1980 GS550E Electronic ignition .... issue

[tatu]

Petcock is on or res.
I took this out and cleaned it.

Flooding 2. Is poss ....
But vacuum line can't get petrol.
Breather tubes are in ok , 2 of.

Anyway it is same with tank off !
Same issue with tank removed .

Habsdoc is right, vacuum line can get fuel if the diaphragm is leaky

[tatu]

You say you have swapped 2 with three and there was no difference in running, so that eliminates spark problem. that leaves compression, very small chance of fuel but that is also very unlikely in view of your previous comments.

[ukjules]

The issue was sudden.
Like ovwrheating I thought. But of course now we know.

I took the carb off yest, I didn't look at the diaphragm but
I didn't really notice anything.
It doesn't soujd like a sudden event ?

What about plug 2 not crackling when Inserted ?
Compression fine

[tatu]

Compression tests can be inconclusive if not done in the correct sequence,
hot engine,
full open throttle,
Crank over, (best pull all the plugs out to maximise efficiency of speed and battery conservation)
To get a better idea of where the leak might be: a couple of squirts of oil down t plug hole will help seal the rings, if there is negligible increase in compression figures then you will have burnt valve/s
From everything you say, this is where I would be focusing.

[tatu]

The issue was sudden.
Like ovwrheating I thought. But of course now we know.

I took the carb off yest, I didn't look at the diaphragm but
I didn't really notice anything.
It doesn't soujd like a sudden event ?

What about plug 2 not crackling when Inserted ?
Compression fine

Not the carb diaphragm, the one in the fuel tap

[tatu]

The issue was sudden.
Like ovwrheating I thought. But of course now we know.

I took the carb off yest, I didn't look at the diaphragm but
I didn't really notice anything.
It doesn't soujd like a sudden event ?

What about plug 2 not crackling when Inserted ?
Compression fine

Ok, take the cap off, so that the wire is bare, hold the wire about 4mm off the plug top and start the engine, you will see the spark.

[ukjules]

Ok but other three cylinders ok ? And no fuel in vacuum pipe ?
Whatever I'll check again.
Petcoxk is ok doesn't leak. Can't see how I can sort that out
without renewing it

I am taking bike back to only garage that offered to help
to 're check compression .
We must assume it is ok but I will do it one more time.

[ukjules]

Ok cap off bare wire - spark jumping across.

[tatu]

Ok cap off bare wire - spark jumping across.

Ok, now you have eliminated ignition. That's it and it's conclusive! The engine runs on the other cylinders so it's not a timing issue. the plug is wet, so you have fuel, You know it's not plug because you have swapped/put new.
Check th compression in the way I explained

[tatu]

Ok but other three cylinders ok ? And no fuel in vacuum pipe ?
Whatever I'll check again.
Petcoxk is ok doesn't leak. Can't see how I can sort that out
without renewing it

I am taking bike back to only garage that offered to help
to 're check compression .
We must assume it is ok but I will do it one more time.

As an aside, when you check this in the field, unplug the carb end and suck, if you get fuel in yr mouth it's bad, squinting down the pipe from the other end means nothing as it's an open hole

[ukjules]

Ok,

I sucked on carb end and I can get petrol in my mouth !

It's on reserve too.mind.

[tatu]

on the vacuum tube?

[ukjules]

Yes on the vacuum tube , carrb end

[tatu]

that is not a problem in itself, But just to eliminate,...You need to block off that pipe, cut it in half and poke a 6mm screw in the two open ends, or cut it short enough to get a screw in to block it off tank end, and then block the piece leading down to the carb. (Leaves you with an option should you wish to change back) from now on you will have to run on the prime position.
Remove the plug from No 2 start the engine long enough to unflood that cylinder, be careful of the spark as it might ignite ejected fuel. swap the recently removed No2 plug with another ,say No1, pet them both back in start up and see what happens.

[ukjules]

Ok, there is no prime only on and res.
Can I.work round that ?.tis a standard original.


Where's a 6mm screw when I need one !
Surely not a 10m cycle ....

I'll start now and should find a screwnsomewhere