A few days after returning the truck to the unit after the New Years day run we headed over to take a look at what it could be. Points, rotor arm and cap were checked. Spark leads tightened up and one lead replaced with part of the core exposed so a timing tight could be attached. Engine seemed ok so what could it be? We took it for a short run and found when it was cruising along it was fine, but when you pressed the accelerator thus demanding more fuel the engine started to die. Fuel starvation must be the cause, but why?
We decided to blow compressed air back through the fuel line to make sure there was no blockage. The Kaiser is known to have a filter ‘sock’ over the end of the fuel pipe in the fuel tank, and that these deteriorate and can block the pipe. Air duly pumped down the line and a gush of bubbled heard in the tank. So, line clear. Next came an inspection of the complete fuel line showing particular attention to any flexible hoses. The new length fitted in the summer was clear. The next flexi pipe goes from the chassis to the engine block. Once removed it didn’t seem quite right so blocking one end a sucking on the other the internal pipe partially collapsed. Replacement pipe was fitted with the correct connectors and reconnected to the system. Another test drive showed that the engine now did not lose power when the accelerator was pressed hard, so the collapsing pipe had been the problem, but there still was the issue of the two flat spots.
Back to the unit it was decide to check the tuning again, but this time with a vacuum gauge. A suitable position was found to attached the gauge, the distributor was loosed and the engine started. The distributor is then turned in either direction until the maximum vacuum is achieved, this then indicates that the timing is bang on. The flat spots were still there, which now pointed to a carburettor problem. The hunt was on to find the correct rebuild kit, especially one that had ethanol resistant diaphragm, as we now knew that the new grade of fuel attacks rubber and also aluminium which would account for the flat spots when pressing the accelerator pedal. I found one in the States and got it shipped over.
Now stripping carburettors is not one of my specialities but having watched a very good video on the internet I felt I was up to the job. The carb fitted to the Kaiser is a Holley 1920, and in comparison, to some carburettors is relatively simple. I removed the carb and proceeded to strip it down. Once apart it was cleaned and all tubes and pipes blown through with carb cleaner and readied for re-assembly. In went the locking ball bearing in the shaft of the new pump diaphragm, which was then positioned into the carb and the pump casing offered up and bolted into position. Next the economiser diaphragm was fitted and bolted in. The new cut off valve was fitted and then the float located. The fuel bowl cover was then bolted back on.
The carb was remounted to the engine and fuel line, throttle cable etc reconnected. The engine turned over without firing as it was priming the system with fuel. After a few goes the engine fired up and all seemed fine. I took it for a test run and it was good, well sort of. The flat spots had gone and the engine pulled like a train, but the engine still stalled unless a small amount of choke was used. So back to the drawing board. The carb was removed again and inspected internally and nothing obvious was seen. I went back to the manuals and watched various videos posted by Mike’s Carburettors. From this I narrowed the fault down to the idle circuit, but there is not a lot to it so what could cause it?
I stripped the carb yet again and now made a direct comparison between the old pump diaphragm and the new one. There staring me in the face was an obvious difference. There were three identical holes in the old diaphragm gasket, but in the new one there were two the same and the third was smaller (arrowed). When this was lined up the small hole was in fact to allow fuel to flow to the idle circuit, but the hole wasn’t lined up perfectly. Carefully I enlarged the hole and offered it up to the body of the carb. Carefully I tightened everything up and put the carb back together and mounted back on to the engine. System primed and the engine fired up and ticked over.
Geed up with this improvement I decided to take it for a test drive. The truck pulled well with no flat spots or loss of power when demanding more. With extra confidence I decided to drive further afield and head for a petrol station to top the tank up. As I was still not 100% convinced, I paid at the pump and refuelled with the engine ticking over. I set off again and the engine started to miss and run rather lumpy. I limped it back to the unit and parked it up. So, was this situation as a result of filling up with fuel and disturbing the sediment in the tank? Well, it shouldn’t be as I’d cleaned the tank out, so it pointed to the carb. Off it came again and stripped down, as you will have gathered by now, I could do this with my eyes closed. Apart I checked the internal and once again I cleaned all the galleries with carb cleaner. I inspected the diaphragm gasket and saw that the were some threads showing from it. I decided to clean up the hole that fed the idle circuit using a leather punch and enlarge yet further.
The new extremely clean hole meant that the when the two halves of the pump casing were married up there would be no obstruction to the flow of fuel and not debris from the gasket could block the idle circuit. After all this fiddling with the carburettor I checked all was tight and the measurement for the float level was set correctly. Confident this was correct I also made a n new gasket for the fuel bowl cover as the one fitted was now definitely dogged eared even though it was relatively new.
Fingers crossed, after refitting the carb and connecting all the cables the moment of truth. After priming the system with fuel by turning the engine over and a little choke applied it fired up, and ticked over very sweetly. Letting it run for a little while the choke was pushed in and the engine continued to run smoothly. Once again, I hit the road and all seemed well so I ventured a little further than my usual three-mile test run. When I returned Bradley jumped in to the cab and he too took it for a drive. The smile on his face on his return spoke volumes. Hopefully the problem of the carburettor has been sorted, but just in case I have sourced another rebuild kit, this time with three identically sixed holes in the diaphragm gasket.