This carby o/haul is one of the trickiest re-kits I have ever done and the solution was so simple.
Somewhere around about 1980, in the infancy of MBS Tuning, a removalist firm booked their international truck in for a carb re-kit. It was an old Holley, very similar to the 350 with side fuel inlet. I didn't have a carb kit specifically for this model but I had a hell of a lot of loose Holley parts that I could make a kit up from. The job was booked in after lunch with the assurance the driver would be on his way by 6 pm for his trip to Brisbane. Plenty of time for a simple job like this. Unlike a normal 350 2 barrel carb, the fuel bowl did not use 4 bolts to attach the metering block and fuel bowl to the main body of the carb. It was what I can only describe as old style curtain wire, spring wound as depicted below, with a stud screwed in on one end and open on the other to accept a self tapping screw.
The spring wire is screwed into the main body threads where the normal bolts would usually go. The metering block and fuel bowl are fitted and held in place by four self tapping screws that screw into the spring wire. In this set-up the fuel bowl cannot be over tightened as the spring just twists and doesn't allow any further torqueing. I re-kitted and refitted the carb back onto the engine. I got it started but realized straight away that there was a problem. It would not idle, in fact I had to open the throttle up considerably just to keep it running. It was starving for fuel, no doubt about it. I rechecked the fuel level in the fuel bowl and it was just at the sight plug, so there was plenty of fuel available in the bowl. I stuffed around for the next fifteen minutes, trying to adjust the mixtures screws and moving the timing around to see if it improved. No change. I connected the oscilloscope to eliminate any electrical possibilities and with the exhaust gas analyser confirmed that it was fuel. The quality of the fuel did pop into my head but if that was the case then the truck would not have made it to my workshop. In fact his complaint was excessive fuel consumption and confirmed by the presence of black smoke billowing from the exhaust every time the engine was revved up. Now after the re-kit, it has gone the extreme opposite.
It was now 8pm and I have removed the fuel and metering block several times to inspect for blockages. I just could not see any problems. I was forced then to take the carby back off and dismantle the main body off the throttle plate to check if that gasket was the correct size and sealing correctly. By the compression of the gasket, I could see that it was sealing and I compared it to the original gasket and it matched perfectly. Time was ticking over and with the carb back together and refitted, the engine was still starving for fuel. "Stuff it", I said, "let's fit a new Holley on and see if it runs". I did that and it ran perfectly. The driver told me to leave the new carb on so he could get going, but the owner did not approve that expenditure. Well, it was something I have done, is the conclusion, but what!
As 11pm crept up, I had one more attempt and took the fuel bowl and metering block back off. I had to think what was different, what did I do to make this happen. One of the things I noticed was that the original metering block gasket was made of cork and I replaced it with the more rigid late model gasket. So this time I refitted a cork gasket and hoped this was the problem. I started the engine and immediately noticed a vast improvement but not totally acceptable. I knew now what the problem was. I looked through my OEM Holley book of spares and found this particular model. Holley use a cork gasket on this particular model, not the later OEM paper gaskets as fitted to the later holly's. I put 2 + 2 together and realized that these stupid little self tapping screws in combination with the spring wire were not capable of applying enough pressure to the metering block gasket to seal it against the main body. Obviously after many years of service and who knows how many times the carb has been pulled apart, must have weakened the spring wire and was no longer able to apply the correct pressure on the gasket. The only reasonable solution was to convert to bolts.
I removed the fuel bowl and metering block and unscrewed the spring wire. I re-tapped the threads to accept the standard bolts and refitted it all back together now using the later OEM paper gasket. The engine started and idled. I was now able to make final adjustments and the job was complete at 2am. That was an experience and a half and after all that time I only charged him for a normal re-kit. He never paid the bill, ungrateful so and so. From then on, learning from my experience, every Holley that came in using the spring wire was converted to bolts. I started to ponder just how many of these carbs got thrown out because of the same problem and how many mechanics actually figured it out.
The spring wire might have been a good idea when the carb was new but after time the wire obviously stretches and looses it twist tension capability and therefore the gasket can't be compressed sufficiently to seal.