Experience Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.
Organizations Associate member SAE
EAA member
Publications Import Car magazine
Education/Credentials ASE Master Auto with L-1 certification up to 2000
A while back I asked a question about missing at load. You gave me a set of items to pursue. I have eliminated spark plug gap as a contributor, as well as wires and distributor cap. Air cleaners are new, static timing is correct, vacuum timing has been checked for appropriate function.
The engine does not miss at idle. As I accelerate, if I press gently on the pedal, the miss does not appear until 4700rpm. If I pres from 50% to 100% down, the engine misses immediately.
As I worked through some of this, it occurred to me that perhaps the dashpot oil is a contributor?
I am running Marvel Mystery Oil in the dashpots. I am experiencing a fair amount of blue smoke at rich (cold) idle setting, and on start-up from warm at accelleration.
Could this be leaking down and 1. burning off, and 2. not damping the carb piston? Diaphragms are new and correctly installed.
Thanks,
Jeff
72 TR6
Answer Hi Jeff,
Marvel oil works ok in the pots. The dampening of the piston takes the place of an acceleration pump of a conventional carb.
Blue smoke on acceleration is a normal ring problem. You need to do a dry then a wet compression test. (throttle open and at least 4 or 5 revolutions) and on the wet test put about 3 or 4 squirts of engine oil in the plug hole and run the compression test again. The wet test will be higher than the dry test but should not be more than 10% to 15% higher.
A high RPM high load miss can come from hundreds of things, so you need to do a lot of testing. I found that if you don't have access to a dyno than you need to be able to monitor fuel pressure and ignition at the high load/ RPM. The method I use is to put a "T" in the fuel line close to the carburetors and and run a long hose out from under the hood and put a fuel pressure gauge under a wiper arm so you can see it at speed. To test for an ignition break down at speed /load put a timing light on the coil wire (not a plug wire) and run the leads out from under the hood and tape the light to a wiper arm and if it is bright and sunny you will need to tape a piece of cardboard over the light end so you can monitor the flash. (tape the trigger down on the timing light) When you get a misfire due to an ignition break down at high speed or high loads you can see the change in the flash.
Let me know,
Howard
