[BoilerUp]

Hi everyone,



I have an '81 GL500 that I'm having a mystery issue with. Up until a month or so ago it was running like a champ, but then one morning while I was out on the road I was suddenly getting poor performance. Out of the blue, I could barely get any acceleration as it took time to even get it up to 40 mph even with high engine RPMs, was backfiring, with a funny smell from the exhaust. So far I changed the spark plugs, took the carburetors off, inspected them then went ahead with cleaning and rebuilding them using a Randakk kit, and I've cleaned and re-oiled the air filter. I tried test riding it yesterday and it was still accelerating poorly with erratic RPMs. Also it is no longer backfiring but the exhaust still smells funny. While I have the choke pulled out when cold-starting the engine the RPM is up around 3,000/min, however the choke as it is now seems to have little if any affect on the engine RPM although it will cause the engine to die after a few seconds with the choke pulled out. Even with it pulled out upon startup I still need to keep cranking the throttle to keep the engine going.



I'm at a bit of a loss at this point what could suddenly cause all these problems and why it's so hard to trace down. I hope my symptom description made sense. I feel like I'm grasping for straws at this point and any help and/or suggestions would be greatly appreciated!



Thanks!



David

 

[Allan]

Check the main fuse, I am not sure if this is your problem but it could be.



See these pages at DaveF's website,



Main fuse modification.



Electrical Troubleshooting

 

[BoilerUp]

Check the main fuse, I am not sure if this is your problem but it could be.



See these pages at DaveF's website,



Main fuse modification.



Electrical Troubleshooting

I replaced my main fuse with the modification he illustrated on his website a year or more ago. That should be a good connection. As it stands, the bike starts up right away. It seems to idle sort of okay, but get it out on the street and there is little acceleration even when cranking the throttle.

 

[phantomcxmenance]

you have carb problems, get larry's carb book and do a rebuild

 

[BoilerUp]

you have carb problems, get larry's carb book and do a rebuild

I did exactly that already, following the cleaning/rebuild book to the letter. I used "Cleaning the Honda CX500 Carburetor" by Mike Nixon using a rebuild kit from Randakk.



David

 

[phantomcxmenance]

can you get hold of another good set of carbs from a forum member to rule this out?

 

[BoilerUp]

can you get hold of another good set of carbs from a forum member to rule this out?

I've been looking for a second set of carbs anyway. So far I've been looking on eBay, but if you know of anyone selling a set please point me in that direction!



Thanks,



David

 

[ramprat06]

Our resident carb guru Larry, LRCXed, He may have a set, and his book is also one of the best guides you can possibly get. Not putting down Mike Nixon, just sayin'. Shoot him a PM, but I expect he'll post here shortly anyway.



That certainly sounds like your problem area to me as well. It might be possible you have a funky stator, but we'd have to know more details on the bike, like mileage and other history.



Joel in the Couve.

 

[JohnW]

sounds like you are running on one cylinder. Compare the heat on the exhausts: don't touch them! just get close and feel the heat to compare. That would explain the poor performance and the smelly exhaust.

If so, check spark, sparkplug and wiring. You may have to dismantle the plug boots to check if you have a corrosion problem on the resistor/spring/stud combo in the boot.

 

[Shep]

Have you tried new plugs and or Plug caps?



Check the resistance of the plug caps.If resistor type plug caps they should not exceed 10k ohms.Even one bad plug/plug cap or bad coil can cause rev limits.



Click here as well,



http://globalcxglvtwins.hostingdelivered.com/viewtopic.php?f=8&t=84



Also check the Advance and Retard unit as according to your post both sides are affected.



Also check fuel filler cap vent hole just in case there's fuel starvation by partial vacuum in the tank.





HTH

 

[richnct]

Also consider that the air filter may be getting clogged up. It's heavy pollen season around here, everything is clogging up. I have seen an air filter go bad in the course of one day's ride when a dirty filter was ridden in the rain, and it choked the filter. Also, you did not mention checking the vacuum hose to the fuel petcock (your GL has a vac petcock), look for splits at the ends if it is original. This causes fuel starvation issues for some time before it stops delivering fuel altogether. What I'm thinking here is that the problem came on fairly suddenly, carb and HT ignition issues are more often from sitting extended periods of time, due to varnish and corrosion.

 

[bandit]

i think you have an air leak,check all 6 joints at the carbs,also the carb to petcock tube.

use brake cleaner with the engine ticking over,spray all around those joints,any change in revs,up or down,you have a leak

 

[phantomcxmenance]

check your air filter for the dreaded mayonaise, smelly carp that i sand it could be th esource of your trouble, other thing is have you checked your exhaust that no resident rodent has taken up residence?

 

[bearman1]

(Essay Question): Did you say you "oiled" the air filter? Just what part of your filter did you "oil"?.......And, WHY?

 

[Cobram]

and I've cleaned and re-oiled the air filter.

(Essay Question): Did you say you "oiled" the air filter? Just what part of your filter did you "oil"?.......And, WHY?

Unless it's a K&N wet filter, I think you may have found a major part of the problem here.

 

[Allan]

Unless it's a K&N wet filter, I think you may have found a major part of the problem here.

I noticed that too, but he said he was having a problem before he re-oiled the filter.

 

[Randall-in-Mpls]

I use an UNI oiled foam filter, and I've had no trouble with it.



Can you describe the smell in the exhaust? With the sudden onset, I'm thinking head gasket failure.





R

 

[ramprat06]

I use a K/N filter, oiled it last spring. Never noticed a whimper of difference from the stock one. The fact that some gripe about them affecting things has not been my case. But I never made any modifications either. (talking about my cx500c)

 

[bearman1]

I'm assuming (and that COULD be a bad thing.........lol), that he has a stock set-up. Without his details, is hard to be sure.