throttle butterflys wont close

[VJ]

my bandit engined rat has got a high idle issue at the moment, Im just in the process of trying to work it out, carbs are clean, Ive taken the throttle cable off, backed the idle adjuster all the way off and still the butterflys are slightly open, not by a massive amount but I think this might be the cause of my high idle.

 

Any idea on what can cause the butterflys to stick open? the throttles operate smoothly, the balancing screws arent siezed and it snaps back with good force but just wont fully close on all 4 

[Oilyspanner]

Is the cable fully seated in the recess by the carbs ? Have had my cable caught outside the recess before - wondered what the hell was happening as my bike revved it's nuts off ! - it would take all the slack in the system to get even close to shutting the butterflies . . . hard to get the bottom adjuster nut tightened too.

[VJ]

Problem happens even with no cable on.

 

Sometimes it'l idle sensibly then sometimes it wont. Ive checked for air leaks but what keeps annoying me is with the idle screw all the way out i can play with the balance screws and get all 4 butterflys to close, I then refit the carbs, try it and get a high idle so then remove them and the butterflys are open. Is there any chance the rack is loose/twisted maybe?

[Jaydee]

Have a look at the little springs under the 3 balancing screws. Are any missing, badly seated or distorted? I once was working a mates slingy. Could not get the carbs to balance or get a stable tickover. Turned out that some one had been at the carbs before me and had lost a balancing spring, which they replaced with a crappy (lighter than stock) spring which wasn't strong enough to push its respective plate. Once spring was replaced, everything was A1. 

[Captain Chaos]

Had it once on a B12, carbs would only close fully when I let them snap shut from wide open, not from a little bit of throttle opening. Turned out the rack was slightly twisted. Rebuilt the set with the mounting plates from another set (which I have for spares) and it was OK.

[HDTboy]

I have the same issue occasionally. As a band-aid solution, I gave the throttle return springs some extra pre-load with a rubber spacer.

[VJ]

Thats my thoughts captain chaos, Im thinking im going to replace all the screws holding the rack together with m5x10 cap heads and inspect a bar at a time for warpage, hopefully that'l sort it, if not im going to bodge a sidestand spring on there and just deal with a heavier throttle. It is a ratbike after all.

 

Cheers

VJ

Edited February 9, 2016 by VJ

[VJ]

SO todays tinkering included stripping the bars off the rack, tweaking them slightly to make sure they are flat (well, they were only a touch out) I then bolted them back on with all 4 manifolds flat on a piece of glass (i hope Mrs VJ doesnt notice the smell of petrol on the bathroom scales) 

I still have a high idle problem though, it seems to only be on cyl 4 thats causing it as i can get the other 3 to close fairly tight when playing with the balance screws. also if I lean on the balance screw between 3 and 4 I can get it to idle sensibly as it closes butterfly 4. I cant see any imperfections or burrs in the throat or on the butterfly itself and for sanitys sake have checked the plugs which are looking spot on.

is there any chance the butterfly has moved laterally at all?

Cheers

John

[Captain Chaos]

is the fuel tap vacuum pipe connected to intake number 4?

[VJ]

nope thats on 2

[teltwosheds]

Slacken the screws that hold the buterflys to the rack and they should, with a bit of gentle wiggling sit flat 

[VJ]

So I took the balance springs out of the gap between 3/4 today and cyl 1 2 and 3 all sat closed on idle stop nicely and worked fine but 4 needed brute force to close. I cant see any burrs at all on the butterfly, there is slight sideways play on the shaft but I assumed this was required and the butterfly closing would centralise this. 

 

Im flat out of ideas here tbh.

[teltwosheds]

Strim em and check the rack rods. you could have a bent one or corroded  cos some things not right

[slingshed]

Strip em down mate, i had a gsxr with similar issue and it was corrosion/lack of maintainence on the spindle. All weather skanky bike. Much like your machine.

[VJ]

Stripped it down, bent shaft and butterfly, the butterfly and screws are now trashed in the process of removing them too. Anyone know where i can get these parts without needing to buy a second hand carb set? Robinsons foundry dont seem to list them.

[slingshed]

What carbs are they?

 

[VJ]

stock b12 carbs, bst36ss chap

[Guest]

sorry to hijack your post but on the subject of carbs i need 2 carb tops if anyone has a couple spare they want to sell for a mk1 1200 ive just broke the vacuum stubs off of mine they fell off the bloody workbench

[VJ]

Yellow, a mate of mine is sorting me out with another bank of carbs so im likely going to strip and sell these for parts seen as its impossible to find the parts to fix them. Let me know if you dont find any carb tops and i'll sort you out with some.

 

VJ

[clivegto]

May be different to yours, but a few years ago I had the same problem and all it turned out to be was the choke cable was to tight. so the choke was on a little all the time.