HKS 700e engine problem
I'm helping a friend struggling to cure a severe rough running problem with his HKS 700e. I consider myself more than fairly competent with engines and the aircraft I fly uses the same style of Bing carburettor as those on the HKS.
Right from the outset, let me assure you that the problem is definitely not related to the ignition or spark plugs. The plugs are new and the first step was to swap them to opposite cylinders, however the rough running remained, with the left cylinder EGT showing only 150C while the right side showed 500C. All plugs had previously been removed from their holes and tested on their leads to show healthy sparks when cranking the engine.
The second step was to completely swap plug leads and their coils between cylinders, effectively swapping ignition systems, which is do-able because the ignition is a "wasted spark" principle in which a spark is produced every time the pistons approach the top of their strokes. No change was seen in symptoms.
After each swapping step the engine was run and the ignition circuits switched off in turn, but the fault remained the same with the engine running violently rough and refusing to accelerate when throttle was advanced. Always left cylinder warm, right cylinder hot.
Cylinder compressions have been tested and found very healthy.
I have been involved with Bing carburettors for decades due to them being fitted to BMW motorcycles and I'll happily strip them to the smallest part. This is what I did to my friend's carburettors and can't find any problem. Slide top springs, diaphragms (not split), needles and their clips, main jets, emulsifiers, floats and their needles and seats, choke valves, butterflies, throttle and choke cables working perfectly in unison, return springs good, rubber flanges, inlet manifolds all check out A-okay. Internal fuel and air passages blown through; clean and clear!
Fuel supply to both float bowls more than adequate and the floats float well with the float needles stopping fuel flow exactly as advertised.
Just in case I've missed something in a carburettor, the next step will be to swap carburettors between cylinders (not easy due to mirror imaging) and see if the fault swaps sides.
Intriguingly the right cylinder, which gets hot very quickly, also makes its plugs black and sooty, while the plugs in the left cylinder look normal. Something doesn't add up!
What am I missing? Help please, because I can't find a clue using google.
Last edited by Colibri49; 11th Aug 2016 at 11:05.