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tatters |
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tatters Exxon Valdez
Joined: 05 Jan 2004 Karma :
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Posted: 21:59 - 02 May 2023 Post subject: 1984 Kawasaki KZ750 high speed issues. |
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I have a high speed running issue with a 1984 Kawasaki KZ750L3 (four cylinder), which has me stumped.
No matter what l cant get the bike to go past 80mph and if l am at full throttle for more than a few mins in top gear l start to loose power followed by rolling off the throttle and back on again the bike bogs down.
1-3rd gears rev all the way to redline but 4-5th the bike is struggling to make power. Fuel eco is also awful.
Cylinder leak down test was carried out on all pots are 2-4% (excellent result).
Carbs rebuilt with stock jetting/settings and float hight is at spec (checked with clear fuel pipe on bowl drains).
Carbs balanced.
Stock exhaust.
Stock gearing.
New ignition coils and spark plugs (electronic ignition).
New carb boots and running stock airbox and filter.
Valve clearances adjusted. ____________________ Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650 Present:G650XC,C12,KZ750,1190ADV |
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
Joined: 16 Aug 2013 Karma :
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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tatters |
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tatters Exxon Valdez
Joined: 05 Jan 2004 Karma :
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Posted: 22:40 - 02 May 2023 Post subject: Re: 1984 Kawasaki KZ750 high speed issues. |
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stinkwheel wrote: | tatters wrote: |
New ignition coils (electronic ignition). |
When were these fitted, was it ok before this? Which electronic ignition (if dyna, which one)?
There are some shite ignition coils out there. Mate of mine fitted a set from a major UK bike parts supplier to his CB750 recently and 10 miles later one of them had caught fire. They were the wrong impedence. |
fitted a few months ago to address this issue but they had no effect. Not stock coils or Dyna but a genric brand with the same ohms as stock coils.
plugs looks good, stock intake, too warm for carb icing. ____________________ Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650 Present:G650XC,C12,KZ750,1190ADV |
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Easy-X |
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Easy-X Super Spammer
Joined: 08 Mar 2019 Karma :
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tatters |
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tatters Exxon Valdez
Joined: 05 Jan 2004 Karma :
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Posted: 02:09 - 03 May 2023 Post subject: |
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Took it for a run with the fuel cap open also with the fuel tape set to prime and that made no difference. I also disconnect the fuel hose going to the carbs and set the tank to prime to allow fuel to flow into a container, flow was good not restricted at all. ____________________ Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650 Present:G650XC,C12,KZ750,1190ADV |
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UncleFester |
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UncleFester World Chat Champion
Joined: 30 Jun 2013 Karma :
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Pete. |
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Pete. Super Spammer
Joined: 22 Aug 2006 Karma :
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Posted: 06:32 - 03 May 2023 Post subject: |
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Pull the carbs again and inspect the needles and emulsion tubes. Check the tapers on the neeldes are straight and the hole in the mulsion tubes aren't worn out of round. ____________________ a.k.a 'Geri'
132.9mph off and walked away. Gear is good, gear is good, gear is very very good |
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MCN |
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MCN Super Spammer
Joined: 22 Jul 2015 Karma :
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yen_powell |
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yen_powell World Chat Champion
Joined: 22 Jun 2008 Karma :
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Posted: 15:11 - 03 May 2023 Post subject: |
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Did you inspect the carb diaphragms for pinholes/tears?
I know a mate of mine was having issues with his Z900 where the ethanol had attacked the seals on the needle valve tips. Cheap and easy fix to get modern ones with viton tips. ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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tatters |
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tatters Exxon Valdez
Joined: 05 Jan 2004 Karma :
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Posted: 17:28 - 03 May 2023 Post subject: |
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Running fresh 98 Ron fuel.
The carb internals look to have been replaced not too long ago (shiny brass and new diaphrams). jets and neddle parts numbers do match stock numbers so all is correct.
I am going to get a high quailty rebulit kit for the carbs and change everything over just incase. ____________________ Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650 Present:G650XC,C12,KZ750,1190ADV |
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Bhud |
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Bhud World Chat Champion
Joined: 11 Oct 2018 Karma :
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tatters |
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tatters Exxon Valdez
Joined: 05 Jan 2004 Karma :
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Posted: 18:08 - 03 May 2023 Post subject: |
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No issues with the choke (on the BS34 carbs its a enrichment circuit.), working fine. ____________________ Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650 Present:G650XC,C12,KZ750,1190ADV |
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Bhud |
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Bhud World Chat Champion
Joined: 11 Oct 2018 Karma :
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Posted: 18:54 - 03 May 2023 Post subject: |
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Has it ever run right since you owned it?
If not check your timing (ignition and valve). Not unheard of for them to spin up a flywheel. Also not unheard of for someone to ineptly fit an electronic ignition or camchain in the wrong position.
Thing is, in the UK if you bought a 750 and it wouldn't go over 80mph, anyone would immediately think there is a problem. But you're in the US right? Most harleys won't go much over 80mph and that's totally normal and Harleys are the best bikes in the world and twice as big as a 750. So 80phm out of a 750cc Japanese bike must be normal. It might have been running like that for a long time. ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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tatters |
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tatters Exxon Valdez
Joined: 05 Jan 2004 Karma :
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Posted: 19:51 - 03 May 2023 Post subject: |
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stinkwheel wrote: | Has it ever run right since you owned it?
If not check your timing (ignition and valve). Not unheard of for them to spin up a flywheel. Also not unheard of for someone to ineptly fit an electronic ignition or camchain in the wrong position.
Thing is, in the UK if you bought a 750 and it wouldn't go over 80mph, anyone would immediately think there is a problem. But you're in the US right? Most harleys won't go much over 80mph and that's totally normal and Harleys are the best bikes in the world and twice as big as a 750. So 80phm out of a 750cc Japanese bike must be normal. It might have been running like that for a long time. |
Has never run right since buying it. It did have a issue starting up and ideling but l corrected this after ultrasoinc cleaning the carbs as the enrichment circuits were blocked.
When l did the valve clearances l did check the timing which was correct as per the manual. The bike has a electroinc ignition which is stock and cant be adjusted. flywheel is also correctly mounted on crank woodruff key.
Its a really weird issue that l have been trying to correct for the past year now. ____________________ Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650 Present:G650XC,C12,KZ750,1190ADV |
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tatters |
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tatters Exxon Valdez
Joined: 05 Jan 2004 Karma :
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Posted: 19:54 - 03 May 2023 Post subject: |
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The other odd things was that when l first took the carbs apart the main jet sizes were two sizes too big.
I replaced theses with the correct size as per the manual. This was odd as the bike is 100% stock. ____________________ Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650 Present:G650XC,C12,KZ750,1190ADV |
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Posted: 20:01 - 03 May 2023 Post subject: |
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No weird California compliant emissions crap?
Your description all sounds like a bike either running rich, or running out of fuel.
Does it pull better if you ease off wide open throttle? How about if you put the choke on when it starts losing power?
Umm. Crankcase breather? ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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Robby |
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Robby Dirty Old Man
Joined: 16 May 2002 Karma :
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bypass2 |
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bypass2 Spanner Monkey
Joined: 12 Sep 2013 Karma :
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that_impulse_guy |
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that_impulse_guy Nitrous Nuisance
Joined: 07 Mar 2023 Karma :
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Posted: 21:42 - 03 May 2023 Post subject: |
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on the assumption were having running our of petrol symptoms...
what the above post says...
plus
float heights. after a minute or two it bogs down...not jets..not needle....float heights or fuel starvation
float heights were mentioned earlier, so lets focus on fuel starvation (the good ole blocked fuel cap/blocked fuel filter.)
we need to talk about BSFC...brake specific fuel consumption...4stroke motors are somewhere around 20-30% efficient...yours makes...57kw?
I stick some numbers in here https://www.omnicalculator.com/everyday-life/brake-specific-fuel-consumption#how-do-i-calculate-bsfc and make some assumptions and come out with about
4g/s of fuel needed...ballpark...give or take...add a bit here and there..lets not split hairs.
take fuel pipe after fuel filter, put in beaker ,open tap, count to 10, or 20 or 30..whatever...take measurement, do some maths (4g/second is NOT 4ml/second), maybe use a scale...and you can work out if that fuel filter is crap, or the replacement ebay fuel tap is restrictive, or the fuel hose is too teeny tiny.
i post this purely for the humour:-)
you said your jets were two sizes too big...but its not clear if this bike is new to you and this problem is after cleaning the carbs and going for your first ride on this bike new to you, or if its a fault thats developed...i dunno.. ____________________ Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R |
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Pete. |
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Pete. Super Spammer
Joined: 22 Aug 2006 Karma :
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Posted: 06:47 - 04 May 2023 Post subject: |
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#i suppose you have the air filter properly cleaned and oiled? You might try a quick run with it removed just to eliminate that. ____________________ a.k.a 'Geri'
132.9mph off and walked away. Gear is good, gear is good, gear is very very good |
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A100man |
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A100man World Chat Champion
Joined: 19 Aug 2013 Karma :
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Posted: 09:55 - 04 May 2023 Post subject: |
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+ 1 for plug chop
could thr choke/enrichmenst circuit be sticking on?
My Yam 600 (BS30s) once bogged at anything over half throttle - I pulled the carbs and found one main jet sitting in the bottom of the float bowl...
The idiot that stripped the carbs hadn't done them all up properly ____________________ Now: A100, GT250A, XJ598, FZ750
Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600 |
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