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upgrade carb jets?

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upgrade carb jets?

PostAuthor: bigwheel53 » Sat Nov 22, 2014 9:02 pm

A couple of years ago I sent my changes to my bike to a company that with this info they send you the carb jets you should be using. I dunno..my gas mileage wasn't the best and felt that it should run a little better. Mabe one of you guys can help me out here. My bike is a 1995 xv750..I removed all the pollution stuff air control mix etc..Blocked off the reeds..installed a foam air filter..and have an aftermarket exhaust with no baffles. Iridium spark plugs..I think the stock jets were 122.5? This company sent me 135,s and if I needed more 140,s.I have to really tune these carbs in order to get it running correctly without smelling a rich mix..Any help would be apprectiated..thx

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Re: upgrade carb jets?

PostAuthor: bstig60 » Sat Nov 22, 2014 9:24 pm

122.5 main jets are stock. With what you described, a 128 would be more like it. Can you remove your plugs and take a pic of the tip and post it here?
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

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Re: upgrade carb jets?

PostAuthor: bigwheel53 » Sun Nov 23, 2014 5:40 pm

Thanks for the comeback rider..I don't get too many responses on this site...mabe im asking too technical questions..Anyway I couldn't find 28,s but I did order 27.5,s and 130, just in case..It bothered me all along about the rejet..going from 122.5 to 135 I thought was a bit much..Thanks again..

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Re: upgrade carb jets?

PostAuthor: bstig60 » Sun Nov 23, 2014 6:01 pm

Check your float settings before you change anything. The 127.5 will give you a bit more flexibility. You will most likely need to adjust the pilot screws. I would turn them into the soft seat counting the turns, then turn them back out 2.5 turns and adjust from there.
No, I don't think your questions are too technical.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

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Re: upgrade carb jets?

PostAuthor: ridgerunner » Sun Nov 23, 2014 6:49 pm

jet kits are only for those who can't tune. I have bought them and always been disappointed. I mean always!
1987 XV-700
1 into 2 Carbon fiber intake manifold. Now 6 years old.
Single Mikuni 34mm VM Carburetor, simple slide throttle design, no vacuum
Pulls from less than 2000rpm to 7000 rpm
Custom Low Bars
Custom seat on modified stock seat base.
No Kits, homemade
Way Cool!
SR500 - RZ350 -RD350 - CR500 - XR400 -VTR250
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Re: upgrade carb jets?

PostAuthor: bigwheel53 » Sun Nov 23, 2014 11:11 pm

I hear ya but once you take all the stock stuff off like the airbox contents and the stock paper air filter and replace the exhaust you change EVERYTHING about the motor and you need to rejet. I have no prob retuning, I have the synchronizer and all the special screw drivers but I always felt going from 122.5 to 135 was a bit of a stretch. Its not like I changed the pistons or the stroke and valves etc. I just needed a little more. I ordered 127.5 and 130,s from J&P cycles. They sell the jets all by their lonesome for cheap. The 127.5 will do me good I think.

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Re: upgrade carb jets?

PostAuthor: bstig60 » Sun Nov 23, 2014 11:27 pm

You can most likely use 127.5 to meet your needs if you have open exhaust. Truth is you probably could have used the stock jets as well. I am running stock jets in my 1100 with K&N air filter, and Jardine Slash cut exhaust with baffles. It was necessary to adjust the pilot screws out a bit to get the mixture right, but it has been running this way for the better part of 3 years and 12000 miles.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

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Re: upgrade carb jets?

PostAuthor: ridgerunner » Mon Nov 24, 2014 9:51 am

I have always found that tuning is a process that should be done from the low end up. The idle mixture screw, pilot jet and needle jetting affect the top end many more times than the main jet affects the mid or low.

How do you know that 135 jets are too big? Did you try them?

When I first got my virago running on a stock single carb and no airbox, I had to shim the needle and enlarged the main jet to 1.36mm. With the carb I could get over 50mpg. Eventually the pilot circuit on remaining carb was blocked between the fixed pilot jet and the idle mixture screw causing me to abandon the carb.

I used duct tape as a tuning aid.
1987 XV-700
1 into 2 Carbon fiber intake manifold. Now 6 years old.
Single Mikuni 34mm VM Carburetor, simple slide throttle design, no vacuum
Pulls from less than 2000rpm to 7000 rpm
Custom Low Bars
Custom seat on modified stock seat base.
No Kits, homemade
Way Cool!
SR500 - RZ350 -RD350 - CR500 - XR400 -VTR250
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Re: upgrade carb jets?

PostAuthor: o c t o r » Mon Nov 24, 2014 11:35 am

:yup:

. . . and to explain a little . . .
1st is the idle jet . . . with new plugs idle the bike for 10-20-30 min.
Turn off . . . check your plugs.

Primary Jet test at speed.
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Re: upgrade carb jets?

PostAuthor: bigwheel53 » Tue Nov 25, 2014 5:46 am

I have been running the 135,s and my mileage took a nose dive like32-33mpg.Its a real pain having to stop every 100 mi. I mean that's quite a jump right from 122.5 to 135 but that was recommended by this guy who puts together the kits. I think im going to be better off with the 127.5 cant hoit right? Im in the process of pulling the motor anyway. the used heads I bought turned out to be crap. Im redoing the original heads..good cams,new bearings etc.

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Re: upgrade carb jets?

PostAuthor: ridgerunner » Tue Nov 25, 2014 9:02 am

Big wheel,
On my 700 with a single 34 mm carb.When cruising at 80 mph the engine is at 1/3rd throttle. Still just on the needle. The main jet doesn't come into play till about 3/4ths throttle.

If your mileage is poor, tuning needs to be done at the primary circuit and needle level. You are not running on the main yet.

Indeed getting your bike to run is the easy part. Getting it to run efficiently takes about 10 times longer. Particularly if you do it seat of the pants like I do.

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1987 XV-700
1 into 2 Carbon fiber intake manifold. Now 6 years old.
Single Mikuni 34mm VM Carburetor, simple slide throttle design, no vacuum
Pulls from less than 2000rpm to 7000 rpm
Custom Low Bars
Custom seat on modified stock seat base.
No Kits, homemade
Way Cool!
SR500 - RZ350 -RD350 - CR500 - XR400 -VTR250
User avatar
ridgerunner
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Re: upgrade carb jets?

PostAuthor: bstig60 » Tue Nov 25, 2014 11:57 am

[quote="ridgerunner"]Big wheel,
On my 700 with a single 34 mm carb.When cruising at 80 mph the engine is at 1/3rd throttle. Still just on the needle. The main jet doesn't come into play till about 3/4ths throttle.

I am glad you are having good luck with your single carb setup, but we are dealing with stock Hitachi twin carbs here, totally different than your set up. I can't speak to what your carb does since it isn't stock.
Unless you have changed the gearing in the transmission, at 80mph, you are running at about 5000 RPM+ Redline is 7000 on these engines, so you are running way more than 1/3 throttle. The main jet comes into play on stock carbs at about 3000 RPM, that would be 40-50 mph. Prior to that the engine runs mainly on the pilot jet.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

SERVICE MANUAL DOWNLOAD LINK
http://viragotechforum.com/viewtopic.php?f=220&t=31501#p279545

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bstig60
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2003 Honda Goldwing GL1800 Touring
2007 Honda ST1300A
Sex: Male

Re: upgrade carb jets?

PostAuthor: ridgerunner » Tue Nov 25, 2014 12:11 pm

Nope it is 1/3rd throttle opening. at 80.
Everything I said was true.
1987 XV-700
1 into 2 Carbon fiber intake manifold. Now 6 years old.
Single Mikuni 34mm VM Carburetor, simple slide throttle design, no vacuum
Pulls from less than 2000rpm to 7000 rpm
Custom Low Bars
Custom seat on modified stock seat base.
No Kits, homemade
Way Cool!
SR500 - RZ350 -RD350 - CR500 - XR400 -VTR250
User avatar
ridgerunner
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Posts: 541
Joined: Sat Aug 23, 2008 5:18 pm
Location: NE Missouri Flag



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