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Author Topic: saving a 1980 KZ750 twin  (Read 62471 times)

Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #410 on: May 13, 2018, 19:05:08 »
First ride was a reasonable success! its got just enough power to be pretty fun, the exhaust has a great tone to it. Not too loud at idle but pretty rowdy when you get on it. The brakes are fantastic. I rode it to my graduation and hooned around a bit there afterwards with my robes on, my parents think I'm crazy. I put about 70 miles on it yesterday.

The jetting is pretty close, think I may need to go one bigger on the main and down a notch on the needle. I'm running into what i think is fuel starvation. When I'm on the highway, after a several seconds of going WOT its starts to miss and wont accelerate anymore like its running out of gas. if i back off for a bit and cruise, it seems like the float bowls refill and I can go WOT for a bit again until it starts missing again. WOT pulls from a stop to 5th gear are no problem its the extended WOT at 60+ where it happens. I have a cheapo petcock, I'm wondering if its not passing fuel fast enough. suggestions?
« Last Edit: May 13, 2018, 19:10:19 by doc_rot »

Offline CrabsAndCylinders

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Re: saving a 1980 KZ750 twin
« Reply #411 on: May 13, 2018, 19:29:10 »
Nice, very nice.
Lighter, Quicker, Faster.
ZX-14, 900F x 2, 1100F, R100, CBR600, SR500, GT500, RZ350, KZ1000 x 2, Moto Guzzi Lemans lll, CBX550, RD 350, 750 SOHC police special, RG250, TL1000R, GT750, KTM Super Duke 1290 R, Harris/Z-1, Norton 750 Commando, Green 77 KZ650

Offline Nebr_Rex

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Re: saving a 1980 KZ750 twin
« Reply #412 on: May 13, 2018, 23:08:34 »
First ride was a reasonable success! its got just enough power to be pretty fun, the exhaust has a great tone to it. Not too loud at idle but pretty rowdy when you get on it. The brakes are fantastic. I rode it to my graduation and hooned around a bit there afterwards with my robes on, my parents think I'm crazy. I put about 70 miles on it yesterday.

The jetting is pretty close, think I may need to go one bigger on the main and down a notch on the needle. I'm running into what i think is fuel starvation. When I'm on the highway, after a several seconds of going WOT its starts to miss and wont accelerate anymore like its running out of gas. if i back off for a bit and cruise, it seems like the float bowls refill and I can go WOT for a bit again until it starts missing again. WOT pulls from a stop to 5th gear are no problem its the extended WOT at 60+ where it happens. I have a cheapo petcock, I'm wondering if its not passing fuel fast enough. suggestions?
Had that same problem on my first KZ1000, it was a small fuel filter for me.


.

Offline canyoncarver

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Re: saving a 1980 KZ750 twin
« Reply #413 on: May 16, 2018, 16:15:46 »
Get a Pingel for fuel, they have a screen filter already and flow second to none.  Congratulations on graduation!!!    I love your KZ twin, riding it to graduation was perfect!
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YZF750/1000R The Fly
KZ 750 Twin
ZRX 1100
KZ400 The Rabbit
KLR650, 65 Norton, my never finished shovelhead chopper, an 86' FXR, and an F9 Bighorn
more YZF750R's, more KZ's, a Zephyr750...and the ever unfinished 75' CB550 cafe.
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Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #414 on: May 17, 2018, 20:00:10 »
Thanks guys.

I took the Pingel off my kz1000. At the very least it makes routing the fuel lines WAY easier, and looks a lot better. Unfortunately it didn't solve the problem. I popped the gas cap open and rode it like that as well thinking maybe it wasn't venting properly but that had no change. I'm gonna pull the carbs off and inspect the fuel inlets and float valves. Scratching my head here. suggestions?
« Last Edit: May 17, 2018, 20:03:01 by doc_rot »

Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #415 on: May 18, 2018, 19:36:02 »
So the float valves were 2.0, I switched them to 2.5 and the problem went away. it also richened everything else up and the bike is happier on the whole. Im thinking about switching them to a 2.8 just to ensure the float valve isn't acting as my main jet.

My question is; why would they install small float valves? wouldn't you want to have the biggest possible float valve to ensure fuel delivery, and let the jets do the fuel metering?

Offline datadavid

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Re: saving a 1980 KZ750 twin
« Reply #416 on: May 19, 2018, 03:19:50 »
Emissions maybe.

Offline CrabsAndCylinders

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Re: saving a 1980 KZ750 twin
« Reply #417 on: May 19, 2018, 03:56:02 »
That's interesting, I don't believe I have heard of going to a bigger float valve before.
Lighter, Quicker, Faster.
ZX-14, 900F x 2, 1100F, R100, CBR600, SR500, GT500, RZ350, KZ1000 x 2, Moto Guzzi Lemans lll, CBX550, RD 350, 750 SOHC police special, RG250, TL1000R, GT750, KTM Super Duke 1290 R, Harris/Z-1, Norton 750 Commando, Green 77 KZ650

Offline datadavid

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Re: saving a 1980 KZ750 twin
« Reply #418 on: May 19, 2018, 03:59:57 »
In europe at least, 2.5 valve is stock for these.

Offline MotorbikeBruno

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Re: saving a 1980 KZ750 twin
« Reply #419 on: May 22, 2018, 13:49:14 »
So the float valves were 2.0, I switched them to 2.5 and the problem went away. it also richened everything else up and the bike is happier on the whole. Im thinking about switching them to a 2.8 just to ensure the float valve isn't acting as my main jet.

My question is; why would they install small float valves? wouldn't you want to have the biggest possible float valve to ensure fuel delivery, and let the jets do the fuel metering?

Doc, where did you find the new ones?  I've had the same nagging issue on mine...too rich one day, too lean after the next change...made me so nuts I put her away for a while....