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Jetting guidance XV 750

P901 Single carb intake, FLAASH Cams, Super Charger, NOS.......
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Jetting guidance XV 750

PostAuthor: Ant.brooks71 » Thu Oct 08, 2020 11:53 am

Heh guys I’m Anthony from South Wales UK a newby to the forum and learning about bikes mechanically. Bit the bullet bought an XV 750. 1995. It had been stuck in a barn for 15 years.
Learned a lot but I’m at the stage now where I’m thinking single carb set up I’ve purchased a PWK 40 . I have a stock exhaust system any guidance on jetting for my bike would be greatly appreciated
Cheers

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Re: Jetting guidance XV 750

PostAuthor: Flyingdog » Thu Oct 08, 2020 12:52 pm

:VTF:

Ant.brooks71 wrote: I’m at the stage now where I’m thinking single carb set up I’ve purchased a PWK 40 .


So, I take it it "is" running at this point? And you want to go from twin Mikuni to single Keihin? I've only fiddled with them on a a HD. That's when I found out that particular carb is highly copied (faked). What's new? Eh? Japanese (genuine) vs China (fake). Not to discourage about going single carb, many do successfully, but it can be a pita. Just use the best stuff you can.

Good luck on your venture.
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Re: Jetting guidance XV 750

PostAuthor: Ant.brooks71 » Thu Oct 08, 2020 1:11 pm

Thanks for gme reply yep she’s running I’ve spent hours dicking about with the carbs . I knew nothing about bike when I bought it. I picked a Haynes manual and some tools and went to work. Read some good things about single carb. And as you mentioned HD did it so it makes sense I’m just clueless with jetting

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Re: Jetting guidance XV 750

PostAuthor: Flyingdog » Fri Oct 09, 2020 12:42 am

Ant.brooks71 wrote: I picked a Haynes manual and some tools and went to work.


You can most certainly do whatcha want on "your" bike...but I would concentrate little more on the OEM carbs. I could be waay off base here, but going by your statement above, sounds like this decision to go single carb was more outta frustration.

Ant.brooks71 wrote: I’ve spent hours dicking about with the carbs .


Doing what exactly? Cleaning? Inspecting? Replacing? Resetting (as in floats and/or pilots)? Sync'n? Checking for vacuum leaks/electrical connections? OR...just turning the pilot screw?? Little more info would be helpful for others to help out.

No doubt, carbs can be tricky at times, but to completely change "how" something should work can and usually "does" lead one down a very deep rabbit hole. Unless those Mikunis are "Broke", you'd be well ahead of the game to get the bike running in "stock" form, before modding to something it wasn't designed for in the first place. Basically..establish a baseline that suppose to work. Then ya have something to fall back to, when upgrades/mods don't pan-out the first, second, third or more times. Specially, if one cheaps-out on the intake manifold. That's area can really give ya tuning nightmares. And...to throw a monkey wrench into the mix....even electrical problems can disguise themselves as carb problems. 15yrs left alone? Anything can happen.
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Re: Jetting guidance XV 750

PostAuthor: vasisyalij » Fri Oct 09, 2020 10:55 am

Ant.brooks71 wrote:Heh guys I’m Anthony from South Wales UK a newby to the forum and learning about bikes mechanically. Bit the bullet bought an XV 750. 1995. It had been stuck in a barn for 15 years.
Learned a lot but I’m at the stage now where I’m thinking single carb set up I’ve purchased a PWK 40 . I have a stock exhaust system any guidance on jetting for my bike would be greatly appreciated
Cheers


This carburetor has one bad feature, the sticking of the throttle valve, so you need to install a reinforced spring.

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Re: Jetting guidance XV 750

PostAuthor: Ant.brooks71 » Fri Oct 09, 2020 1:21 pm

Thank for the reply, I’ve been working on the bike for over a year throttle cable changed TCI was replaced with new because it was broken, carbs were stripped completely and rebuilt with OEM rebuild kits . No vacuum leaks no electrical issues. It’s running

But it took me about 5 months to sync and sort them out. I must have taken them off about 25 times
After reading up about it I was thinking of switching to a single carb setup for ease of maintenance and apparently better fuel economy mainly though the former. So I have nothing to lose by trying a single carb set up because if it doesn’t work out I’ll shove the twin carbs back on.
Rather than have weeks or months Of pain I thought I’d ask for guidance to help me The jetting quicker. I figured there must be someone on here that’s done it. I know each bike is different
I was hoping a few people give me their jetting and a pattern would start to for Plus I don’t think it’s fair for my wife to See a grown man cry in frustration or anger. :-)

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Re: Jetting guidance XV 750

PostAuthor: nanno » Fri Oct 09, 2020 3:01 pm

I've built (some) 2in1 manifolds, but never use a Keihin PWK, but Mikuni VM carbs. A VM38-9 was meant as a replacement for Ironhead Harleys and when going with a #20-25 pilot and approx #190 mains with a pancake-filter should be a good starting point.

BUT: sell the 2in1 kit and carb to the next poor soul, put the stock carbs back on, sync them and enjoy the bike. If you really want different carbs, go with a pair of VM38 (if you want roundslides), Dellorto 40ies or Mikuni TM38-flatslides. You will find good jetting info on here for these carbs and they will actually help you in unleashing the true potential of this engine. A single carb is the most efficient way to strangle it.

(Sorry to be so harsh, but what you endured with the stock carb is nothing like the rabbit hole you're trying to throw yourself into with a carb that is not commonly used on here on a single-carb manifold.)

Talking of which, if you can't get front and back cylinder to work equally well, then you have pretty much reached the best you can do with most 2in1 inlet manifolds. I've built a few y-shaped ones myself and these distribute relatively equally and still... honestly, they are just for some friends of mine, who wanted to buy Harleys and simply can't afford them or accept the fact that they sacrifice a lot above midrange.

Cheers,
Greg
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

*Look to my profile for a link to my blog*
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Re: Jetting guidance XV 750

PostAuthor: Flyingdog » Fri Oct 09, 2020 3:11 pm

That's odd it won't hold a sync. If your "not" changing jetting all the time...and..got the floats set, you don't have to remove the carbs to sync. And even then, there ways to go about re-jetting without removing the carbs. But that's another story. There's alotta air/fuel jets in those things. Some hidden quite well, too. Why I prefer Hitachi over Mikuni..But that's another/another story.

If he doesn't already pop in here, you may wanna PM Greg/nanno in these forums. He deals mostly dialing in TM/VM's. But, might of messed with them too.


Whoa..speak of the devil...jump in just as I was typing. Take err away. :bg:
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Re: Jetting guidance XV 750

PostAuthor: Ant.brooks71 » Fri Oct 09, 2020 3:17 pm

Flyingdog wrote:That's odd it won't hold a sync. If your "not" changing jetting all the time...and..got the floats set, you don't have to remove the carbs to sync. And even then, there ways to go about re-jetting without removing the carbs. But that's another story. There's alotta air/fuel jets in those things. Some hidden quite well, too. Why I prefer Hitachi over Mikuni..But that's another/another story.

If he doesn't already pop in here, you may wanna PM Greg/nanno in these forums. He deals mostly dialing in TM/VM's. But, might of messed with them too.


Whoa..speak of the devil...jump in just as I was typing. Take err away. :bg:



The current setup is now working perfectLy it just took me an age to get there. I fancied looking at single carb

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Re: Jetting guidance XV 750

PostAuthor: Ant.brooks71 » Fri Oct 09, 2020 3:21 pm

nanno wrote:I've built (some) 2in1 manifolds, but never use a Keihin PWK, but Mikuni VM carbs. A VM38-9 was meant as a replacement for Ironhead Harleys and when going with a #20-25 pilot and approx #190 mains with a pancake-filter should be a good starting point.

BUT: sell the 2in1 kit and carb to the next poor soul, put the stock carbs back on, sync them and enjoy the bike. If you really want different carbs, go with a pair of VM38 (if you want roundslides), Dellorto 40ies or Mikuni TM38-flatslides. You will find good jetting info on here for these carbs and they will actually help you in unleashing the true potential of this engine. A single carb is the most efficient way to strangle it.

(Sorry to be so harsh, but what you endured with the stock carb is nothing like the rabbit hole you're trying to throw yourself into with a carb that is not commonly used on here on a single-carb manifold.)

Talking of which, if you can't get front and back cylinder to work equally well, then you have pretty much reached the best you can do with most 2in1 inlet manifolds. I've built a few y-shaped ones myself and these distribute relatively equally and still... honestly, they are just for some friends of mine, who wanted to buy Harleys and simply can't afford them or accept the fact that they sacrifice a lot above midrange.

Cheers,
Greg


Cheers for the info you’ve given me food for thought

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Re: Jetting guidance XV 750

PostAuthor: Flyingdog » Fri Oct 09, 2020 3:22 pm

Ant.brooks71 wrote:The current setup is now working perfectLy it just took me an age to get there. I fancied looking at single carb


Ah..got it. Guess I was thinking differently, that you still had something going on. Good you got it all sorted out.


Was also going to add..I understand perfectly the "attraction" of that air filter/carb stick'n out there, cuz it does look little more muscle(ly). Form over function and all that jazz. But as nanno pointed out..getting the A/F ration "even" for each head is extremely difficult...and...kinda pricey to get it right-on. Besides..Keihin is just not that popular for our bikes. A "real" Keihin is going to cost a few hundred $$, not the $50 ones that are widely offered up.
Good luck.
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