I'm picking up my parents midget next weekend. It's just bene MOT'd and the only thing that was a cause for concern were the eemissions.

Now thinking back, the carb's were tuned last year for the MOT to get arround the same problem, so its nothing wrong with the fueling/air.

On the overun it makes a loverly snap/crackle/pop noise, which although nice to listen to, could this possibly be the exhaust valves leaking? Which would also explain the borderline emissions.

Short of getting the cylinder head off and checking the valves (not too dificult, but with the ever present danger of the Shitish Layland bolts shearing off turning a quick check into a nightmare and an expensive trip to the engineering shop) is there any way to confirm this suspicion? The car's not down on power (not that they have much to lose anyway!) and still hits 60 in about the same time it did 30+ years ago. So I'd probably leave it till it's next MOT and see if it's still as bad, unless I'm sure they need doing.

(1500 engine if theres any Rover/Triumph boffins in the house)

I didn't think old cars were subject to the emissions regs in anyway like more modern cars

Anyway, I'd just lean it right up until after the test – you obviously need to start it so don't go too far

I assume it is running on a pair of 1 1/8" SU's but if it is on Strongburgs the same will apply.

You say the carbs were tuned, do you mean just had the mixtures set, to get the Co OK for the MOT? The car is 30 years old and in all probability the needle and jets are worn and the float height will be way out and possibly the slide spring weak, settting the miture at idle to get correct Co for the MOT will not get round the wear, so once you are off idle the mixture will probably be all over the show.

You can very eaily overhaul these carbs yourself, all the bits and instructions are available from someone like Southern Carburettors (www.southerncarbs.co.uk)

Hope that helps

It's a '78, so subject to whatever emisions regs were in place at the time.

SU's (IIRC). Not sure what they did, but apaprently they had to rev the tits off it to get it through (I presumed that meant they were looking at the emmisions higher up?). I'll have a look into re-building the carb's, could make a nice weekend project if nothing else.

what engine, Triumph or older bmc 1.3?

As Michael says.

Take it for a really good run before you take it in next time to get it really warm & cleaned out. Try some redex treatment(or whatever is around now)

could be a bit of valve stem wear allowing oil to pass, enter cylinders and then be burnt.

Popping sound from exhaust could just be a baffle bust in the exhaust system?

Have engine timing/dwell angles set properly, new plugs and air fulter if full service has`nt been done already.

The old SUs also tend to suffer from spindle wear on butterfly shaft which means any new parts like needles & tubes will be ineffective.

Old strombergs may just need new diaphragms.

If someone has fitted new needles at any time they may not have set them at correct hieght?

Both carbs need the correct oil and level in the damper tubes

Well over 30yrs since I last played around with these things. If you want a spare set of carbs I have some under my bench, aquired for an abandoned mini project that I wish I had kept now 😥

ahhh, the joy of old car ownership. It's a 1500 triumph.

New(ish, well not new at all realy, but not 30 years old) stainless exhaust so shouldn't be any problems there. I'm not an expert but it definately sounds more like unburnt fuel igniting to my untrained ear, theres no rattle and its only on the overun from high revs.

Dampers kept topped up regulalry.

Doesn't appear to be burning oil, the exhaust is crystal clear even when cold and it's not using it at an apreciable rate.

Not sure when it was last given a full service, there's enough little things that go wrong it never seems to get to one before XYZ has already been replaced!

So the plan is………….

Overhaul the carbs, new needles, tubes & butterflies check the float level etc.

Big K&N pancakes to replace the little triumph airbox

New spark plugs.

(geat a garrage to) Check timing/advance

Oil + filters (and make a note to keep an accurate log of how much it's burning)

Any other relatively easy/inexpensive things it could be?

Dampers kept topped up regulalry.

To correct level and not too heavy an oil?

Thermostat ok? Is it getting up to normal running temp or perhaps running cold?

I'd be looking at the carb as prime suspect, sounds like overfuelling.

correct level is full isn't it? Unscrew cap, pull damper up, top-up with oil, let damper sink down, screw cap back on, wipe up the dribble that overflows? I'll dig out the haynes manual when I get home. Not sure what oil weights been used, just took my dad's word for it beign the right one.

Thermostat
appears to be working, engine temp sits just on the cold side of the middle of the guage and barely budges from that even in town or on a long run.

Carbs are IMO definitely the main suspect, popping in the exhaust on overrun sounds like excess fuel (mixture too rich) burning after the combustion stroke and therefore burning in the exhaust.

If you're going to get a garage to check the timing and dwell angles ask them to put the 'sniffer' up the exhaust and see what reading your getting, depending on what readings you get will depend on course of action to a certain degree. Exhaust gas analysers can be wonderful pieces of kit in the right hands.

Must admit I haven't looked at the legislation for a little while and just going by memory but think the MOT will only be looking for CO and HC readings and they are a lot more relaxed and reasonably easy to get within specification, usually a play with the mixture will get her through.

SU carbs are wonderful things and in the world of carburettors they are pretty simple, try setting up and jetting a pair of Webber twin 40's!

ohhhh webbers

mate used to have a GT6 for track racing with 3 of them, oooo the noise 😆

He then got an Imp ❗

Another had a 1293 Cooper S complete with straight cut gearbox, talk about noisy ❗

Myself I had a set of Delortos for my Cooper when I went road rallying, just a swap on the manifold & back again for work

Could also be badly balanced carbs. One could have been richend up to compensate for the other.

correct level is full isn't it?

No…should be enough room for the plunger to fit into pot if memory serves me correctly. We used to use 3in1 for winter fast pick ups but needs topping up lots. General engine oil does, gtx eg. Dukhams was always too thick.

Have you stripped and cleaned the carbs? Take top of and look inside, if it is black, dirty clean with brasso,or brake fluid, same with pistons. Something we did every service with stroms/su.

Is it the Triumph engine?
If it is they fitted a little flap valve thing to the butterfly valve. A later mod was to solder this contraption shut because of various idling and other set up problems. It was the start of the emissions era

Were the 1500 converted to run on unleaded?

The 1275 unit I had, needed converting to run on unleaded (different head), something to do with lubing the valves and problems using unleaded if you don't convert over?

If the valves are worn, that could mess up the emissions, no expert btw, just reminiscing?

On the overun it makes a loverly snap/crackle/pop noise, which although nice to listen to

My 1275 version used to do that too, best done in a tunnel with the roof down to experience it in its full bubbly/bangy glory 😉

The previous owner said he had it converted it to run on unleaded (they were built for 4-star) , I'll have a rummage for a recipt to back that up (it comes with a box of photos and recipts that fills the boot!) if it hadn't been done it would indeed burn the exhaust valves which was one of my thoughts as to why it may be letting unburnt fuel through.

Where are you? I would reckon that if you are asking these questions you have no idea what to do and could turn it into a non runner. I would have thought the prime suspect would be an air leak on the inlet manifold. Do you have the emission results from the mot, if it has high HC's then that would also point to a manifold/carb air leak.