16-05-2023, 09:04 AM
I have an intermittent running problem with my A7 Ulster Rep which has happened twice now, ruining the day and possibly stranding me.
The car runs a (virtually new) 1.25” HS2 SU with blue spring and No6 needle, the original cam-driven fuel pump (properly rebuild by an expert [not me] with an ethanol-proof diaphragm) and an original (virtually new too) BOSCH 009 with the Accuspark electronic kit fitted (with the white insulation paste underneath it) and the blue insulator to manage the advance. I should say that the carb sits quite high and points towards the front of the car (to keep it away from the heat of the Ulster-type exhaust manifold) – I measured it and the throttle spindle is approx 6” above the level of the top of the cylinder head for clearance etc and the fuel tank is in the scuttle.
At the Centenary last year it ran well on the couple of hundred miles journey to get there, but on the second (very hot) day on a challenging run it started dying away would ‘pull’ only with the choke pulled out. Thinking it was a fuelling issue, I adjusted/checked the mixture setting (not sure that much change was actually made) and replaced the oil in the damper (it seemed too ‘difficult’ to push up) the car ran reasonably well again – but I’m not sure that anything I did actually contributed to that.
The car has ran well since. However, I was doing a PCT Trial last Saturday and the problem reappeared and I had to use the choke to get up any hill on the trial and also to get up any hill on the way home.
I have since stripped and rebuilt the carb – all looks fine, stripped and rebuilt the pump and all looks fine. I haven’t had time to run the car yet but I bet that it will be fine.
On both days when there were problems, I was going up/down steep hills at relatively lower revs, the weather was fairly hot at the Centenary but a lot cooler last Saturday.
It is either a fuelling problem or ignition (which I assume is either ok or not, full stop – I have a spare Accuspark unit available but am not convinced it is the issue).
I’m now of the mind to swop to an SU fuel pump. This Is based on two observations (1) my last A7 with SU Carb and pump, BOSCH etc always pulled like a train and (2) this carb is much physically higher in the engine bay than the A7 pump was ever designed to supply and so on lower revs it struggles to keep the float bowl full resulting in hesitation and needing the jet lowered to get sufficient fuel to pull.
Grateful for your thoughts and suggestions – am I right in thinking that an SU Pump is the solution?
Thanks.
Hugh
The car runs a (virtually new) 1.25” HS2 SU with blue spring and No6 needle, the original cam-driven fuel pump (properly rebuild by an expert [not me] with an ethanol-proof diaphragm) and an original (virtually new too) BOSCH 009 with the Accuspark electronic kit fitted (with the white insulation paste underneath it) and the blue insulator to manage the advance. I should say that the carb sits quite high and points towards the front of the car (to keep it away from the heat of the Ulster-type exhaust manifold) – I measured it and the throttle spindle is approx 6” above the level of the top of the cylinder head for clearance etc and the fuel tank is in the scuttle.
At the Centenary last year it ran well on the couple of hundred miles journey to get there, but on the second (very hot) day on a challenging run it started dying away would ‘pull’ only with the choke pulled out. Thinking it was a fuelling issue, I adjusted/checked the mixture setting (not sure that much change was actually made) and replaced the oil in the damper (it seemed too ‘difficult’ to push up) the car ran reasonably well again – but I’m not sure that anything I did actually contributed to that.
The car has ran well since. However, I was doing a PCT Trial last Saturday and the problem reappeared and I had to use the choke to get up any hill on the trial and also to get up any hill on the way home.
I have since stripped and rebuilt the carb – all looks fine, stripped and rebuilt the pump and all looks fine. I haven’t had time to run the car yet but I bet that it will be fine.
On both days when there were problems, I was going up/down steep hills at relatively lower revs, the weather was fairly hot at the Centenary but a lot cooler last Saturday.
It is either a fuelling problem or ignition (which I assume is either ok or not, full stop – I have a spare Accuspark unit available but am not convinced it is the issue).
I’m now of the mind to swop to an SU fuel pump. This Is based on two observations (1) my last A7 with SU Carb and pump, BOSCH etc always pulled like a train and (2) this carb is much physically higher in the engine bay than the A7 pump was ever designed to supply and so on lower revs it struggles to keep the float bowl full resulting in hesitation and needing the jet lowered to get sufficient fuel to pull.
Grateful for your thoughts and suggestions – am I right in thinking that an SU Pump is the solution?
Thanks.
Hugh