While I am working on getting my rear wheel and axle set up done I'm also working on my carbs. I bought 2 racks of Carbs for I think it was $75. A 77 set of PD41A's and a 78 set of PD42B's. I was looking for those carbs in particular because they have the accelerator pump. Now that I've gotten into it I may have been better off getting the early carbs. There's hardly any OEM parts available for them and there is a very limited offering of aftermarket parts. I intended to buy K&L supply rebuild parts but they offer nothing for them. I even called them and had them check. The only thing they had was the accelerator pump parts.
I did some reading and ended up with Keyster parts from Z1 Enterprises. I also ended up buying new Carb Isolator boots from vintage CB750. From the research I've done they are the only boots worth buying. OEM boots are not available.
Since they are both 1yr carbs only, and there is a lack of parts available and the volumes are low. All of the parts for those carbs are more expensive than the others. Most parts are interchangeable between the 77's and 78's.
The 77 PD41A set of carbs appears to have never been removed from the rack, so I planned to build them. They operated smoothly by hand.
The 78 PD42B set of Carbs had been removed from the rack at some point and wasn't re assembled completely. The Slide needles on these would stick in the Needle jet making it hard to open the slides.
Since I wanted to thoroughly clean them and replace the slide needles and jets ect. I decided to us the 78 PD42B carbs. At the time I thought I had to separate the carb rack to change the slide needles. Since the 78 Rack was already goofed up I figured I start with them and would have the other better set if I had to start over. The only risk was money, the carb rack themselves were a basketcase and I could do no harm to them.
I did research and used pine sol to dip them (2 day soak). Afterwards I read that you shouldn't do that. I don't regret it yet though. It cleaned them up great, all of the passages are clean. The surface finish was dulled a bit and I could tell the finish was affected on some of the plated parts also. When I removed them from the soak I thoroughly rinsed them, scrubbing with a toothbrush before the pine sol solution could dry on them. Then while still wet I sprayed all of the passages with Gumout carb cleaner making sure that I had good spray streams out of all of the passages. I used a torch tip cleaner and a strand of copper wire to clean everything I could including all of the holes in the jets.
When I removed the slow jets I bent a couple slightly, I figured I'd pull the ones from the set of 77 carbs. There were two issues with using them.
1. they jets were slightly different they had 6 holes vs 8 holes on the 78 carbs in the emulsion tube section of the jet.
2. Someone one drilled out the jets to a huge size. As soon as I saw it I was like wtf, I'll bet they drilled them with a 1/16" bit (the smallest common size), grabbed a bit and checked it . Yup drilled out to 1/16".
Below you can see the holes size difference. Now I know why that rack of carbs was no longer in use. The hole was 20.5 times bigger than it was supposed to be.
I ended up buying brand new Keihin brand Jets from JETSRUS. It cost about $70 just for the main jets and pilot jets.
I bought 42 pilots and 120 Mains to start out
The only thing I have left to get is Needle shims, I'm planning to pick them up today. Once I get them I can start putting the carbs back together. I plan to start with 1 shim on each needle.
