and the cylinder head on the right-hand side, the engine speed immediately increased – definitely a leak!

Back off with the carbs and then the manifold. The problem was obvious: an O-ring seal between the manifold and head had split, and a bit was missing (shown above).

New O-ring fitted, and the bike was transformed. Sweet tick over and no hesitation when the throttle was cracked open. Result.

Read about Martynn’s other bike issue here

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