10-04-2019, 07:56 PM
Here's a problem for all the cognoscenti on the forum.
For the sake of completeness, my car is a 1933 RP box saloon with a standard Zenith 26VA carburettor. Ever since I have had the car, the tickover has been uncomfortably quick. Although I haven't checked it with a tachometer, it sounds almost as quick as my Mk2 Polo and that idles at around 850 to 900 rpm.
The tickover is perfectly even and the mixture screw seems to work O.K. I have checked for air leaks at the manifold and at the carb flange and all appears well. Indeed, when I had the engine out to replace the rear main bearing, I took the opportunity of replacing some of the manifold studs and making sure that the manifold was flat and that the carb flange was flat too. The carb and manifold were put back with new gaskets.
I have had the carb to bits and cleaned it out thoroughly, The throttle spindle is a reasonably good fit in the carb body. I've seen much worse! I have replace the throttle butterfly as the original had been butchered in the past and I could see daylight round it in places. Indeed, when I saw that, I thought that I had found the problem.
The car itself goes very well, especially now that it has a refurbished distributor. It climbs the hills around Bala with aplomb and is capable of something just over 50 flat out, given enough road. The fuel consumption is not good, however. I am getting anything between 30 and 36 mpg, usually 32 to 33. Checking the mixture with a 'Colourtune' shows that the combustion flame is yellow rather than the blue it should be throughout the range. I have got it down from an orange to a yellow by fitting the thickest needle valve washer that came with my carb overhaul kit.
One thing I have noticed is that my carb does not have a jet at the top of the compensating well. The hand book shows one, but my carb looks as if one was never fitted. There is no thread in the top of the compensating well to take one and looks as if there never was.
The throttle stop screw is wound down so that the throttle is completely closed and yet the tickover remains stubbornly high.
I'm sorry that this post is a bit prolix, but I wanted to give everyone as much information as possible.
Anyone got any ideas?
For the sake of completeness, my car is a 1933 RP box saloon with a standard Zenith 26VA carburettor. Ever since I have had the car, the tickover has been uncomfortably quick. Although I haven't checked it with a tachometer, it sounds almost as quick as my Mk2 Polo and that idles at around 850 to 900 rpm.
The tickover is perfectly even and the mixture screw seems to work O.K. I have checked for air leaks at the manifold and at the carb flange and all appears well. Indeed, when I had the engine out to replace the rear main bearing, I took the opportunity of replacing some of the manifold studs and making sure that the manifold was flat and that the carb flange was flat too. The carb and manifold were put back with new gaskets.
I have had the carb to bits and cleaned it out thoroughly, The throttle spindle is a reasonably good fit in the carb body. I've seen much worse! I have replace the throttle butterfly as the original had been butchered in the past and I could see daylight round it in places. Indeed, when I saw that, I thought that I had found the problem.
The car itself goes very well, especially now that it has a refurbished distributor. It climbs the hills around Bala with aplomb and is capable of something just over 50 flat out, given enough road. The fuel consumption is not good, however. I am getting anything between 30 and 36 mpg, usually 32 to 33. Checking the mixture with a 'Colourtune' shows that the combustion flame is yellow rather than the blue it should be throughout the range. I have got it down from an orange to a yellow by fitting the thickest needle valve washer that came with my carb overhaul kit.
One thing I have noticed is that my carb does not have a jet at the top of the compensating well. The hand book shows one, but my carb looks as if one was never fitted. There is no thread in the top of the compensating well to take one and looks as if there never was.
The throttle stop screw is wound down so that the throttle is completely closed and yet the tickover remains stubbornly high.
I'm sorry that this post is a bit prolix, but I wanted to give everyone as much information as possible.
Anyone got any ideas?
