Rich running CR TR6

[pcw64]

I booked my 1974 TR6 in for a check up on the rolling road and was surprised by the result.

On idle it was showing 6% CO

10 AFR at cruising & 11 AFR at full throttle and producing 104 BHP.

The guy doing it said that the the metering unit needs attention ( is that correct ?) and I would welcome any advice on the best way to correct this.Thanks Paul

[Mk2 Chopper]

First thing to check is your vacuum, at idle a CR should be around 12 Hg, if it's lower than this, might mean you have a leak somewhere, such as the balance pipes (4 on a CR) servo/pipe, MU pipe, throttle bodies to head, throttle butterfly's need to be closed for idle and balanced for correct fuel/air when throttle is open. 

It can also mean wear in the engine. But if everything else is fine, then the MU can be tweaked all over the fuel curve if you know what your doing. 

Gareth

[astontr6]

12 minutes ago, Mk2 Chopper said:

First thing to check is your vacuum, at idle a CR should be around 12 Hg, if it's lower than this, might mean you have a leak somewhere, such as the balance pipes (4 on a CR) servo/pipe, MU pipe, throttle bodies to head, throttle butterfly's need to be closed for idle and balanced for correct fuel/air when throttle is open. 

It can also mean wear in the engine. But if everything else is fine, then the MU can be tweaked all over the fuel curve if you know what your doing. 

Gareth

Do you know how old the M/U is? What color are the spark plugs? As above check for leaks and balance of butterfly's, check Fuel line pressure and compression check?

Bruce.

[pcw64]

Thanks for the reply and i think the MU is about 12 years old,i have checked for leaks and found none and i did a compression test and they were all between 190 & 200 psi hot and the plugs are brownish at the tip and black round the outside of the plug.

[Mike C]

You have probably checked this, but is the fuel enrichment lever releasing fully?

My engine must have 10"Hg @ 900 rpm vacuum measured with a vacuum gauge on the brake booster hose to run properly.

[Tim D.]

It's possible the mixture is only rich at idle if your plugs are not black. Only way to really tell is to set up an air fuel ratio meter and go for a drive. 

Tim

[Peter Cobbold]

Do the tongue test:

 

[pcw64]

Im sending the MU to Neil Ferguson to be overhauled and then put it back on the rolling road to see if thing have improved and thanks for all the reply's.Paul