[Healeys] BN1 misfire

Alan Seigrist healey.nut at gmail.com
Fri Jun 25 17:04:50 MDT 2010

Peter -

Usually with supercharging you want to bring the compression down to
around 7:1 or possibly even less.  This explains your low CR readings.

It shouldn't cause misfire but the car would have no power.

Have you tried using the lowest octane gas you can find?

Motor needs to come out and be gone through...


On 6/25/10, Peter Linn <greylinn at ozemail.com.au> wrote:
> G'day list
> Today I spent 6 hours trying to get a friend's BN1 to run properly. He's had
> persistent problems with the car misfiring under load. He hasn't had the car
> long and doesn't know a great deal of its history, except that it has
> apparently been used as a race car and was at one time supercharged. I went
> through everything today - valve clearances, compression test, points, dwell
> angle, carbs etc. We found that, apparently, it has a non-standard cam as
> the
> lift for the exhaust valves seems considerably higher than that for the
> inlets
> (looking at the compression of the valve springs, the exhausts appear to
> compress around 1/2" more on opening than the inlets) We set the exhausts at
> 18 thou, the inlets at 12. This appeared to improve things with the car
> stationary, but under load it still misfired and backfired. We changed out
> the
> condenser, the distributor cap and leads. The coil is new. Points seemed OK
> &
> dwell angle 60 deg. I was unable to check the valve timing as there's no
> mark
> on the pulley and we didn't have time to establish TDC. Carb tune is OK and
> the plugs looked right. The car has 1 3/4" HS6 SUs. The vacuum advance is
> working. The only thing that didn't look right was the compressions, which
> were between 105 and 125 psi (another car I did this week had 165 - 175). We
> wondered if the cr had been reduced when the car was blown. The car doesn't
> blow oil smoke nor does there apppear to be excessive crankcase pressure.
> Bottom line - after all this attention the car would rev cleanly when
> stationary, but on the road under load would misfire and backfire to the
> extent that it was virtually undriveable.
> Any suggestions listers?
> Cheers
> Peter Linn
> Brisbane Oz
> BN1 Ward Spl coupe
> BN1 Holden V6
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