Dies with choke, runs without, idle increases as heats up.

[MikeBb]

The bike indeed will run whilst cold and whilst hot, though it is not a very smooth idle. starting it is just a crank and maybe a blip of the throttle or if its fully warmed up just crank and go. whilst cold it wont idle unless i increase the idle speed setting. And in doing so, when it does warm up, it has a much higher idle. In all conditions choke kills the engine by drowning. if i have the vacuum ports open (causing massive lean scenario) then the choke seems to operate normally.

Plugs carbon foul a little bit but dont come out wet, and the bike does not seem to be particularly down on power. But haven't dyno'd to confirm.

[675craig]

Hi,

Just been reading through this thread and I have to agree with magg. Sounds to me like this is completely a choke issue. Warm your bike and set the idle so it runs properly (as you have stated you can) then LEAVE the idle adjustment from there on.

Have a good look at your choke plungers and mechanism by turning the carbs upside down and manually operating where the choke cable attaches. Make sure all the plungers open fully when operated and also that they close fully when returned. You should ensure there is a little slack adjusted in so that they don't start to open for the first small amount of movement (the springs will ensure they stay closed).

I had similar issues with my NC30 that was stood for years. When I operated the choke, the lever was quite stiff. The movement took up the slack then flexed the linkages/brackets without opening the plungers. I had to strip the rods and give them a good polish with fine wet & dry before greasing where they slide through the guide brackets and adjusting them all up.

I've also seen the opposite recently on an SV650 where one of the plungers were fouled and wouldn't seat properly, causing one cylinder to constantly run on choke, but that resulted in high idle all the time!

Concentrate on one area at a time or you will just run around chasing your tail. Try the above and let us know how you get on and we'll go from there. Good luck,

Craig

[MikeBb]

I had recently disassembled the choke plungers and confirmed that no parts were missing, damaged, or dirty, they were carb cleaned and air-blasted as well, all the plungers operate smoothly.

Am I interpreting what you and magg are saying correctly in that when the choke is operated, the pilot jets are disabled and all fueling comes from choke? If that is the case, and if the choke gets its fueling from higher up than the pilot jets, then its possible that a low float level/too high float height could be causing this.
That scenario relies on the assumptions that :operating choke disables the pilot jet feed(i didnt see any linkage going anywhere but the choke plungers themselves but ill look again) and the chokes fuel feed is starved by a slightly low float level (although IIRC when shooting carb cleaner/compressed air into the choke a squirt came from the main jet suggesting that is its feed)

My latest suspicion was that all chokes are not seating right, and that when "off" they are actually "on"-ish, and by turning them 'on', they become very heavily on, drowning the engine. My doubts for this are that i did in fact recently check the choke plungers and clean them, and that i cant think of a way to test this, maybe by taking the choke plungers out and blocking them somehow and then testing for a leaner idle. Perhaps my choke plungers are missing an o-ring on the end of them, although there are no such orings at the bottom of this post : viewtopic.php?f=24&t=37073&hilit=pilot+ ... er#p268467

Thanks.

[magg]

Different carby but I suspect same/similar function: viewtopic.php?f=35&t=12571

Thought the boots sealed the choke plunger and rubber ring at bottom of plunger sealed port: https://encrypted-tbn0.gstatic.com/imag ... UK5p5j4y2w

[magg]

Try this link http://www.nrp-carbs.co.uk/shop/image/c ... 00x500.jpg

[MikeBb]

Heres a quick vid, australian internet is very neutered so its a long time to upload even a short one like this.https://www.youtube.com/watch?v=RsXMz2- ... e=youtu.be

Conditions are, idle speed was set at the end of a ride to have it idle at 1300 whilst warmed up. bike was not run for ~40hrs and it was roughly 12 degrees (C) outside at this video. It actually did a lot better this time than i thought it would., When it fired i had blipped the throttle to help it start and when i let go i was expecting it to die. It seems a TINY ammount of choke raises the idle a TINY ammount, where anymore kills it. Although i think thats just me seeing things that arent there. IIRC i still have the pilot screws set 2 turns out here.

My next plan of attack is to stick o-rings in the pins of all the choke plungers under the suspicion that they are not seating shut causing the rich idle.

[magg]

You are an oz resident, where abouts.

[Neosophist]

Well this issue continues to drive me insane.

Some experiments tonight,
wound out pilot screws 1/8th to 1 6/8ths per advise on here that doing so will lean it out. It ran worse. fire from exhaust on idle + dies with choke.
From here wound them in one half turn, to 1 2/8ths.. Bike seemed to run a bit better, as in idle adjustment screw seems to need to be wound on less to keep it running, still dies with choke.
Tried in another half turn, no change, still dies with choke burping a little fire at idle.
From here went overboard. 2 1/4 out. creating theoretical very lean. No difference. Dies with choke immediately and with only a small amount.
went out 1/2, 2 3/4, no change
went out again, 3 1/4 (!!!!). no change.
All experiments were tried with and without the airbox/filter, with no difference to any result. No result is notice if i hold my hands over the trumpets and no vacuum is felt, so the idle air must be fine.

After experiments i pulled one of the plugs, and predictably it was wet and looked like shit.

As it came out: http://imgur.com/SlbK47T Wiped down: http://imgur.com/igHQYjM

carbon on them seems to come off with my fingernail. next step is to pull em all and clean em. Plugs are only 400kms old so buying new ones would piss me off, especially if they didnt fix the issue.

So, from the fact that wildly fucking with the pilot screw didnt affect how the bike idled very much, it would suggest that the pilot screws are missing parts or are blocked. Which they are not, and which cant be the case, as only a week ago i had them apart and cleaned out with degreaser and an air compressor.

Which leaves float heights... which is a completely subjective measurement, leaning against the knob on the valve, slightly slightly compressing it, making sure the float is seated, gives roughly the same result as simply having the carbs upside down, this measurement with a steel rule and vernier calipers is correct at 12~13mm.. if the knob on the needle is not at all touched the measurment could be ~14... which would make it leaner?!?!!

Just removed the carbs and pulled out all the pilot screws to confirm that no parts are missing or the needles broken off. Will take in to work with the air compressor again tomorrow, focusing on the pilot circuit. To clarify, going in reverse, this circuit goes from a hole in the carb near the butterfly, up through the pilot screws needle valve to one of the 3 brass fittings in top of the carb, with no fuel added along the way? (i just want to know where i should be focussing on unblocking)
Thinking about this seems like such a stretch, as it is so odd that it would be blocked equally on all 4, but if the shit running was caused by the plugs and the pilot circuit had no fault, and if the pilot screw setting is as sensitive as i am led to believe.. then wouldnt it have eventually died when i wound it to the extreme values above?..

Just a thought after re-reading this.

Are these NC35 carbs??

If they are NC30 carbs and you have the float height at 12.5 mm it will be so super rich youll be getting all the issues you mention...

It has been known to fit nc30 carbs onto an nc35...

[Neil22]

Well this issue continues to drive me insane.

Some experiments tonight,
wound out pilot screws 1/8th to 1 6/8ths per advise on here that doing so will lean it out. It ran worse. fire from exhaust on idle + dies with choke.
From here wound them in one half turn, to 1 2/8ths.. Bike seemed to run a bit better, as in idle adjustment screw seems to need to be wound on less to keep it running, still dies with choke.
Tried in another half turn, no change, still dies with choke burping a little fire at idle.
From here went overboard. 2 1/4 out. creating theoretical very lean. No difference. Dies with choke immediately and with only a small amount.
went out 1/2, 2 3/4, no change
went out again, 3 1/4 (!!!!). no change.
All experiments were tried with and without the airbox/filter, with no difference to any result. No result is notice if i hold my hands over the trumpets and no vacuum is felt, so the idle air must be fine.

After experiments i pulled one of the plugs, and predictably it was wet and looked like shit.

As it came out: http://imgur.com/SlbK47T Wiped down: http://imgur.com/igHQYjM

carbon on them seems to come off with my fingernail. next step is to pull em all and clean em. Plugs are only 400kms old so buying new ones would piss me off, especially if they didnt fix the issue.

So, from the fact that wildly fucking with the pilot screw didnt affect how the bike idled very much, it would suggest that the pilot screws are missing parts or are blocked. Which they are not, and which cant be the case, as only a week ago i had them apart and cleaned out with degreaser and an air compressor.

Which leaves float heights... which is a completely subjective measurement, leaning against the knob on the valve, slightly slightly compressing it, making sure the float is seated, gives roughly the same result as simply having the carbs upside down, this measurement with a steel rule and vernier calipers is correct at 12~13mm.. if the knob on the needle is not at all touched the measurment could be ~14... which would make it leaner?!?!!

Just removed the carbs and pulled out all the pilot screws to confirm that no parts are missing or the needles broken off. Will take in to work with the air compressor again tomorrow, focusing on the pilot circuit. To clarify, going in reverse, this circuit goes from a hole in the carb near the butterfly, up through the pilot screws needle valve to one of the 3 brass fittings in top of the carb, with no fuel added along the way? (i just want to know where i should be focussing on unblocking)
Thinking about this seems like such a stretch, as it is so odd that it would be blocked equally on all 4, but if the shit running was caused by the plugs and the pilot circuit had no fault, and if the pilot screw setting is as sensitive as i am led to believe.. then wouldnt it have eventually died when i wound it to the extreme values above?..

Just a thought after re-reading this.

Are these NC35 carbs??

If they are NC30 carbs and you have the float height at 12.5 mm it will be so super rich youll be getting all the issues you mention...

It has been known to fit nc30 carbs onto an nc35...

No it would be super lean as the fuel level would be set lower.

Cheers

[MikeBb]

In Sydney in the parramatta area. Definitely NC35 carbs.

Have not done the test with O-rings in choke pistons as i have had thoughts that it will not work. If they were not seated properly, and letting fuel through, then indeed it would cause a rich idle, but it wouldnt change the designed maximum and mid settings for choke flow. So if my problem was that the choke pistons werent seating, it would not cause the thing to die with choke, Just idle rich.

So again i am stumped, my next thought is to carb clean+air blast (for the 3rd/4th time) all the jet air sources, only this time with the pilot screws, emulsion tubes/jets, float bowls, and choke valves all removed, as previous times when i did this most of them were mounted. My theory is that previous attempts at cleaning them might not have been thorough as having the jets mounted when cleaning might have just made any gunk settle at the emulsion holes. and that removing those parts whilst doing a clean will increase airflow from the air compressor.

This is the last straw (in a 'clutching at straws' way) that i have left. failing this i will go back to trying wild pilot screw settings.