Triumph Repair: Spitfire Emissions and Hydrocarbons, h2se, valve clearances

Question
Hello,
1977 Spitfire 1500 - SU H2SE carbs

Recently failed my MOT on emmisions.  Failed as the hydrocarbons were too high.  Passed on CO2 which read at 4.5 grams and the CO reading was high at 4.5 but not a cause for failure.  The high CO goes in hand with a reading of 6000 HC(hydrocarbons) when allowable limit is 1200, as both indicate fuel not being burned properly.

There is quiet a sweet smell of fuel when the car is idling.  Using a colourtune I can see that the 3 and 4 cylinders are running rich but even leaned all the way out on the carb I cannot get them running at the right level.  Cylinders 1 and 2 are running lean but I am having trouble getting into normal range.  I took the spark plugs out and 1 and 2 are light brown but some glazing is starting to show (a side effect of running lean).  Plugs 3 and 4 are oily black.  I have removed the rocker cover to check the valve guides.  Inside the rocker cover it is quiet 'wet' with oil but also an aromatic smell of petrol and the top surface has some caked on oil residue.  I believe that this leakage might be the cause of the hydrocarbons but would like to ask for your comments on the following.

1. I can change out the valve guides but is this reponsible for the oily spark plugs, and/or the high hydrocarbons?

2. I have resistance checked all four distributor plug wires and 1,3 and 4 read 4.10 kilo-ohms and 2 reads 4.75 k-ohms.  Will this make a difference?

3. The points are set to 0.38mm and I have checked the resitance through the distributor cap and the spark on each plug wire and they are all a good blue spark.  Is there a definitive way of testing the spark?

4. The engine seems to idle a bit rough, could this be the valve clearances.  I set them all to 0.25mm but how accurate should this be?  What effect will this have on the idle and HC's?  

I hope I have provided enough information for you to amke an accurate assessment but if not let me know I will provide more detail.

Really looking forward to your answers as the warm weather is here know but it is England, so not for long!

Regards,

Mike

Answer
Mike,

Rather than answer your questions point for point can I suggest that you investigate a bit further why you're getting such an imbalance with the SUs?

First off, its normal for the Spitfire 1500s to burn a bit of oil, especially with increasing mileage.  Yes, new guides can help cut that down a bit.

A good first step to determine a baseline would be to perform a compression check.  That'll answer whether the valves are set incorrectly or whether the rings in 3 and 4 are truly worn.

Next would be to dig into the SUs to determine why you have the front carb running lean and the rear carb appearing to run rich.  Are the floats set to the same level?  Float valves sticking?  

Do the carbs have the same needles, and do the jets or needles show signs of excessive wear?

Are the throttle shafts worn?  You can test for this using a can of carb cleaner and carefully spray a bit of cleaner at the throttle shaft ends while the engine is running.  If the engine note changes it's a sign that you're getting air leakage past the throttle shafts.

Are the dashpots topped up?  Is one leaking?  Do the dashpots move smoothly up and down if you stick a finger into the carb throat (engine off, of course!)?

I suspect that once you sort the carb issues then you'll be closer to passing your MOT.


Cheers,

Jim