17 replies to this topic

[sean552uk]

Hi I have recently put my mini in for an mot, and it failed on a few things most of which where an easy fix but I have been left with 2 problems that I am running out of ideas as to how to fix them. They are........

• Poor brake effecencey: the mot tested said that he could get his foot all the way to the floor and it didn’t stop the rollers.
• engine emissions where too high (not sure what he was measuring them in but he said that the reading was 1800 and the limit is 1200)

the mini is a 1980 mini 1000 that I have been restoring over the last few years it has had a 1275cc engine from a 1992 British open mini classic fitted (with a stage one kit and hif38 carb) and the brakes have had new copper brake lines fitted all round, braded hoses on the front and new rubber hoses on the rear, new rear brake pistons, its got 7.5" disc and callipers on the front, the callipers are used ones which I rebuilt with new pistons and seals, its had a second hand yellow brake master cylinder fitted.

Basically with the brakes when you put your foot on the pedal, you have to push really hard but you can get it to reach the floor. the local mechanic said that its probably the master cylinder but if you pump the brake pedal it doesn’t build up pressure in the brake lines almost like there’s still air in the system, but I have bled the brakes countless times now using both an easy bleed kit and someone sat in the car pumping the pedal and I cant get any more bubbles out. If it was the master cylinder I though that I should be able to pump up pressure, but it wouldn’t hold the pressure and slowly leak pressure allowing the pedal to slowly reach the floor?

with the engine emissions the mini had a hif44 carb fitted when it went for the mot but it was leaking the dash pot oil into the carb (which I think was part of the reason why the emissions where so high) and it would only run for about a 1.5 miles before the car would just stop when its used all the oil in the dash pot. so I swapped the carb for a spare hif38 that has had a full rebuild with new seals and was ultrasonically cleaned, the emissions are now fine (reads 2.5 on the gunson emissions tested) and the dash pot doesn’t seem to loose oil but it now runs fine for a while you can drive the car up and down the road but it suddenly stops and back fires through the carb? Not sure where to start in fixing this as the engine has electronic ignition and it sounds like its running fine then just suddenly back fires?

As I have said I have now got to the point that I have run out of ideas as to how to fix these problems, sorry for the long post but I hope I have given you enough information to give an idea as to what might be wrong. Any suggestions would be grateful

Thanks Sean

[tango gt]

With your brake problem, have you adjusted the rear brakes? if these are way out, you will have a lot of brake travel before you get any pedal pressure. Something a lot of people forget! Also check that the clevis pin at the pedal is installed correctly, this can fall out, making a lot of slack in the linkage, also causing a low pedal.

[donjarr]

Hi m8

On the brakes as mentioned check the back ones. Easiest way is do them up till they lock then back off until the wheel turns freely. Sometimes you have a slight bit of rub as in a certain spot as you turn the wheel, which I have been told is ok, as in you can feel it as you turn the wheel but it doesn't stop the wheel.

As for the emissions if that's sorted it's ok, but mine just doesn't pass on tick over it seems due to 1380 with high lift cam, but the local MOT guy who is a ex mini racer, said there is a clause in the MOT for modified engines which can be rev'ed up to 3000. If you had problems with the emissions you would need to find this online and print it off and show them, as many MOT testers just don't know whats in the manual it seems.

[minidaves]

brakes bleed them and check the adjustment to pass a brake test is not hard.
exhaust gases just needs the mixture adjsuting and check timing

[sean552uk]

hi thanks for the replys, i did adjust the rear brake shoes as it said in the haynes manual. which was to turn the adjusted untill the rear wheels locked and then back it off 1/4 turn (you can still hear the shoes slightly rubbing on the drums) but it was a while ago so i'll double check them tomorrow.
does anyone have any ideas why the engine runs but then back fires through the carb normally after about 5 mins of running?

[jaydee]

1800 ppm sounds like its too lean or too advanced, i'd expect it to be at 2%CO with such high ppm readings

[sean552uk]

right i have had a play with the rear brakes today, but it did'nt seen to make any difference? the hand brake works fine and the rear drums are set so that there backed off 1/4 turn from the shoes stopping the wheel from turning.
also had a go at tunning the carb, the engine was running at idle after it had warmed up (800rpm) and i was adjusting the carb with the colour tune attached and the emisions tester in the exhaust. when the colour tune was reading blue the emisions where about 1.7%CO? i have been told that the legal limit is 4%CO (but not sure what rpm?) but what is it suppose to be at idle? i expect that the co% will go up with the engine revs as theres more fuel being burnt. any way i set the adjustment screw with the colour tune showing blue, then picked up the revs to 1500rpm the colour tune when to a yellow colour and then it suddenly stopped sparking the engine turned over a couple of time and it back fired through the carb and stopped? i have no idea what the problem could be? any ideas?

[jaydee]

Its lean, rise the idle at 1500 rpm and enrich mixture until you get about 2.5 or 3 %CO, then set idle back to 800 rpm.
Colour tune showing yellow flame as you pick up the revs is normal.

[sean552uk]

ok i'll give that a try tomorrow thanks

[sean552uk]

Right only just got round to trying to adjust the mixture today. I increased the rpm to 1500 and adjusted the carb as much as I could in both directions (making sure the rpm stayed at 1500) and I couldn’t get any where near 2.5% CO? It only seems to adjust between 1% and about 1.5%. This was going from yellow on the colourtune through blue to white at the other extreme?

[jaydee]

That would make sense if its got a cat..hence a much lower CO reading, but the ppm reading wont be that high..Can you work out the ppm value with carb set up at 1.5 CO ?
i've experienced that colour tune not always works but you should be looking for a turquiose blue at stationary revs, apply throttle up to 4k rpm it should look yellow under acceleration, some red at high rpm, blueish as you're stady at about 3k rpm.

[sean552uk]

sorry bit of a busy week i have'nt had chance to look at the mini again yet, but it does'nt have a cat, just a silencer and back box. i'll try to adjust it again, but do you know mow to work out the ppm? also when they test it for the mot does it just get tested at idle speed or do they go through the rev range?

[jaydee]

You need to borrow a proper gas tester which reads CO-CO2-ppm and oxygen..
At the MOT they take the reading at idle speed.

[sean552uk]

yes i have the correct needle for each carb fitted

[mattbeddow]

I know its an old post but i thought id put my knowledge into the mixing pot.
Going off the printout from the machine of my mot test, the measurements are taken at both idle and 2500 rpm.

1200ppm is the limit for HC (ie unburnt fuel) so you want to get this as low as you can with the engine still running, this will also bring down your CO reading. I dont know what these guys are on about when the say "get your CO to 2%", ideally you should have 0% CO, CO is an indication of too rich a mixture and therefore wasted fuel (hence your super high HC)

Too rich a mixture could also be causing your backfiring problem.

Also there is no way to just calculate HC levels, you need the measuring gear/get a garage to test it, but if youve got the CO as low as you can by making the mixture leaner and it still runs then chances are it will pass the test. Mine got 5.16% CO (fail) and 308ppm HC (pass) s it is possible to have a high CO and low HC and visa versa