31-05-2021, 08:44 PM
(This post was last modified: 31-05-2021, 08:48 PM by John Cornforth.)
Hi flywheel1935
To answer some of the points raised.
You say the engine was tested by the rebuilder. Was this with the same Zenith 26VA carb you are using now, or another ?
Fuel spillage on priming suggests a too-high fuel level in the float chamber for some reason. If so, this must be sorted before anything else. A leaking needle valve or punctured float are two favourites, but other things might be the cause.
Modern A7 replacement pump diaphragms are sold as Ethanol resistant. I use 98 octane as some brands are reputed to presently have little or no ethanol, though the legal limit is 5% so this situation could always change. I can't see it having any marked effect on starting/running difficulties. The published density of modern fuel (0.72 to 0.78) doesn't seem to be significantly different to that used in the 1930's, so any change in float chamber level will be pretty small.
New 26VA jets are listed by Austin Reproduction Parts (Willie McKenzie) and possibly by others. Burlen in Salisbury also handle Zenith spares. However, I doubt if wrong sized jets alone would account for the symptoms you have.
I don't think the higher CR would be enough to weaken or prevent a spark even with standard ignition. Bear in mind that the throttle is near closed when starting, so you won't be getting as high as the 110 PSI you quoted until the engine is under load. I suggest you don't go wider than the standard plug gap of 20 thou (0.5 mm) unless there is a good reason.
One last thought. Electronic systems and unsuppressed ignition leads make unhappy bedfellows, so I recommend resistive plug caps if you have electronic ignition.
To answer some of the points raised.
You say the engine was tested by the rebuilder. Was this with the same Zenith 26VA carb you are using now, or another ?
Fuel spillage on priming suggests a too-high fuel level in the float chamber for some reason. If so, this must be sorted before anything else. A leaking needle valve or punctured float are two favourites, but other things might be the cause.
Modern A7 replacement pump diaphragms are sold as Ethanol resistant. I use 98 octane as some brands are reputed to presently have little or no ethanol, though the legal limit is 5% so this situation could always change. I can't see it having any marked effect on starting/running difficulties. The published density of modern fuel (0.72 to 0.78) doesn't seem to be significantly different to that used in the 1930's, so any change in float chamber level will be pretty small.
New 26VA jets are listed by Austin Reproduction Parts (Willie McKenzie) and possibly by others. Burlen in Salisbury also handle Zenith spares. However, I doubt if wrong sized jets alone would account for the symptoms you have.
I don't think the higher CR would be enough to weaken or prevent a spark even with standard ignition. Bear in mind that the throttle is near closed when starting, so you won't be getting as high as the 110 PSI you quoted until the engine is under load. I suggest you don't go wider than the standard plug gap of 20 thou (0.5 mm) unless there is a good reason.
One last thought. Electronic systems and unsuppressed ignition leads make unhappy bedfellows, so I recommend resistive plug caps if you have electronic ignition.