Idling issues

D

dumbkid

New Member
Hi. I have a 1974 cb450.

I have just brought the bike back to life from 1982, put on the recently cleaned carbs and started her up. She is running good, but I am getting uneven idling. It will idle at 1500 and the go all the way up to 4-5000 rpm without me touching the bike, then settle back down to normal idle speed. While syncing the carbs I noticed one of the vacuum pistons sticking, so I disassembled both carbs and polished up the vacuum pistons so that they would slide freely.

I have also checked my throttle cable, but it is brand new and doesn't seem to be an issue. When I do increase the throttle from the handle, sometimes the rpms will remain high, even after I let go of the throttle. I checked the carbs and the throttle lever was completely closed. Then after 10-15 seconds, it will settle back down.

Any advice is appreciated.
 
im having the same issues with my 72 450, so im interested in what people suggest. im running velocity stacks
 
Right now I have no air filters on it. I'm just in the process of tuning the bike since she's alive again. I figured it shouldn't make a difference at this time since I haven't set the air/fuel to the air filter yet. I did play around with the pilot screw, but didn't really have an effect in the over revving. Just did what it was supposed to do and raised the engine speed a bit turned one way and slowed it down when turned the other direction.
 
Oh man- you'll never get it to run right without air filters- Making the bike run even reasonably well with pod air filters is more
than likely going to be a daunting task. There has been probably hundreds of threads on this site about trying to tune CV carbs with pods- please do a search and read up. I'm in the same boat myself with a KZ400 that basically uses the same carbs. They just don't like to work properly without the favorable condition that the stock airbox creates. In my situation, the carbs on the bike are so obscure that you just can't try different jets- they don't exist. I don't know exactly what carb a CB450 uses, but I don't think they're too much different. I'm not saying it can't be done, but be prepared for a lot of frustration!
 
Im guessing this is the case with all the cv carbs I have a 72 cl350 and i just got it back to life ... no air box .... and no pod filters and no mufflers on the pipes .... I hear both of these conditions will cause my bike to idle poorly and run poorly until The conditions are right for the jets in the bike.... I just got done adjusting the valves and the timing and it seems to have made it run stronger than before.... So pod filters will make it run better than no filters... but still a daunting task even after that and mufflers....
 
Im guessing this is the case with all the cv carbs I have a 72 cl350 and i just got it back to life ... no air box .... and no pod filters and no mufflers on the pipes .... I hear both of these conditions will cause my bike to idle poorly and run poorly until The conditions are right for the jets in the bike.... I just got done adjusting the valves and the timing and it seems to have made it run stronger than before.... So pod filters will make it run better than no filters... but still a daunting task even after that and mufflers....
Click to expand...

Short answer- yes.
And here is why. Basically, all of these factors are leaning out your fuel mixture. There would be no point in trying to tune the bike this way, because as soon as you put any type of air filters and mufflers on it, it's like pressing the reset button. You are now enriching the mixture with air filters and more restrictive exhaust. Yes, pods are better than no filters. Hell, a sock or pantyhose stretched over the carb would be better than nothing. (No air filters = bad.) The problem with the CV carbs and pods lies within the "magical condition" that your stock air box creates. There is a level of restriction that is needed in order to make them work correctly. Pods are very free-flowing and just don't allow the carbs to work the way they should. A common symptom is to have a "hanging throttle" where you rev the engine, and it takes a loooong time to idle back down. Another is that the idle will increase as the engine warms. You can typically "jet around" some of these problems, to an extent, but it will take time.... and jets! Old CV carbs typically don't have a very wide range of jets available for them. (If you have an old KZ400, forget about it!) This is why so many guys will ditch these CV carbs in favor of mechanical slide carbs. They are much more easily tuned and there are a plethora of jets available for carbs like Mikuni VM series. All in all, the best way to make an engine run happily with CV's is to keep things as close to original as possible. If you must tinker, you'd be well advised to switch over to slide carbs.
 
Are you 100% positive the throttle cable is routed properly. Try turning your handle bars from full left lock to full right lock back and fourth noticing any rpm changes. Its so easy to get it pinched. Sometimes you have to just kinda jiggle the cable to a slightly different position to make them slide properly. It only has to slightly crack the butterfly open to make the rpms skyrocket.
 
If not sure about the air filters fixing the problem try this little trick..

Run a piece of tape across the carb openings probably cover about 2/3 of the opening but do not completely block the opening and see if that helps settle the idle down and run a little smoother.

If it does then she should settle down after the air filter is installed.
 
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