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1982 Honda GL500 Silverwing / Cafe Racer
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Discussion Starter · #1 ·
Hi all, first time poster and new GL500 owner here.

I bought the bike around 2 weeks ago , which had been rebuilt in 2020 as a cafe racer, but subsequently left stored for around a year after minimal use. I’ve given it a recommission (sticky brakes, clutch adjustment , carb & choke cleaned up) and all seems to be working as it should now , however when testing top end I found a strange problem.

The bike won’t go beyond 82mph/120kph ish , despite everything I’ve read indicating it should reach 100+mph.

Obviously I don’t intend on sitting at 100, but at present motorway driving is a real problem as engine absolutely screaming.

From observations it seems to be a gearing quirk because when in 5th gear at 82mph engine is up at 10,000 RPM -when trying to throttle beyond this point I can hear the valves bouncing and loss of power.

It doesn’t feel like the clutch is slipping , because acceleration & RPM are linear together up to this point. For background the bike has the 16” rear wheel, but surely that wouldn’t account for 20+mph loss off top end?

I would really welcome any ideas and help on solving it, thank you!
 

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You sure you're actually in 5th? Sounds like you're in 4th. These bikes are geared pretty short compared to modern stuff though, they generally are around 7000 rpm at modern highway speeds.

Redline is 9500ish. There is no rev limiter stock. Hopefully you haven't damaged anything over-revving the engine; if the valves were floating badly enough that you could hear them, you've probably taken some life out things. Often a valve head will break off the stem doing that, or you'll tag a valve with a piston.

Rim size doesn't necessarily matter, the rolling diameter of the tire does. If it has the wrong size tire on it, sure, that could account for some loss of top end, but it probably also looks a bit odd. I'm not sure anyone even makes a 16 small enough to cause that much of an overall gearing difference. With stock size tires, the outer diameter of the 16" and 18" rear is very similar.

The stock speedometer (and tach for that matter) are often somewhat inaccurate. While these bikes, in a good state of tune, can touch 100, they take a long time to get there and are right around redline in 5th at that speed.
 

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1982 Honda GL500 Silverwing / Cafe Racer
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Discussion Starter · #3 ·
Hi LC8 ,

thanks for the reply , also hoping nothing damaged but seems to sounds smooth and pull fine still. It did occur to me there might be another gear up , but I’ve counted as I shift up to double check and it’s definitely in 5th gear redlining at 82mph, also when I try to shift up again there is just free play in the lever … there is no resistance as you would expect if it was contacting something… it’s really weird
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Check the shift lever. It might be contacting engine case before reaching top gear.
(I know, the lever position doesn't step up with the gearing, but 5th might be a longer throw than the others.)
 

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'84 CX650E that is evolving into a GL500
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Having lived for a year with a transmission that wouldn't stay in 5th gear on the rare occasions when I could even get it to shift into 5th it really does sound like it isn't in 5th to me too. Mine was a 650 so its top speed was close to 130 Km/h and that's more than enough for the roads I used it on.

Note also that the 16" wheel is stock for the GL500 (& later CX500 models) and that unless it has a tire significantly smaller than the recommended 130/90-16 that shouldn't affect the top speed or the speed vs RPM the way you describe. FWIW, it is the circumference of the tire that counts, not the wheel diameter and the circumference of the 130/90-16 is within a couple of percent of the circumference of the 3.75-18 tire they recommended for the 18" wheel on earlier CX500 models.

Welcome to the forum 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 (in spite of what the Previous Owner did to customize it) may or may not have had all of 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. 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). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid). And don't forget things like the rad hoses and the boot between the engine and swingarm (they can crack on the bottom where you don't see it).
 

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1981 CX500C
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Hmmm...... Last time I used circle math..... The diameter and circumference were intimately related by PI (3.1416....).

Maybe things have changed since New Math made its way into schools.


OP, when you make the initial shift into 5th gear, do you see a drop in engine rpm at the bike's speed? If so, then the bike is making 5th and something else is constraining.
 

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'84 CX650E that is evolving into a GL500
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Yes, but it is the circumference of the tire that matters, not the circumference of the wheel the tire is mounted on. A fat tire on a smaller rim can easily be the same size or bigger than a skinny tire on a bigger rim.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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A fat tire on a smaller rim can easily be the same size or bigger than a skinny tire on a bigger rim.
I was surprised to discover that the OD of a knobby tire on a 21" CR125 front wheel is the same as a GL500's 19".
 

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1982 Honda GL500 Silverwing / Cafe Racer
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Discussion Starter · #9 ·
Hmmm...... Last time I used circle math..... The diameter and circumference were intimately related by PI (3.1416....).

Maybe things have changed since New Math made its way into schools.


OP, when you make the initial shift into 5th gear, do you see a drop in engine rpm at the bike's speed? If so, then the bike is making 5th and something else is constraining.
I’m sure it does drop yes .. I’m going to double (triple ) check this on another test run tomorrow .. will count the gears as I go up and try note speed at 9500rpm for each
 

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1982 Honda GL500 Silverwing / Cafe Racer
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Discussion Starter · #10 ·
Having lived for a year with a transmission that wouldn't stay in 5th gear on the rare occasions when I could even get it to shift into 5th it really does sound like it isn't in 5th to me too. Mine was a 650 so its top speed was close to 130 Km/h and that's more than enough for the roads I used it on.

Note also that the 16" wheel is stock for the GL500 (& later CX500 models) and that unless it has a tire significantly smaller than the recommended 130/90-16 that shouldn't affect the top speed or the speed vs RPM the way you describe. FWIW, it is the circumference of the tire that counts, not the wheel diameter and the circumference of the 130/90-16 is within a couple of percent of the circumference of the 3.75-18 tire they recommended for the 18" wheel on earlier CX500 models.

Welcome to the forum 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 (in spite of what the Previous Owner did to customize it) may or may not have had all of 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. 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). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid). And don't forget things like the rad hoses and the boot between the engine and swingarm (they can crack on the bottom where you don't see it).
thank you for the welcome and appreciate this sage advice , thorough inspection and replacing all perishables is high on the list ..notice brake pistons are missing couple of rubber dust boots etc so absolutely needs too to bottom check over which I hope to complete soon
 

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1981 CX500C
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@Roostr........

No. You misunderstand my post.

Take note of the engine speed (rpm) when you shift from 4th to 5th. When engaging 5th from 4th, your bike speed (mph) hasn't changed. AS 5th is engaged, note the engine speed (rpm).

You should see the engine speed (rpm) drop when engaging 5th gear from 4th.

I hope you are shifting before 9500 rpm. If you're shifting at 9500 rpm, then I suspect your engine will soon disintegrate.
 

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1982 Honda GL500 Silverwing / Cafe Racer
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Discussion Starter · #12 ·
OK so I double checked this today , and if I maintain speed in 4th , I definitely do get a drop in revs into 5th .. and counted the gears again and absolutely positive there are 5 gears and every one progressively drops RPM when changing at fixed speed . Very confused .. Any ideas where I could look next?
 

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OK so I double checked this today , and if I maintain speed in 4th , I definitely do get a drop in revs into 5th .. and counted the gears again and absolutely positive there are 5 gears and every one progressively drops RPM when changing at fixed speed . Very confused .. Any ideas where I could look next?
if you are 1000% sure you're getting into 5th, check the clutch cable and make sure its adjusted correctly. If it is, I'd look into replacing the clutch.
 

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1982 Honda GL500 Silverwing / Cafe Racer
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Discussion Starter · #15 ·
if you are 1000% sure you're getting into 5th, check the clutch cable and make sure its adjusted correctly. If it is, I'd look into replacing the clutch.
It doesn't feel like clutch slip because acceleration pulling OK and fairly linear up to redline, the plot thickens here too ... I just found that if the wrong clutch had been fitted by previous owner it would effect final drive ratio, now I'm wondering if that could be the case with mine.

 

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Discussion Starter · #16 ·
What size rear tire are you running? If the tire is correct I would suspect the clutch is slipping. Something is definitely amiss to be at 10,000 rpm’s at 82mph. If I am remembering correctly I think I was right at 8000 rpm’s at 85 mph with my 1982 gl500i.
Rear is the 16" , but others mentioned overall outside diameter is the important factor and tyre size looks correct to factory spec
 

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Rear is the 16" , but others mentioned overall outside diameter is the important factor and tyre size looks correct to factory spec
if the bike is at redline at 82mph, your clutch is more than likely slipping. youd have to have a micro wheel on the bike for it to drop the top speed by over 18mph.

Theres only two known clutch baskets to fit these bikes, the factory 500 and the 650 basket. The 650 basket would drop your RPM's, not raise them.
 

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'84 CX650E that is evolving into a GL500
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I was thinking the same thing. The smallest tire anyone could get to mount might be a 110/90-16 and that would make less than 6% difference so unless the clutch is slipping badly I would suspect the speedometer &/or tachometer.
 

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The clutch is most likely to slip when under a load, such as the wind resistance at speeds over 80 mph. If you have some steep hills in your are see what happens when riding up the hills. The extra load of riding up a hill will also induce clutch slip.
 
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