Normal running for a 4 cylinder 1500 SC engine ???

[alan.gilbert_6384]

Hi All,

Just after a base line check here about what is and what is not normal for the 1500 sc engine.  So the carbs have been balanced, set to the correct mixture using colour tune and checking plugs etc after a good run.  I have checked all plugs they are new and good as are the HT leads etc.  I have every changed the dissy cap and rotor arm to an original english made one (no difference).  Timing set to bang on 10 BTC.  When accelerating it is good and no problems, however when cruising ie throttle pedal set to maintain constant speed, it seems not be smooth, the same can be seen in the video attached.  So is this normal ?? Can I do anything to improve it ?  I have checked compression hot and cold all good (118 all cylinders cold and 120 hot).  It's the same with points or electronic ignition (currently running electronic).

Any Ideas ????? thanks very much.

[Pete Lewis]

sorry cant open the video clip

things like a failed dizzy vac unit can over advance on light throttle cruising and give you a pulsed /hesitant  power input 

try with it disconnected 

Pete

 

[alan.gilbert_6384]

Hi Pete, 

Thanks have tried this but it made no difference   plugged off both ends as well.  It runs well in acceleration, the mixtures are set correctly, carbs balanced, all ignition checked out.  I have a spare dissy that I might try if the weather permits.  Just thinking of the timing chain, what would the effect of that be, she has done 88K I think its the original chain ????

[johny]

Cant see the chain causing this but you could try making the mixture a little richer as a trial...

[Pete Lewis]

well a worn chain only makes more noise  and makes the valve timing a little late  it will not give you 3000 rpm from idle 

do the carb throttle plates have the poppet valves in place  if so solder them up

Pete

[NonMember]

I'm not really clear on what that video is supposed to be showing us. It idles for a bit, then you open the throttle to rev up, hold at 3000, then return to idle. So what's the problem?

There does seem to be a bit of vibration on the steering wheel, which may be down to something slightly out of balance but isn't entirely unusual.

The rev counter needle doesn't exactly sit rock steady but what do you expect? This is a 1970s version of a 1950s engine. It has no idle speed control and no damping of the dial.

What exactly is it that you think is wrong?

[1969Mk3Spitfire]

The only comment I would add to the above post is “nice wooden dash, by the way” 😀

I had a similar, but the not the same, issue with my car and also changed many of the ignition components, reset carbs etc. I haven’t as yet fully eliminated the problem but it’s made me appreciate the simplicity and recognise that car technology has moved a very long way in 50 years. 

[johny]

If the problem persists a compression check and valve clearance adjustment is another step I would take....

[Pete Lewis]

sorry wasnt thinking  straight    its the pills you know !!

a shot of the engine movement may help   

if you retard it does it smooth out more ??

the 1500 is not a silky smooth beast 

over advanced will give kicks at light throttle driving 

ignore the marks  use the ears  

 

just add have you got rid of the waxstats by addin2 x 1p in place of the wax capsule???? in the SU jet holder 

Pete

 

 

[alan.gilbert_6384]

Cheers Pete, will have a play with the timing. It’s currently at 10 BTDC, will try both ways to see what effect it will have.

The  jets are non wax stats. And no poppet valves installed.

@Jonny

will recheck compression this was 118 cold and 120 hot on all 4 cylinders, will also check the valve clearances, cheers.

[johny]

With the compression check you could also try a bit of oil through each sparkplug hole and redo it to see if that makes much difference to the reading (discounts bore wear...). 

[dougbgt6]

4 hours ago, alan.gilbert_6384 said:

will have a play with the timing. It’s currently at 10 BTDC, will try both ways to see what effect it will have.

I would think that's too much, my GT6 is supposed to be 13 BTDC, but that was for 5 star, which you can't get anymore. I would guess mine is way below 10. I don't know because like Pete says I do it by ear. Turn the dizzy until the revs stop increasing then back a gnats. Alternatively, I have a vacuum gauge, turn the dizzy until you reach maximum vacuum, then back one bar. I have done them both at the same time and very satisfyingly they correspond exactly. 

Doug

[Pete Lewis]

certainly over advance and tight valve clearances  and weak mixtures  will give unsmooth light   throttle running 

well  worth a revisit 

Pete