Hi all

The mini has been running sweetly the past 6 months if not slightly lean and slightly too advanced in timing. To get it there I played with the timing, carb jetting and tappet clearances.

It’s now got a little hiccup on acceleration when cold and takes much longer to warm up. So, while running sweetly in summer, does the colder weather mean I have to adjust something? Is it to do with the carb mix and timing? Or is it just time for a little tune up?

The carb is old and needs rebuilding but it works well enough.

1275 1100s with HS4 and points dizzy.

Cheers
Bugs


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.

Maybe curing the mixture from lean has caused the slow warmup.

I have twin HS2 (rebuilt a few years ago) that now experience 'hiccup' when cold. Goes away once warmed up. I noticed it was made worse after damper oil topup.

I'm thinking I may need to check that my need is centered and not sticking. Does the damper go up and down unimpeded?

Does the choke make a difference to this hiccup?

Sorry. It’s still running lean and slightly advanced. I never changed it because it worked really well. It was pushing the boundaries that I was a little uncomfortable when I floored it.

So out of interest, I’m wondering if this level of tune can be affected by colder weather or do I just have to re tune the carb and timing again.

I’ve got a pair of twin hs2 in pieces. Do you think they are worth it? Haven’t checked the damper or the choke!!!! I will check that out.


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.

We are dealing with 1940s technology when owners were expected to maintain, lubricate and adjust everything, every weekend.
Carb tuning and timing don't usually need seasonal changes but should be set up as close ideal.

One of the main issues when running a single SU is making sure the carb piston can slide easily inside the housing, like fffffred said. A drop of sewing machine oil on the outside of the piston rod is needed occasionally. If the piston gets stuck up (open) the motor will be hard to start; if the piston sticks when rising it will cause a hiccup on acceleration. Check the piston movement by unscrewing the plastic hexagonal damper on top of the piston housing, removing the intake filter and elbow so you can reach into the piston and flick it up by about 20mm and let it drop under its own weight. It should rise and fall easily.

Twin SUs help to average out, or hide, any of these sticking problems.

You might also consider experimenting with a different grade of oil inside the dashpot. The books all quote 20 SAE grade but from my limited experience, every mini requires a different grade! A thicker grade of oil slows the movement of the carb piston, which has the effect of enriching the mixture for better acceleration response to overcome a flat spot on acceleration. Any grade of engine oil is OK to try.