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MG Midget and Sprite Technical - Plugs and gap question

I need some advice on choosing and gapping new sparkplugs
'72 midget
.20 overbore
.10 on the crankshaft
21253 Hepolite pistons
Kent 276 cam
Crane X 700 Ignition

The car is a little sluggish off the line if I don't have the RPM's high enough, and it doen't idle very slow. I'm thinking I could benefit from new plugs even though mine 'look' ok.
I'm currently usseing Autolite #63 gapped at .30

Thanks, Phil
Phil Burke

Cam timing? Once you get to 270+ degrees, then mis-timed cam can kill low-speed running / torque...

A
Anthony Cutler

NGK BP6ES at .025 - .030 (with electronic ignition).

If you start running high C/R and a wilder cam, consider BP7ES.

Are you sure your distributor advance curve is suited to the engine spec....?

Mark.
M T Boldry

So....I have the correct plugs and gap.
I suspect the distributor curve may have gone off a little, or the advance may not be working to 100%
The cam timing went well at rebuild and I beleive it's spot on.
How would I check/ ajust the advance curve?
Phil Burke

Hi Phil

What CR are you running?

Check the dynamic timing at idle with no vac advance then check the advance as you increase the rpm, I would reckon you should see 14ish at idle going up to 30ish at 3000 plus rpm

Peter
P Burgess

Phil
No your curve did not go off.
Your curve is made for the stock midget engine.
You changed the cam, bore and CR so you engine needs an other curve.

My engine for example seems to work verry good with an 850 mini 25D ignition.
Fit a midget 45D one and all the lowdown torque is gone.

Check the dynamic timing as mentioned by Peter.
And to perfect lots of trial and error up and down the road or a trip to the Roling Road

Peter
How is the 7 port comming along?
Onno Könemann

Hi Onno

We are still finishing the head off to power test it, all flow bench work finished. Customer has been on rolling road with his engine with 'Standard' head which turns out to be a modified 1.401" inlet valve one! Still we will see difference between modded 5 port head power and with 7 port head so maybe a better before and after test?

Peter
P Burgess

I don't know too much about the cam except that it was a reground Kent 276. No idea about the lift/duration
I think the deck was -.20, but it could well be more.

I don't know the compression, so I'm not sure where to start with dist. curves.

From the above info can someone estimate the CR?

Thanks, Phil
Phil Burke

Phil,

No, you haven't given enough info for someone to guess a CR. At least not that I see.

However, if you just run a compression test on it someone could at least say if it is high or low, and might take a guess at CR.

Do the compression test with all plugs out and the throttle wide open. Some people believe in doing a specific number of compression strokes for the test and some believe in cranking it until it stops climbing. I kind of split the difference and shoot for when it stops climbing, but try to keep the number of strokes about the same on each cylinder.

Make sure the battery is good and hot when you start. If the cranking is slow, or gets slower durning the test, it will have a significant effect the results.

Charley
C R Huff

This thread was discussed between 15/11/2010 and 24/11/2010

MG Midget and Sprite Technical index

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