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Author Topic: CB400F jets  (Read 913 times)

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Offline Fred T

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CB400F jets
« on: February 11, 2012, 10:48:58 AM »
I just cleaned my carbs, and replaced old gaskets, but need advice on choosing the right jet sizes, the bike has stock airbox and filter, and exhaust is an MC Again.  The wierd thing is that before cleaning the carbs, throttle response was much better, now kind of lags a bit. I was thinking going up to a 90 size jets but I'm not sure it is the best option. Anybody have experience with a similar set up? 
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Offline jessezm

  • '77 cb400f cafe build
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Re: CB400F jets
« Reply #1 on: February 11, 2012, 11:10:36 AM »
It's totally stock aside from the exhaust?  If so, I would think 90 would be a bit too big.  Maybe 80 or 85 at the most to start off with.  As far as the hesitation that appeared after cleaning the carbs, I would check around the manifolds to see if you have an air leak from when you put them back on.  If not, you may have to pull them apart again and make sure all the air passages are clear (compressed air, guitar strings are good for this), and you didn't mention--did you pull the emulsifier tubes under the main jets and clear out all the tiny holes?  Just some thoughts...
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Offline Fred T

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Re: CB400F jets
« Reply #2 on: February 11, 2012, 04:36:39 PM »
Jessezm, the bike was caffeed, and the exhaust replaced, but engine carbs and airbox are stock.  I will chek the manifolds for leaks, that's a good point I missed. I also found out the carbs air screws are missing the o'rings, that could also be a factor.           
Thanks for the help
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Offline jessezm

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Re: CB400F jets
« Reply #3 on: February 11, 2012, 07:03:38 PM »
Hmm, I don't recall there being o-rings in the air mixture screws.  I think it's just the tapered screw and a spring inside to hold the tension so it doesn't change positions.
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Offline Fred T

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Re: CB400F jets
« Reply #4 on: February 12, 2012, 07:52:53 AM »
Quote from: jessezm on February 11, 2012, 07:03:38 PM
Hmm, I don't recall there being o-rings in the air mixture screws.  I think it's just the tapered screw and a spring inside to hold the tension so it doesn't change positions.
                                                                                                                                                                                  I thought there was from reading and old post, but you're right, only the tapered screws and springs.  I will keep looking to see if I can identify the source of the problem.
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