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« on: July 20, 2020, 08:37:53 PM »
When I started the thread I thought the custom carb was a 780 because that’s what the original owner told me. After a little research I learned it was a custom 850-HP. After a dozen unsuccessful adjustments I pulled that carb and installed a 25 year old 850 double pumper. Both carbs started on the engine is stock form.
The 850-HP I started with (that I originally thought was a 780) had the builders original settings in it and it would run 20 to 1 lean at mid throttle then 10 to 1 rich at WOT. I pulled this carb and sent it back to the builder for rebuild/recalibration.
Next I installed my rebuilt/cleaned out totally stock 850 double pumper that I originally purchased 25 years ago. This carb ran a little lean at part throttle and less rich at WOT. After pulling the secondary PV and changing some jets it ran MUCH better than the first carb ever did. After the changes indicated a few comments ago it is now running 12.7 to 13.0 at WOT, idling at 13.5, cruising at 13 to 1 (this is why I’m interested in dropping the idle jet 1 number), and mid throttle (just before PV opens) at 14.5 to 1. Then 12.2 to 1 when PV opens.
As you can see none of these numbers are lean despite all the small jet sizes.
However, after all this, the motor pulls strong up to 5000 RPM then feels held back. RPM climb slows down and the sensation of acceleration seems to slow down.
I’m thinking the 2” restriction in my side pipes may fully explain this. The cam timing could be a huge part but I’ll know more after I replace the side pipes. New pipes are ordered and will be on the car soon. I also anticipate the new exhaust may let me put the carburetor tune back to normal. I hope.
Basically I’m going to stop chasing my tail until the new less restrictive exhaust is installed.
I just mentioned I’m running non-ethanol fuel because I thought some where thinking the variations in ethanol content was complicating my tune.