Author Topic: Engine cuts out if throttle twisted shut while ticking over  (Read 788 times)

Offline bigmockuk

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Engine cuts out if throttle twisted shut while ticking over
« on: December 15, 2017, 09:37:51 PM »
I stripped the carb bank early this year and followed to a tee the pdf instructions for the pd46a carbs,at first it looked a daunting task being my first time but read first before anything and as usual i like to understand how things actually work and why.did everything methodically step by step and when it got to no 3 i decided it ws easier to tap out the pin on the throttle stop rather than mess with the throttle actuator! so after thorough cleaning and removing pilot jet using twist/pull i got everything clean.the fuel rail tube seals snapped trying to remove one of them and them each one thereafter.i bought this o-ring set from halfords (i`ll need to take a pic) they worked a treat,perfect fit and also the smaller ones are exact diameter for the mixture screws too!.built the lt back up and refitted the throttle stop in exact place i removed it from.bench synronized using thin metric rule from top of slides and each one appeared to lift the same,got them fitted and bike ran fine,started first time each time but to date if when its ticking over,i try to twist throttle further in the off position,engine will cut out! each slide lifts and closes the same and when the throttle is closed against the throttle stop screw there still appears to be enough movement to shut off engine.ive tried using a microscope to see if the slides are moving further down but cant detect they are yet must be as nothing else could surely move? the throttle actuator does move,yes but not a slide.the carbs have still to be balanced but dont think this could cause this? should the actuator hit a bump stop as it looks like it could if it were to travel far enough ?any ideas from anyone welcome thanks

Offline Ashdowner

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Re: Engine cuts out if throttle twisted shut while ticking over
« Reply #1 on: December 16, 2017, 08:26:20 AM »
Is the choke cable and the choke actuating screw on the carb shaft properly adjusted?
CB550K3, CB550K1, Yamaha Midnight Star, and CA77 in 2473 pieces (at the last count)

Offline bigmockuk

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Re: Engine cuts out if throttle twisted shut while ticking over
« Reply #2 on: December 16, 2017, 09:34:34 PM »
it is yes i replaced the standard pull-out choke with a chrome slider and all is good,the adjustment screw for the fast idle/choke is set to tick over at 3000rpm with full choke.wheather choke is on or off or even when engine is warm it`ll cut out if i twist throttle fully shut.the travel is only a few degrees too.im wondering if the pull or push set up was disturbed causing this?

Offline Rob62

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Re: Engine cuts out if throttle twisted shut while ticking over
« Reply #3 on: December 19, 2017, 01:14:49 PM »
you should be able to set up the bike to idle perfectly without the throttle cable even being attached.... get that bit right then attach the cable and go from there if you're having trouble.

Offline K2-K6

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Re: Engine cuts out if throttle twisted shut while ticking over
« Reply #4 on: December 20, 2017, 07:29:53 AM »
Like you,  I want to know how things really work so that you can set them up properly. From that it might be worth a look through the setup to see if there's anything you can spot on yours that may be out of range.

The design of these throttle systems usually has a fixed return cable with no facility to adjust,  just fit it to the twistgrip and carbs then it's set for you. It seems like this to make sure it has the ability to fully close the throttle slides in emergency so they don't give options to alter it.

The pull cable is set after install and they normally give a slack setting in manuals ( often a diagram of the end of twistgrip showing how much rotation should be there without activating the carbs) it's here it looks like you may have a conflict. If you take out too much cable slack, the carb slides are effectively hanging on the cable to give tickover and not on the idle stop screw on the carbs. It's because there is space under the stop screw that you can winch the slides down more by turning the throttle backwards to close them further.
It looks like you need to put more slack into the pull cable to allow the slides to drop onto the idle set screw. It should drop the tickover, which you'll have to bring up to normal with that screw.
You can do a quick check to see if the pull cable is too tight by turning the steering fully to one side and opening the throttle ( engine not running) if the throttle is stiff / won't return when released,  it shows the pull cable is too tight. Do it on both left and right steering to check.

The reason for having enough slack in the cables is because they don't follow the same route their entire length, so they make a conflict of changes as you rotate them round the headstock which you have to allow for. If you get them with no slack at all it can pull the end off the cable as the steering is moved from lock to lock.

Offline bigmockuk

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Re: Engine cuts out if throttle twisted shut while ticking over
« Reply #5 on: December 20, 2017, 09:56:11 PM »
I see what you mean rob about getting the tick over first then working on the cables.K2-K6 you bring up an interesting point,firstly its my throttle stop screw that is indeed in control but maybe just barely? i have no slack in any cable push or pull.i suposse they are both pull,one pulls the slides up and the other pulls them back down.im curious tho,if all slides are screwed tight to the one shaft and it bears on the throttle stop screw i would think it should be impossible for the cable to be able to close any slide even a fraction?Im getting what you mean by the space created under the slides.ive got a theory but could be wrong,when i stripped carb bank i tapped out the spring loaded roll pin that retains the throttle stop lug,now,if this lug is against the screw and i twist the pull-shut cable could it be the roll pin is being compessed a fraction allowing slides to drop a tad? probably not just a thought tho

 

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