Re-Jetting Carbs Question - Yamaha XVS650

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Mr Tuscan
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Re-Jetting Carbs Question - Yamaha XVS650

Post by Mr Tuscan » Sep 25th, '19, 14:25

Re-Jetting Question - XVS650

Is this a simple job for someone to do at home ?

Briefly I have read the following, looks like it’s missing loads of stuff to me, carbs in detail is leaving me some what overwhelmed, I’m feeling it’s a garage job but just want to be sure I’m not going to get ripped off.

I’m fitting a set of aftermarket custom pipes and don’t want the engine to run lean and cause damage.

What my best options and if I’m looking at a garage are we talking expensive

This is what some garble on a bike forum read:

1.Remove Carbs
2.Slide Float Chambers to the side
3.Unscrew Jets
4.Screw in with new jets
5.Slide Floats back
6.Reinstall Carbs
7.Adjust Limiter Screw ? To maximum
8.Run Bike and return Limiter screw until bike runs smoothly

This limiter screw that's mentioned is this the same as mixture screw or something else.

Im wishing to understand the mechanics of this before moving any further, without being a mechanic should I be entertaining this or is it a garage job to be done properly?

BTW this job will be for a aftermarket custom made more free flowing exhaust.

any guidance is appreciated
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Re: Re-Jetting Carbs Question - Yamaha XVS650

Post by billinom8s » Sep 27th, '19, 06:21

Over thinking it.

If you've done the pipes and air filter you just need to get the carbs balanced.

Doing the jets and needles is over kill.
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Re: Re-Jetting Carbs Question - Yamaha XVS650

Post by Mr Tuscan » Sep 27th, '19, 08:35

Interesting.

Reason I mention it is a couple of Dragstar owners like me have pipe upgraded and now have overheating issues
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Re: Re-Jetting Carbs Question - Yamaha XVS650

Post by Jug_Inspector » Sep 27th, '19, 10:05

You have several options really.

Sometimes a bike will be a known quantity due to having a large user base who modify them, and as such jetting for known mods is posted on forums.

Dyno tuning - get to know your carb, buy a set of jets, book a dyno session and then make adjustments based on the tests. You may also find some tuner familiar with your bike and carb so will be able to do the whole job for you.

DIY tuning...

There is something known as the plug chop. This is where you buy a box of spark plugs, do a run on a fresh plug, kill the engine, pull the plug and then cut the thread away. The deposits on the insulator can tell you what is happening and the jetting can be adjusted.

AFR gauge - you have a wide band O2 sensor boss welded on to an exhaust header and rig up the AFR gauge on your bars. You can either just watch it or video it but do several runs on a straight bit of road to build a picture of how the mixture is, from that you can adjust and retest until you're happy then remove the gauge and sensor.
It's less accurate but you can also buy or make a sniffer tube that clamps on to a tailpipe so doesn't need the welded boss, this will work for say 1/4 to full throttle but isn't good for small throttle openings or idle settling.

I am very tempted to buy an AFR gauge as I'd like to get my trail bikes' carb dailed in better, cheap ones start at about £170 including the sensor, I'm just not sure if I can be bothered though. :)):

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Re: Re-Jetting Carbs Question - Yamaha XVS650

Post by ptolemyx » Sep 27th, '19, 12:20

Get in touch with the manufacturer of the pipes. IF it needs rejetting they should know and be able to recommend what jets to use. I'd guess the "limiter" screw is the idle adjustment screw. Being a low state of tune motor you probably don't need to fiddle with the carb's other than perhaps adjust the idle so it's probably okay to run it with the free flowing pipes and only adjust things if it then proves necessary.
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Re: Re-Jetting Carbs Question - Yamaha XVS650

Post by Firebeast » Oct 1st, '19, 21:31

A quick 2 mins online showed they are set up quite lean standard, likely for emissions, so it depends how hard you riding it ,but it never hurts to get things right and reap the benefits.. Full open pipes will likely cause a loss of torque without the back pressure , but more mid / top ( tho it’s a low rev 40 bop twin) so may feel lacking low down a bit. However, you can likely get it back if you knew how to fully tune the carbs working one stage at a time,oh and whilst in there I would junk whatever emissions crap it is running , info would no doubt be online on a owner forum. You lose a bit of weight from emissions junk, gain say .5 bhp from the vacuum , never seen or heard it cause issues if all done properly so everything is sealed up and in some cases it helps sort issues that were there from day one. .. if the tuning goes well you get a better overall torque curve/ power so why not have a go yourself and learn a bit, it’s not rocket science , like some make out., just trial with occasional error till you get to the correct setting .try finding factory pro carb tuning guide online, that gives a full breakdown on how to tune carbs, unlike dynoshite, so you could just do some searching about main jet sizes , buy a manual if you don’t have one and get your hands dirty . It’s only a v twin so easy enough to work on and between the carb guide and a manual , you could get the bike running a LOT better whilst also getting a big grin if doing it yourself and saving a shedload over paying someone say £40 an hour to lob a couple of main jets in or maybe a lot more for a dyno tune which is frankly overkill for a little twin , a few dyno /mechs of which I wouldn’t touch with a large stick tbh, tho there are also very good folk out there as well mind , . I looked at afr myself for tuning my aky system but was told it’s not good enough for full blown carb tuning on say 4cyl or high power stuff and if you can spend enough time on finding the right jet size and tweaking the rest of the settings to match,,you save a load and maybe buy a carb tune with money saved to finish the job off proper. Simples, lol

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Re: Re-Jetting Carbs Question - Yamaha XVS650

Post by Mr Tuscan » Oct 2nd, '19, 15:05

Love all the responses and a fair chunk of info to take in and many many different views from here and other places.

I've ordered the pipes and they are being knocked up now, they will be baffled also.

Lets see where it takes me from here, :)
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