The XS Triple Sidecar - new needles and a complete re-jet

The XS-Triple Sidecar is my daily mule during the cold, snowy and salty months. As such it has endured a lot this Winter and to be honest, even after more than one attempt the jetting of the flatslides still wasn't fully satisfactory.

Most importantly fuel consumption was heavy and it has stopped to idle. After doing quite a bit of research, I found out that the 6DP1-needles out of my VM38 carbs are the same length and should give me the much needed richer mid- and top-range.

Finding out  why it had decided not to idle properly anymore became rather apparent, once I took the old pilot jets out. Turns out there's two sizes of idle jets for Mikuni TM-carbs. 

It's very hard to see in the picture, but the needles (6DP1 on the left, 6DGM5 on the right) are actually quite dramatically different. From the midrange to the top, the 6DP1 is much slimmer and thus allows for more fuel and air to flow.

And that becomes VERY apparent when rejetting. Before I was running the bike on 37.5 pilots and 135 mains and it was running rich on the top, now I have upgraded to 45 pilots and 145 mains and when you read this, I will probably be trying out some 147.5s or 150ies. Suffice to say, the power available. grew in the same fashion, so I can't complain. Also the bike is a lot torquier now, which is a good thing as it is geared way too long for sidecar use from the factory. (Hint: it was never meant to pull a chair...)

Other than that, Spring will bring a new exhaust and a modified rear subframe, so I can finally swap rear tyres, without taking the exhaust off, which to be fair is a bit lame. 

Syncing vacuum gauges

I have a suspicion that I know, what you're thinking... shouldn't that read as "syncing carbs/throttle bodies WITH vacuum gauges"? Well, not if you have had a little backfire through the carbs and that properly messed up your gauges.

Now here is the moment, when you realise that you bought tools from a reputable manufacturer, if you can simply buy spares (in this case a new set of clcoks 15 years after you bought them) and they'll basically overnight them to you and respond to your emails at absolutely ungodly times of the day, i.e. late in the evening.

Let's have a little look at this picture, do you see what has gone wrong?

There are copper-beryllium springs inside these gauges, which are very sensitive to even the slightest changes of vacuum (or pressure). Unfortunately these don't take very kindly to being overstretched in either direction. A good indicator is for example #4 which doesn't sit at 0 anymore.

After parting with quite a handful of my hard-earned (definitely more than for a cheap set!), I received four new clocks which had (slightly) adjustable scales.

As you can see with the attached y-piece, in order to sync them, two (or more) gauges have to be hooked up to one vacuum port and then adjusted to show exactly same value.

Which in the end looks something like this and once again proves that sidecars absolutely rule as mobile workbenches. 😀

A quick word on the elephant in the room: Why didn't you just get a set of cheap... Simple really, you can only adjust carbs as accurately as your tools will allow you to measure pressure differences, so the more accurate, the better the job. To be honest, the level of accuracy that can be achieved with these is (usually) absolute overkill, but the other thing about cheap gauges is that you can't sync them to each other inducing another error aside from the already given inaccurracy aside from a less sensitive spring. Also: it's nicer to know you could absolutely nail it and then call it good enough than the other way round. 😏

The new TR1 engine - squishing things together to make more power (part 31)

Aside from ruining perfectly good engines, there's some more that needs to be done in the advent of the upcoming season. The recent situation of detonation on one cylinder and the fact that the gap between squishband and piston was incredibly large led me to look for solutions to increase the effectiveness of the squish. And the best way to improve things was to get the piston and the squishband closer together by removing the cylinder base gasket.

First the baseline had to be established with some 2mm (super-soft) solder.

This came out as 1.71 to 1.75mm, which was just at what literature would consider the uppermost limit of squish-gap to still be working to a minimal extent.  Time to pull off the cylinder head and cylinder have a look at things.

Quite a few carbon deposits and signs of the engine running a tad richer than I would have hoped, but aside from that all seems to be well. After quite a bit of swearing because I haven't used enough grease on the base gaskets and lots of subsequent cleaning a thin bead of gasket sealer was applied and the engine re-assembled.

So which results did the whole process yield: The base gasket is 0.50mm thick when compressed and that's pretty much what the cylinder came down. Everything spins over freely and nothing seems to touch.

Theory says one should strive for a clearance of 1.00mm or even slightly less for achieving maximum effectiveness of the squish, but this leaves out of consideration that after all this isn't a racing engine and shall still work reliably even 30,000 or 40,000km after this overhaul and without any doubt, tightening up the squishband should help quite a bit in the future.