912 ULS miss
Well I didn't think that I would end up here asking for help, but here I am. My 912ULS has developed a notable miss at all revs. Carbs have been removed, cleaned with all new diaphragms / orings / gaskets, needles and jets, over and over again, with no change each time. Floats weighed and in spec. Fuel level in bowl is 1/2 inch from the top of the bowl, with the floats sitting in the fuel perfectly. New spark plugs, new carb sockets. Carbs synched. Using an IR temp gun, aiming in line with the exhaust flange nuts, all seem ok except for cylinder #1, about 30 degrees difference. No difference in mag drop between A and B, both around 100RPM. Plugs on cylinder 1 were found to be sooty, both top and bottom. All others were ok. Swapped out plugs and no difference. So here lies the question. Cylinder 1 sooty, Cylinder 3 ok....same carb...Mind you, this engine ran perfectly before overhauling the carbs.
Moving forward, my plan is:
1. to run engine at 3000RPM up to normal operating temp, shutdown and check plug color / condition. Do the same again around 2000.
2. Squirt some ether or similar between carb and intake port to try and identify any leaks.
3. Leakdown test on all cylinders.
4. Standard compression test.
Any suggestions / advice will be gratefully received.
Rod.
