15 replies to this topic

[Metty53]

Hi guys

My 1990 RSP with HIF44 carb (1275 MG Metro lump) failed its MOT this week due to emissions. The CO2 won't go below 4% even when hot ( it needs to be below 3.5%) and the hydrocarbons are also too high. Anyone know how much I should turn down the mixture to get it through, assuming this will do the trick?

Thanks.

[blacktulip]

Has it ever passed the mot before?

[CityEPete]

Shove the sniffer up something else during the test, pass!

When was it last serviced including valve clearances and timing set properly?

[deanc]

find a more friendly mot man?

[absx2]

Usually your friendly MOT man would turn the screw quarter to half a turn and then tell you the amount so you can reset it if it runs bad when you get home.

An oil change helps emissions before MOT so its good practice to give the car a service just before an MOT.

Any SU carburetor with a spring biased needle will wear the jet oval as the needle is constantly rubbing up and down in the same place so a new jet might be worth considering.

Assuming its a standard MG Metro cam with standard rockers set the valve clearances to 15 thou not 12 thou. This setting was updated in the Rover service manual as it gave a smother tickover and lower emissions.

Bung the MOT man a fiver and get him to give the screw a turn. 

[carbon]

As mentioned by absx2, could be worn needle and jet if these have not been replaced.

 

Also retarded ignition will tend to give lumpy idle and high h/c in exhaust, due to incomplete combustion. A MG Metro unit is high compression and to get the best performance out of this really needs 99 octane fuel with ignition timing set accordingly.

 

If you're using 95 octane this may not be helping.

[Metty53]

Thanks for the tips guys. Sounds like half a turn on the carb may be a good place to start?

The car passed MOT last year, it was borderline on emissions but ok when it was hot (so I'm told).

Since then I've had the head rebuilt with valves reseated and that was set up on the rolling road in May. I thought it was set up to pass the MOT but it must have been done for performance. The tappets were set to 12 thou.

[blacktulip]

Remember to screw the screw out to lean the mixture.

[Haynes]

find a more friendly mot man?

 

Can you actually get away with this these days, as its all logged on line, you cant just find someone else who'll pass it?

[neon1991]

sounds likr your MOT tester is a little bit on the strict side.  none of my cars have ever passed the emissions tests. but they dont go down as a reason for refusal.  I dont know if thats because they are all 70's but the last time I had the vw tested I offered to turn it down and he said,  "nah dont bother if it's running fine,  dont mess with it, they like to be a bit rich donr they?"  

[chrissyb007]

That's crazy the mot tester at the place I go laughed at me when I talked emmsions last year. He just said old car don't worry about it.

[deanc]

 

find a more friendly mot man?

 

Can you actually get away with this these days, as its all logged on line, you cant just find someone else who'll pass it?

 

Yeah you can usually get away with it depending on the issues, the computer only knows what you tell it. if Mr Mot tells the computer it has passed then its all good.

[Metty53]

Is it definitely anti-clockwise to lean the mixture? That's what I've done but was told otherwise by a local garage! MOT retest tomoz, fingers crossed.

[ACDodd]

Worn carbs will not hold the emmission setting very long. Ie set it, drive around the block its now wrong! You cannot expect a carb in this condition to hold emissions for 24hrs let alone weeks and months. A properly rebuilt one on the other hand will hold settingsmuch longer. As a rule of thumb, Su carbs should be overhauled every 30,000 miles or 5 years whichever happens sooner to maintain optimum performance.

Ac

[Metty53]

Passed! Happy face.

Good point AC. My cars done 51k. How involved is a carb rebuild?