Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: philward on March 19, 2017, 09:38:53 PM
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Hi Guys
Just got carb rebuild kit and before I put it all in, whats your views on main jet sizes and needle position settings - I'll be the cruzin image standard compression 836 big bore kit running bellmouths and the virtually straight through CR Rep 4 into 4 pipes. I know that I will have to experiment with settind but just looking for opinion on initial starting settings.
My standard K2 with standard airbox/exhaust runs standard settings with same 836 piston kit.
Thanks
Phil
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At a guess up 2 or 3 sizes onmains and work from there
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I think not using the standard air box on the CR will make a big difference, I've got modified K&N type pod filters on mine (grafted the rubber inlet trumpets from the standard air box into the K&Ns to get a smooth airflow into the PD41A carbs), a 4 into 1 exhaust, I've gone up to 135 mains , standard primary's, I get a good plug colour and no flat spots, every set up is of course going to be different though.
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Thanks Guys - just occured to me that Simom Tappin (Moonpie) who provided exhausts would probably have a good idea as he run one with similar set up - so have emailed him.
Thanks again
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Emailed Simon Tappin who only has data on CR race carbs but recomended I speak to Allens Performance (Nottingham) - he says they are really knowledgable and might even be able to make recommendations. Had a look on their website and looks very useful. Forum members may already know them but thought I'd post the link for future reference.
http://www.allensperformance.co.uk/carb-kit/keihin-jet-identification-chart/
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Mine has a rebuilt stock motor K6 with K7 PD carbs, I am running 138 mains, stock idol jets, needle on last notch [highest point]
When we first fitted the bigger main jets it was still lacking fuel & it was jumping & jerking like a Kangaroo, we gradually move the needle a notch at a time but it finished up on the last notch & then Bingo cracked it.
with your big bore kit K&N's & straight through exhaust I am guessing you will be playing with it for a while before you get it near enough spot on
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I am expecting that too Greebo - it will probably be next summer before I get to run it on the road but just need a starting point while building carbs. There's loads of info on the set up with CR Keihin race carbs (matching the exhaust I'm using) but very varied views on how they work effectively for road use - and they are bloody expensive! This will be a ride to biking venues type bike and so won't be used in real anger on the road - you wont be able to with those open exhaust!
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Phil I do hope you get those CR carbs sorted, from what I have heard from guys who have tried them they are only good for the track & even then can be a pain. apparently & again from "hear say" the adjustment screws are very difficult to get at unless you take the carbs off.
you may find that you will be going to more venues with it on a trailer rather than riding it.
Good Luck with it & keep us all posted
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I will be sticking with the standard carbs - too much uncertainty on how the CR type carbs perform on the road - especially when you have to spend a 1000 squid!
Next is getting the exhausts welded up in correct position - unfortunately, they are not just 'bolt on'
Cheers
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I will be sticking with the standard carbs - too much uncertainty on how the CR type carbs perform on the road - especially when you have to spend a 1000 squid!
Next is getting the exhausts welded up in correct position - unfortunately, they are not just 'bolt on'
Cheers
Quote "I will be sticking with the standard carbs"
Good Call Phil