Topic: 135# main in Stock 750? Big bore?

[mathias2803]

Hello I discovered that my 750k sohc 73 had 135# main jets! The bike had orginal airfilter and exhaust. But isn't stock jets 110? As far as I could tell the bike ran good. Now it has a 4-1 exhaust. Can it be that the bike has a big bore that I or PO don't know about? Since it runs with 135#
I'm going to try it with 110# first and then move to 120# to see what happens. Bike ran good and felt powerful with the 135# but I've had alot of struggle getting it running property lately

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[ekpent]

 You may be able to peek down a spark plug hole with a flashlight and see if the piston has a dome to check for a big bore/higher compression piston. Borescope  would tell for sure whats in there.

[mathias2803]

You may be able to peek down a spark plug hole with a flashlight and see if the piston has a dome to check for a big bore/higher compression piston. Borescope  would tell for sure whats in there.

Will a compression test tell me anything?

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[seanbarney41]

There is no reason for a big bore to require that much more jet.  More likely large jetting required by previous  owners boneheadedness.

[slikwilli420]

Hard to say. Im running 140 mains in my 760cc race bike. Thats only 1mm overbore from stock but its much thirstier, more likely from the higher revs than anything.

[PeWe]

I found 147.5 Mikuni mains in my K6 carbs! Needles 1 notch richer from middle, pilots 40, air screws 0.5 turn out.

836 with slightly lower compression due to 24cc chambers made for other pistons. Ported head and a AF SS-1 cam. Rather open 4-1 and conical pods.

I know it ran well in the 80's on real fuel. Mains adjusted by road tests. Full speed, release throttle just a little, if it then ran better, larger mains.

[mathias2803]

Thanks for the input guys. I'm going to test 110 since it's the only size I have atm. But im thinking around 115-120 since I have a 4-1 yoshimura.
I'm thinking maybe he had a leak and pulled more air? And compensated with larger jets

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