Choke Plungers Failing ?

I have a 76 KZ 900 with Mikuni VM 28sc carbs and I'm getting fuel in the nipple caps on the carb holders, my idle is poor but when I run it up to 3 to 6k rpm it runs great. From time to time it will pop/backfire at idle and blow one of the nipple caps off the carb holder and when I check the cap it has fuel in it and the fuel makes the cap fit very loose. Could this be caused by the choke plungers not sealing with the choke in the off position?

Closely following. Some time ago I asked if fuel in the vacuum caps was normal. I’d like to see what answers you get compared to my replies. 

Yes it is normal, especially if checking just after switching the motor off. All the fuel vapour in the throat will condense back into liquid and run to the lowest point. It will evaporate off over the next few mins/hours which is why its not always present when checking. 
Modern fuel softens the vac caps and they become loose. Easiest solution is to fit fuel line clips on them. 

Fuel in the rubber nipples is normal.
Blowing them off isn't but it may just be that they are too loose and need some new ones.
Also if they are very loose they can draw air causing the weak mix and backfiring.
The popping back at idle needs addressing and if not cured by new/tighter vac nipple rubbers could be down to idle mix ,valve clerances or air leaks at the carb boot etc
As for the choke plungers, regardless of any other issues i can guarantee they are worn and leaking if original.
 

wrote:

Fuel in the rubber nipples is normal.
Blowing them off isn't but it may just be that they are too loose and need some new ones.
Also if they are very loose they can draw air causing the weak mix and backfiring.
The popping back at idle needs addressing and if not cured by new/tighter vac nipple rubbers could be down to idle mix ,valve clerances or air leaks at the carb boot etc
As for the choke plungers, regardless of any other issues i can guarantee they are worn and leaking if original.

 

I'm glad you replied to my thread zed 1015 I may need your services with the choke plungers in the near future, I'll PM you later.

A little back ground on my bike, It sat idle in my garage for fourteen years, I have since cleaned fuel tank & carb jets and checked float level, set valve lash, installed a new Dyna S ing., set timing with both test light and strobe light (it's spot on) new battery and new main wiring harness also replaced carb holders with aftermarket from Z1 interprises. I'm starting to question the quality of the aftermarket carb holders. In the past I've had my bike pop/snort/backfire when cold and never had a vacuum cap pop off. If the choke plungers are not sealing wouldn't that cause excess fueling during idling ? and possibly be the cause of the pop/backfire during idle ?

Thanks to all who replied !!!!

Leaking plungers cause over fueling, rough running, low mpg and power loss amongst other issues.
The also don't wear evenly across all cylinders so the symptoms can mimic other carburation problems that become unsolvable if you don't know what you are looking for.
At the extreme they can make the bike unridable once warm as it becomes the equivalent of riding with the choke fully on.
 

Thank you Sir....be talking to you soon.

I know I'm gonna hate myself for trying this but I'm diving in..... weeeee! 

 

Im contemplating getting the choke plunger seals replaced as the plugs are very sooty despite cleaning the carbs and setting up.
I really dont relish pulling the carbs off again so was wondering if they can be changed with the carbs still in situ.
Also has anyone else had similar with sooty spark plugs and found this to be the cure.
Other than the sooty plugs it runs quite well apart from a slight hesitancy if the throttle is blipped very quickly.

wrote:

Im contemplating getting the choke plunger seals replaced as the plugs are very sooty despite cleaning the carbs and setting up.
I really dont relish pulling the carbs off again so was wondering if they can be changed with the carbs still in situ.
Also has anyone else had similar with sooty spark plugs and found this to be the cure.
Other than the sooty plugs it runs quite well apart from a slight hesitancy if the throttle is blipped very quickly.

Except for number 4 carb you can't get the other plungers out with the carbs in situ and it's still difficult with the carbs off but still on the backplate.
You need to remove the choke bar and lifters and then make a special wrench to undo the 14mm retaining nuts.
For all the messing and time it takes it's quicker to split the carb bank and use the opportunity to give the rest of the assembly a good going over.
As for the sooty plugs etc, then yes! the plungers will cause all that and more.
 

Thanks for the reply Zed even though it wasnt what I was hoping to hear.
Lots more work than I had hoped plus cost of new airbox rubbers as the current ones are pretty solid and struggled to fit them back on again a few years back.
Is there any other rubber seal on the choke plunger assys apart from on the tip (o ring inside the recess etc) ? 
Also is there a rubber boot that sits over the top?