Compression testing

Bike problems

Just before Christmas 2025, I rode my 23-year old Honda Innova ANF 125 to our local plant nurseries and parked it up. I could smell petrol as I walked off and thought it might be from another vehicle. When I came back to the bike some time later, I noticed a small pool of petrol on the ground. So, it was my bike. And it looked like there was oil leaking from the engine too. Urrrk!

I rode home and parked on my driveway while I opened the garage door. A few more drops of petrol had leaked out and the smell was very strong. Even Chubs could smell it in the house as the lounge windows were open for ventilation. Clearly, I'd got a problem.

Last summer, I'd found that the original automatic petrol stopcock (autopetcock) was faulty. Repair was a going to be difficult and success was not guaranteed, and a new original Honda part was going to be around 80 quid. So, I replaced the autopetcock with a manually operated one - while doing that I replaced all the petrol lines linking the tank with the carb, and replaced the small inline filter. Six months later, something had gone wrong with my new system. Cold, dark December days aren't conducive to garage work so, just before Christmas 2025, I turned off the bikes petcock manually, closed the garage door and left the problem until another day.

Solution

With a move down to 3 days a week at work from the New Year, I had some more time on my hands and so set about tracing the petrol leak and seeing what else needed doing.  To have a really good look and get access to the mechanicals, I took off the plastic body panels. After 23 years, the panel fixture points were not in great shape and very few of the original fasteners were still there.

It was really obvious what had happened to cause the leak. The cheap petrol pipe was clearly the problem - it had pulled off the brass inlet pipe on the carburettor. Removing this pipe all the way back to the tank revealed that it had become brittle and hard - and possibly shorter - as it had probably reacted with the petrol. Possibly it was caused by the E10 petrol, although I think it was more likely to be down to very cheaply made inferior quality material. 

A quick trip down to my local bike shop meant I was able to buy a metre of decent quality pipe and a new inline filter for a tenner. All fitted and secured, I opened the petcock and fuel flowed into the carb with no leaks The bike started first time on full choke. Result! Notes to self: "Buy Cheap, Buy Twice" and Don't be such a skinflint!

An opportunity

I'd bought a compression tester a couple of years ago and had meant to use it on my project bike. I'd also planned to use it on the Innova as I suspected poor performance might be down to worn or leaky valves or even piston blowpast.  With the bike up on the ramp with the spark plug accessuble, now seemed a good time to do it. And why not?

So, I decided to give it a go, First the valve clearances need checking and adjusting if necessary (mine were a bit tight), Then the engine had to be warmed up to operating temperature; just a 5 minute idle while up on the ramp did the trick. Then, working quickly, I was able to remove the spark plug and scxrew in the compression tester. I put the plug back into the plug cap and made sure it earthed against the cylinder fins. 

 To perform a test is very simple: ignition on, wind the throttle to the fully-open position and then hit the starter. As the engine turns over, the pressure inside the testing apparatus builds up and the needle on the gauge edges upwards. There comes a point where the needle won't climb any higher and so you can stop cranking the engine. The compession value is read of the gauge.

 The dial read around 11.7 Bar. The Haynes workshop manual provided a guide figure of 12 Bar. I was really pleased that my 23 year old, 30,000 mile engine returned such a decent compression.