Valve broke.so I replaced all 4.and piston rings.wont start no more. low compression 90.put oil in spark plug hole.and compressing when up to 120.valve clearance within spec.cant figure out what's wrong. I will appreciate for your help
Did you orient the rings per the service manual?
The guy at the shop where I had the valve seat redone did it for me.but I don't know what you mean by oriented.can you explain
There are basically 3 Piston rings on each piston - and the gaps of the rings are supposed to be spaced out 120° from each other. Speaking of ring gap......they may be spaced out to far (out of spec).
Since you went from 90 psi to 120 psi, it shows that the piston rings are part of the problem. But your valves might very well be a factor too. Were the seats lapped with the valves when they were installed?
Honestly man, you really should take it back to the shop and explain to them what's going on.
I got the bike running and it was the carburetors.not sinc.and abou the low compression it seems fine when for a ride and it runs strong.but I have one more issue.when I'm shifting gears. idle is to high even when I release throttle.
Quote from: Gmoscajal69 on August 15, 2016, 01:12:42 AM
I got the bike running and it was the carburetors.not sinc.and abou the low compression it seems fine when for a ride and it runs strong.but I have one more issue.when I'm shifting gears. idle is to high even when I release throttle.
have you found the problem? mine does the same. it has low compression, 6 bar per cylinder and idling at 3-4 k when fully wormed up
p.s. valves is in spec. and i've just rebuilt engine too
1. the carburetor adjustment is not going to cause a compression problem. OP's compression numbers look to me like both the rings are not done right and the valves are also not seating correctly. Take it back to the shop and have them fix it. They will have to redo it. I am guessing they really should refer you to another shop. If those compression numbers are accurate on a fresh top end rebuild then it's a sign that they really don't know what they are doing.
Regarding the high idle, you just need to adjust the idle. Big knob facing down between the carbs. See the wiki, tons of information on how to do it. The shop that did the rings & valves should have done this too.
Check valve timing first if both cylinders are that low.
http://img.photobucket.com/albums/v443/jcp8832/gs500signalgenerators_zps6gldzd0e.jpg
+1 on the valve timing :thumb:
i'm guessing I've done the compression test incorrectly.
I found out yesterday that i should have opened the throttle while taking measurement :D is it right?
Yes, hold throttle wide open.
And do about 6-8 cycles before taking a reading.
thanks for help. i'm guessing compression will be in spec with open throttle.
shims is in specs i have checked it 10 more times :D its a strange problem why idle hangs when engine fully worms up.
i had this problem 1 years ago and it was tight exhaust valve. but now after rebuild i have no idea whats causing the problem.
i even replaced that shim just in case :D
Quote from: system32 on November 01, 2016, 07:11:39 AM
thanks for help. i'm guessing compression will be in spec with open throttle.
shims is in specs i have checked it 10 more times :D its a strange problem why idle hangs when engine fully worms up.
i had this problem 1 years ago and it was tight exhaust valve. but now after rebuild i have no idea whats causing the problem.
i even replaced that shim just in case :D
Is it a hanging idle (revs up fine, but stays high for a bit then eventually drops back down on its own) or a high idle (revs up, then drops to a certain point and stays there indefinitely)?
The former means you are running lean, the latter means you need to adjust your idle screw.
it's hanging idle revs up fine, but stays high for a bit then eventually drops back down on its own.
today i checked the compression with open throttle but no difference, i was still 6bar (87psi) on both cylinders.
that i added the oil in it and it went up to 8bar (116psi) on both cylinders.
the guys who repaired my engine has polished all valves and said that the rings were in good shape. :dunno_black:
what do you think guys?
many thanks for help
116 is very low. 150-160 plus is a typical figure for an engine in good condition. Are you sure the guage is accurate?
Rings, worn bore/piston, valves not seating, incorrect valve gap, timing, cracked head/seat :dunno_black:
Without opening it up and taking a good look its impossible to be specific. I would take it back to your man and ask him to explain.
Have you checked valve timing?
(http://img.photobucket.com/albums/v443/jcp8832/gs500signalgenerators_zps6gldzd0e.jpg)
Quote from: system32 on November 06, 2016, 01:19:44 PM
it's hanging idle revs up fine, but stays high for a bit then eventually drops back down on its own.
...
Your engine is probably running lean, as hanging idle is normally a symptom of a lean condition. I would maybe adjust your mixture in your carbs.
However, if your're getting low compression, I would probably try to rectify that first as that's the more serious of the 2 problems.
Quote from: qcbaker on November 07, 2016, 06:57:22 AM
Your engine is probably running lean, as hanging idle is normally a symptom of a lean condition. I would maybe adjust your mixture in your carbs.
However, if your're getting low compression, I would probably try to rectify that first as that's the more serious of the 2 problems.
Low compression can cause the hanging idle regardless of idle mixture. It's a waste of time and counterproductive to try and adjust the carbs when the compression is this low.
Fix the big rocks first. Take the bike back to the mechanic who did the head/rings work and get them to make it right.
Quote from: mr72 on November 07, 2016, 07:20:34 AM
Quote from: qcbaker on November 07, 2016, 06:57:22 AM
Your engine is probably running lean, as hanging idle is normally a symptom of a lean condition. I would maybe adjust your mixture in your carbs.
However, if your're getting low compression, I would probably try to rectify that first as that's the more serious of the 2 problems.
Low compression can cause the hanging idle regardless of idle mixture. It's a waste of time and counterproductive to try and adjust the carbs when the compression is this low.
Fix the big rocks first. Take the bike back to the mechanic who did the head/rings work and get them to make it right.
Didn't know low compression could cause hanging idle as well. Interesting.
Anyway, yeah that's definitely the thing you should try to get fixed first, OP. Then, circle back to the other issues if they persist.
Quote from: qcbaker on November 07, 2016, 07:55:48 AM
Didn't know low compression could cause hanging idle as well. Interesting.
It did on my bike!
I have theories as to how and why, but I can't test or verify any of them and frankly I have ceased to care. It is a very durable opinion that motorcycle carburetors are enigmatic and pointless to try to understand, and the internet is so loaded with wrong information about motorcycle tuning that it's useless as a resource.
Who can explain why a lean mixture causes hanging idle? There's good info here: http://alt.motorcycle.sportbike.narkive.com/oHTaYnXK/blip-throttle-and-revs-hang-rich-lean#post4 but this suggests that the hanging idle is caused by a RICH mixture.
So I am not a true believer that in all cases hanging idle means a lean mixture. And it's a red herring anyway since in a 20+ year old motorcycle the likely cause of a lean condition is vacuum leaks which really add a difficult to diagnose wrinkle in this, enticing the home mechanic to enrichen the mixture which will only make things worse.
Quote from: mr72 on November 07, 2016, 08:28:14 AM
Quote from: qcbaker on November 07, 2016, 07:55:48 AM
Didn't know low compression could cause hanging idle as well. Interesting.
It did on my bike!
I have theories as to how and why, but I can't test or verify any of them and frankly I have ceased to care. It is a very durable opinion that motorcycle carburetors are enigmatic and pointless to try to understand, and the internet is so loaded with wrong information about motorcycle tuning that it's useless as a resource.
Who can explain why a lean mixture causes hanging idle? There's good info here: http://alt.motorcycle.sportbike.narkive.com/oHTaYnXK/blip-throttle-and-revs-hang-rich-lean#post4 but this suggests that the hanging idle is caused by a RICH mixture.
So I am not a true believer that in all cases hanging idle means a lean mixture. And it's a red herring anyway since in a 20+ year old motorcycle the likely cause of a lean condition is vacuum leaks which really add a difficult to diagnose wrinkle in this, enticing the home mechanic to enrichen the mixture which will only make things worse.
I would agree that carbs are enigmatic, but I don't think its pointless to try and understand them. As for why different f/a mixture conditions cause certain symptoms, I haven't a clue. All I know is that I've read all the time that a hanging idle is usually due to a lean f/a mix; no clue as to why that's the case. For all I know the carbs just contain a tiny sorcerer who casts a spell to get the fuel and air to mix, and if they didn't pour enough goats blood into the goblet or they didn't sprinkle enough unicorn hairs into the fire or whatever, then you get a hanging idle. :dunno_black:
Interesting qc and mr, I bought my 97 GS new in the spring of 99 and that summer on a very hot day I had hanging idle. I adjusted the problem out by turning the idle speed down very slowly until it dropped off while sitting on the bike at a stop and did that another time or 2 until it was gone never to return for the 4 years and 80k miles I rode it. I've always attributed it to the lean jetting which I never changed.
Quote from: gsJack on November 07, 2016, 09:44:13 AM
Interesting qc and mr, I bought my 97 GS new in the spring of 99 and that summer on a very hot day I had hanging idle. I adjusted the problem out by turning the idle speed down very slowly until it dropped off while sitting on the bike at a stop and did that another time or 2 until it was gone never to return for the 4 years and 80k miles I rode it. I've always attributed it to the lean jetting which I never changed.
OK this is a really good point. You had the idle speed set too high and you discovered (as I have) that there is a range of setting of the idle speed adjuster where it doesn't actually affect the idle speed directly, but it does affect the "hanging idle" or "drooping idle" conditions. If the air passageways in the pilot circuit are clear then the bike will probably idle with the throttle nearly closed, and closing it too much makes it idle rich and you get an "idle droop" while running it too high makes it idle lean and you get "hanging idle".
I have observed this phenomenon.
Here's hoping the shop sets all this correctly when my bike goes back together. I am guessing "top end rebuild" will include setting idle speed, mixture, and balancing the carbs, since flow and vacuum should change a lot when going from 80/120psi compression to 160+psi on both cylinders.
That, by the way, brings it back to the original problem. Vacuum is a direct result of compression. Low compression will mean low vacuum. Low vacuum will mean less fuel being sucked through the pilot jet, and thus a lower idle speed, since you have less fuel and must match it with less air. Adding too much air via the idle speed knob would make it lean and you'd get hanging idle. Making it richer is hardly the answer since you're going to go to 3-4 turns out and still not have nearly enough vacuum to pull enough fuel, and once you rev it off idle vacuum goes WAY up and it'll run mega rich at part throttle and low (under say 7K) revs. Ask me how I know all of this...
This is precisely the same thing that happens when you have a massive vacuum leak... low vacuum means poor fueling from the jets blah blah you wind up with a lean-rich-lean kind of condition that's undiagnosable without fixing the root problem first... in this case the root problem is low compression but it may as well have been (and may still also be) vacuum leaks.
FYI, gold nuggets in here too.
http://rec.motorcycles.tech.narkive.com/X7yWLgwN/yamaha-xs400-mikuni-bs34-what-s-this-hole-in-my-carb#post5
I'm going to wind up reading that entire archive at this rate.
Anyway, the point here is about setting the idle mixture too RICH, then upping the idle SPEED to try and compensate (more air), then when the engine is warm, idle hangs at 4K rpm.
And if you do this for very long, you wind up with carbon on the valves, bent valves, and an engine rebuild bill (again, ask me how I know).
Psshhhh, everyone knows drooping idle is caused by the carb sorcerer forgetting to add the second newt eye to his potion.