Ignition question for John T

Okay I had fouled my plugs { 71 FLH Harley] . Dual plugs per head. Coils in series. If all four plugs fouled and you only change out two per cylinder ; are the two remaining fouled plugs going to " steal" the energy away from the new unfouled plugs. I think I had this happen, but I'm not really sure.

Change out one plug per cylinder not two . leaving one fouled plug in and one fresh plug is what I meant.

It should run and since it is shorted it keeps the voltage low enough that it doesn't ignite furl. Steel voltage Not to my way of thinking. The engine is designed to have two flame fronts in the chamber traveling to the extremities as the flame progresses. With only one, the engine will not perform as well nor be as efficient. The plugs that are fowled may come back from the dead if it is operated to temperature for a while. What fowled the plugs? Jim

depends on how the coils are wired... if only the primary in series.. each and the input is working correctly, then each secondary will produce voltage... and each plug would be fed. One via carbon to ground and the other will arc and fire off the fuel.

Dr, Im in the dark on that particular ignition system (two coils in series for 2 plugs in one head, that's my assumption, right????) but will take that as my guess and proceed.

Okay, if the two coil LV primarys are in series, still when current is interrupted each coils HV secondary will ramp up the voltage until its high enough to fire a good (non fouled) plug. However, if one plug fed by one of the coils is fouled, that coils stored secondary energy will bleed off current through the shorted fouling path (conductive oil or carbon) and there wont be any sudden HV arc i.e. that plug wont fire. HOWEVER I don't see any of that as diminishing the spark the other non fouled plug will produce. I see the other coil still producing as high of an energy spark in the good plug as if there were 2 good plugs. Because the plug fed by one coil is fouled, I dont see that reducing the other plugs spark energy. REMEMBER MY ASSUMPTION IS TWO COILS IN SERIES FOR 2 PLUGS IN ONE CYLINDER That right or wrong?????????????

Now as to how that affects performance????????? I cant say, other then if two explosive wave propagations (one on each top side of combustion chamber) meet in the middle and that is more efficient THEN ONE FOULED PLUG (even if other plug works as good) then maybe theres less efficiency and less power????

Im just NOT familiar with that ignition system, sorry

John T

Please post a pic of plugs. What is causing the plugs to foul?

Best way to answer your question may be to take an old plug, bent the metal tip on plug to short it out completely. If engine them runs on one good plug and one shorted plug, then there has to be enough energy from coil to run bike.

Do your plugs foul because engine is burning oil, oil fouled? Or are they just carboned up because you don't have complete combustion?

I have a kohler command, 20 hp. One cylinder would turn plugs black because of incomplete combustion. Engine passed compression and leak down test. I finally pulled head, lapped in the valves, works great.

I was experimenting with carb jets . It is a fresh rebuild.

testing richer jetting.

Back in my youth, I worked on my own bikes, Triumph, goldwings. When you get the jets just right, the crome exhaust pipe near head will turn criome blue, I think. That's when you you know you got close to the right jet setting.

Could use an IR gun and measure exhaust temp too to make sure both cylinders are the same and no compression problems like I had on kohler.

My boy had a 4 cylinder honda. One carb was totally blocked. It was caused by a mouse that made a nest in breather. Mouse poo choked all the jets. That was a battle to clean.

Good luck. May want to go to HF and buy a cheap spark plug cleaner instead of buying new plugs all the time.

Dr Sportster,

I have been fooling around with my panhead engine 81 fx, single fire etc. I have found a lot of knowledge and experience on the harleytechtalk.org site. There is some fun reading on "Earls Place" section of the forums too.