Most liked posts in thread: Into the unknown: Tuning the 1275 A-series engine

The above post is why I like this MINI community. Hell, Dave Thank you and it is not my Classic.

 

Here are a couple of easy things to check on the carbs.....take the air cleaners off, then loosen the caps on top of the suction chambers all the way. Stick a finger into the throat of the carb and lift up on the piston all the way, it should go up easily and drop right back down again when you remove your finger. It should not drag or scrape either direction.

If that's good, put the caps back on top (make sure there's oil in there) and do the same test, there should be resistance going up and it should free fall down again.

If it doesn't pass these tests, something is wrong in the assembly of the piston and dome, it could be related to those screws or it could be the jet is not centered or the needle is bent or incorrectly installed. The piston should move cleanly and smoothly.

If it does pass these tests then I'd bet on the carbs being set wrong, which surprises me if you took it to a shop that's used to working on these cars.

One other possibility - make sure no vacuum lines are off, especially the one for the brake booster.

 

As more of us old farts are retiring and dying off, a lot of this knowledge is being lost to the ages....so I like to try and teach young people the old ways.

I take my Jag and my old Mini to school to show my students old tech, but I know they will probably never encounter any of this is their careers.

 

Sounds to me like your carbs are just too lean, but one easy thing you can check first is to see if there's any oil in the tops of the carbs - use something light like ATF to top them off.

I think the timing is too far advanced too, back it off to about 8* either at idle or static. It's easy to do a static check of the timing - you car should have marks on the lower pulley and a corresponding tab on the timing cover. Put a test lite on the minus (-) side of the coil, turn on the ign and pull the center coil wire out so it won't try to start, put the car in 4th gear and roll it forward till you see the mark on the pulley, as you continue to roll it forward the light will light when the points open, at that instance check the timing marks. If it's too far advanced, loosen the clamp on the dist. and turn it counter clockwise a bit, then back the car up and roll it forward again watching for the test light to light. The light should go on just as the pointer lines up with 8* or so.

However, the timing being off will not cause the symptoms you're describing....

 

This so true & oh so sad.

 

General thoughts:

- Get to love your SUs - maybe not the highest performing carburettor, but one of the most durable, will be working fine after a nuclear hit. Webers may give more horsepower but will stay in tune for several minutes, max. Expect to adjust your SUs at least once every decade, max.

- Balancing two SUs by taking off the air cleaners and running a small plastic tube from your ear to the carb inlet works surprisingly well - and you don't need 30 years' experience to use this method.

- Everywhere it says to check/top up the oil level in the SU dampers but you will never, ever see or feel any improvement from doing this, so treat it as some weird semi-religious rite that everyone does but no-one can say why.

- Your A-series engine should leak oil - this was the advanced rust-prevention method used by the manufacturer. Plus if you fix the oil leaks, your remote gearchange will become stiff from lack of lubrication.....

 

Matt, feel free to call me if I can walk you thru anything that might help. You can get a test light from any auto parts store for only a very few Bux, you don't need to buy a timing light.....you don't need webers, you just need these set correctly and I'm sure you'll be happy with the performance.

913-648-6339 is my number

 

Yes, the clip-on 12V test light is all you need for static timing.

Clip one lead to the minus (-) on the coil and the other to ground. Then just follow what I wrote, if it's confusing call me and I'll walk you thru it.

 

.....but then again, so are the cars that these talents can be used on. :sad:

 

See?

Knew you'd get on top of it.....

 

As I said before, balancing the air flow can be done with a hose, but if you want to get it accurate you use a Unisyn. Does it make a difference? Yes, the engine will be more responsive, especially immediately off idle.

The oil in the tops of the pistons does have a function, it keeps the piston from moving too far or too quickly, which can cause large fluctuations in the mixture, as the fuel metering needle is directly attached to the piston. Not having oil in the dampers can cause the engine to backfire especially when cold, and it will go thru a lot more fuel too. However, it doesn't need attention every time you fill up with gas, once a year or so is plenty.

I agree with the durability of the SU and yes, once set correctly it needs virtually no maintenance to keep the engine in tune. Although like any mechanical thing parts do wear out eventually - in the case of the SU the throttle shaft bores will wear, causing idle fluctuations. The needle and main jet will wear too which will make it start to run rich, and the dashpots need periodic cleaning but these issues only come after many miles of driving.

Webers also will stay in tune once set up correctly, as the only moving part is the throttle, no pistons, moving needles or other parts to wear on them.

My A Series does not leak oil, not should they IMHO.....comic comments aside.

 

My experience with Weber carbs is once set up correctly they tend to stay that way. My experience with SU carbs is the same as the Webers. Folks like to blame the SU's for everything, but it usually is not the case. Car doesn't run right? Look at the ignition system first. Just my .02 shillings.

 

That's 1/8th pipe thread not a regular bolt thread, so get pipe plugs and use some Teflon tape on it so it will seal.

Glad to hear it's running well, did you get the brake lights sorted yet?