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'83 KZ750 F high idle issues 07 Jun 2024 18:39 #900442

  • Dunemaster
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I've got an engine from a KZ750 F parts bike that I have put in a go-kart. After not starting it and simplifying the wiring harness to remove unneeded features such as brake lights and blinkers, the idle shot through the roof to around 8,000 rpm without the choke on. Since then I have fully rebuilt the carbs and made sure the floats are at the correct height, checked the floats were sealing properly with a hand pump, installed new carburetor boots and new exhaust gaskets, set the fuel mixture screws correctly, bench synched them, and have installed new spark plugs. I checked for leaks using carb cleaner with the new boots installed but have found nothing. The engine is still idling 7,000 rpm higher than it should and is backfiring. Does anyone have any ideas about what I should try next? 

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'83 KZ750 F high idle issues 07 Jun 2024 19:22 #900443

  • Nessism
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Make sure there is slack in the throttle cable, and back off the idle stop screw?

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'83 KZ750 F high idle issues 08 Jun 2024 09:25 #900452

  • TexasKZ
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Are the vacuum ports used for synchronizing covered with tightly fitting caps?
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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'83 KZ750 F high idle issues 08 Jun 2024 11:15 #900461

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I’ve got slack in my throttle cable and the idle screw is backed all the way out. I’ve got vacuum caps on all of the vacuum synchronization ports because I took out the cam fume recirculator. I’ve also blocked those ports off. Could my intake and exhaust valves not sealing properly cause such a high idle? My exhaust valves are white, which I heard could be a sign of running very lean (which would make sense if I had a vacuum leak).
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'83 KZ750 F high idle issues 08 Jun 2024 11:36 #900462

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What type of air filter are you running? 
1977 KZ650 B1
Pods and Denco header


This is my Z

OLD KAW OWNERS SMILE ALOT

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'83 KZ750 F high idle issues 08 Jun 2024 11:52 #900463

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I’ve got slack in my throttle cable and the idle screw is backed all the way out. I’ve got vacuum caps on all of the vacuum synchronization ports because I took out the cam fume recirculator. I’ve also blocked those ports off. Could my intake and exhaust valves not sealing properly cause such a high idle? My exhaust valves are white, which I heard could be a sign of running very lean (which would make sense if I had a vacuum leak).
Valves won't effect idle speed, high idle can only happen as a result of excess air ( either a leak or the throttle flaps aren't closing)

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'83 KZ750 F high idle issues 08 Jun 2024 20:40 #900480

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Well I'm glad I won't have to tear apart the cylinder head to fix the valves. I'm unfortunately running pod filters since the bike didn't have the stock air box when I bought it. To fix the issue of running lean, I 3d printed some restrictive inserts to go between the pods and the carburetors. Even with the high idle, the throttle is responsive.

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'83 KZ750 F high idle issues 09 Jun 2024 07:12 #900497

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Well I'm glad I won't have to tear apart the cylinder head to fix the valves. I'm unfortunately running pod filters since the bike didn't have the stock air box when I bought it. To fix the issue of running lean, I 3d printed some restrictive inserts to go between the pods and the carburetors. Even with the high idle, the throttle is responsive.
Are those restrictors blocking the air intake ports around the rim of the carburetor? They are necessary to the proper function of the carbs, and must have access to unrestricted, non-turbulent airflow.
Restricting the airflow is not the best way to fix a lean mixture. Proper jetting is.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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'83 KZ750 F high idle issues 10 Jun 2024 12:07 #900567

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I’ve found the problem! (At least I think I have). TexasKZ mentioned my restrictive inserts may have been blocking the air inlets (which they were), but the reason I designed my inserts with a large outer rim was because the cheap pod filters I bought also had a large outer rim. I haven’t been able to get the engine to run well without the pods on it, but it putters out instead of idling at 8k (which I think is an improvement). Any recommendations on what I should replace my cheap pod filters with? Would foam pods be better than the “classic” style pod filter?
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'83 KZ750 F high idle issues 10 Jun 2024 18:37 #900584

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APE and K&N make good filters that will not block the air inlets. UNI is another good choice, especially if you prefer foam.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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'83 KZ750 F high idle issues 11 Jun 2024 04:55 #900594

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If it were me, going into a "dirt" situation because you said go-kart. I'd go foam. No dirtbike i know of uses pleated paper elements, at least within the last 40yrs. Uni makes one of the best foam ones, use them all the time on RM/CR/YZ's.

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