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New 1978' CX500 Owner in SE Michigan

2K views 33 replies 11 participants last post by  2ndCXowner 
#1 ·
New to the world of CX500's and new to this forum. Just brought home yesterday a 1978' CX500 with 17,000 miles that hasnt run in years. All original non modified bike that is a little rought and needs to be completely gone thru. Need to see if I can sort out low compression in both cylinders, 60 PSI in left cyl and 90 PSI in the right. Hoping these numbers will come up once I get it running. I have wanted one of these CX500's for years and have been playing with older (90's) Harley's. Just finished a custom 97' Harley Sportster 883 Scrambler build in March this year and decided I needed another project. Originally I wanted to do a custom build with this bike but thinking about restoring it? Need to get it running first and then see how I feel. G.B.
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#3 ·
The low compression could be simple as poor valve adjustment or stuck piston rings or testing technique.

You are making a good choice to get it into running condition before any modifications.

At 17K miles, that bike is barely broken in. Likely only needs a good maintenance job.
 
#5 ·
It just dawned on me after trying to look the bike over from top to bottom when I was buying the bike that I did not hold the throttle open when I did my compression checks. I just reran the test removing both spark plugs and making sure to put a little grease on the compression tester o-ring. With the full throttle cold I got 85 PSI in the left cyl and 100 PSI in the right. Still not happy with the 20% difference but it is what it is right now. However, the motor will definitely run with those numbers and still hope it comes up a little more after it is running.
 
#7 ·
Keep it stock, at least until you can ride and find out if it wants any changes. My Standard is mostly stock, and there's little that I would want to be different.
 
#9 ·
They are only original once, here is another vote for bringing it back to its former glory as opposed to customizing it.
 
#10 ·
Welcome aboard! I grew up just North of Detroit. 11 mile & John R

That's beauty! I vote for Restore! Learn what you can from this bike and get an ugly basket case to customized.
 
#12 ·
Thanks to all for your comments and support. My first priority is to hear it run. Unfortunately I am stumped at the moment with this bike? I cant get it to even pop once. It just cranks and cranks regardless of what I do. I almost think the compression it too low? This is what I have checked or tried.
  1. Compression has dropped in the right cylinder from 100 PSI to 60 for some reason
  2. The left cylinder is still at 80 PSI
  3. I pulled the rocker covers and the valves seem to operate as they should
  4. The bike had the wrong spark plugs in it which were almost 3 mm longer in length than the correct NGK D8EA
  5. Have what looks like really good spark now in both cylinders
  6. If I spray starting fluid in thru the carbs it doesnt seem to get to the cylinder?
  7. Even spraying starting fluid in each cylinder I get nothing but cranking
  8. It almost seems like the engine is over pressurized?
  9. The mufflers and H pipe were full of mouse nest. Running just head pipes at the moment
I have worked on all kinds of engines and not sure why this one wont run. What am I missing?
Thanks, G.B.
 
#15 ·
  1. Have what looks like really good spark now in both cylinders
  2. If I spray starting fluid in thru the carbs it doesnt seem to get to the cylinder?
  3. Even spraying starting fluid in each cylinder I get nothing but cranking
  4. It almost seems like the engine is over pressurized?
Hi Gone Blue. A good spark at the wrong time won't work. Have you checked that spark is occurring at the proper time?
Have you tried to spray starter fluid through the ports on the intake runners?
What symptom makes you think that the engine is over pressurized?
 
#13 ·
Have you checked for spark? The CDI system is a known weak point...

Welcome to the forum. Please add your location to your profile and your bike's model and model year to your signature so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).

And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old and the Previous Owners may or may not have done the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. I'm sure you already know to check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet) and that that original rubber brake line should have been be replaced every 2 or 3 fluid changes (5 or 6 years) and modern stainless braided ones last practically forever and double the life of the fluid but don't forget things like the rad hoses and swingarm boot too.

Nolimitz: If no bike has ever told you what needs to be changed to make it do what you want/need better either you have been very lucky to find bikes that already do what you need or you just aren't listening ;-)
 
#17 ·
Have you checked for spark? The CDI system is a known weak point...

Welcome to the forum. Please add your location to your profile and your bike's model and model year to your signature so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).

And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old and the Previous Owners may or may not have done the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. I'm sure you already know to check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet) and that that original rubber brake line should have been be replaced every 2 or 3 fluid changes (5 or 6 years) and modern stainless braided ones last practically forever and double the life of the fluid but don't forget things like the rad hoses and swingarm boot too.

Nolimitz: If no bike has ever told you what needs to be changed to make it do what you want/need better either you have been very lucky to find bikes that already do what you need or you just aren't listening ;-)
I had spark originally but have even better spark with a correct set of new plugs.

I have had my location in my profile from when I first registered and just added my bike info to my signature, Thanks
 
#19 ·
Yeah I was thinking a leak down test would be helpful. Need to canvas my friends to see who has one. I know all the valve seemed to be working ealier but that might have been when I had 100 PSI in the right cylinder. Now that this cylinder has dropped to 60 PSI, could it be a stuck valve or stuck piston ring? Thanks
 
#16 ·
D'oh! I missed when you said you have good spark. Yeah, check that the coils &c are connected correctly so it isn't sparking one when the other should be firing.
 
#18 ·
Are the plugs wet? If they are dry it oculd be gummed up carbs. Try removing the screw on the vacuum port on one of the intake manifolds and spraying the starting fluid in there (this should put it directly into the cylinder, bypassing the carb)

If they are wet (= fuel is getting to the cylinders) and you haven't seen it actually run try swapping the plug wires left to right.
 
#21 ·
The only time the plugs were wet was when I sprayed starting fluid right into the cylinders. When spraying starting fluid thru the carb with the throttle plates help open and thru the intake runners, the plugs are dry?

Thanks, G.B.
 
#22 ·
Hmmm... You could try taking the valve covers off and turning the engine by hand (remove the small round cover below the rad and insert a wrench) while watching what the valves are doing. Whenever a valve is closed its rocker will not have tension so if one of the rockers is never loose that valve is probably stuck.
 
#26 ·
Yeah earlier when I had the rocker covers off, I did crank the engine enough to make sure all of the valves did go for tight uinder tension to loose with some free play. It is worth doing it again. I have to say, that I am leaning to that I just dont have enough compression to fire the motor? With the factory spec new at 170 PSI, I am a long way from there at 80 and 60 PSI? Thanks again, G.B.
 
#23 ·
Do you have access to a bore scope Gone Blue? Having one would let you inspect the condition of the valves through the spark plug hole.
Air blowing out of the carb could be an indication of bad valve timing or more likely a stuck or burnt valve.
 
#25 ·
My bore scope has a little mirror which can be attached to the camera.
 
#27 · (Edited)
Ah. Mine (the box says "endoscope" but I haven't found anyone willing to try it for that) doesn't.

If you had more compression than you do now it might be a good place to look. It is certainly an easy thing to check...
 
#29 ·
Gone Blue try adding some oil to each cylinder and redo the compression test. If the compression improves indicates a piston ring problem. If no change probably a valve problem.
 
#30 ·
Thanks for the suggestion reclinedrelic.I checked the right cylinder again tonight and it was still at 60 PSI. I then dumped in some engine oil and I got 180 PSI. So I would say I have some stuck rings. I then checked the left cylinder that was last at 80 PSI and it now read 130 PSI. It appears all of the starting fluid I sprayed in the cylinders loosed that side up. So I plan to just dump some more oil in the cylinders and let it set for a couple days to see if that would loosen up any stuck rings. This will give me a chance to go thru the carbs so I can try and start it using them and some gasoline instead of starting fluid. Thanks to all for your sugestions and idea! Stay tuned. G.B.
 
#32 ·
If you’ve sprayed a bunch of starting fluid and or other fluids in the cylinders I’d change the oil before you run it for any length of time since the oil will be diluted.
 
#33 ·
Any starting fluid (ether) that gets past the rings should evaporate and pass out through the breather the first time the engine warms up and regular oil as used for the test shouldn't hurt if it mixes with what is in the crankcase but if you use anything else (such as the heating oil I mentioned) it wouldn't be a bad idea to change the oil afterward.
 
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