Honda CX 500 Forum banner
1 - 18 of 18 Posts

·
Registered
Joined
·
1,493 Posts
Discussion Starter · #1 ·
OK, so I have a 2-1 MAC exhaust and I believe 1980 carbs on my 1980 engine, which is in my 1979 CX500C. When I start the bike up it seems to purr right away, but after I run the throttle on the road and decelerate, I find the engine still running high rpms. Along with this there is considerable sputter noises around 4 - 5 grand. I'm led to believe this is jetting/mix screw stuff, but just wondering if it could be because of the MAC system running on stock carbs and this is "normal".



The carbs have not been deep cleaned or redone, the engine makes a nice little tapping noise as well, so clearly more than one gremlin at play on this ride.



Which direction do I run first?
 

·
Registered
Joined
·
4,104 Posts
I;d do a quick visual

stand by the bike and open the throttle then release the grip while watching

the mechanism at the carbs

you should see it snap shut quickly

If it doesnt I'd suspect the cable.
 

·
Registered
Joined
·
2,282 Posts
Ditto what Reg says. It may be the vacuum slides are hanging up a bit too. I think you can remove their covers and clean them without removing the carbs. Don't oil them tho, that just attracts dirt. Usually just a good polish is all they need. Some have tried graphite, I have not, but a little probably wouldn't hurt anything.

`
 

·
Registered
Joined
·
4,104 Posts
Yeah, what he said





When I assembled my carbs I was lucky in that I had a choice of pistons/slides

and used very good ones.

I've seen some which had obvously been chafing the carb body and had some heavy

scoring.

you usually find it on the side nearest the manifold and I assume its due to the incoming air

pushing the piston against the body.

This plus any oily crud could make them sticky and slow to sit back down

when you close the throttle.
 

·
Registered
Joined
·
546 Posts
I'd wager you have air leaks at your carb/intake connections. Had the same issue on my 650 last year.
 

·
Registered
Joined
·
402 Posts
did you rejet your carbs? be sure to check your plugs for the mixture! I had a super lean mixture in another bike once it kept running even after i pulled a plugwire it was dieseling and it destroyed my crank my rods and the jug and piston so... it was destroyed worthless... make sure your careful you dont want to be buying an engine
 

·
Registered
Joined
·
1,493 Posts
Discussion Starter · #7 ·
Thanks people. I'm hoping to work on her in a few short days. I'll let you know the outcome.
 

·
Registered
Joined
·
8,423 Posts

·
Registered
Joined
·
1,493 Posts
Discussion Starter · #10 ·
Funny you should ask. I just got around to tinkering the other day. I've had a bug going around my house and now I'm on horse pills!



So far I have tested the throttle response while turning the bars, doesn't seem to have any effect.

I did notice that once the engine got warm the revs tended to stay up more frequently.

The rubber boots (mainly from carbs to engine) look a little dry rotted.

I definately have air displacement going on from my header region.

Couldn't check the slides as the boots to the air box are still on. By still on I of course mean after wrestling to get them back on. I really, really, REALLY hate to take them back off. I know I'll have to, but man, do I have to?



I'm also checking my push cable. If the motors stays reved, shouldn't pushing the throttle back stop them? Mine is not, so I'm thinking this is a bad thing.
 

·
Registered
Joined
·
2,282 Posts
Those boots to the airbox shouldn't be that hard to remove and install. I take the intake side loose first, using a screwdriver to pry off the rubber, after I have rotated the intakes in toward the center of the engine. This should give you about a half inch of free space. Then the carbs easily slide out of the airbox connectors. Wiggle the carbs out the left side of the engine, and then detach the choke and throttle cables.



After a couple of times, you should be in the 15-20 minute time range for taking off the carbs.
 

·
Registered
Joined
·
1,493 Posts
Discussion Starter · #12 ·
Well, the taking out, putting in part I'm actually getting good at. It is the liking it part that I still have to master! So you're telling me I actually have to take the carbs out again, not just look at them while the bike is running. Man, this must be why people love these bikes so much.
 

·
Registered
Joined
·
1,493 Posts
Discussion Starter · #14 ·
Don't take the Airbox side boots off unless absolutely necessary!They are a PITA to get back on
That's what I'm talkin' about! It took me two days to get those things back on! One day of cursing and knicking knuckles, and a second day of using my head and a hair dryer to make them more plyable.
 

·
Registered
Joined
·
546 Posts
Funny you should ask. I just got around to tinkering the other day. I've had a bug going around my house and now I'm on horse pills!



So far I have tested the throttle response while turning the bars, doesn't seem to have any effect.

I did notice that once the engine got warm the revs tended to stay up more frequently.

The rubber boots (mainly from carbs to engine) look a little dry rotted.

I definately have air displacement going on from my header region.

Couldn't check the slides as the boots to the air box are still on. By still on I of course mean after wrestling to get them back on. I really, really, REALLY hate to take them back off. I know I'll have to, but man, do I have to?



I'm also checking my push cable. If the motors stays reved, shouldn't pushing the throttle back stop them? Mine is not, so I'm thinking this is a bad thing.


While running, spray some carb cleaner around all 6 intake connections. @ airbox, @carb to intake, @ intake to head. Any change in RPM and you can pin the air leak down as the issue, and pinpoint the spot of trouble.
 

·
Registered
Joined
·
1,493 Posts
Discussion Starter · #16 ·
That makes sense.



What about the push cable? Is it not functioning properly, or can't I tell from this?
 

·
Registered
Joined
·
839 Posts
I had a set of carbs that would not let the engin idle down well and found that the mid-jets had to be replaced.

cx500c 81
 

·
Registered
Joined
·
1,493 Posts
Discussion Starter · #18 ·
I had a set of carbs that would not let the engin idle down well and found that the mid-jets had to be replaced.

cx500c 81
Thanks, I'll look into that too.



I just took a look at the cables, they seem to be doing there thing, however, , ,



After forcing the throttle closed a little too rough, I sent the rpms down to 1000, 750, stall. I think I may have stretched the cable/fitting or something, so that's not good. Looks like I'll just have to bite the bullet and take the carbs out, check out the slides, cables, and boots, and start from square one. What a piss, and I just got it on the road too, damn it!



So to recap:

cables not binding

push/pull working as expected



next step, removal of carbs.
 
1 - 18 of 18 Posts
Top