14 replies to this topic

[freshairmini]

Hi,

Just a quick question, nothing amazing wrong with my mini (I hope).

When I was driving on the weekend, spiritedly, changing from 1 to 2nd, 3rd and 4th, at about 4k - 4.5k, when I changed up I was getting an 'engine braking effect, it was slowing down slightly when changing up.

Is this normal for that kind of standard-ish engine? Mine is a 1275 with stage one type parts fitted. (maniflow 1.75" exhaust system, ITG foam filter/stub-stack, been set-up on rolling road with re-profiled needle).

Any advice would be great.

Thanks!

[Cerberus]

Brakes could be binding, which when you change gear and lose the forward power from the engine, starts to slow it down.

I would have thought they would have to be binding quite considerably though to slow you down, which I would expect you'd be able to smell.

When the brakes on my fiesta were binding, the car only slowed down when going uphill and changing gear. Squeaked when pulling away from a stop, and stunk of brake pad material. The wheels also got very hot.

I'd check that first.

When you say slowing down, what are we talking about? The car would slow a bit as you change, as there's no longer any power going to the wheels.

[xtr hardcore]

Could also be a fuel / air problem with the Carb. Used to get this all the time on my old Tahiti

[freshairmini]

What I mean is when I engage the next gear up, so once I've put it into say 4th from 3rd and take my foot off the clutch, it engages, and I get the 'engine brake' feeling then it picks up again.

Its almost like its too higher rev to then change up and it cant keep up, but after a second or two it picks up.

And I recently serviced and changed the brakes and pads. But its been doing that before and after that so I don't think its brake binding.

Strange anomaly basically, never heard or experienced it before.

[DeanP]

You don't say whether it's carb or injection? Check all the above first but are all the cables to the carb free and all the levers on the carb move freely. Nothing sticking? Get someone to press the accelerator while your head is under the bonnet (and stationary) and look at the lever motions and if they open and return properly. Is the dash pot filled correctly.

[xtr hardcore]

while your head is under the bonnet (and stationary).

haha

[freshairmini]

Its a carbed 1275. All running fine. Recently serviced so I have already checked these things, and the carb seems to be OK, all oiled and free moving, and dash pot is filled correctly.

[Dan]

Do you mean it's not picking up fast enough when you reapply the throttle, so it hesitates? What happens if you make a clutchless change?

[freshairmini]

its a similar feeling when you change down a gear at a high rpm, so you get an engine braking effect.

its basically that but when changing up. so at like 4,500rpm going from 3rd to 4th it feels like engine braking then picks up again.

its not a hesitation like bad fuel/air settings, i had that before i got it set up a while back, so know what that feels like.

Its quite hard to explain, but very obvious when driving :s

Edited by freshairmini, 05 March 2012 - 09:04 PM.

[Cerberus]

I'm struggling to think how its even possible on an up-change.

The engine RPM should drop on an up-change, not go up, so there shouldn't be any actual engine braking and I can't think how you could get the feeling of it.

Think you need to do some testing. Like Dan says, clutchless change.
Possibly see what happens if you just put it in neutral and not go into the next gear.

Too vicious with the clutch? Not quick enough with the change so the revs have dropped below what they would do in the next gear, so have to go back up again?

Edited by Cerberus, 05 March 2012 - 10:59 PM.

[TopCatCustom]

Could be worth checking the timing, and the vacuum advance pipe on the dissy, also dashpot oil and has the carb been fiddled with lately?

[DeanP]

You seem to be eliminating anything engine wise, which really only leaves the brakes. Does each wheel spin easily when jacked up? I'm sure you'd feel it pulling though... It could be a personal thing... are you sure you haven't forgotten to release the handbrake?

[ACDodd]

What damper piston is fitted to the carburetter?

AC

[bmcecosse]

It does sound like the engine is 'gasping' - has anything been done to the carb? Is there definitely a spring in there - and what colour are the spark plugs???

[freshairmini]

Spark plugs kind of a sand colour, which is normal I think?

Yeah carb has a spring and the damper piston is standard (or at least what came with it).