mid range RPM sputter

beaver · Apr 23, 2013

hey man.
i got a 83 xs650 with a PMA, PAMCO, Stock Carbs(main jet 137.5) with open pipes

around 50-60 mph, when i give it some gas. it sputters out. i cant figure it out.

any advice?

TwoManyXS1Bs · Apr 23, 2013

Hey, beaver, I've seen a lot or your situation on this forum and been contemplating doing a write-up on the detrimental effects of short/open pipes. You're largely being influenced by 'reversion', do a forum search on that term, consider redesigning the exhaust, use anti-reversion cones, or such.
We dealt with this a lot in the `70s. An experiment you can do is get a couple of one foot pipes that will slide over your exhaust ends, slit the ends so you can clamp them tightly on the ex pipes, put them on (this is just temporary), and ride it. If there's a marked change in your throttle response at that problem area, you've found reversion is the culprit...

EvenmoreXS · Apr 23, 2013

beaver said:
hey man.
i got a 83 xs650 with a PMA, PAMCO, Stock Carbs(main jet 137.5) with open pipes

around 50-60 mph, when i give it some gas. it sputters out. i cant figure it out.

any advice?

I have a 47.5 pilot and a 140 main. That works for me with bs34's. I had trouble going faster than 60mph until I put back my 140 main. 60-70 mph is very quick now.

Just my 2 cent. Had the same problem. Up'd the main, worked for me.

XSLeo · Apr 23, 2013

What air cleaner are you using. The K&N pleated element filters cause air turbulence going through the carb. This causes slide lift issues. THe sort tapered are the worst. The longer straight ones are better but not great. The low budget knock offs are just as bad if not worse.
I reccomend using Uni-Filter air filters. They are a long round foam element and flow air smoothly. No slide lift issues. That fixed the issues I was having on my 75 with the 750 kit.
I also agree with TwoMany. exhaust reversion is a real killer of low to mid range power. Using too large or too short an exhaust make it worse. The 1.75 pipes are popular but too big. 1.5 works much better. The length of the pipe makes a big difference. As I recall the length should be 33 or 36 inches from the valve through the centerline of the pipe. This gives about the best at lower rpms.
After all they don't call short open pipe drag pipes for nothing. They give good power under the situation they were designed for. WOT running, anything less they just make noise. They are designed to get max power up at or just above redline. Longer, smaller pipes move the power down into the 5000-6500 range that is much more usable.
Properly designed headpipes with good mufflers will give better power at the rpms the bike uses on the street. Easier to tune to as well.
Leo

EvenmoreXS · Apr 23, 2013

XSLeo said:
What air cleaner are you using. The K&N pleated element filters cause air turbulence going through the carb. This causes slide lift issues. THe sort tapered are the worst. The longer straight ones are better but not great. The low budget knock offs are just as bad if not worse.
I reccomend using Uni-Filter air filters. They are a long round foam element and flow air smoothly. No slide lift issues. That fixed the issues I was having on my 75 with the 750 kit.
I also agree with TwoMany. exhaust reversion is a real killer of low to mid range power. Using too large or too short an exhaust make it worse. The 1.75 pipes are popular but too big. 1.5 works much better. The length of the pipe makes a big difference. As I recall the length should be 33 or 36 inches from the valve through the centerline of the pipe. This gives about the best at lower rpms.
After all they don't call short open pipe drag pipes for nothing. They give good power under the situation they were designed for. WOT running, anything less they just make noise. They are designed to get max power up at or just above redline. Longer, smaller pipes move the power down into the 5000-6500 range that is much more usable.
Properly designed headpipes with good mufflers will give better power at the rpms the bike uses on the street. Easier to tune to as well.
Leo

I do have Uni's.......PK-92's. Lolli pops for baffles. Open pipes. 1.5 inch. Come out just behind my feet. Uni's are in the last pic, XS performance pods in the first pic have been replaced.

Just for reference. Hope it helps.

beaver · Apr 23, 2013

ill be honest. at the beginning. i loved the sound of my open short pipes. loud! but i want more performance. im starting to do little road trips on my bike and the way my bike is set up right now sucks. im running the XS performance air filters. im thinking about re doing my exhaust but i dont knoe what to do. im thinking about go under the engine and split out right before the rear wheel.

i wanna try these baffles

HERES A PICTURE OF MY BIKE.

angus67 · Apr 23, 2013

My 1980 has the same length pipes as yours, I run those short( I like to call them" can- opener baffles". I also have 140mains, and 46 pilots, short uni foams, and adjustable needles. Runs and sounds excellent!
But soon Ill be putting on the small 12" megaphones, they look like small chrome glass pack. I will prolly have to drop the main one step, but I need the length to stop burning the heels off my boots!

TwoManyXS1Bs · Apr 23, 2013

Nice bike, beaver.
I did MANY cross-countrys on a rig almost identical to yours.
Running TT pipes same length as yours gave me the same 60 mph dead spot.
Plus, although the sound is cool, it has been proven that it leads to premature fatigue.
When I lengthened the pipes, the dead spot went away, the sound mellowed, the cops backed-off, and I didn't get as tired.

beaver · Apr 24, 2013

this weekend. im going to weld 2 feet to each exhaust and get some internal baffles. fingers crossed. i just wanna get my bike running good so i can do other things to it.

twomanyxs1bs, id love to see your 10" over XS. im about to put a 6-8 over durfee girder on mine.

TwoManyXS1Bs · Apr 24, 2013

Beaver, look in my 'album'...

EvenmoreXS · Apr 24, 2013

beaver said:
ill be honest. at the beginning. i loved the sound of my open short pipes. loud! but i want more performance. im starting to do little road trips on my bike and the way my bike is set up right now sucks. im running the XS performance air filters. im thinking about re doing my exhaust but i dont knoe what to do. im thinking about go under the engine and split out right before the rear wheel.

i wanna try these baffles

HERES A PICTURE OF MY BIKE.

I have those baffles. Couldnt get em into my pipes. I still have em in case I ever decide to cut of my chrome turnouts. Loli pops work, but I have nothing to compare them to really. Other than my old exhaust, but thats not really fair.

mid range RPM sputter

beaver

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1981 XS650

XSLeo

XS650 Guru

EvenmoreXS

1981 XS650

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