pilot screw

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26 May 2024 17:59 #899783 by kzken750
pilot screw was created by kzken750
1980 kawasaki 750 bored out to 810. 
I finally have the bike jetted so it runs really good under power since the rebuild. I look at the sparks plugs and they look good but show signs of fuel not being fully burned as the ring around the electrode has excessive carbon on it. The bike also seems to surge slightly and not run as smooth as it should while cruising at speed. Pilot screws are set at 2 1/2 turns up or close, I forget exactly but it is close. Up for more air to smooth it out?   Would it be wise to use a hotter spark plug than stock since it has been bored out. Like I said, the bike runs great under power. I would just like to smooth it out on the cruising side of things.
Thanks for the help

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  • Nessism
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26 May 2024 19:55 #899789 by Nessism
Replied by Nessism on topic pilot screw
I would not use a hotter plug.  If anything, colder may be in order.

The pilot screw only has a small effect on the mixture, mostly at idle and just off.  You can try different settings, but I doubt you will see significant differences.
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27 May 2024 05:45 #899800 by kzken750
Replied by kzken750 on topic pilot screw
thanks for the response. but what do you think is causing the feeling of the bike surging when I try to maintain an even speed? I have gone up twice on the pilot jet and there are 3 washers under the needle. I started with two and didn't feel it was right. Went down to one and it was worse. Went to three and as I said the bike runs great under power. Its just that it doesn't want to cruise smoothly. 

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27 May 2024 08:50 #899810 by ckahleer
Replied by ckahleer on topic pilot screw
Can you fit another washer or two under the needles? If one is no good and 3 are better, 5 might do the trick. I sometimes cut small sections of weed trimmer fuel line to slip over the needles. It is easer than dealing with all those washers. 

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27 May 2024 12:07 #899815 by kzken750
Replied by kzken750 on topic pilot screw
thanks for your response. I'm not sure that's the answer though. It runs great under power but looking at the spark plugs I can see that it is a little too rich now. Giving it more gas I think will not help. Two washers not enough, three plenty. I think.  I'm thinking it needs more air. I don't know. What is this surging and failure to run smoothly?

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  • SWest
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27 May 2024 12:43 #899816 by SWest

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27 May 2024 13:04 - 27 May 2024 13:06 #899817 by TexasKZ
Replied by TexasKZ on topic pilot screw
Surging can be caused by a lean mixture . Improvement by raising the needles also suggests a lean mixture. Three washers suggests there is a problem elsewhere.
Are the carb holders old, hard and maybe starting to have surface cracks?
Are the carbs not fully seated in the carb holders?
Wrong needles or jets?
correct fuel level confirmed by the clear tube method?
Cheap pod filters blocking the air corrector jets?

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Last edit: 27 May 2024 13:06 by TexasKZ.

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28 May 2024 09:56 #899867 by kzken750
Replied by kzken750 on topic pilot screw
thanks for the replies. 

but..........   carb holders are new, as is almost every thing on this engine. I know the carbs are also seated properly. Looking at the spark plug indicates a slightly rich mixture. The electrode is almost the brown color it should be but the base of the plug is black. That seems to indicate a mixture that is a little too rich. Unburned fuel is what I'm being told.  Maybe I shouldn't have gone two up on the pilot jets?

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  • SWest
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28 May 2024 10:03 #899870 by SWest
Replied by SWest on topic pilot screw
Are the valve guide seals new? If not they could lead you to believe it's rich when it's running lean. The surging is the tip off but diaphragms could also be the culprit. Have you tried the thumb test on the slides?

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28 May 2024 10:36 #899877 by Rolf1976_KZ900
Replied by Rolf1976_KZ900 on topic pilot screw
If it surging at steady throttle it is often lean. Have you tried to give it a little choke when surging if it runs better it is lean for sure.What is rpm at when surging?
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28 May 2024 10:39 #899878 by kzken750
Replied by kzken750 on topic pilot screw
all valve guides are new and the valves have been professionally seated. Not sure what you mean by the thumb test on the slides.
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28 May 2024 10:41 #899879 by kzken750
Replied by kzken750 on topic pilot screw
thanks for the reply.

It surges at anytime I try to keep a steady speed. 
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