Author Topic: Need Help Jetting for Cafe Racer Build  (Read 317 times)

Offline ams14

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Need Help Jetting for Cafe Racer Build
« on: May 19, 2021, 04:06:32 PM »
I finished my cafe/Frankenstein build with a GS500 donor motor.  To be fair, I didn't know these carbs were so finicky when I made some of the choices I did early on (pods, straight pipes, etc).  I recently went through the carbs (twice) and did a carb refresh kit.

It is running, but terribly.  It only runs with about 3/4 choke applied.  I'm guessing this means it has too much air (lean).  I added a baffle to the mufflers and it helped a little. Low end is terrible.  it does eventually kick in and pull once it gets into midrange.

I have stock jetting still.  I am also mile-high (in Denver).  Any jetting advice\guesses?



 

Offline mr72

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Re: Need Help Jetting for Cafe Racer Build
« Reply #1 on: May 20, 2021, 04:24:48 AM »
The carbs aren't that finicky but they are designed for the stock GS engine and changing the flow and vacuum conditions puts them out of their designed spec.

Anyway, you can work around it to some extent with jetting but it's not likely to run as well with pods and straight pipes as it would stock no matter what.

is it mk1 (2 jet) or mk2 (3 jet) carbs? If the old ones, depending on what pods are in it, maybe start with jets in the range of 142.5 to 150. Just buy a bunch and plan on tinkering. 40 pilots. Get it idling right on the pilots and then he it working wot/high revs on main then fiddle with shims to get midrange working as good as you can. But remember the needles and slide return spring and diaphragm are all made to work with an airbox, so running them on pods will be suboptimal at best.

Offline The Buddha

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Re: Need Help Jetting for Cafe Racer Build
« Reply #2 on: May 20, 2021, 08:23:13 AM »
I finished my cafe/Frankenstein build with a GS500 donor motor.  To be fair, I didn't know these carbs were so finicky when I made some of the choices I did early on (pods, straight pipes, etc).  I recently went through the carbs (twice) and did a carb refresh kit.

It is running, but terribly.  It only runs with about 3/4 choke applied.  I'm guessing this means it has too much air (lean).  I added a baffle to the mufflers and it helped a little. Low end is terrible.  it does eventually kick in and pull once it gets into midrange.

I have stock jetting still.  I am also mile-high (in Denver).  Any jetting advice\guesses?


K&N and pipe on a pre 01 carb is 150 mains, 40 non bleed pilot, 1 washer under the needle, 3 turns on mix screws and float at the top of the bowl.
Now you guys think you need to jet leaner due to the altitude - try leaving the stock pilot and leave out that washer under the needle, but you guys get that wonderful 85 octane, god nows what it will do, but worth trying. If other old cars round there dont detonate on it, maybe the thin air works with low octane.
Cool.
Buddha.
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Offline ams14

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Re: Need Help Jetting for Cafe Racer Build
« Reply #3 on: May 20, 2021, 08:27:53 AM »
Cool, thanks for the info!  Yes, it is the pre-01 carbs.  I will order some jets and start tinkering and let you know how it goes.

Ha, I hear you on the 85.  All my vehicles are turbo or supercharged so I have to buy 91 anyway:-)

Offline cbrfxr67

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Re: Need Help Jetting for Cafe Racer Build
« Reply #4 on: May 21, 2021, 06:48:14 AM »
Sub'd!
Good luck!
"Its something you take apart in 2-3 days and takes 10 years to go back together."
-buddha

 

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