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Keihin Cr´s breaks-up at full throttle
- Patton
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Weak spark is one of the suspects that might possibly cause the reported symptoms.leitz wrote: ...Bike pulls clean and hard at all the revs and gears but starts to break-up the mix at 4th gear full throttle (100 mph) and on 5th don´t pulls to more speed. I´ve to roll off the throttle because the bike deads....
Inadequate voltage to the coils is one of the suspects for weak spark.
Good Fortune!
1973 Z1
KZ900 LTD
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- leitz
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- Old Man Rock
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You'd want to lower the clip position down to raise the needle for more gas flow....
Possibly different needle... In case you need...
Plug conditions...?
1976 KZ900-A4
MTC 1075cc.
Camshafts: Kawi GPZ-1100 .375 lift
Head: P&P via Larry Cavanaugh
ZX636 suspension
MIKUNI, RS-34'S...
Kerker 4-1, 1.5" comp baffle.
Dyna-S E.I.
Earls 10 row Oil Cooler
Acewell 2802 Series Speedo/Tach
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Phoenix, Az
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- BlackZ1R
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Since you gained mph with smaller mains, you know it's too rich for your ignition to fire.
One thing you need to be aware of is the quality of fuel you have in the tank now. Bad gas could be part of the problem. Try fresh fuel, or maybe a good splash of av gas to see how it pulls. Av gas has a bit lighter specific gravity, so keep an eye on your plugs at WOT.
Kawasaki
Someone once told me to marry that motorcycle I was riding ......there's times I wish I hadda listened .
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- leitz
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Have a good start, idles well for a racing carbs on street, less hp at 4000-7000 revs than originals VM´s but get an enjoy fast ridind from 7000 to 10000 rpm where bike likes to be. Of course engine mods like porting and cams would make the diference, but as we say in Spain "todo se andará": everything will come.
Thanks to all you guys for the info, I will keep you informed of progress
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- 650ed
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1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)
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- turboguzzi
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no sabia che hablas español.... con ese nick aleman ni me lo hubiera imaginado! y el filmado en pista se me escapo antes.
Sure, it could be temperatures, but honestly, even in my very highly tuned 750/810 that runs with CR29's, i dont have to change jetting from 8C in the morning to 22C in the afternoon (like i had yesterday on the track at my last race of the season).
If anything, that proves even more that you still have ignition problems as with bad ignition the motor becomes much more sensitive to small mixture changes. a good ignition burns it all even when not on the sweet spot
Ed, I constantly run my 750/810 (essentially a very big bore 650) to 11K without much problems with only HD springs to help against the race cams.
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- LarryC
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The first thing you want to do is address that situation. It is the single number that immediately jumps out as being out in left field. Regardless of the fact that you're having top end issues, that's got to be way too much fuel being dumped in through the pilot circuit.
It appears you have electrical issues also but you need to start with a reasonable jetting spec. Something around a #60 slow jet is much more reasonable.
Larry C.
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- 650ed
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I don't doubt it, but there has been at least guy on another forum who has blown his motor using stock valve springs and con rods at high rpm. I don't know whether his rods stretched or the valves didn't close quickly enough, but there was contact between piston & valve. So over revving a stock engine introduces a risk of blowing it up. I do not hesitate to take mine up to the 9k rpm redline, but I don't go beyond that (even though the engine is very willing), and I have not had any problems since buying the bike new (53,000 miles).
The other issue is that the stock KZ650 motor, perhaps unlike your modified motor, has a power drop-off after 8500 rpm. By the time his stock engine gets to 10k rpm it's making about the same or less power than it was at around 7k rpm - so revving that high is not only risky to the engine it also provides less power. The power curve below is for the 1977 KZ650, several later models lose power at even lower rpm. This is why I recommended he run it on a dyno so he can see his engine's actual performance curve. I think he would be surprised at how little power the engine makes at 10k rpm. Ed
Attachment hp0001.jpg not found
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)
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- LarryC
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650ed wrote: turboguzzi wrote: "Ed, I constantly run my 750/810 (essentially a very big bore 650) to 11K without much problems with only HD springs to help against the race cam."
I don't doubt it, but there has been at least guy on another forum who has blown his motor using stock valve springs and con rods at high rpm. I don't know whether his rods stretched or the valves didn't close quickly enough, but there was contact between piston & valve. So over revving a stock engine introduces a risk of blowing it up. I do not hesitate to take mine up to the 9k rpm redline, but I don't go beyond that (even though the engine is very willing), and I have not had any problems since buying the bike new (53,000 miles).
The other issue is that the stock KZ650 motor, perhaps unlike your modified motor, has a power drop-off after 8500 rpm. By the time his stock engine gets to 10k rpm it's making about the same or less power than it was at around 7k rpm - so revving that high is not only risky to the engine it also provides less power. The power curve below is for the 1977 KZ650, several later models lose power at even lower rpm. This is why I recommended he run it on a dyno so he can see his engine's actual performance curve. I think he would be surprised at how little power the engine makes at 10k rpm. Ed
Attachment hp0001.jpg not found
Shouldn't need a dyno to feel it going flat Ed...but I know where you're coming from. The chart clearly shows the power falling like a stone on a stock engine. A well built engine with the correct cams, carbs and porting will hang on better after the peak.
Larry C.
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- leitz
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"I read this entire thread How is it that nobody even questioned the #80 Slow Jet? I can't see how it could possibly want that much pilot jet. Where are your air screws? 4 turns out I'll wager.
The first thing you want to do is address that situation. It is the single number that immediately jumps out as being out in left field. Regardless of the fact that you're having top end issues, that's got to be way too much fuel being dumped in through the pilot circuit.
It appears you have electrical issues also but you need to start with a reasonable jetting spec. Something around a #60 slow jet is much more reasonable."
When i bought the carbs from new they were jetting for my bike: 65 sj, 1 turn out air screw and YY8 needle, but idle "hangs" after blipping the throttle and the engine be slow to retun to idle after running. I couldn´t solve it turning the air screw, even Colortune indicated leaness whith all the turns of air screw. I tried with several sj: 70, 75 and 80 and always 1 or 3/4 turn out but less than 1 turn out because when blipping the throttle, the rpm fall back down below the set idle speed and then recover, and turning out the screw the engine "hangs". I know 80 sj is so high but it´s the only one that let the idle stable and almost perfect at 1250-1500 rpm. Maybe with richer needle diameter i can try with smaller slow jets. I knew installing these carbs would be a little adventure because i haven´t found any info in all Internet about cr29´s on a Kz650. I´ll post a video at idle
Anyway I'm not an expert and probably doing something wrong.
650ed wrote:
"By the time his stock engine gets to 10k rpm it's making about the same or less power than it was at around 7k rpm - so revving that high is not only risky to the engine it also provides less power."
I feel my engine have a lot of more power at 9000-10000 than at 7000 rpm. It´s difficult for me not to reach 10000 on track and mountain roads without revs limiter, revs up fast, but i try not to overcome 9500 rpm.
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- leitz
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