Backfiring

  • TexasKZ
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Re: Backfiring

25 Sep 2014 17:06
#648835
For sure. I once discovered a hairline crack in a rotor inside the recess where it fit over the distributor shaft. Electricity was evidently running from the contact plate on top of the rotor through the crack to the shaft.

(Insert your favorite Prince of Darkness joke here.) :silly:
!Seymore wrote: You're quite welcome Brett...

Cracks can lead to a short to the frame. Electricity is an amazing thing... it can jump gaps small and large. If you have something to insulate them with... like a small, thicker rubber mat, might adapt that as an experiment to see if this is what's causing your problem. Yea, trial-n-error... but ya gotta start somewhere and just follow the bouncing ball...
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1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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  • KZBrett
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Re: Backfiring

14 Oct 2014 17:50
#650669
Ok guys, sorry for the delay...
I've been out of town and basically started over from the beginning with everything.
I think I figured it out!
My suspicion is that the float needle isn't sealing. The reason for this is that when I cover the carb intake on 3 of the carbs the engine attempts to stall. But on the #4 gas builds up inside and pours out when I remove my hand. I also think the carb vacuum piston is bad although I cannot find a single hole in it... I believe this because I feel no vacuum as I do with the others.
Any thoughts for when I turn out to be wrong?
2006 CBR800RR
1981 KZ750 LTD H2

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Re: Backfiring

14 Oct 2014 20:50
#650691
Well scratch that.
I swapped all the internals and it's the same result...
2006 CBR800RR
1981 KZ750 LTD H2

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  • Patton
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Re: Backfiring

14 Oct 2014 21:20
#650694
KZBrett wrote: Ok guys, sorry for the delay...
I've been out of town and basically started over from the beginning with everything.
I think I figured it out!
My suspicion is that the float needle isn't sealing. The reason for this is that when I cover the carb intake on 3 of the carbs the engine attempts to stall. But on the #4 gas builds up inside and pours out when I remove my hand. I also think the carb vacuum piston is bad although I cannot find a single hole in it... I believe this because I feel no vacuum as I do with the others.
Any thoughts for when I turn out to be wrong?

If there's acceptable compression in #4 cylinder, am thinking cylinder #4 must be sucking air through #4 carb, because otherwise there would be no air being sucked into #4 cylinder to be compressed in #4 cylinder.

Is fuel leaking from #4 carb?

Is there combustion in #4 cylinder (as evidenced by spray water test onto #4 exhaust header a few seconds after starting cold engine)?

Good Fortune! :)
1973 Z1
KZ900 LTD

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Re: Backfiring

16 Oct 2014 16:28
#650848
Cylinder 4 definitely has good compression.
I have rechecked the valve clearances. They're good.
The exhaust is not heating up. I was told this may be due to getting too much fuel.
I'm rechecking float height today.
2006 CBR800RR
1981 KZ750 LTD H2

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Re: Backfiring

16 Oct 2014 17:51 - 16 Oct 2014 17:51
#650867
KZBrett wrote: Cylinder 4 definitely has good compression.
I have rechecked the valve clearances. They're good.
The exhaust is not heating up. I was told this may be due to getting too much fuel.
I'm rechecking float height today.

was told this may be due to getting too much fuel -- or maybe not enough fuel, or maybe insufficient spark (for whatever reason).

Hopefully meaning the "fuel level" as verified by the clear tube test . And NOT the unreliable dry upside down float height measurement that's theoretically supposed to result in the correct fuel level but usually doesn't.

Carbs really care about the fuel level. And they don't give a crap about float height measurements so long as the measurement results in the correct fuel level.

Good Fortune! :)
1973 Z1
KZ900 LTD
Last edit: 16 Oct 2014 17:51 by Patton.

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Re: Backfiring

16 Oct 2014 17:57
#650868
Is it for certain that cyl #1 is combusting normally (evidenced by water spray sizzling and instantaneously evaporating off the #1 exhaust header)?

Good Fortune! :)
1973 Z1
KZ900 LTD

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Re: Backfiring

16 Oct 2014 17:57 - 16 Oct 2014 17:58
#650869
Hey!
Clear tube checked out.
And I think I really found the problem!
Apparently these new wires have an issue...
I'll keep you guys posted!
After switching number 1 and 4 wire the gas coming out of the carb switched with it.
2006 CBR800RR
1981 KZ750 LTD H2
Last edit: 16 Oct 2014 17:58 by KZBrett.

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Re: Backfiring

16 Oct 2014 18:15 - 16 Oct 2014 18:27
#650871
KZBrett wrote: . . . Apparently these new wires have an issue . . . After switching number 1 and 4 wire the gas coming out of the carb switched with it.

A cylinder with decent compression should suck mixture from the carb as normal and push it out the exhaust -- and whether combusting or not combusting is likely unrelated to carb leakage. The carb doesn't know or care whether or not the cylinder is combusting.

If not already done, would assure that the coil with green primary terminal wire is connected to the two inside spark plugs, and that the coil with black primary terminal wire is connected to the two outside spark plugs.





Good Fortune! :)
1973 Z1
KZ900 LTD

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Last edit: 16 Oct 2014 18:27 by Patton.

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  • 60ratrod
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Re: Backfiring

17 Oct 2014 13:54
#650951
It sounds as if it's either a bad wire or bad plug cap. I'd check the cap and see if it's any good
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Re: Backfiring

17 Oct 2014 17:58
#650971
Is the backfiring or popping through the cabs or exhaust?

If carbs, might be a too tight or leaking intake valve.

If exhaust, on deceleration, might be a too lean pilot circuit.

Good Fortune! :)
1973 Z1
KZ900 LTD

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  • lowie182
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Re: Backfiring

27 Oct 2014 14:59
#651900
yeah im running into the same problem and im going to do some of these checks, i got the carbs in pieces so i think im not doing too bad yet hahahaha. just to be clear 2 turns of the pilot screw is a total of 360 degrees or 720?

thanks
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