Will77
XS650 Member
Ok I’m sure this has been asked before but I have a 1979 xs650 and I’m gonna be running factory style air filters and straight pipes and I’m sure someone else is doing the same so I wanna know where to start with jet sizes
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Jetting for straight pipes
- Thread starter Will77
- Start date
You may not need to re- jet. After rebuilding the engine, I used the original jetting the bike had when I bought it (stock air filter and 2 into 1). Engine ran great with no filters and short straight through pipes.
With large exhaust ports the XS motor with no mufflers tends to pull raw fuel ALL the way through the motor during valve overlap at higher throttle openings. A complete exhaust will make for more efficient, better running, as a standing back pressure wave "stuffs" the mix at the exhaust valve, keeping it in the cylinder. There's info on header length, muffler size to make best power around. These motors have been run, tested, researched to death for decades by flat trackers, there's some serious knowledge, development been done.
There you've been warned. You just want "look at me" ugly loud, and poor running for a bar cruiser go for it.
Yeah I'm that old fogy.
There you've been warned. You just want "look at me" ugly loud, and poor running for a bar cruiser go for it.
Yeah I'm that old fogy.
Will77
XS650 Member
You are right I just want ugly loud look at me but I want it to run good so is is there like a glass pack muffler that will give a just enuf back pressure to run good?
Assuming BS38s, start here: go up 3 or 4 sizes on the main jets, go up one size on the pilot jet, raise the clip on the slide needle from the middle position to the second-from-the top position. This assumes stock jetting -- verify what stock jetting is for your year carbs.
Experiment with baffles. A simple, home-made baffle how-to can be found here:
https://www.xs650.com/threads/homemade-baffles-for-short-pipes.26822/
Experiment with baffles. A simple, home-made baffle how-to can be found here:
https://www.xs650.com/threads/homemade-baffles-for-short-pipes.26822/
Will77
XS650 Member
Yup stock jetting #135 main jet #27.5 pilot jet
Will77
XS650 Member
And I like your idea for a homemade baffle I will have to try that
probably a couple of those little cocktail shakers would do the job. Never have cared for the looks of them. Walker cherry bombs are cheap have an old rat rod look. But something with a wall to reflect the sound wave is my thought.
from the factory racing manual.
Others came up with different ideas later.
These work awesome but are unobtainium.
from the factory racing manual.
Others came up with different ideas later.
These work awesome but are unobtainium.
Take a #2 phillips screwdriver, heat the tip with a torch until cherry red and plunge it into your eye. It will hurt less. Really. Bikes with CVs have airboxes. Bikes with slide needle carbs have pods. Even Mark Dobeck, former owner of Dynajet, cops to a loss of midrange using his kits.
And you want straight pipes ?
And for the other eye heat a 3/4" drill bit chucked up in an air drill ...
I can get BS38's to almost work on the 650-700-750 with one serious caveat . They will pull hard with the throttle arbitrarily pinned with a YUUUUUGE flatspot in the middle, OR they will mix fuel cleanly at part throttle cruise . Pick one I don't know how to give you both .
just a partial list
various attempts at
springs
needles
needle jets with and without discharge shields
pilots
mains
main air bleed
air horns within the air filters
closer to or further away from the head
adjustable cam sprockets
different headers ....
All because in one case the owner wanted to look like all the other cool kids
and the other thought it was a pain to get the carbs in and out with the stock aribox
In both cases "Loud Pipes Save Lives".
coincidentally both of these mental midgets went from 45-52 mpg to 30-31mpg and might have gained a couple of hp on top at the expense of having me spend untold hours filling a huge hole around 4k .
So I was asked recently if I would jet another for straight pipes ? Good thing I kept my notes .
So now that I've demeaned, denigrated, derided, called you out as a fool in public and questioned your sanity....
I can get this to work on a limited basis. It will look like a straight pipe and almost sound like a straight pipe without the flat spot in the midrange.
Make a cut in the straight pipe from the inside to the outside one half way through the pipe , make this about 4-6" from the end of the pipe. Put a piece of sheet metal in the slot, braze or weld it in place, trim the excess, and move in another 5" and this time make the cut from the outside in. Wash, rinse, repeat as necessary to get the throttle response you need while still looking like and sounding like all the cool kids.
Now I feel dirty ....
~kop
And you want straight pipes ?
And for the other eye heat a 3/4" drill bit chucked up in an air drill ...
I can get BS38's to almost work on the 650-700-750 with one serious caveat . They will pull hard with the throttle arbitrarily pinned with a YUUUUUGE flatspot in the middle, OR they will mix fuel cleanly at part throttle cruise . Pick one I don't know how to give you both .
just a partial list
various attempts at
springs
needles
needle jets with and without discharge shields
pilots
mains
main air bleed
air horns within the air filters
closer to or further away from the head
adjustable cam sprockets
different headers ....
All because in one case the owner wanted to look like all the other cool kids
and the other thought it was a pain to get the carbs in and out with the stock aribox
In both cases "Loud Pipes Save Lives".
coincidentally both of these mental midgets went from 45-52 mpg to 30-31mpg and might have gained a couple of hp on top at the expense of having me spend untold hours filling a huge hole around 4k .
So I was asked recently if I would jet another for straight pipes ? Good thing I kept my notes .
So now that I've demeaned, denigrated, derided, called you out as a fool in public and questioned your sanity....
I can get this to work on a limited basis. It will look like a straight pipe and almost sound like a straight pipe without the flat spot in the midrange.
Make a cut in the straight pipe from the inside to the outside one half way through the pipe , make this about 4-6" from the end of the pipe. Put a piece of sheet metal in the slot, braze or weld it in place, trim the excess, and move in another 5" and this time make the cut from the outside in. Wash, rinse, repeat as necessary to get the throttle response you need while still looking like and sounding like all the cool kids.
Now I feel dirty ....
~kop
Dirty? Go to the showers, Dennis mah man, and shame on ya for telling hard truths to the hard of head. Loud pipes save lives? Hell no, Opie! Loud pipes make targets. With all the crazy that's out there, the last thing any sane person would want to do is to draw attention to himself in traffic with something that can give a rage addict the excuse he wants to cut loose and kill. But it's your bike and your life, live and let die is a motto on my wall, not gonna try to save any free American from himself.
Will77
XS650 Member
Ok I made the baffles and love the sound but I was wondering if you still rejet the carbs ?
Universal 3 in. Complete Straight Pipe Rejet Kit
Your mileage will vary.
Only if you need to. Bike probably runs poorly now, with flat spots and spark plugs indicating leanness, so yes, you re-jet. Try what I suggested.
