Just wanted to say thanks to all who posted to the "Air fuel ratio 836 engine" and "Yet ANOTHER dyno result" threads in regards to tuning my carbs. All the info you guys gave was very helpful in diagnosing troubles I was having with the idle circuit and transition between idle and 1/4 throttle.
I pulled the carbs off yesterday for what I hope is the last time for some years to come
Here's what helped.....
When measuring fuel heights initially, I found that the fuel level was 1/2" below float bowl gasket. When I pulled the carbs and remeasured the floats they were measuring at the suggested 14.5mm with the lowest one measuring at 15mm at the front(still within +/- .5mm spec. Put the carbs in a vice and, using a clear line to measure fuel levels, bent each float "tang" until the fuel height reached 1/8" below each float bowl gasket. Remeasured the floats at this point and found that the rear of the floats were still at 14.5mm but the fronts were at 13.5mm( for those not familiar with 77-78 floats they are flat on the bottom, not round like earlier carbs ).
While the carbs were in the vise I swapped the float needle in my #1 carb since it didn't seat properly and would overflow if fuel tap was left on. I had a pack of 4 aftermarket float needles and tried a couple different ones until I found one that actually shut off the fuel. Damn aftermarket float needles! They seem to be "hit or miss"
I checked the operation of the accelerator pump(thanks eurban) and found that the outer fuel pipes(#1,#4) weren't pumping as much as the inner two(#2,#3). On closer examination I saw gas leaking out of the back of #2 float bowl where the accelerator pump attaches to the carb body. The small rubber accel pump o-ring that fits in between the float bowl and carb body was no longer up to the task. Replaced it and now each carb gets equal geyser of gas when the throttle is twisted
With carb cleaner and compressed air I checked that all four slow jets were clear and that the air jets(airbox side) and small fuel delivery holes(engine side) were clear and doing their jobs. Set the fuel idle screws at 2 turns out, buttoned up the carbs and put them back on the bike.
I've now got carbs that don't leak when the petcock is left on overnight. Engine accerates very well when I "roll" on the throttle. And it idles very well (and very quietly) at 900rpm
I've still got to dial in each idle screw for maximum performance. Averaging 2 1/2 turns at the moment. And I may fiddle with the accel pump arm gap to fine tune the transition between idle and 1/8 throttle. Also, I'll probably take out the last "shim" washer beneath each jet needle to lean out the midrange. Since the accel pump is working so well now the mixture becomes VERY rich when the throttle is "snapped" open and there is some hesitation in the acceleration while the motor catches up, hope the needle drop will limit this effect. All that aside, the carbs are functioning very well for daily riding and the test ride through the twisties this morning put a big, fat grin on my face
Thanks again, fellas. You ROCK!
