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Lack of Top Speed in 5th gear

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02 Aug 2022 10:28 - 02 Aug 2022 10:29 #871512 by tatters
Lack of Top Speed in 5th gear was created by tatters
Hi, l have a 1984 KZ750L4 Canadian model that is completely stock pipes/airbox etc which l had an some idle issues with that turned out to be blockages in the enrichment circuit within the float bowls. Now the bike is runs and idles good but the issue l am now having is that the bike runs out of power in 4th and 5th gears and no matter what will not pull past 90mph. In all other gears the bike pulls to the redline. Just incase my 240lb weight was the issue l also had my 110lb wife take the bike for a ride and she also had the same issue.   

Valve clearances are good, leak down and compression tests showed perfect, carbs clean and balanced, clean air filter with no air leaks, both coils and all spark plugs have been replaced along  with the relay power modfication. I was thinking that the engine could be running lean so replaced the main jets from 110 to 112 but that made no diffrence.

Current carb settings are:
BS34 carbs
Main jet 110
pilot jet 37.5
needle Y270 (clip in middle)
pilot screw 2 turns out (have tired both in and out 1-1/2 that made no difference).
My altitude is 1600 feet


Thanks,
Last edit: 02 Aug 2022 10:29 by tatters.

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02 Aug 2022 10:37 - 02 Aug 2022 10:39 #871515 by Wookie58
Replied by Wookie58 on topic Lack of Top Speed in 5th gear
Is the ignition timing correct ?
Has the gearing been altered to lower the revs for highway cruising (sprockets changed) ?
Is there any damage to the exhaust collector that could be limiting flow ?
Last edit: 02 Aug 2022 10:39 by Wookie58.

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02 Aug 2022 11:17 #871516 by Nerdy
Replied by Nerdy on topic Lack of Top Speed in 5th gear
This might sound like a dumb question, but is your clutch slipping?

1979 KZ400 Gifted to a couple of nephews
1967 Yamaha YCS1 Bonanza
1980 KZ440B
1981 Yamaha XT250H
1981 KZ440 LTD project bike
1981 GPz550
2013 Yamaha FZ6R

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02 Aug 2022 11:33 #871517 by Mikaw
Replied by Mikaw on topic Lack of Top Speed in 5th gear
What did you recently change that has caused this. A wild stab, cam lobes worn and engine down on power and it can’t overcome the load in 4-5th gear. 

1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

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02 Aug 2022 12:03 - 02 Aug 2022 12:06 #871521 by tatters
Replied by tatters on topic Lack of Top Speed in 5th gear
I purchased the bike back in the winter with an idle issue that the previous owner could not figure out, so have never rode the bike without a running issue.


I did check the timing after the valves were adjusted and it was correct, (Camshaft/timing chain/crank as per the manual). This model has electronic igntion and doesn't appear to be adjustable.

Bike still has the original chain and sprockets which l have confirmed are the stock ratio.

Exhaust pipes and collector has no damage or leaks, only minor rust.

Clutch plates have been recently replaced, clutch was slipping before but now doesn't which l suspect was due to the last owner using car oil with a friction modifier.

Cam lobes are in great condition with very little wear (bike only has 12k on the clocks)
Last edit: 02 Aug 2022 12:06 by tatters.

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02 Aug 2022 12:12 - 02 Aug 2022 12:15 #871522 by Warren3200gt
Replied by Warren3200gt on topic Lack of Top Speed in 5th gear
Restricted air intake? What filters are fitted? If stock, when was the air filter last renewed. If pods are they quality pods in good condition? It sounds like you have a restriction in either fuel or air. 
Also if pods ensure they are clearing the pilot air take ports. Pilot jets are contributing for the entire rev range. 


Z1000J2 somewhat modified!

Last edit: 02 Aug 2022 12:15 by Warren3200gt.

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02 Aug 2022 13:28 #871528 by BobZ
Replied by BobZ on topic Lack of Top Speed in 5th gear
Have you checked the float levels?....might just be running out of fuel under high load
 

Had I known I'd live this long I'd have taken better care of my Led Zeppelin albums


1983 Goldwing Interstate
1982 KZ750 LTD

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  • Scirocco
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  • Never change a running system
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02 Aug 2022 16:05 #871539 by Scirocco
Replied by Scirocco on topic Lack of Top Speed in 5th gear
Leaking old brittle carb boots can cause a lean A/F ratio!!! They are on the top of every bike "re-build-to-do" list!!!

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02 Aug 2022 16:14 #871541 by Nessism

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