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Discussion Starter #1 (Edited)
Hey again forum. Nearly done with a rebuild on a 1980 cx500 custom (picture and video for kicks below!); but just trying to sort out one last mechanical issue.

Bike overheats after 5-10 miles of constant riding (assuming wind/temperature are doing basic cooling during the starts). Have checked, and don't have any coolant leaks or leaks in the coolant reserve tank. We replaced the thermostat as well so we know that is good. Seems to us that the coolant flow is the problem, maybe a water pump issue?

Tach works fine for RPMs but the temperature gauge needle doesn't register the temp rising so when the bike bogs down after a while that is our sign that its a cooling system problem.

We haven't made any whole sale changes to the mechanical portions of the bike (other than pods, exhaust, and re-wiring; all of which we had the bike professionally done. He rebuilt & rejetted carbs based on the new exhaust and re-wired the electrics to the LED turn signals) so we are 85% done.

Would really just like to try and iron out the cooling problem before getting out there. Friends/family have suggested a radiator flush.

Thanks in advance for all your help to date and future advice!

 

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First thing I would check is the 7v regulator output.
If it is putting out more than 7.2vdc it will read as hot.
When it fails it will typically read 9vdc.
 

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Discussion Starter #4
How do you know it's over heating w/o a gauge that works? You may have a bad coil that is temp sensitive
It will bog down after riding and lose power. We shut it down and let it cool off, and then operates normally.

I don't have a ton of riding experience with it, but my partner on the build is pretty convinced it is a cooling issue (He's been riding motos for 40+ years and just rebuilt an SL70 to mint condition! haha)
 

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Couple thoughts for you....

First coils have a tendency to fail when warm....usually the bike will stumble, buck, fart, wheeze,......around 5000 rpm. Check the coil resistance when warm and cold. Both the primary side and secondary side.

Second, what have you placed in front of the radiator?
 

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Couple thoughts for you....

First coils have a tendency to fail when warm....usually the bike will stumble, buck, fart, wheeze,......around 5000 rpm. Check the coil resistance when warm and cold. Both the primary side and secondary side.

Second, what have you placed in front of the radiator?
Thats sort of what happened to mine, later I found a crack in one of my coils.. But it was running great then just bogged down bad.. sat for 10 minutes and it started back up.
 

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Discussion Starter #9
Thanks guys,

we'll take a look and report back on any findings. we haven't put anything in front of the radiator that I know of? It is missing the radiator "shroud" as the PO had removed it, and haven't modified it further.
 

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If it was me, the first thing I would do is get the temp gauge working, otherwise your just guessing. Make sure the 7V reg is properly connected and giving 7VDC (6.95V to 7.05V). Make sure the connection to the sender is not broken (should have about 7V on the sender wire at the sender). If all looks OK, ground the wire from the sender and the gauge should start climbing up to the max position, if not its dead.
Last thing you want to do is have the engine tell you its overheating by bogging, great way to end up with a paperweight. Buy a temp gun and then you can see exactly how hot it gets (measure at the cylinder wall)
 

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The pic that shows the engine from the front looks like it might have something other than the original grille but when viewed full size it reveals that there is no grille at all. Either the part of the pic that shows the rad is badly out of focus or the rad is badly blocked with some sort of dirt or a lot of the rad's fins are bent. If that is the case you could need to spend a couple of hours with a rad comb...

Nothing you have mentioned points specifically to overheating and unless you actually measure the temperature, either with a working temperature gauge or some external measurement device (like an IR non-contact thermometer) you are just making a guess.

Bogging down and working normally again after resting is a classic symptom of poor fuel flow. You don't have a vacuum petcock, do you? I don't think an '80 should have one but if you did and the vacuum and vent hoses were reversed you would have similar symptoms... How about the fuel cap vent? The easiest thing to test would be to open the cap when it bogs - if it picks up again the vent is blocked.

BTW: The bike sounds pretty ratty in that video. Have you balanced the carbs? Do you have an air leak somewhere? The muffler on the left is higher than the one on the right and might be farther out sideways too (a straight on shot from the rear with the bike on the centrestand would confirm). Is there a loose clamp somewhere?
 

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Discussion Starter #12
That in and of it self does not necessarily mean it's a cooling system issue. Have you tried to measure engine temp in any way?
We haven't yet. Getting new tires fitted soon, so we will hopefully check this out once they're off and we're in the process.
 

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Discussion Starter #13
have you checked for fluid in the rad and fluid circulation whne running in the rad?

there could be a issue with the water pump impeller not turning
We are planning on inspecting radiator and potentially a radiator flush as we aren't sure when the last time that was performed (and bike most likely sat a prior to us). We too think it is a water pump impeller issue as well; We shall see.
 

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Discussion Starter #14
If it was me, the first thing I would do is get the temp gauge working, otherwise your just guessing. Make sure the 7V reg is properly connected and giving 7VDC (6.95V to 7.05V). Make sure the connection to the sender is not broken (should have about 7V on the sender wire at the sender). If all looks OK, ground the wire from the sender and the gauge should start climbing up to the max position, if not its dead.
Last thing you want to do is have the engine tell you its overheating by bogging, great way to end up with a paperweight. Buy a temp gun and then you can see exactly how hot it gets (measure at the cylinder wall)
Amen, fingers crossed it doesn't get to the paperweight point and we iron it out before then! Thanks for the temp gun tip, we'll get back on how the Reg and heat testing goes.
 

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Discussion Starter #15
The pic that shows the engine from the front looks like it might have something other than the original grille but when viewed full size it reveals that there is no grille at all. Either the part of the pic that shows the rad is badly out of focus or the rad is badly blocked with some sort of dirt or a lot of the rad's fins are bent. If that is the case you could need to spend a couple of hours with a rad comb...

Nothing you have mentioned points specifically to overheating and unless you actually measure the temperature, either with a working temperature gauge or some external measurement device (like an IR non-contact thermometer) you are just making a guess.

Bogging down and working normally again after resting is a classic symptom of poor fuel flow. You don't have a vacuum petcock, do you? I don't think an '80 should have one but if you did and the vacuum and vent hoses were reversed you would have similar symptoms... How about the fuel cap vent? The easiest thing to test would be to open the cap when it bogs - if it picks up again the vent is blocked.

BTW: The bike sounds pretty ratty in that video. Have you balanced the carbs? Do you have an air leak somewhere? The muffler on the left is higher than the one on the right and might be farther out sideways too (a straight on shot from the rear with the bike on the centrestand would confirm). Is there a loose clamp somewhere?
Correct, the PO removed the grill/radiator cover. The fins have some wear/bent pieces, but don't appear to be too terrible, good shout on the comb idea, worth some time I'm sure. No vaccuum petcock; We don't think it's a fuel flow issue but we'll pop the cap open when it bogs to double check; Not sure if the audio from phone recording is great, but we had the carbs re-built & re-jetted from a builder here in our area, pretty content with the sound performance, not sure if the shorty's are the cause for the "ratty" sound you described. Center Stand was removed, I think the angle of photos doesn't give a good representation, but we'll take a look and double check for loose clamps.
 

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This might seem like a silly question, but how do you check the oil properly without a centrestand?
Hold the bike level or use a bike jack? Its how I do it..
 

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Unrelated to the temperature issue - I suggest you replace the front fork brace/fender mount bracket to stiffen up the front forks , and that you slide the fork tubes back down through the triple trees till there is only about 3/4" max of tube above the top tree, These two actions will make your bike much safer to ride , as the front ends on these are notorious for flexing without the brace , and your front wheel wont connect with the bottom tree under heavy suspension compression , which will be the cause of a major accident for bike and rider.
 

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Maybe if you used 2 jacks and a level.... A few degrees of tilt can make quite a difference on the dipstick.... And removing a wheel must he a real pleasure...
Many bikes don't come with a center stand, just saying.. My Jack holds my bike up without any issues, and I generally just sit on my bike and pull the dipstick to check.. its accurate enough, my bike has never had an issue nor any of my other bikes that never had a center stand from the factory.
 
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