[Healeys] BN1 misfire

Peter Linn greylinn at ozemail.com.au
Fri Jun 25 02:33:49 MDT 2010

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?


Peter Linn
Brisbane Oz
BN1 Ward Spl coupe
BN1 Holden V6

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