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1981 Gpz 750. problems over medium high rpm
- labrendola
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06 Nov 2024 02:09 #905810
by labrendola
1981 Gpz 750. problems over medium high rpm was created by labrendola
Good morning guys, writing from Italy here searching for a solution overseas
I have a 1981 gpz 750 that gives me problems at medium-high rpm: when I get to around 5k rpm the bike drowns down, like when you run out of gas and there is no way to pass that limit. Actually, mounting standard jets (37.5 pilot + 110) on Mikuni BS 34 (later, with no hole between pilot and main channel and so with no drilled pilot) and no rubber caps), standard air box and standard mufflers. I tried lowering the clip on the needle, but it doesn't change anything. The carburetors are clean and I have no air leaks (tested by spraying the area with carb cleaner spray). Now I'm going to check again the carb floater level, but I'm pretty sure i did a good job there when I reworked those carbs last time. Could be a main jet problem?
I have a 1981 gpz 750 that gives me problems at medium-high rpm: when I get to around 5k rpm the bike drowns down, like when you run out of gas and there is no way to pass that limit. Actually, mounting standard jets (37.5 pilot + 110) on Mikuni BS 34 (later, with no hole between pilot and main channel and so with no drilled pilot) and no rubber caps), standard air box and standard mufflers. I tried lowering the clip on the needle, but it doesn't change anything. The carburetors are clean and I have no air leaks (tested by spraying the area with carb cleaner spray). Now I'm going to check again the carb floater level, but I'm pretty sure i did a good job there when I reworked those carbs last time. Could be a main jet problem?
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- gd4now
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06 Nov 2024 10:31 #905821
by gd4now
1977 KZ650 B1
Pods and Denco header
OLD KAW OWNERS SMILE ALOT
Replied by gd4now on topic 1981 Gpz 750. problems over medium high rpm
Do not know if this will be of any help or not. But I have seen some info that indicates the needle and needle jet were different on the carbs without the connection/passageway between the pilot and main jets.
Anyway here it is
read L-R like this:
Model, Cross Pilot & Plug(Yes or No), Main Jet, Pilot Jet, Jet Needle, Needle Jet, Main Air Jet, Pilot Air Jet
GPz750R1, Yes, 110, 37.5, 4BE3, Y9, 250, 300
Z750L3,4, Yes, 110, 37.5, 4BE3, Y9, 250, 300
GPz750A, No, 110, 37.5, 4BC7, Y8, 250, 300
Z1000K1,2, Yes, 122.5, 37.5, 5FL52, Y1, 85, 350
Z1000J1,2, Yes, 127.5, 37.5, 5FLZ50, Y6, 85, 350
Z1000J3, No, 117.5, 37.5, 5CF58, Y2, 85, 350
Z1000R2, No, 127.5, 37.5, 5C48, Y4, 85, 350
Z1100A1,2, Yes, 120, 37.5, 5GX29, Y1, 85, 350
Z1100A3, No, 117.5, 37.5, 5CF58, Y2, 85, 350
Z1100R1, No, 130/5, 37.5, 5B5, Y8, 85, 350
Anyway here it is
read L-R like this:
Model, Cross Pilot & Plug(Yes or No), Main Jet, Pilot Jet, Jet Needle, Needle Jet, Main Air Jet, Pilot Air Jet
GPz750R1, Yes, 110, 37.5, 4BE3, Y9, 250, 300
Z750L3,4, Yes, 110, 37.5, 4BE3, Y9, 250, 300
GPz750A, No, 110, 37.5, 4BC7, Y8, 250, 300
Z1000K1,2, Yes, 122.5, 37.5, 5FL52, Y1, 85, 350
Z1000J1,2, Yes, 127.5, 37.5, 5FLZ50, Y6, 85, 350
Z1000J3, No, 117.5, 37.5, 5CF58, Y2, 85, 350
Z1000R2, No, 127.5, 37.5, 5C48, Y4, 85, 350
Z1100A1,2, Yes, 120, 37.5, 5GX29, Y1, 85, 350
Z1100A3, No, 117.5, 37.5, 5CF58, Y2, 85, 350
Z1100R1, No, 130/5, 37.5, 5B5, Y8, 85, 350
1977 KZ650 B1
Pods and Denco header
OLD KAW OWNERS SMILE ALOT
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- Wookie58
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06 Nov 2024 10:40 #905822
by Wookie58
Replied by Wookie58 on topic 1981 Gpz 750. problems over medium high rpm
Sounds simple but have you tried running it with the gas cap open (possible blocked breather in the cap)
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- labrendola
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06 Nov 2024 11:29 #905823
by labrendola
Replied by labrendola on topic 1981 Gpz 750. problems over medium high rpm
yes Wookie58, I got your same thought and so I tried that option,but didn't work.
thank you,gd4now, as well for that list: I have another old serie of BS34 coming from a suzuki katana provided with the connection hole between the pilot and the main jet channel...of course I could assemble that carb set with the proper jets and trying those with this GPZ. but, in anycase, I know (atleast here in Italy) these bikes were factory provided with drilled and not drilled BS34, plus keihin, and so I'm upset as I don't understand why it doesn't work properly with these carbs....
thank you,gd4now, as well for that list: I have another old serie of BS34 coming from a suzuki katana provided with the connection hole between the pilot and the main jet channel...of course I could assemble that carb set with the proper jets and trying those with this GPZ. but, in anycase, I know (atleast here in Italy) these bikes were factory provided with drilled and not drilled BS34, plus keihin, and so I'm upset as I don't understand why it doesn't work properly with these carbs....
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06 Nov 2024 11:46 #905825
by Wookie58
Replied by Wookie58 on topic 1981 Gpz 750. problems over medium high rpm
I believe your model still uses the "mechanical" advancer for the ignition, have you checked the components move freely to advance the ignition as the revs build ?
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