[jro75]

Hello all, new member and have hit a dead end with my bike...hoping someone can help me out.

I have a 75 CB500T, have been riding it for about a year and a half. This is my first 4 stroke road bike, and I have learned a lot since owning it. In addition to doing basic preventive/catch-up maintance, a few issues have popped up that I have been able to figure out/solve.

Anyway, recently I fired it up, it ran poorly for a few seconds, and then died. I haven't been able to get it started since.

Gas flows freely from the petcock, floats fill up. Both plugs get a spark (not as good a spark as I would like but decent considering the age of the coils etc). I checked the compression cold (as I cant start it up) and I average 135 left and 140 right. This is with throttle open, choke off, and kicking it over about 5-6 times to get these numbers (it hits about 90 on the first kick). These #'s are pretty low for the 500T, right? could this really account for the sudden non-start?

Any ideas or suggestions appreciated. Merry Christmas/Happy Holidays! -JRO75

 

[tbpmusic]

No mention of it in the Honda 500T Manual.
The compression ratio is listed as 8.5 to 1, somewhat lower than the 450.
So I'd guess optimal compression is somewhere around 170 or so.

Make sure you hold the throttle wide open and NO CHOKE when you check th compression.
The numbers you are getting are pretty poor. Try taking readings again - then pour a little oil in each side through the spark plug holes, and take readings again..

As for not wanting to start, assuming your battery is ok, really bad compression will indeed make it most reluctant to start and run right.
Check your timing too - there's an article here about that.....

 

[jro75]

Thanks, looks like you replied right as I was editing it. Ironically I realized I did not have the throttle open & re-did it.......better numbers but still low. I think there MUST be something else going on though......

 

[ihatespeed]

being hot was worth a good 30 psi on my cl450, but it tops out just over the lower service limit when the test is done as prescribed

 

[tbpmusic]

I think there MUST be something else going on though......

You're probably right - the compression is low (probably 150 is the "red flag"), but most Hondas will still run with compression like yours.

Check the points and timing. Throw in some new spark plugs.
Is the battery ok, you can use the electric starter ok??

 

[tbpmusic]

being hot was worth a good 30 psi on my cl450, but it tops out just over the lower service limit when the test is done as prescribed

Wow, most of the time you don't see such a dramatic increase, usually it's 5-10 pounds.....

 

[ihatespeed]

Probably indicates I'm due for a rebuild

 

[RicH2]

Time for a leak-down test....

 

[66Sprint]

"Anyway, recently I fired it up, it ran poorly for a few seconds, and then died. I haven't been able to get it started since."


A rebuild is due or near, but I'll bet if you just clean the carbs, it will run.....Doesn't take long to plug the jets just sitting for a bit....(Fuel still has to get from the bowl to the cylinders, a full float-bowl means nothing if there's no gas at the spark plug.......)
How long did it sit?......

 

[jro75]

Thanks everyone...

Battery seems good, I have a fancy smart charger at work that in theory will give you a code if it is bad....charges up no prob.

I did recently set the timing "static" using a little bulb......and got it near damn perfect (well, as perfect as you can do it with the 500T set of points). I replaced the left points at that time as they were not looking so good.

But to back up, and this may help with the diagnose, it always hesitated on the left side. I cleaned the carbs, made sure the carbs were mechanically synced (they both had the same slack and pulled the levers at the same time), and adjusted the set screws to idle at the same rpm. Still, the left would not always idle and would take a little acceleration before it kicked in. Hmmmm.

 

[Bird76Mojo]

Sorry to stir the pot here but my 450 had 125 average compression on both cylinders when tested cold and it started easily and ran very well, and also seemed to have plenty of power?? Although I can't vouch for the accuracy of my uncles compression tester... I'm also not aware of the power that a freshly rebuilt 450 has..?

BUT, the specs on compression are what they are. I'm sure you're due for a rebuild...

GB :mrgreen: