1 cylinder not working

[montjuic]

Hello my name is Glenn from the UK.

I am tearing my hair out with my sons 1978 gs550e running problem which is as follows,

no1 cylinder keeps dying (no spark from plug) if I put a new plug in it runs fine for about 10 miles then kills the plug again, since having this problem both coils and plug caps have been replaced but the problem still persists on the same cylinder, the carbs are fine/clean and all float heights set to the correct heights and all bowls getting fuel through.

I cannot understand what would cause a plug to stop sparking after such a short time, not every new plug I put in can be defective so there must be a problem elsewhere, it's as if there is a surge in voltage or  something to cylinder no1 which is taking out the spark.

Any ideas gratefully accepted

[Sheep]

I would have thought if one plug has spark issues so would its coil sharing partner (1&4,2&3)...Did you change the leads to the plug?...how does the plug look?...valve clearancesand compression all ok?

oh and what plugs are you using as I went through a few before and heard some may not be genuine but it is hard to tell I thought.

 

[Gixer1460]

^^^ as above and if is definitely ONLY #1 then it will usually be fuel related! Sorry to be negative but that's the way of the world !

[montjuic]

Thanks for the prompt replies, it has had new coils c/w new leads and new plug caps new ngk br8es plugs, plug is wet/black and if put in the corresponding plug cap and rested against the engine it produces no spark when kicked over or even when run on 3 cylinders but when a new plug is put in the plug cap the new one sparks if I then put the new plug in the head and ride it after about 10 miles then for some reason that plug ends up not sparking like its previous plug.

valve clearances are spot on on all cylinders and all cylinders give 125-130psi readings.

I understand that the coils are linked (1+4 2+3) that is what is so frustrating with this problem, plenty of fuel getting through the only problem is the plug stops sparking

Edited August 8, 2018 by montjuic
spelling mistakes

[nlovien]

take a  look for signs of oil - maybe a leaking valve seal / worn guide causing contamination

signs of the piston crown being obviously muckier / wetter than the rest - crud build up at the bottom of the inlet valve etc..

Edited August 8, 2018 by nlovien
where to look

[Sheep]

I have a tray full of plugs of various ages although non older than a year.I was going through them like sweets....it was all down to an over fuelling issue which killed plugs like there was no tomorrow.They do not like being soaked in fuel.You are simply washing away the spark whether it's in the head or out of it.....Sometimes a burn off in the oven brought them back to life....Now I have the fuelling sorted I have never had a problem and even have one or two of those killed plugs in the engine to this day.

I would be looking at a possible leaky float needle on that cylinder for a start.

[gs7_11]

2 hours ago, Sheep said:

 

I would be looking at a possible leaky float needle on that cylinder for a start.

This.

Wet and black says fuelling to me, as Gixer1460 said, must be fuel.

[wraith]

+1 on the above, wet and black says carb to me to unless the black set is oil and if as you say you have good compression it could be a valve seal.

You could try (just to rule it out) swapping the HT leads over from the one that's giving you the problem to the same timing one (ie 1-4 2-3) if they will rich.

Otherwise have you got it can you borrow a spare set of carbs to try?

Are you running air box or filters and standard zorst or open ?

One more thing, are you running with the old points or electronic ? 

Just I've seen the condenser go (you see a big spark on the points) and they can take out the plugs sometimes just one plug (the weakest one).

[KATANAMANGLER]

If the plug is fouling then either the ratio of air to fuel is wrong or it's being fouled by oil.

Either way the  basic ingredients to a clean burn are compression, air, fuel and a spark.

You know you are getting a spark when the plug is clean and you know you are getting fuel and air because it fires with a new plug.

I would do nothing more until you do a compression test. Read the compression across all 4. If the compression is close across all 4 then you know it's got to be the air fuel ratio on number 1 cylinder or possibly a bad oil ring or leaking valve stems seals. Look at the plug once it has dried off. Is it black and sooty or black and oily?

If you get low compression on 1 then that will create a weak burn which will foul the plug. Once it fouls it won't spark.

If the compression is low you need to know if it's  rings or valves. 

First thing I would do is a compression test though.

 

 

[busa1300]

I had the same problem to some degree on #1 plug.... after cleaning carbs several times I replaced the choke plunger and spring. Then cleaned everything else spotless again..... Has been working OK now. 

[montjuic]

thanks a lot for all your replies I will try all these and let you know the results

 

[BigT]

Check the choke lifters to see if they are all installed the same, with the notch down.

[johnr]

kickstart gs550 you say? is it running on points or cdi? if its points it could be a condensor, or the ignition timing could be out. if its not points then it could be the valve stem oil seals leaking through into the pot, when you said it kills the plug, does that plug not spark if you put it on a different cylinder?

[Wolf]

On 8/8/2018 at 10:57 PM, KATANAMANGLER said:

If the plug is fouling then either the ratio of air to fuel is wrong or it's being fouled by oil.

Either way the  basic ingredients to a clean burn are compression, air, fuel and a spark.

You know you are getting a spark when the plug is clean and you know you are getting fuel and air because it fires with a new plug.

I would do nothing more until you do a compression test. Read the compression across all 4. If the compression is close across all 4 then you know it's got to be the air fuel ratio on number 1 cylinder or possibly a bad oil ring or leaking valve stems seals. Look at the plug once it has dried off. Is it black and sooty or black and oily?

If you get low compression on 1 then that will create a weak burn which will foul the plug. Once it fouls it won't spark.

If the compression is low you need to know if it's  rings or valves. 

First thing I would do is a compression test though.

 

 

And a wet compresion test will show if its rings 

[Wolf]

Gooday have you found the problem ? I had the szme 300 km on 12 plugs ..

Had a look in the manual as i was trieing t find Nipo Denso plugs and found this (image) i changes to the hotter plug and the shit stoped un till i used my kick stand more than normal , at yhe zngle my 1000 leans on the kivk stand she czn floud in +- an hr as the float level is not as it should be.