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dies without choke, but the carbs are clean! 06 Oct 2011 17:47 #481742

  • abrambila
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1978 KZ650 D1. The bike started alright with the choke, but the throttle was really sticky and it would rev up very high (6000ish) without touching it at all. Because of this we rebuilt the carbs with the kit from z1.

now the choke needs to be all the way out to start the bike, and letting it down at all once it's started causes it to die, opening the throttle at all also causes it to die (except for the very first milimiter or second you open it it sounds like it wants to rev up then it dies whether you hold it there or open it more... it tries and then dies).

the carbs were just rebuilt and cleaned with soaking, compressed air, new parts and 0 rings. they were bench synced and then synced again with the choke running on the bike. Float levels were measured and set as well.

we also did valves.

It still didnt run without choke on HIGH so we screwed out the air screws from 3/4 to 1 1/2 with no change

any ideas? If i understand right, the problem is that the throttle isnt pulling gas through the carbs. why would this be? at least before the throttle increased rpms, even though it was really loud and scary.
1978 KZ650 D1

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dies without choke, but the carbs are clean! 06 Oct 2011 19:21 #481758

  • bountyhunter
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vacuum leak
1979 KZ-750 Twin

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dies without choke, but the carbs are clean! 06 Oct 2011 19:22 #481760

  • trianglelaguna
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your pilot or idle circuit is obstructed and even though you have done all that,at least in my case once...i had cleaned and re-cleaned...but still had a blockage somewhere,argh i knew i had em spotless clean, i hated the friggin thing and was stumped...i asked and was told,"you still have something lodged somewhere"
so for the last time they came back off and i had to triple clean the tiny tiny ports....third time was charm


that was my experience with the exact same type symptom
1976 KZ900
2003 ZX12R
2007 FZ1000
2004 ninja 250R for wife

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dies without choke, but the carbs are clean! 06 Oct 2011 20:12 #481770

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trianglelaguna wrote: your pilot or idle circuit is obstructed and even though you have done all that,at least in my case once...i had cleaned and re-cleaned...but still had a blockage somewhere,argh i knew i had em spotless clean, i hated the friggin thing and was stumped...i asked and was told,"you still have something lodged somewhere"
so for the last time they came back off and i had to triple clean the tiny tiny ports....third time was charm


that was my experience with the exact same type symptom


If you're running pods on your carbs instead of the stock airbox, they may be blocking the vacuum inlet. If this is not the case, I would check the fuel filter and T fittings in the fuel line as well.
Southern Maryland, USA

1980 KZ250 LTD (traded, but still missed)
1982 KZ750 E3 (Cafe Project) (Dyna-S, Dyna Coils, V&H 4-1, K&N Pods, 6 Sigma Jet Kit, Acewell Computer, Woodcraft Clip-ons, Custom Rewire)
1966 A1 Samurai (Restoration Project)

Wish List:
KZ1000 P (For a "touring" bike)
Z1 (need I...

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dies without choke, but the carbs are clean! 06 Oct 2011 21:34 #481788

  • baldy110
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Pods on VM24's will not effect the vacumn they are manual slides not vacumn slides. Like trianglelaguna said your carbs are still dirty.

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dies without choke, but the carbs are clean! 06 Oct 2011 21:48 #481791

  • abrambila
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alright, sounds like the carbs are coming back off again. it seems odd to me that it could be dirty when the new jets all came in completely clean. we'll see I guess.

any tips on cleaning besides blowing compressed air through everything? Last time I soaked in a carb cleaner bucket and then scrubbed with an old toothbrush, but apparently that didnt work. should I try a spray can of carb cleaner?

i know fuel is getting to the carbs because the bowls are filling up, it just must not be getting taken up into the airstream. odd...

thanks everyone

stock airbox on the bike by the way.
1978 KZ650 D1

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dies without choke, but the carbs are clean! 06 Oct 2011 23:33 #481814

  • Motor Head
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bountyhunter wrote: vacuum leak

;)
1982 KZ1000LTD K2 Vance & Hines 4-1 ACCEL COILS Added Vetter fairing & Bags. FOX Racing rear Shocks, Braced Swing-arm, Fork Brace, Progressive Fork Springs RT Gold Emulators, APE Valve Springs, 1166 Big Bore kit, RS34's, GPZ cams.
1980 KZ550LTD C1 Stock SOLD Miss it
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dies without choke, but the carbs are clean! 07 Oct 2011 00:17 #481822

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abrambila wrote: alright, sounds like the carbs are coming back off again. it seems odd to me that it could be dirty when the new jets all came in completely clean. we'll see I guess.

any tips on cleaning besides blowing compressed air through everything? Last time I soaked in a carb cleaner bucket and then scrubbed with an old toothbrush, but apparently that didnt work. should I try a spray can of carb cleaner?

i know fuel is getting to the carbs because the bowls are filling up, it just must not be getting taken up into the airstream. odd...

thanks everyone

stock airbox on the bike by the way.


Wear eye protection because pressurized spray can carb cleaner always backfires toward your eyes. Always.

This pilot circuit cleaning method applies to carb with side-located pilot air screw.



The same basics may be applied to cleaning pilot circuit with bottom located pilot mixture screws.



Racing idle may result from outside air being drawn through old leaking carb holders. Or from other leak sources such as vacuum caps, cracked or loose vacuum line to petcock, etc.

There are also a few mechanical reasons (often throttle-cable related) which may cause a racing idle.

Good Fortune! :)
1973 Z1
KZ900 LTD
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dies without choke, but the carbs are clean! 07 Oct 2011 09:45 #481854

  • Jeff.Saunders
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When you rebuilt the carbs, did you reset the float levels?

There can be some minor differences in the lengths of float needles - it's important to make sure the fuel level in the carb is correct. If you have too little fuel in the bowl, the carbs won't pickup the fuel effectively. The choke circuit pickup is deep down in the bowl (it's the long brass tube).
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dies without choke, but the carbs are clean! 07 Oct 2011 11:59 #481860

  • Patton
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abrambila wrote: ...Float levels were measured and set as well. ....


Should also bear in mind that the actual fuel level inside the float bowl is the critical measurement, and not the "float height."

The correct "float height" measurement is whatever results in the correct "fuel level."

Doe to varying buoyancy and mechanical factors, the measured "float height" may be slightly different among the carbs (which isn't unusual and is perfectly okay) so long as the "fuel levels" are correct.

Perform the "clear tube" test to accurately determine actual fuel level, which some FSMs refer to as the "service" fuel level.



Good Fortune! :)
1973 Z1
KZ900 LTD
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dies without choke, but the carbs are clean! 14 Oct 2011 14:06 #483162

  • abrambila
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Hey everyone, thanks for the advice, the diagrams were especially helpful. I did find an air leak and fix it, and I re-cleaned everything and set the float levels the wet way. Things definitely have progressed, but here's where I'm stuck now:

Initially my problem was that it was running too lean: I could only rev it up with the choke from idle. Any throttle just killed it. Through the process of fiddling with the air screws (turned them way in, to like half a turn out) i got it so that in neutral the throttle would rev up amazingly, although in gear it still dies around 2500 rpm (not very useful as a vehicle). My assumption was still too lean, so i turned them in more, but this just made it die while idling. This seems to indicate to me too rich, which i tested by moving the choke and sure enough it died if I gave it any choke.

Any idea what gives? How can it be too lean and too rich at the same time? Is it that I'm running the idle circuit really rich and then the high speed circuit is lean and they're switching off as I rev up? If so how would I solve this? My needle is already set at 2nd from the bottom, it seems weird that that would be so lean still. Argh!
1978 KZ650 D1

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dies without choke, but the carbs are clean! 14 Oct 2011 15:15 #483180

  • apbling
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Do you have a manual? What is the stock position for the pilot screws? I'd start there. Really those screws shouldn't have a really large effect at 2500 rpm...

I recently had a similar problem...thought my pilots were dirty. After cleaning them a bunch of times and adjusting my fuel level really carefully I got good performance at higher rpms and idle, but I had to really really really nurse it off the line until I got my RPM's up. Then I realized that I mixed the seafoam in the gas way way too strong. Threw some different gas in and she was good to go.

Have you checked your electrical system out? Good spark? What about the timing advance mechanism? Maybe need to lube it up.

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