Honda CX 500 Forum banner

1 - 20 of 39 Posts

·
Registered
Joined
·
18 Posts
Discussion Starter #1
Good morning everyone. I am new to forums and an old guy so if I am in the wrong place to post this let me know. I bought My second cx500 after the last one was toasted by a u turning postal truck. I really liked that bike so I bought this one. It runs well at idle, and will accelerate with the choke on. With no choke it has no power and backfires when asking for some. 150 psi each cylinder. carbs clean new coils, new intake boots, and all potential leaks fixed. I took off the intake boots from the airbox to the carbs. When it is running the carb slides are pulsing up and down rapidly. this seems wrong to me but I am not that familiar with this style of carb. So any suggestions? I really appreciate the knolege base, thanks!

RM
 

·
Super Moderator
Joined
·
14,042 Posts
How CV carbs work

Is it backfiring (firing back through the carbs) or afterfiring (igniting unburned fuel/air mixture after it has passed through the engine into the exhaust)?

BTW: Welcome to the forum. Please add your location to your profile (there may be a member nearby who can help you in person) and your bike's model and model year to your signature so that you don't have to remember to tell us every time you ask something and we don't have to keep asking when you forget.
 

·
Super Moderator
Joined
·
20,779 Posts
Have you tried adjusting the idle mixture?

Did you use aftermarket float needles? These can vary in length and give odd fuel levels. Low will give a lean condition.

Check your fuel level with a piece of clear 4 mm fuel line.

Fit it to the float bowl drain screw, open the petcock and the carb drain and the fuel level will show in the line when held up along the side of the carb.

2 mm below the carb/bowl joint is ideal.
 

·
Registered
Joined
·
18 Posts
Discussion Starter #4
Hey Thanks for the replies! I Live in Perkasie Pa 18944. It is backfiring through the carbs. I did not change any parts in the carbs, but I suspect someone else along the way did. Are the slides supposed to pulse? And by Pulse I mean pump up and down like pistons, while I hold a steady throttle.
 

·
Super Moderator
Joined
·
20,779 Posts
They would pulse some I think, but I have never actually watched.

The vacuum pulse will fluctuate with the opening and closing of the valve and this is likely what you are seeing. The same means you need to damp your lines to synchroniser gauges or the needles jump all over making them unreadable.

I put an ebay set of aircut valves in mine and it ran so lean the sparkplugs were stark white and the bike ran badly.

I would start with the fuel level.
 

·
Registered
Joined
·
18 Posts
Discussion Starter #6
Well I think you may be on to something. Any recommendations for a good site for a good site for parts?
Hope you all are staying well in this strange time.
 

·
Super Moderator
Joined
·
20,779 Posts
What colour are your floats?

If the black plastic and metal ones they are adjustable.

If white/tan/brown full plastic they are not adjustable.

Is it possible toget a good close up pic of the ball head of one of your ACVs? The left one has easy access.
 

·
Super Moderator
Joined
·
20,779 Posts
Mine made the bike run badly and lean all the time Bob. And I don't really get it.

If inoperative it won't richen on the over run but otherwise should be normal. Unless they trigger at high revs due to maximum vacuum for an open throttle?

But fitting used OEM ones sorted it out.

I'm still trying to understand why.
 

·
Super Moderator
Joined
·
20,779 Posts
Yes, that makes the aircuts inoperative. That's fine.

But if they are making the bike run badly when NOT in operation it will not help.
Whatever the reasons for bypassing the ACVs it actually still relies on having functional ACVs = unperforated diaphragms and the metering ball being in the correct place. if an aftermarket ball form is incorrect it will not have any effect.
 

·
Registered
Joined
·
18 Posts
Discussion Starter #12
You mean just pull the diaphragm and try it? I’m getting really good at pulling these carbs! What does the air cut off
8FEDF67F-DD3F-488D-8722-9FE709E94C3C.jpeg
valve do?
 

·
Super Moderator
Joined
·
3,886 Posts
all potential leaks fixed.
RM have you actually checked for leaks? A new O-ring which slips out of place while installing the intake runners for example, or a carb not sitting properly in the boot. Your bikes symptoms could be due to too much air rather than to little fuel.
 

·
Super Moderator
Joined
·
14,042 Posts
Yes, that makes the aircuts inoperative. That's fine.

But if they are making the bike run badly when NOT in operation it will not help.
Whatever the reasons for bypassing the ACVs it actually still relies on having functional ACVs = unperforated diaphragms and the metering ball being in the correct place. if an aftermarket ball form is incorrect it will not have any effect.
From Mike's page (linked above)
Bypassing the system is as simple as blocking off the vacuum source, the valve's trigger. Do this by substituting a solid piece of rubber in place of the tiny o-ring at the vacuum port. Leave the diaphragm in place even if failed, as in all cases it serves as a gasket for the aircut valve cover, and in some cases is also needed to keep the aircut valve open.
 

·
Registered
Joined
·
1,434 Posts
Didn't Larry have some odd problem with the cover for the acv being drilled to a larger hole ?
 

·
Super Moderator
Joined
·
20,779 Posts
OK. it doesn't need to be functional

But if the head is the wrong shape/distance it won't alter that.

We are talking about aftermarket ACVs.

Why do you feel compelled to complicate a simple discussion?
 
1 - 20 of 39 Posts
Top