Bonneville America Forums Forums General Motorcycle Forums Other Bikes I need help with a 1980 Honda Cx500 Custom...

Ok, so my buddy just got his first motorcycle... it was laid down so we are fixing it up and learning along the way (neither of us having any prior mechanical knowlege). Here is the situation, we replaced the gas tank because it had a hole it it, the one we got had rust in it, so we soaked it with boric acid, rust gone thouroughly rinsed. The bike was laid down on the right side although it doesn't look like the throttle took much if any damage (bar bent and replaced) The bike, runs pretty good, but we added a little seafoam to the gas just until we could take it in for a professional tune up, but thought that if we could figure out the problem, we might try and wrench on it ourselves to learn... seeing as the warranty ran out a long time ago. Here goes, the bike red lines at about 10k, the bike accelerates strong to about 7k and then will act as though it is hitting a rev limiter and just pulse around 5k. If I let off the throttle a little bit it will start accelerating and I then shift to second. In second, it will do the same. It kinda seems like it could be related to throttle position, but i am unsure at this point, is it possible that it could be related to the carbs? I haven't checked the sparkplugs yet, but it didn't seem like there was an issue with either. Just a little lost and would like to get his bike running any ideas i would be happy to investigate. The maintenence regiment is unknown because the guy that he got it from, got it not too long ago and then he laid it down... So within probably the last 4 months it has changed hands twice... Thank you in advance for any help or ideas.

You need to remove, totally disassemble the carbs, clean the heck out of them, reinstall them, then ride away happily. I bet they are all glazed up inside and it's starving for gas. Very common on the old Hondas, especially if it hasn't run in over 6 months or so. With the description of the gas tank, I bet this is the problem.

Agreed, swap out the fuel lines too we had an old one that would clog in the line enough gas to still run but it would starve at full throttle.

And the petcock too, pull it and clean it out.
I forgot that one.

All right, love this, now as i said before, not mechanically inclined, is there something in particular that i should clean the carbs with? I will change out the fuel line as well as the in-line filter.

Carb cleaner??
If they are really glazed up, you can just soak the entire carb (rubber boots off first) in a big sealed tub of the stuff for 24 hours.
For really nasty stuff, you can even use paint thinner or acetone on the metal parts.

I just rembered my buddy has the same bike and I cleaned out his carbs last week. The carbs themselves are almost identical to the ones on our triumphs. if you use pats rejetting guide it will show you how to open them all up, so that you can clean them all out. On one the carbs you will notice a "growth" on the bottom be sure to take apart seprate and clean it, it looks like a diafram so that could also be the cause of the problem.

Well, that is do-able, suppose ammonia would work too. Now, gotta find new gaskets before i tear into this thing, that is proving to be more difficult than i imagined... on hold with a honda dealer...

Have you tried any CX500 forums? Might be a good place to find out where parts can be had. I found these 2:

http://groups.msn.com/HondaGLCX500650

http://groups.yahoo.com/group/cx-500/

Cant give you any advice on how to get it running right, BUT. When you do get it running right, they are great bikes. The engine is anyway, will run for ever and will take some serious abuse. CX500's were the work horse of London Despatch Riders for years. Probably still are. I had a couple of them, thrashed the bollocks of the things. Dropped them repeatedly but it didnt seem to affect them much. Even with bent frames the handling didnt seem to get affected. Maybe that was because they handled like $hit of the show room floor.

Many a time i would come out of a corner, bike pitching and wallowing and shaking all over the place laughing my head of thinking "how did i get away with that one". ha ha Good times

before you do anything, get a new air filter. sounds like it's starving for air.

now is that the guzzi looking twin?

those are nice.
cat web pagehttp://cx500.gobinet.se/[/url]

Okay, This has been delayed a bit... buddy left town, he wants to wrench and learn too, so by next weekend we will try the easy things first. Air filter, fuel line/filter, and if neither of those fix it, the carbs go next... So plan of attack is covered... I'll let you know how it turns out step by step. Bragging rights will definately go to the guy that diagnosed the problem based on my $h!tty discription. Thanks again. (For the parts schematics too)

Here is the update, good news and bad... here's the bad first: My buddy laid the bike down. There was a three car pile up on a four lane and a fourth car swerved into his lane to avoid it, he swerved, but the other car cliped him and he went over the handlebars... Bike is done. The good news: My buddy, few minor scrapes and a torn muscle in his shoulder was the total damage... Lucky for him, but probably a long time before, if ever, he will ride again. Thank you all for your input.

Ouch, sorry to hear the bike had a short life after getting it running again, but glad your buddy made it out alive.

Just out of curiosity, what did you end up doing to get the bike running again?

That is the crappy part, he was riding the bike in less than optimal condition... he kinda halfa$$ed this deal and that may have lead to his problem in the accident, that and inexperience (only had permit). The bike ran for the most part fine except for the above mentioned problem, he couldn't find the time to devote to replacing the air filter which i now own, gas line and filter, or taking the carbs apart... so it never was restored to proper working order... It was a shame, but i guess he didn't care that the bike was not really functional in my opinion. Oh well... maybe he learned something from this... I guess he hadn't got insurance yet either... Big ticket and loss of license for 90 days... With friends like these... i should have been a lawyer.