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1984 XV750 main jet size advice please

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1984 XV750 main jet size advice please

PostAuthor: FlyingTiger » Tue Jun 11, 2019 2:35 am

Hi guys
My 1984 (sorry about typo as to the age of my bike on another thread!) XV750 has standard jets, but came with K & Ns fitted. It also has straight through pipes which I will change but will probably be a bit more free breathing than standard. Can anyone suggest if I should go up on main jet size please?

Thanks in advance

Regards

Mark

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Re: 1984 XV750 main jet size advice please

PostAuthor: Flyingdog » Tue Jun 11, 2019 3:51 am

I'm going to assume to have the 1st generation 750, meaning they are fitted with Hitachi carbs. Now some even had Keihin carbs, but I'm not sure if that was just a UK/Asian thing. Anyway, you most likely have oem #122 (or 122.5) jets. Personally, I wouldn't suggest how to jet one's carb until a proper plug reading is done. I always pointed toward a few pair of new plugs and a "Plug Chop", to get the most accurate plug read. This does take some commitment and time to do it right, but worth it..IMO. Yes, gutted exhaust, modified air intake, on the surface, would point towards carb work, but which direction (mains/needles), "I" wouldn't say until ya knew what you're dealing with. And...any carb I've gotten into (be it inline four/duel carbs for twins), I've "always" staggered the sizes of the jets. Due to the different air densities for each carb/cylinder. For our V-twins, rear runs hotter, so the intake is denser, which makes for a different A/F ratio for rear vs front. Even Yamaha (Virago) started using different sizes of jets (Frt. vs Rear) in their Gen.2 bikes. For the air intake reason?...I wouldn't have a clue. The most widely used reasoning for the size difference, for years, was for the cooling the fuel at the rear. Sounded good at the time. But, back in the 80s, when I started doing some gutting of parts (on the 1000), when I came up with this, cuz the cooling thing didn't make sense. As the jet size would be "increasing" instead of the opposite, to balance the A/F ratio between the two carbs. That's just "my" take and it's always worked for me. You know the ole saying: Different strokes.. :bg: Guess one could say: Yea..going ahead, bump-up to #128 and you may hit the right number. But I wouldn't be so arrogant as to say I know exactly which way for ya. My 750 (probly same as yours), have different exhaust (with baffles), stock style (but oiled) air filter and with alittle carb work runs fantastic. But you also have to consider regions, so my setup may not even come close to what would work for you. Waay long winded, just didn't know how else to get the info out. (As I see it) :cl: :bg:
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Re: 1984 XV750 main jet size advice please

PostAuthor: FlyingTiger » Tue Jun 11, 2019 6:34 am

Thanks for the comprehensive reply - I do appreciate the time taken.

My 750 has Mikunis - sorry I assumed the year would have defined that. Am a definite Virago newbie!
Anyway the bike is almost stripped now and I have refurbed the carbs so when I run it up I will see how it runs and have a play with the jets accordingly.
Best Regards

Mark

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Re: 1984 XV750 main jet size advice please

PostAuthor: bstig60 » Tue Jun 11, 2019 9:30 am

Are you sure of the year of your bike? Mikuni carbs were not put on 750's until 1988. Anything prior to that would have been Hitachi's. Either someone has changed the carbs or you have the incorrect year in your title. There should be a white sticker on the left side of the steering stem. It has the model year and month of manufacture. That is the model year of your bike no matter what your DMV title says.
Your profile shows 1983 750, please modify your profile to show the correct year.
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Re: 1984 XV750 main jet size advice please

PostAuthor: Flyingdog » Tue Jun 11, 2019 9:50 am

Mikuni.huh? Don't think 83's used those. Thought it was somewhere round 88 the 750 made the switch. Coarse you're locate pretty far away, so suppose anything is possible. But Hitachi, Mikuni, Keihin, outside of the mechanical differences...fuel & air is all the same. Cept for the individual needs that is used, of coarse.

Hitachi:
https://www.yamahapartshouse.com/oempar ... retorhttps:

Mikuni
https://www.yamahapartshouse.com/oempar ... rnia-model

Random info..showing even Keihin
https://www.motorcyclespecs.co.za/model ... o%2081.htm
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Re: 1984 XV750 main jet size advice please

PostAuthor: bstig60 » Tue Jun 11, 2019 12:26 pm

Flyingdog wrote:Mikuni.huh? Don't think 83's used those. Thought it was somewhere round 88 the 750 made the switch. Coarse you're locate pretty far away, so suppose anything is possible. But Hitachi, Mikuni, Keihin, outside of the mechanical differences...fuel & air is all the same. Cept for the individual needs that is used, of coarse.

Hitachi:
https://www.yamahapartshouse.com/oempar ... retorhttps:

Mikuni
https://www.yamahapartshouse.com/oempar ... rnia-model

Random info..showing even Keihin
https://www.motorcyclespecs.co.za/model ... o%2081.htm


They did not get the 700 in Europe, but the change to Mikuni's occurred with the 88 model year. Keihin carbs on a Virago, Unless someone added a harley carb, never heard of that.
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: 1984 XV750 main jet size advice please

PostAuthor: Jake » Tue Jun 11, 2019 1:03 pm

FlyingTiger wrote:Hi guys
My 1984 (sorry about typo as to the age of my bike on another thread!) XV750


So that you get the best advice for your bike, we need to be sure of the year that you own, the 1983 and 1984 differ.

Is your bike a mono shock or twin shock ? 1981,83 and 83 were mono shock and 1984 until the last 750 in 1997 are twin shock.

If you do have a 1984, please make the correction on your profile at http://viragotechforum.com/ucp.php?sid=487653eec7bbe675c934fe4d8c46dbd3&i=264
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Re: 1984 XV750 main jet size advice please

PostAuthor: Flyingdog » Tue Jun 11, 2019 2:14 pm

bstig60 wrote:They did not get the 700 in Europe, but the change to Mikuni's occurred with the 88 model year. Keihin carbs on a Virago, Unless someone added a harley carb, never heard of that.


I "later" saw that they downsized the 750 over there.. knew bout the carb change. Still thought he'd like to read alittle. But yea.. saw that saying 750 using Keihin. Said to myself: Self... that's not right..picture even shows a Hitachi. Only Keihns I've ever come across were on a Honda and early harley. Think Kawi use them, IIRC..it was mainly on the KZ series. Ah well..this isn't my thread to gab in.
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