Things are moving along nicely with Beryl. I had noticed that the carbs would slip out of tune as the weather changed. The exhaust was also smelling pretty rich, if I leaned the mixture at idle she would run very poorly.
I tested the spindle seals on the carbs by spraying carb cleaner by the bushes. Sure enough, the engine would stumble when I did suggesting the bushes and spindles are worn. I have HIF6s fitted and I've never been convinced of the rubber seals on the spindles they used. There's nothing to keep them in place and it does nothing to stop wear on the spindles allowing for mis-alignment.
Id found a blog by Tom Bryant, a Volvo enthusiast that had modified his HIF6s to use machined delrin bushes and thought it showed promise. I decided to try something similar.
I pulled the carbs, and dismantled them. Sure enough the spindles showed a lot of wear.
I had turned up some delrin bushes with undersized bores on the lathe, here's the dimensions:
I drifted out the original worn steel bushes, here they are next to the new ones:
As you can see the new bushes are almost twice the length, more bearing surface plus a longer seal area. I drifted the new bushes into the body of the carbs. Once in I filed the outer surface of the delrin bushes flush with the boss on the carb's aluminium body.
I had sized the internal holes of the bushes to be a nice fit on the shank of the 5/16th reamer I was going to use for the final line boring operation. With pressing the bushings into the carb body that had closed up very slightly. So I used the 9/32" reamer in a cordless drill to make sure they were correct.
Once that was done I set up an angle plate on the mill. With a jacob's chuck in the spindle I was able to assemble the reamer into the body of the carb with the cutting flutes at the bottom and the shank sticking out the top. I tightened the chuck onto the shank of the reamer then clamped the carb to the angle plate. Once that was done I nipped the clamp down on the angle plate to the bed of the mill. This meant the carb was exactly square to the spindle axis and perfectly aligned.
I ran the mill and pulled the reamer up through the bushes. This made a perfect, smooth bore through the delrin. nce off the mill I used a sharp craft knife to trim the delrin to match the inside surface of the carb throat. Another advantage of this method is the perfect seal at the spindle end to the disc. Next step was to re-assemble the spindles back into the bodies.
So, that was Saturday. I managed to find time on Sunday to refit and tune the carbs. What a difference! Much, much easier to tune the mixture on both carbs. No smell from the exhaust, even more torque at the bottom rev range, smoother and more powerful delivery through the rev range too! Another advantage is that the throttle feels lighter due to the lubricating qualities of Delrin plastic. I would definitely recommend this if you have access to the equipment.