It had all the potential for a Some Mothers Do 'Ave 'Em plot - that's a 1970s TV series with which those of us of a certain age will be familiar. In summary, what could go wrong, did go wrong for well-intentioned lead character Frank Spencer, usually ending up in chaos.
The plan was to balance or synchronise the four carbs on my 1993 Honda CB1000, and tweak its slightly lumpy idle and low-revs shunting.
I'd been psyching myself up for it for weeks, assembling the bits and pieces I'd need, bar one, which I planned to borrow from a mate: a carburettor vacuum synchroniser. The 5P rule - proper prep prevents poor performance and all that - was the mantra I'd been repeating to myself.
I'd watched YouTube videos and consulted another mate with a multi-carb bike, and made sure I saved the video links for in-project panics.
I announced to a couple of friends I'd be diving in to the job one Saturday morning. Then one came back to me with a classic Harry Enfield comedy sketch line: "You don't want to do it like that", delivered by an annoying, interfering flat-capped late-middle-aged-dad character.
My mate couldn't have been further from that character, so I wasn't annoyed: I was about to find out something I didn't know. Actually, a lot I didn't know.
The advice was "the last thing you should do when tuning a bike, particularly an ancient, old or modern classic, is tackle the carbs, because if you do it first it'll likely completely throw you off the scent of what actually needs doing to get the bike in perfect tune."
After you've bought the workshop manual, there's an order, he said, and this is it:
1. Make sure the air filter is clean and dry.
2. Run the engine for quarter-of-an-hour, otherwise you'll be adjusting things that are cold and will change shape or size when warm.
3. Tappets. Turn the engine over by hand (after taking the spark plugs out to avoid fighting compression…) and find Top Dead Centre. There'll be instructions online or in a workshop manual how to do this. Remove the rocker cover (and very likely the fuel tank before that…), then check the gap with those feeler gauges you bought with good intentions ten years ago. There's a lock nut to loosen, then turn the adjuster screw until the gauge will slide in with just the slightest of drags.
4. Remove the spark plugs, rest them one at a time on the cylinder head, and turn the engine over with the ignition on; you're looking for a nice blue spark.
5. Most classic bikes have points, which purists will like, but most of us hate to mess with. If you're lucky, a previous owner has installed fit-and-forget electronic ignition. If it still has points, switch off the ignition, then turn the engine until the points open widest. Using your feeler gauge, set the gap according to the bike's workshop manual recommendation, adjusting it with what should be a very obvious screw.
6. Timing. This is the real sanity test. Adjust the backing plate or use a timing light or voltmeter so the spark fires at the exact moment specified for your engine. This bit really warrants some studying, whether your bike's workshop manual or YouTube.
7. It's only then that you should set about the carburettor/s… First, familiarise yourself with the various screws and knobs that affect settings. That's crucial, because to the novice which adjuster screw does what can be indistinguishable.
Then wade in: adjust the throttle stop screw so the engine idles smoothly at the recommended RPM, which is normally somewhere between 1,000 RPM and 1,500 RPM.
All good? OK, then turn the mixture screw inward until the engine slows down, then turn it outward until the engine reaches its highest smooth idle speed.
Multiple carbs? Use vacuum gauges or a synchronisation tool to make sure they open together equally. There'll be instructions on the box.
Then, like a seasoned tinkerer, you'll have the perfectly-tuned bike.
Or, like me, get on the blower to my trusted classic mechanic to sort out my mess…
