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

[magg]

Blocked choke passages will cause starting and initial running problems with a cold engine and no fast idle, may inspire the operator to adjust the manual idle high and thus upset idle mixture setting. Opening the choke on a running at operating temperature could stall the engine as described above because the mixture becomes over-rich as the engine vacuum at a forced high idle could draw excess through partially blocked choke circuits.

[vfrman]

I'm calling BS on the manual idle upsetting the idle mixture setting. The idle adjuster just changes the throttle stop, so the butterflies stay open a little. It has zero to do with idle mixture.

[magg]

Vfrman, perhaps my commnets have been mis-interpreted. High idle should be a choke function. Trying to use a high manual idle to overcome a too lean starting problem ie no choke function, would require a richer "idle mixture" that then needs to be leaned off once the idle speed is returned to normal.

If the engine will not start and run until warm using the choke, then I would start with the choke circuit, particularly if once warm, the engine can be made to run at normal idle rpm and mixture settings. Another complaint appears to be that once the engine is running opening the choke stalls the engine, I do not think this is abnormal even with a choke problem. The choke could still provide a sufficient added fuel to unsettle the nominal idle mixture.

This is my understanding of the problem. Playing with the idle mixture and idle speed to overcome an initial start problem is not the process I would follow, but I may have a poor understanding of the problem.

[vfrman]

I agree. Increasing the idle using the adjustment knob instead of getting the choke to work properly is a band aid fix that isn't solving the problem.

[MikeBb]

Unfortunately, new pilot jets did not fix this issue.

However, and i am REALLY hoping this isnt the placebo effect, it seemed to want to run a bit better with the pilot jets changed. It SEEMED as if adding the tiniest bit of choke, raised the idle, by the tiniest amount, before raising it any more killed it. Testing with the airbox removed yielded the same results however it also afterfired a bit (bangs). i cant remember if it also afterfired when i fitted the airfitler/box, but it didnt when it warmed up fully.
It sounds like a 13b, so my next suspect is shitted plugs, does that seem plausible?
After giving up for the night, i noticed some spits in the exhaust pipes, and the top one, which is linked to the front cylinders, had a little visible smoke after running. These plugs only have ~400kms to them, but if it was the pilot jet issue, then is it possible that running it at this richness for 400kms has stuffed these plugs?. I pulled them out before changing the jets and they were both wet and covered in carbon,which im pretty sure i cleaned up enough before putting them back in. I havent inspected them this afternoon, im all biked out for now ., Could i get away with cleaning them since theyre that young? would wringing the bike out clear them (have not ridden since i ballanced the carbs, changed jets etc.. just had it idling.) Or should i fork out $130 for another set?
As mentioned earlier, before i pulled the bike down to resolve this, it didnt seem to be particularly down on power.

[Neil22]

Bugger sorry to hear!

Give them a good clean out, soak them in brake cleaner and remember its right down the bottom that you need to get clean, blow them out then take it for a run and see what the plugs tell you after that.

Cheers

[MikeBb]

Pulled the plugs this afternoon, all were carbon fouled but were not wet with fuel. Gave the plugs a really good clean, lots of blasting with carb cleaner and scrubbing with steel wool and a toothbrush to get em clean. then dried over the barbeque.
Whilst the bike seemed to rev a bit better, this did not fix the issue.

For record, the issue is that the bike will not run at all with any amount of choke added. I must increase the idle speed when starting the bike from dead-cold, and then later in the ride lower it as the bike heats up. It is my understanding that choke is supposed to increase the revs of the idle to assist with cold starting the engine as in this video:https://www.youtube.com/watch?v=WQA-EvvA1pA

The issue was persistent with no airbox/filter, filter is new.
Pilot screw settings had no effect (tried from 3 turns out to all the way in with no change)
float heights have been checked as correct, and float valve is not leaking causing overflow
carbs have been pulled apart and carb-clean/air compressor blasted several times, with several tests confirming that pilot air circuit, idle air circuits, chokes, and jets are all clear.
valve clearances were recently checked, all intakes were well within limits, all exhaust were near their limits but still within specified limits
Plugs new less than ~400kms ago
---------------------------------------------------------
Pilot jets changed to new ones, pilot screws set to 1 5/8 turns.
issue remains, although it seems to increase idle audibly a tiny ammount when adding a tiny ammount of choke, any more kills it.
with the vacuum screws (for ballancing) open, the idle increases, if idle is lowered by the screw to compensate, then choke operates properly up to 1/2 - 3/4 choke before beggining to kill the engine.(with carb-balancing screws open)
---------------------------------------------
plugs removed and cleaned of carbon fouling
Does not start with choke, does not run with choke, airbox on, all other settings not tested yet.

between this and the leaking fuel tap i am really not winning with this bike!

[magg]

The choke increases the revs by simply adding fuel. When working correctly, on a cold engine a fully open choke will raise the engine "idle" speed to more then 3000 rpm. No need to touch the throttle or adjust idle mixture screws. Choke should never be used on a warm engine as it will supply an over-rich mixture and stall the engine.

If your bike does not respond in this manner then IMHO there is an issue with the choke system. Perhaps the plungers are not being pulled fully open. Insufficient fuel flow will also adversely affect the choke system as the added fuel is drawn directly from the float bowl. A fuel tap issue may be contributing to your choke start problem.

[MikeBb]

the fuel tap issue is just a bit off seepage/ leak from it not sealing with the fuel tank properly. the tap still feeds fuel under vacuum fine.
I have not tried playing with the pilot screw settings since changing the jets so I will try that this afternoon.

I just had a thought that if my choke plungers are missing parts or not sealing shut properly then they may be always on.. and 'opening' the choke just dumps fuel in there killing it. I had already pulled the choke system apart and was pretty sure it was all good but I will check that again

[magg]

Perhaps I have misunderstood the situation.

Assuming you get the engine started and warmed up, can you get it to idle and run well with the idle mixture screws set as per spec and the choke closed. Does the engine restart when warm simply by hitting the start button with maybe a little throttle, without making any mixture setting changes.

If the the issue is simply getting the engine to start when cold, using the choke (fuel enrichment system), then it suggests a "choke" issue. As mentioned earlier a low float bowl fuel level will adversely affect the "choke" performance, thus any limitation in fuel flow that inhibits float bowl fill at cranking rpm will aggravate the problem.