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'83 KZ750 F high idle issues
- Dunemaster
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07 Jun 2024 18:39 #900442
by Dunemaster
'83 KZ750 F high idle issues was created by Dunemaster
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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- Nessism
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07 Jun 2024 19:22 - 07 Jun 2024 19:22 #900443
by Nessism
Replied by Nessism on topic '83 KZ750 F high idle issues
Make sure there is slack in the throttle cable, and back off the idle stop screw?
Last edit: 07 Jun 2024 19:22 by Nessism.
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- TexasKZ
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08 Jun 2024 09:25 #900452
by TexasKZ
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
Replied by TexasKZ on topic '83 KZ750 F high idle issues
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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- Dunemaster
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08 Jun 2024 11:15 #900461
by Dunemaster
Replied by Dunemaster on topic '83 KZ750 F high idle issues
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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- gd4now
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- Denco where did you go?
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08 Jun 2024 11:36 #900462
by gd4now
1977 KZ650 B1
Pods and Denco header
OLD KAW OWNERS SMILE ALOT
Replied by gd4now on topic '83 KZ750 F high idle issues
What type of air filter are you running?
1977 KZ650 B1
Pods and Denco header
OLD KAW OWNERS SMILE ALOT
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- Wookie58
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08 Jun 2024 11:52 #900463
by Wookie58
Replied by Wookie58 on topic '83 KZ750 F high idle issues
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)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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- Dunemaster
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08 Jun 2024 20:40 #900480
by Dunemaster
Replied by Dunemaster on topic '83 KZ750 F high idle issues
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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- TexasKZ
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09 Jun 2024 07:12 #900497
by TexasKZ
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
Replied by TexasKZ on topic '83 KZ750 F high idle issues
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.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.
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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- Dunemaster
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10 Jun 2024 12:07 #900567
by Dunemaster
Replied by Dunemaster on topic '83 KZ750 F high idle issues
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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- TexasKZ
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10 Jun 2024 18:37 #900584
by TexasKZ
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
Replied by TexasKZ on topic '83 KZ750 F high idle issues
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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- asphalt900
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11 Jun 2024 04:55 #900594
by asphalt900
Replied by asphalt900 on topic '83 KZ750 F high idle issues
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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