Author Topic: 1975 xs500b runs great for 20min then dies everytime???  (Read 3891 times)

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Offline Cobra

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #30 on: October 26, 2018, 07:49:26 AM »
Why does it die after it is warm and run fine cold with stuck rings?

Offline nk140

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #31 on: October 26, 2018, 12:29:39 PM »
Low vacuum will probably cause a lean condition at idle.  I have this problem.  I think I have fixed it for the most part.  I did have to re-ring my motor this past spring because the rings were stuck to the piston.  Your compression is pretty low.  Mine compression after a re-ring is 150+.  What are your vacuum readings?

Offline Cobra

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #32 on: October 26, 2018, 06:12:12 PM »
Never checked vacuum before, I have a motion pro manometer but it doesnt read vpi (or what ever) simply does you number 1 cylinder match the others that all.  I suppose I need to purchase a vacuum gauge. 

I think this is the problem stuck rings, the bike sat for 30+ years runs good when cold but when when the cylinders expand once warmed up the rings do not expand and compression drops to a unsustainable level for combustion.

Has anyone actually freed up rings inside an engine with ATF, Marvel Mystery, SeaFoam, Kerosene, diesel, ha I saw alot of suggestions out there.   When I cleaned the tank out acetone worked pretty well.   Could I fill the cylinder with evaporust then some acetone, and repeat that cycle for a bit?   Or do I just bite the bullet and break out the wrenches....sigh :'(
« Last Edit: October 26, 2018, 06:14:43 PM by Cobra »

Offline nk140

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #33 on: October 26, 2018, 06:57:21 PM »
With your compression that low I would say wrenches are in your future.  You will measure the vacuum when you sync the carbs.

Offline Cobra

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #34 on: October 27, 2018, 05:55:10 PM »
Can I re ring the pistons with out removing the engine or do I have to remove the engine to preform this operation?

Offline Cobra

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #35 on: October 27, 2018, 06:51:03 PM »
Just to confirm suspicions the compression while cold with a little oil in the cylinders is 150psi left and 165psi right (how is this now above the standard 150??).   I have some marvel mystery oil in there for the last day and will try some atf and acetone next.  I will put some seafoam in the tank and try and ride it hard and get it real hot next time and see if it helps at all. 
« Last Edit: October 27, 2018, 06:55:14 PM by Cobra »

Offline dailydose1

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #36 on: October 28, 2018, 11:50:12 AM »
you have to remove the engnie to do new rings and split the chain. i have heard of good success with diesel fuel too....but change ur oil after

Offline nk140

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #37 on: October 29, 2018, 12:19:38 PM »
Just to confirm suspicions the compression while cold with a little oil in the cylinders is 150psi left and 165psi right (how is this now above the standard 150??).   I have some marvel mystery oil in there for the last day and will try some atf and acetone next.  I will put some seafoam in the tank and try and ride it hard and get it real hot next time and see if it helps at all.

That compression seems more than acceptable.  Sounds like the mystery oil helped break those rings free.

Offline guylr

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #38 on: October 29, 2018, 12:57:09 PM »
Adding oil to retest compression is not a fix and only temporarily raises compression by taking up the gaps between the ring faces and cylinder walls. It does not prove the rings are stuck or worn but only that the ring seal is the problem. Stuck rings are typically more of a two stroke engine problem while worn rings and cylinders are common in both two and four strokes.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline nk140

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #39 on: October 29, 2018, 01:37:28 PM »
Adding oil to retest compression is not a fix and only temporarily raises compression by taking up the gaps between the ring faces and cylinder walls. It does not prove the rings are stuck or worn but only that the ring seal is the problem. Stuck rings are typically more of a two stroke engine problem while worn rings and cylinders are common in both two and four strokes.

Guy

I was assuming those compression figures were after he ran it for a bit.  You are correct that if oil is in the cylinder that it will inflate the compression numbers.  I guess the OP wasn't clear on how he measured after the oil.

Offline dailydose1

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #40 on: October 31, 2018, 04:41:35 AM »
If your pressure went from 115 to 150 with oil I think you are going to need new rings, im dealing with the same thing now. That seems like a massive jump though i thought oil would only increase a little bit

Offline Cobra

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Re: 1975 xs500b runs great for 20min then dies everytime???
« Reply #41 on: November 01, 2018, 01:38:35 AM »
here is my theory, when the engine is cold I get better compression but once it gets hot the cylinder expands maybe and the rings are stuck not expanding to the wall of cylinder (i think) causing the drop in compression and the bike dies.  I tested the low numbers while the bike was warm.  The higher numbers come from when the bike was cold with a bit of oil in the top. 

I think this means the rings are the problem which require the engine to come out as you all pointed out.  So I filled the engine with atf - Marvel Myst Oil - acetone mix in a 1-1-1 mixture. When I say fill the engine I mean keep the pistons covered so they soak.  I then put a heater underneath the bike and set my vibratory tumbler on its side with the seat up so the tumbler makes contact with the frame to agitate the bike like a sonic cleaner.  Maybe I can get the rings unstuck if not its coming out anyways and Ill know for sure.