What does a strong spark look like?

[robertbarr]

Those are horrible compression numbers.

They are, but would they cause the specific problem laid out here -- dying when hot? I can think of a number of problems that result from low compression, but not this one.

Too bad we don't have a spare ignition module to swap in temporarily. Thermal problems with electronics can be a beech to troubleshoot.

[cowboyup3371]

I have the ignition module from my 550 I could swap in but I'll do that if the problems persist. In the meantime, I took some more measurements today using the same gauge but cold this time and then cold but adding oil into each cylinder. The results are:

Cold
1 - 70
2 - 70
3 - 70
4 - 72

Cold with Oil in cylinders
1 - 89
2 - 88
3 - 90
4 - 90

I'll keep the progress updated on the other thread

[rphillips]

All 4 are very close to the same, that should be considered a big plus. Usually if compression is the problem 1 or maybe 2 cyl. will be way lower than others. Seems odd rings on all cyl. would be equally weak or valves on all cyl. would be equally out of spec. I'd need to try a different gauge & would still need to see the spark when problem exists.

[roeme]

Note that compression readings can jump quite a bit depending on how much torque is applied when screwing them in.

Edit: ...how many miles on the engine though?

[cowboyup3371]

Edit: ...how many miles on the engine though?

Just over 14,000 miles on this Odometer. We were told of problems keeping an idle on it from the young lady who sold it to Charmayne but thought we solved it some time ago.

[wymple]

With those numbers on all 4 and 14K on the bike I would go straight to a valve adjustment.

[Brendan W]

Those pressures are so close together that I would be inclined to do a valve timing check first.

[roeme]

With those numbers on all 4 and 14K on the bike I would go straight to a valve adjustment.

Those pressures are so close together that I would be inclined to do a valve timing check first.

I'm inclined to agree.

[rphillips]

Good thought, timing off could lower compression on all 4, while keeping them near equal. Still wouldn't explain eng. quit & very hard to re-start when hot. Earlier you mentioned an orange spark, if that's the case, that needs to be fixed, blue or white is OK, orange is not good.

[cowboyup3371]

Valve clearances were checked in September 2019 and again today; all within spec though intake and exhaust of both 3 and 4 tightened up since September. And yes, a valve clearance does not explain the engine quitting like it did only at long stops and only when hot since it ran great when it did run.

Either way, I have decided to go the route i have and the engine is now apart. We'll proceed with this piece and continue any other troubleshooting as necessary once we have it back together. We will also remove the wiring harness to thoroughly clean all connectors.

[adam290]

I have a 1980 gs550l with almost the exact same issue and its driving me crazy! the bike starts right up on choke, idles and revs fine off of choke and then when it gets hot to will start to sputter and die. then it cranks and cranks without acting like it wants to start at all. let it sit and cool down and it starts right up. I am really curious to find out what your problem is. please keep us updated

[cowboyup3371]

I have a 1980 gs550l with almost the exact same issue and its driving me crazy! the bike starts right up on choke, idles and revs fine off of choke and then when it gets hot to will start to sputter and die. then it cranks and cranks without acting like it wants to start at all. let it sit and cool down and it starts right up. I am really curious to find out what your problem is. please keep us updated

We decided to rebuild the top end. I’m posting more about the progress and results in her rebuild thread which you can find here - https://www.thegsresources.com/_foru...ld-of-her-550L