Lifting pin test

You're not alone Tommy, I seem to have trouble getting it right.

At first I'll think it's running rich given the nature of the plugs, so I lean it off a bit, then it starts to struggle going up hill etc, so must be too lean etc.

Currently she doesn't seem to want to start nicely, sounds too rich (granted the choke is on, but has that slow baaaaah baaaah baaaah noise), but once she's warm she seems ok.

She also doesn't like hills it seems, some I have to change down to 2nd otherwise it's foot to the floor and she'll barely make it.

-Andrew

What you need to remember is that the constitution of the fuel has changed quite significantly since the engine, ignition timing and air fuel ratios set by the carb needle profile were established.

While a certain mixture or ignition timing may be correct at idle now, it may not be correct at say 3,000 rpm where it appears that the standard needles run too weak. The fuel also requires a higher energy spark to ignite it correctly and the standard ignition coil may be marginal unless the whole ignition system is perfect.

I am sure this accounts for most of your problems - although Andrew's engine's lack of power uphill looks like something more basic that needs to be sorted unless he is expecting too much?

The only way to really tune these engines to run at their best on modern fuel is to use a programmable ignition and to profile the needle using a wide band air fuel monitor and a rolling road! This is expensive and unless you are really serious a non starter (sorry for the pun).

The option is a compromise. Just two things to remember. (1) Don't let the engine run weak at higher speeds - eg 3000 rpm or it will overheat and damage rings, valves etc. (2) Don't let the engine run over advanced leading to knock and damage. If you meet both these criteria then the idle may not be so smooth and the lifting pin test no longer work. You may need to increase the idle speed - and then run the risk of running on when you switch off (there are several anti run on devices available for MGBs that can be fitted).

Hope this gets you thinking even if it's not too helpful?

Regards

David

Thanks all! Seems I'm not alone on this then, and Dave's description makes sense as always!

I wouldn't say I have a big problem, but it seems the slightest adjustment to mixture makes great difference to the engines behaviour. I'm pretty sure the occasional hesitation at speed I've had is down to a too weak mixture at speed. BTW the carb is new and the jet centred. I'm tempted to try the rich needle stated for the 1800 to see if it improves things.

I would agree it seems you have a more fundamental issue, Andrew. The 1800 should really have no problem going up a hill in 4th gear, even in Norwegian mountains:-)

Regards, Tommy

Hi Tommy

If you look at a graph of engine power v air fuel mixture (plenty of examples if you just Google it) you will see that as the mixture weakens away from the stoichometric value of 14.7:1 the power fall off very suddenly - indicated by a steep line on the graph. On the other hand as you richen the mixture the torque / bhp increases gradually to a max and then falls away very gently.

If you have a critical setting and there are no air leaks etc then this suggests to me that you are operating the engine close to the too weak zone.

This may mean having to run a little too rich at idle and you will then see carbon deposits on the plugs, but the biscuit colour immediately after a run. The Colourtune may help you as could the vacuum gauge.

Regards

David

Here is a graph I picked at random with an easy to read explanation to illustrate the point better.

www.mummbrothers.com/SRF_Stuff/Secrets/Driveline/Air_Fuel.htm

Remember that if you do have an engine that seems to is difficult to tune and is very critical to small changes in the mixture you need to check very carefully for air leaks if everything else seems about right . Ie if you check the timing, valve clearances and start the carb setting with the adjusting nut fully tightened then undone 2 turns (Chris can advise on the HIF44) this would suggest to me that an air leak was a high probability.

Regards

David

Your lowish compression on the one cylinder certainly won't help tuning. Did you ever establish for certain whether it was a head or piston ring issue? I have had engines in the past with worse readings than yours that have been OK, but going back to where we started that was with leaded fuel.

Air leaks, refer to the Tommy thread but placed to check include

Carb throttle spindle (seal both ends with grease as a temporary measure to see if they are having an effect)

All pipes leading off the carb and manifold including the brake servo - does it hold vacuum for at least half an hour after turning the engine off - press the brake pedal to listen for the swish

Engine manifold gasket, are the nuts tight etc

Closed crankcase ventilation system , either PCV - check diaphragm or direct pipe to carb from tappet cover

Oil filler cap filter breather

I'm sure there are some I have missed!

Good luck

David

Maybe the Colourtune is flagging up a real issue? Were there any specs with the sports coil re the spark gap? If the gap is too large for the coil it will cause the coil to break down as the larger the gap the higher the voltage generated. The size of the spark gap sets the voltage. In fact spark gaps are routinely used to clamp voltages - they were used in many CRT TVs for example to avoid damage to the tube etc. Also too large a gap can damage some electronic ignition systems as there is a higher back EMF generated - always read the literature!

Increasing the gap to 0.75mm (30 thou for us old uns) shouldn't cause any problems though as plugs set at 25 thou can wear to this gap or more in service. Just make sure plug leads and the rotor arm and distributor cap are in good condition though.

regards

David