1980 CX500 - Won't go above 55mph

[jmorgan]

I purchased my first bike last night, an 1980 CX500 Custom. I think I made a very good deal, however the guy told me his father gave him the bike when he got too old to ride and ever since he had it the bike would not go above 55mph.

He says if you get on it, it will take off and go but when you hit 55 it "falls on its face", if you back off and ease up to it you can go over 55mph. The bike sounded fine, and didn't' hear any motor noise. I am not nearly as knowledgeable on bikes as i am cars but I really didn't' see how this could be anything engine related. I am just hoping its not one of those kind of parts that cost an arm and leg and a known issue with these bikes.

I did some google searches, and looking around and couldn't find any information about this problem. Maybe I am wording it incorrectly? I haven't driven it yet, so I can't say first hand what the problem is, I felt comfortable with the guy and got one heck of a deal on the bike. I'd like to think its something along the lines of something like a governor causing this issue, but honestly have no clue if this bike even has such a thing.

Any help is appreciated, I will be looking for a forum to call home now that I am getting into bikes! I have always wanted one, and well after a family crisis I finally decided to get one!

[Kickstart]

Hi

How much use has the bike had, or has it just spent ages sat around?

Is the problem speed related or rev related? Ie, if it hits 55 in top at 4000rpm (guess), then will it go significiently over those revs in lower gears?

Personally my first guess would be in the carbs. Take them off and clean the jets, and check the carb diaphragms.

All the best

Keith
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[stinkwheel]

At 55mph, is it even running on both cylinders?

Are both header pipes getting hot?
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jmorgan]

From what he told me its not rev related, its speed. I wont' know till I ride it which won't be sometime next week at the earliest. I decided to get a bike, and started watching and found this great deal so I loaded it in a pickup and brought it home. I still have to get a helmet, take the class, etc etc. I've ridden dirt bikes when I was younger and loved them, but I am sure this will handle quit different so I wont' take the course for both insurance, and safety reasons. I just couldn't turn down that I thought was a good deal!

The bike was purchased by his father, then gave to the son when he got too old to ride it. He tagged and drove it some last year then put it away for winter. The bike has about 42k miles on it. I am going to guess it has sat quite a bit.

Part of the reason I got a good deal was that he couldn't get it running for me. It would fire right up on starting fluid then die, he said gas sat in the tank all winter(could smell it), and his wife put it up for sale before he had time to get it running. I was comfortable with what I hear, when it ran off what he sprayed in the carbs that the motor was most likely ok. I also had a good feeling about the guy, apparently he had several dirt bikes, jet ski, a race car etc and his wife is making him sell most of it except the race car since thats all he does now.

I will be pulling the carbs off and cleaning them, I just wanted to get some ideas in case while I was doing the maintenance on it before I ride there was something else I should check/replace that is known to cause this issue.

I plan on getting it running next week, so any suggestions or things to check I will check then. Any comments, or suggestions welcomed:) I have been around bikes since my father owned a pawn shop and we got them in from time to time, however I have never owned one personally.

[Cigaro]

So the engine will quite happily rev to the top in, for instance, first gear, but the bike just won't go over 55? sounds odd. I'd get it running first (clean the carbs out, fresh tank of fuel and new spark plugs should do it) and then see exactly what happens.

[stinkwheel]

Check there are no dead animals/wasps nests in the airbox too.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[hmmmnz]

i used to have a cx400 same bike but sleeved down barrells,
when i got it it ran like pants, but new spark plugs and oil change and she was away,
42000 miles is nothing on a cx,
i got well over 100000 on mine before i sold it
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the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[jmorgan]

I got the thing running after cleaning the tank, replacing plugs and replacing fuel lines.


If you drive it, it is sluggish for what i'd expect.. I drove it in a circle for a while in case it broke down I wouldn't have far to walk. In first gear it is usually ok, however in 2nd it is getting to where it will just lose RPM and no matter how much throttle u give it, it just dies.

I messed with the idle screw, and I imagine i have it all kinds of screwed up now.. but it idles at about 1200-1500 rpm with choke in.. if you pull the choke the rpm doubles.

I noticed tonight that the right cylinder was warm to the touch, while I burnt the crap out of my hand on the left cylinder after lugging it around the parking lot a couple minutes. I pulled the plug, and confirmed it was getting fire. I pulled the air hose going to the air box off and it appeared the second cylinder started firing? I have the air filter out, but that screen is still in there(No clue how to get that out..

Also, if I put my hand over the inlet on the carb where the hose was, the rpms would go up and the engine sound would change..

[Odie]

Sorry to say it guys but i think you are all wrong.......... CX's suffer from the dodgy alternator problem that wont let the ignition advancer go past 4,000 to 5,000 rpm if its on its way out or buggered, sounds like thats the problem.
only cure is engine out and replace alternator and ignition advance coils.
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You are so ugly when you were born the doctor said "I?m gonna drop it, if it falls is a rat, if it flies is a bat."

[jmorgan]

Well I finally drove the stupid thing!

Ended up taking the float bowls off, and sure enough full of crap.. cleaned both of em and now it runs on both cylinders. Also replaced the air filter with a KN, the old one was nasstty

It runs ok, some backfiring/popping on overrun and driving... thinking just sync issues and pilot screw settings..

however, it will not.. I mean will not go over 5k~ rpm. Its like you hit a wall. When you hit 5k~ it starts sputtering, the more gas you give the worse it is.

My stator voltages check out, not even "within" a range, but dead on 100volts in the blue wire and 90 in the white.


I'm a bit stumped at this point, I removed both coils and scraped around the mounting spots and remounted, no change.

[Kal]

If Oddie suggested a fix for a CX it is worth investigating.

Rather you than me wih dropping the engine out though... good luck.
____________________
Kal...
I Like To Hoon It Hoon It I Like To Hoon It Hoon It I Like To Hoon It Hoon It Ya Like To (HOON IT!).
1984 GB250 Clubman,1983 CB250N Superdream, 1999 GPZ500S

[jmorgan]

oddie is right it "could" be that stator, but im sure he will agree the symptoms of a stator can be the same as anything from a clogged air filter, bad plugs, bad wires, bad coil, bad connections, a short.

I've tested my stator's voltage and it appears correct(blue=100, white =90). At 2500rpm my battery is at the 14.x voltage. i'll finish checking the resistances tomorrow. The sad part is, everything can check out "correct" with the stator, and it still be faulty or dying.

I need to do the "white wire fix", as a test with a Y cable, but to be honest im afraid of what the results might be

I did notice today when I took it out, I was in 2nd gear and hit the 5k~ wall, I pulled the choke out and it kept on going up past 7k~rpm like no problem. This to me points at the carbs, or maybe thats just wishful thinking:)

[virus]

Going purely on what you said about the choke, and the fact you've put a K+N on without putting bigger jets in, then Id think its running lean.

Time for more carb work.


Cheers
John
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own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[Finglonga]

[jmorgan]

What is so bad about KN?

I put the old filter back in with no change in performance. I thought it fixed it at first, since before the bike full warmed up it went over 5k~ however once it got up to full temp the bog came back.. (found this out on the highway %_%)

If I crank it, let it idle till its warmed up to not die and hop on it.. it will just scream past 5k.. however once the engine's temp is up past halfway it bogs at 5k, unless you just ever so slowly approach it and get the throttle just right and it will slide past it.. however it will randomly bog back down to 5k /t