1 cyliners not working

[montjuic]

Help please.my sons gs550ec 1978 keeps killing the spark plug on no1 cylinder, put new coils on, new plug caps and new plugs (again) it was ok for about 40 miles then same old story no1 pot not working as soon as I put a new plug in it works fine for a bit.
The bike is standard with points & condensers but to my way of thinking the cylinders/sparks are joined 1+4 2+3
so if a set of points/condenser was playing up it would affect the corresponding cylinder. does anyone have any ideas.

 

[tom203]

Killing it how? Fouling the plug? With Gas? Oil?

 

[fastbysuzuki]

Hi if it's defiantly only affecting no1 cylinder having done what you have already I would try taking off the plug cap and trim about 5/6 mm off the ht lead this will get the cap screwing into fresh/clean copper wire and change no 2 cap onto no1 just to eliminate a faulty plug cap. When was the last valve check/adjustment made?

 

[montjuic]

plug wet just not sparking to burn mixture off

 

[Guest]

It would help to know what the plug looks like when it fails. It sounds like a non electrical issue, though it still could be from a weak spark if the wire is not transferring the current to the cap. Is it black and wet when you pull it(too much fuel)?

 

[montjuic]

trimmed the leads on the brand new coils before fitting brand new ngk plug caps, shims were adjusted about 6-700 miles ago, done a compression test and al 4 are healthy and within tolerance range and all similar readings, totally flumaxed.

 

[montjuic]

has a 4-1 on, no smoke plug wet/blackish but not sparking compression test fine so bore/rings/valves sealing

 

[Guest]

trimmed the leads on the brand new coils before fitting brand new ngk plug caps, shims were adjusted about 6-700 miles ago, done a compression test and al 4 are healthy and within tolerance range and all similar readings, totally flumaxed.

You may have something clogging your air jet or possibly the float is set too low allowing more fuel in the bowl. It does effect all circuits. You might want to check in the dark to see if the #1 wire is jumping to the block or another wire. It will find a fine crack in the wire and follow the shortest path to ground, but you may never see it unless your looking for it.

 

[londonboards]

Once you have eliminated electrics, start on the carbs.

When were they last stripped and cleaned? Gummed up carbs will cause problems. A blocked jet will also cause that.

So will:

- incorrect float height (floods float bowl)
- leaking needle valve (floods float bowl)
- leaking needle valve seat O ring (floods float bowl)
- carbs incorrectly synchronised (one carb opening more than the others).

 

[montjuic]

it had the same problem with the old/original coils so bought brand new ones along with brand new plug caps but problem still persists so it cannot be the plugs/coils/caps.
he carb have been ultrasonically cleaned float heights set and double checked, if a pilot jet was blocked at full throttle main jet would come into play and full power would return but isn't.

 

[Guest]

it had the same problem with the old/original coils so bought brand new ones along with brand new plug caps but problem still persists so it cannot be the plugs/coils/caps.
he carb have been ultrasonically cleaned float heights set and double checked, if a pilot jet was blocked at full throttle main jet would come into play and full power would return but isn't.

plugs/coils/caps.

Did you replace the wires also?

 

[montjuic]

no didn't replace the wires Rick, as my understanding being that any problem with the low tension side would affect 2 cylinders ie 1&4 or 2&3 as this problem is linked to no1 cylinder only I have ruled out points/condenser/low tension side having replaced coils and plug caps with brand new ones I have ruled them out as well.
no1 carb has plenty of fuel in the float bowl so i've ruled out fuel starvation but I'm stumped now

 

[montjuic]

just to confuse the situation more if I put a new plug in the bike runs fine for about 10 miles after this it kills the plug on no1 cylinder, by that I mean it won't spark put a new plug in the cap and spark appears put old plug back and no spark, it's as if there is an electrical pulse on no1 cylinder that keeps snuffing out the plugs.

 

[Steve]

One other suggestion: swap the plug wires for 1&4.

If #1 still fouls out, you will KNOW it's not electrical.

.

 

[montjuic]

already tries this steve and problem moves with the lead/plug cap but it has brand new coils/leads/caps because it was doing the same thing before and the only thing I could surmise was a faulty coil/lead/plug cap

 

[Guest]

Did you say that valve clearances were checked/adjusted recently? You may have a tight intake valve thats dumping fuel all the time, plus ruining your combustion chaber vacuum. It'd only be a matter of time before any spark plug gives up to those conditions.

 

[Steve]

One other suggestion: swap the plug wires for 1&4.

If #1 still fouls out, you will KNOW it's not electrical.

.

already tries this steve and problem moves with the lead/plug cap but it has brand new coils/leads/caps because it was doing the same thing before and the only thing I could surmise was a faulty coil/lead/plug cap

Are you saying that if you swap wires, then #4 will foul out?

If that is true, you don't have very much to inspect there.
1. wire
2. cap

By the way, new parts can be faulty, and there is always the possibility that they are assembled just a little bit "not quite right".

.

 

[Guest]

pretty much narrows it down....

Are you saying that if you swap wires, then #4 will foul out?

If that is true, you don't have very much to inspect there.
1. wire
2. cap

By the way, new parts can be faulty, and there is always the possibility that they are assembled just a little bit "not quite right".

.