MOT Failure - HC Exhaust

Hi All,

Just had an MOT and unfortunately she failed! Couple of easy fixes but one that's got me scratching my head is the exhaust gas results.

It failed on Hydro Carbons - HC. The limit is 1200ppm and the test came back at 1475ppm

Anyone had this before? Anything to try before taking it back?

Thanks

You don't say what engine or fuel type
First off, check the air filter

kermit_rr said:

You don't say what engine or fuel type
First off, check the air filter

Click to expand...

Sorry, fair point.

Its a 3.5 v8 petrol, with SU's

OK thanks, will do.

I thought Strombergs were the standard, has it been upgraded? Is much rather have SUs any day
Have you checked they're not running rich? Is the engine getting fully to to temp?

kermit_rr said:

I thought Strombergs were the standard, has it been upgraded? Is much rather have SUs any day
Have you checked they're not running rich? Is the engine getting fully to to temp?

Click to expand...

From what I know these are standard, i think LR changed to SUs for the later V8 carb models.

I was about to have a look at mixture, but wanted to see if there is anything else to try first as I'm not particularly confident with it.

The engine get ups to temperature no problem.

The easy way to check your carbs are set, when it's up to temp, blip the throttle then let it idle a few seconds to stabilise. Lift the piston slightly and the engine revs should stay the same or rise ever so slightly. If there's no push under the carb then you can use a thin screwdriver down the inlet

High HC reading means the engine isn't burning all of the fuel , replace air filter , check and adjust mixture , balance carbs.......all thats assuming the compressions are good and dont forget the Italian tune up on the way to the testing station ........HTHs

With carbs I would be checking the needles move correctly. If these carbs have a diaphragm, pop the tops off and make sure there are no holes in the diaphragms. Check any choke mechanisms - make sure the choke is able to be fully off. If it's an automatic choke that works with a bi-metallic spring arrangement make sure the mechanism is correctly adjusted and works freely. HTH.

Thanks All,

I'll play around tomorrow, I took it for an "illegal" trip as it hadn't been run in a while so that may also help.

benpalmer said:

From what I know these are standard, i think LR changed to SUs for the later V8 carb models. .

Click to expand...

Not sure what model the OP has, but the 110 (etc.) changed to SU's in '86
RRC's were available with SU's for a year or so post intro. of EFI in Oct '85

nb. Strombergs had diaphragm's, not SU's

Well I spent the whole of Sunday messing around with it. Fingers crossed for Saturday!