Unrestricting Zephyr 750 C1 - Kawasaki Motorcycle Forums
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post #1 of 25 (permalink) Old 08-13-2019, 03:46 PM Thread Starter
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Question Unrestricting Zephyr 750 C1

Hello,

I am from Sweden and the bike is also bought there. I found out when reading the registration papers of the motorcycle, that it is restricted from 53 kW (71bhp) to 37 kW (49bhp)by restriction added to carbs. I also found out that ALL Zephyrs sold in Europe were restricted due to emission standards to be met.

I tried to look for cable, shims, draughts etc restriction and found none. Until I checked the diafragm slide and I found out there is 4 holes drilled in there, two at each side. When consulting Haynes book and/or looking at spare parts in US I do not see any hole in the slide. They're also very expensive to afford buying new spares from US. So, my plan, is to add chemical metal and plug those holes. However, should I plug all those 4 holes or is it just one of them? I become unsure which holes I should go for.

I will add two photos, I hope you can help my Zephyr to breathe real wind again!




A bit dark on the right side, but its a hole there too. This side faces the valves


This side face airbox


There is also a hole at the bottom however it's as it should be, from what I gather.

Thanks in advance!
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post #2 of 25 (permalink) Old 08-13-2019, 06:51 PM
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Hi, I've seen several different carb rebuild kits on E-bay and none of them showed any holes in the diaphragm slide.
https://www.ebay.com/itm/Motorcycle-...MAAOSw7nZatG3N


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post #3 of 25 (permalink) Old 08-13-2019, 07:43 PM
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... also manufacturer (P/N:16126-1160) shows no holes on either side. Good luck!
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post #4 of 25 (permalink) Old 08-14-2019, 04:08 PM Thread Starter
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I bought chemical metal and goddamnit the fumes was noxious and probably not good for health. However added it and it dried metal hard almost at once.




I'll let them dry over the night, tomorrow, I will mount it all back and go for a test ride!
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post #5 of 25 (permalink) Old 08-14-2019, 06:15 PM
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Sounds good. Hopefully that "chemical metal" is fuel resistant and doesn't dissolve.
You may have to make some carburetor adjustments to account for the plugged holes.


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post #6 of 25 (permalink) Old 08-15-2019, 03:48 AM Thread Starter
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Originally Posted by DannZ View Post
Sounds good. Hopefully that "chemical metal" is fuel resistant and doesn't dissolve.
You may have to make some carburetor adjustments to account for the plugged holes.
It is fuel resistant and doesn't melt until temperature is over 160 degree Celsius (320 degree Fahrenheit).
I might, will have to ride first and check plugs afterwards.
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post #7 of 25 (permalink) Old 08-15-2019, 05:09 AM
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No, in the US they do not have the 4 holes. The one in the bottom is only an indentation, not a hole, I presume to indicate the orientation of the slide. The indention should face the intake side.
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post #8 of 25 (permalink) Old 08-15-2019, 07:01 AM Thread Starter
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I put everything back in, went out for test ride. Let it warm properly first. And then tried WOT, results:

positive

# It revs much faster when using clutch or no gear in.

# Very aggressive rev/acceleration when in high range rpm.

negative

# Much more apparent stuttering (hestitation) in midrange, its like its starved for fuel when WOT around 4-5k rpm. With that I mean it is not smooth power transistion as when above 8k rpm.


What can I learn from this? Is jetting bad for such fast power surge when wot?

Last edited by TimOfSweden; 08-15-2019 at 07:07 AM.
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post #9 of 25 (permalink) Old 08-15-2019, 01:16 PM
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You could try raising the needles a couple of notches, it sounds like itís being starved of fuel in the mid range.
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post #10 of 25 (permalink) Old 08-15-2019, 01:18 PM Thread Starter
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Quote:
Originally Posted by TimOfSweden View Post
I put everything back in, went out for test ride. Let it warm properly first. And then tried WOT, results:

positive

# It revs much faster when using clutch or no gear in.

# Very aggressive rev/acceleration when in high range rpm.

negative

# Much more apparent stuttering (hestitation) in midrange, its like its starved for fuel when WOT around 4-5k rpm. With that I mean it is not smooth power transistion as when above 8k rpm.


What can I learn from this? Is jetting bad for such fast power surge when wot?
Countinuation of latest reply!

Ok, went out for another ride. Still same symptoms, motorcycle do not bog. It's just like when riding against heavy winds. Acceleration do not have linear power output all the way, there is weakness there and there. As if it would be starved and not getting full fuel power as needed. Mid-range is where problem lies. No hestitation or bogging when idling and wot.

Pulled out the spark plugs and they look like this;



I know Zephyr 750's are oil and air cooled, so they generally runs hotter than nowadays fluidcooled machines. However if you ask me, I would say it runs too lean/hot. I think the carb setup is original/untouched.

However it's just a laymans give and take.

So before going to clean carbs and s*** which is just bothersome, I would like to add S1 injectioncleaner and rejet to make it go richer.

My questions, what jetting should I go? You who have no holes in slide in US, which jetting? Help me!
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