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Author Topic: Need to size jets  (Read 2476 times)

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Offline Freaky1

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Need to size jets
« on: December 31, 2008, 08:12:02 am »
I need to know what size jets my carbs are currently holding, they are early 750 K types but not off my bike. How do I figure this out? I think it should be simple but I just don't know and would like some help, any ideas?
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Offline 754

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Re: Need to size jets
« Reply #1 on: December 31, 2008, 08:29:54 am »
They should be marked..
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Offline KB02

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Re: Need to size jets
« Reply #2 on: December 31, 2008, 08:54:33 am »
A picture for refrence:
On the main just you can see a number on the side of the Hex top.
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Offline Freaky1

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Re: Need to size jets
« Reply #3 on: December 31, 2008, 09:34:55 am »
So the number on the side of the main jet is for the whole set?
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ev0lution7

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Re: Need to size jets
« Reply #4 on: December 31, 2008, 11:23:12 am »
the number on the main jet is only for the main jet there is a size on the pilot but thats for idle and you dont mess with that jet...

now the main jet bigger numbers mean more fuel... at peak RPM now you will need to adjust your slide needle to fix the rich condition of the bigger jets..
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Offline Freaky1

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Re: Need to size jets
« Reply #5 on: December 31, 2008, 07:00:25 pm »
The back story is, the place I'm getting my rebuild kits from asked what size my jets are so they could match them up. I live in Denver and the air is kinda thin up here so I think I might still have to play with them to get them just right. With less air, I should maybe go a little smaller on the main jet? I plan on going with the same size that are in the carbs now but just in case.
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KingCustomCycles.com

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Re: Need to size jets
« Reply #6 on: December 31, 2008, 08:02:36 pm »
Quote from: ev0lution7 on December 31, 2008, 11:23:12 am
the number on the main jet is only for the main jet there is a size on the pilot but thats for idle and you dont mess with that jet...

now the main jet bigger numbers mean more fuel... at peak RPM now you will need to adjust your slide needle to fix the rich condition of the bigger jets..

If your idle is way lean, as I just experienced on a 76 Hondamatic, and you run out of adjustment on the air screw, they can be drilled slightly oversized with good results.  They are also replaceable in different sizes.  Jetting for your elevation and modifications is half the fun, and all the frustration, of these old carbs.   ;D
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ev0lution7

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Re: Need to size jets
« Reply #7 on: December 31, 2008, 08:36:41 pm »
normaly you dont have to replace jets when rebuilding just clean really good replace the "oring" on the bowl and replace the float needle
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Offline Freaky1

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Re: Need to size jets
« Reply #8 on: January 01, 2009, 03:37:08 am »
I have had them apart and cleaned them and the inside looked quite clean for not knowing the last time they were run. I have had people tell me that if your careful you can get away with just bench synchronizing, any advice on this?
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Offline Freaky1

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Re: Need to size jets
« Reply #9 on: January 01, 2009, 03:38:28 am »
I tried to be very careful pulling them apart, and haven't messed with any adjustments.
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Offline Bowswell

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Re: Need to size jets
« Reply #10 on: January 02, 2009, 10:08:30 am »
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Offline Flying J

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Re: Need to size jets
« Reply #11 on: January 02, 2009, 12:27:42 pm »
if there stock this is the jet sizes
http://hondachopper.com/carb.specs.html
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ev0lution7

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Re: Need to size jets
« Reply #12 on: January 02, 2009, 10:24:26 pm »
look up bench sync'n in a search i will need a drill bit...
now as far as that being "OK" i wouldnt i bought a good set of gauges off ebay for $100 and worth every dollar i dont trust bench sycn'n it only is supposed to get you close to start up and tune... not ideal for power or economy.. i would try getting some gauges and have some fun.
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Offline Freaky1

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Re: Need to size jets
« Reply #13 on: January 03, 2009, 03:31:37 am »
I think I will get a set and tune them right, thanks everyone.
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That which does not kill you leaves cool scabs which turn into awesome scars.

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Offline Tower

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Re: Need to size jets
« Reply #14 on: January 04, 2009, 12:55:26 pm »
@Freaky1, Denver is at an altitude that will require reducing the jet size about 10% from stock at sea level.  i.e #100 main jets would be a good place to start your tuning.

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Offline Freaky1

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Re: Need to size jets
« Reply #15 on: January 05, 2009, 12:04:49 pm »
Thanks Tower, most of my mechanical experience has been with cars and I know up here we have changed jets around in them. I had to believe in motorcycles it would be more nessasary than cars, thanks for giving me a place to start.
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That which does not kill you leaves cool scabs which turn into awesome scars.

'77 CB750F Come on...were almost there!
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