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TOPIC: Lean Idle

Lean Idle 3 months 1 week ago #24227

  • Daro
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Hi Frank, so now we are sure that the gauge is working, if the AFR drops when you apply the choke and the bike dies on idle from too little fuel it means theris a problem with idle cirquit. What is your fuel level?

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Lean Idle 3 months 1 week ago #24229

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Stan, did you know that this bikes like to boil the fuel out of the carburetors in to the intake tract? I will describe this fenomenon whitch I ever only seen on kz1300. While back because of my cam problem I was wildly rejeting the carburetors trying to tackle the problem, even adding weights to the slides etc. which is connected with taking the carbs out of the bike. When testing previous jetting I run the bike quiet often very hard to see the efects and so it got really hot sometimes when little lean. After the run I waited half or one hour so it cools a little to take the carbs out for another jet swap. Now, very often I saw the fuel in the intake rubbers at first it didn't occur to me, and once in the intake tract, the valve was closed and the fuel was just standing in there. All this is due to heat build up in the rear of the engine, righ hand carb is more prone to this when on side stand. So if you let the bike stand there for an hour thats what happens with the fuel. I don't have insulation underneath the tank so it makes it even worse. In you case this explains why you dont need the choke to start, but generally if the engine is atleast a little warm you dont need it.

I forgot to add, that I have a stainless steel inline fuel valve and the pump so it eliminates the possibility of floding due to original fuel tap.
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Last edit: by Daro.

Lean Idle 3 months 1 week ago #24234

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That's very interesting Daro. I've never heard of this. I've heard of the tap just leaking and filling the cylinders, resulting in hydro-lock and a disaster.

My original fuel tap is behaving fine. I've rebuilt it and tested - no leaks at all, so I'm trusting it. But I think it would be a good idea to have an extra inline shut off, like you have, as a back up. Just in case of a failure.

Last rainy night I warmed up the bike in the parking lot. Shut off, let it sit maybe 20 minutes or so, enough for the temp gauge needle go all the way down. 0f course the engine's core temperature was still high. It was easy to start with the choke lever completely disengaged. It was really cool just listening to how the engine starts with low rpm's, then picks up gradually.
I could swear I can hear individual cylinders fire! haha 0f course it was just my imagination, but it sounded really cool. And in case anyone would wonder, no oil pressure light coming on. I repeated it a few time, lol.

I also must say that I haven't seen this before the synch and Colortune adjustments. Then again, I've always ran it in colder weather. It will be interesting to see how it behaves in very hot weather and traffic. I also don't have the heat shield. I think I will make small scoops to direct air when the radiator fan kicks in to under the engine, so there will be more air flow directly under the tank. I am also keeping in mind the resistors and coils. In a stock set up, lots of air just bounces off the engine and escapes to the sides. I think it would be beneficial to have a stream of cool air when riding go upwards to under the tank area.
1982 Kawasaki KZ1300 A4
1981 Kawasaki KZ1300 A3
assembling engine, chassis & electrical from 79 - 89 parts

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Lean Idle 3 months 1 week ago #24235

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Daro wrote: Hi Frank, so now we are sure that the gauge is working, if the AFR drops when you apply the choke and the bike dies on idle from too little fuel it means theris a problem with idle cirquit. What is your fuel level?


The carb float levels are correct. This bike was a basket case (literally). The PO sent the carbs out to someone. I’ve gone through them and took care of a couple issues, but the float levels were spot on.

I believe the idle pilots are only metering air, so me switching them from 42.5 to 50 only made the problem worse. I have 35s on the way.

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Lean Idle 3 months 1 week ago #24237

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Hi Frank, Yeah it is difficult to say what PO-s do with carbs and their other mechanics to, but they for some still unknown reason are not functioning properly, maybe it has something to do with the "repair" which has been done theme or big bore kit, but i highly doubt the second one, and if yes ill be surprise. One thing is hoever possible, that the charge delivered to the cylinder by carburetor can be leaner due to air volume being sucked in is larger but rejecting the carb must still cause expected behavior, in the case of BSW32: bigger idle jet = more fuel = richer mixture. That's my experience at least. Any remote diagnostic of carb with passages as small as 0.425 mm are extremely difficult and my language barrier on the top of that, so i made the picture how the fuel is going past the main jet than the idle jet and than is getting mixed up with air after the idle jet, creating "mixture". Like Scotch have said: The idle screw only meters the volume of the mixture not the proportion of fuel air, that's very important t understand.

Lastly I'm sorry about the childish made picture but like i said the language made the thing more difficult to explain for me and also if you see this is probably better anyways. So once again the idle jet meters fuel only, not the air. The symptoms could indicate that the fuel is being pushed back away from the idle jet towards main jet, thus creating idle mixture leaner and when you change the idle jet to smaller size so the effect is less. Hmmm.. could be.

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Lean Idle 3 months 1 week ago #24238

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That's the troublesome restriction in this carbs, not the hole it self only how the gallery is pointing up towards the fuel exit and so the debris and rust particles are settling down there.

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