improve performance?

[mjpxs11sh]

i was reading a post from Avoroth about the 11.7 1/4 mi. i still feel my 81SH is being held back in the power output area. my 78F def had more power than the 81SH i replaced it with 20yrs ago. back then i didnt know the 81 was detuned for emissions, but when i bought it as a bank repo, i felt the difference. id still have the 78 if some AWOL navy guys wouldnt have stolen it. it was found in Lake Michigan by the cops.
so after reading this, am i correct in saying the only way to improve the 81S is larger carb jets, air filter pods and exhaust. i did take the Kirker 4/1 off my blown 78 and put it on the 81 without jet changes, and it def improved the exhaust flow and took some wieght off. last season i R&R'd the varnished 81 carbs for a cleaning, reinstalled the 110 mains and adjusted the mixture till i finally got the sweet spot thru trial and error and am satisfied with the results. i didnt want to change jet sizes untill i was sure i could get it running right without any changes. after sitting with bad gas for many years, so now ive got it right and i can move on to increasing the power output. i bought a UniFilter for the air box since my 78 individual pods dont fit, and have a Kirker. im ur opinions, would it even be worth putting 115 mains in without any other changes, due to the 4/1/? i know the mains come into play at 3/4-full throttle. it runs great right now with the 110's across the board but would like to feel more power. i wont be buying pods since i was looking to use what i had from the 78. i have the feeling its either all or nothing. am i correct?
thanx

[mjpxs11sh]

sorry

sorry! i meant Azoroth.

[Lonerider62]

To be brutally honest, you might be able to get a few more ponies and shave a few tenths off the ET by swapping parts from an earlier model, taking the time/money to use someone's dyno to make sure the fueling is spot on, but if the bike is running well now, I think you'll end up being a happier guy by spending your money somewhere else. Go to any motorcycle forum on the internet and you will find guys who spend enormous amount of money to boast about a few more H.P. The best average I've been able to come up with is about $100 per H.P. and that's at the begining, as time goes on (and quickly) that gets a lot more expensive. You'll never take an XS Eleven and get it anywhere close to the modern day Sportbike numbers or performance. I was just looking at the 2012 Aprilia Tuono, 153.6 h.p. 77.1 lbs. tq. corrected at the rear wheel. Numbers...10.07 1/4 ET at 140.84 mph. and you can bet your life, new owners will be buying stuff to make them faster. And, of course it's not the fastest, quickest or most powerful. Ride the XS with the satisfaction that it's yours, more than likely paid for, and older than a hell of a lot of riders out there.

[DiverRay]

The 115 mains WILL HELP, but you may want to try 112.5 first. No, you will not get the kick you had from the "E", but you WILL get more top end, and be able to feel the difference in higher speed roll-on situations. I had to re-jet an 80 special that had headers and a K&N in a drilled airbox. The bike runs MUCH better, and it does not backfire anymore.

[BA80]

Is your SH one of those that still had the vacuum advance unit?

[clcorbin]

I was just looking at the 2012 Aprilia Tuono, 153.6 h.p. 77.1 lbs. tq. corrected at the rear wheel.

I see I am not the only XSer that likes this bike!

[TopCatGr58]

Is your SH one of those that still had the vacuum advance unit?

Hey Greg, time to bust your chops again! The XS's all have the vacuum advance pots, it was only removed/eliminated with the XJ model, but it still uses a special vacuum module /box, just not connected to the timing plate.

But I think I know where you're going with this question, if his vacuum advance module is either not working(vacuum leak), or not moving smoothly, he may not be getting the proper timing for the best power. However, the Cent. Adv. curve is built into the TCI, and the vac. adv. really only kicks in when cruising to take advantage of the leaner A/F ratios there, but when getting ON the throttle, it actually releases/retards the timing back to the more powerful less adv. position necessary for richer A/F ratio of more throttle.

Aside from putting in a big bore kit, other mods that would probably help would be stronger spark plug coils..Dyna or Accel....the 30+ y/o oem ones are adequate, but I've got an 81, and it definitely responded stronger with the newer hi output coils, wires, plug caps, plugs!

And the main jets DO contribute thru a considerable part of the throttle range, and especially above the 3.5-4k rpm range which is also where the engine's power curve kicks in, and so having it a little richer in the mains can help with the seat of the pants feel.

Just curious, you say the pods from the 78 don't fit? Is the mounting portion too small for the 81's. The 79 thru 82XJ all use the 54mm inlet bell size, but I can't find a thread discussing this, and I can't remember if the 78's have the smaller 52mm inlet, or are the same as the other years?? If yours are 54mm, then I'm wondering why they won't fit?

T.C.

[natemoen]

All the XS and XJ carbs have the same size inlet and outlet bell size. So one of the 2 bikes has the wrong carbs.

[BA80]

No, actually I was thinking that if he took the head, cams and carbs from the E and put them on the H it would improve the performance. However, it would require the mechanical and vacuum advance units be swapped also in order to have the correct timing curve.

It may even run better than the E because the H pistons have a slightly higher dome and would increase compression.

I was thinking that the later 81s were set up like the XJs. But, as you so gracefully pointed out, i've been wrong before.

[crazy steve]

....am I correct in saying the only way to improve the 81 is larger carb jets, air filter pods and exhaust....

That might gain a few HP at the top end, but in reality you'll likely be stealing it from the low and mid-range part of the powerband where you will most often be operating the bike during street riding...

If you want to know the complexities of adding more power to these, search out and read threads/posts by Dan Hodges. He spent more $$$ on dyno time looking for power combinations than most owners have in their entire bike. On your '81, to get a meaningful increase across the board will mean replacing the nearly the entire ignition system with earlier parts and probably the cams too. That '$100-per-HP' number isn't that far off for initial gains, and you'll quickly reach a point of diminishing returns.

[mjpxs11sh]

78 vs 81

unfortunately, the 78E is gone, but b4 i sold it for parts i took the wheels/tires, air pods, Kirker and misc parts off. the pods are probably 52mm because the almost go on, but not all the way. too bad i cant find a way to adapt them. i bought the 78E from a race car mechanic, so he had a jet kit, air pods and the Kirker on it. when i bought the 81S it had a Windjammer on it and was all stock.
i get more interest on my Yammy than i do with my Honda CBR. i think mostly the current trend is in the retro nude bike look. i wouldnt expect the power of my Honda (its fast), but i feel theres more in the Yammy. if i was able to adapt the pods, put in 120-122.5 mains and 45 pilots, i think thats where the sweet spot would be. does anyone have experience adapting the 52mm to 54mm?

[SFerinTEXAS]

I temporarily used some 52mm pods on my XJ during restoration. Soaked the round rubber flanges in hot water for a few minutes and stretched them on.

[natemoen]

unfortunately, the 78E is gone, but b4 i sold it for parts i took the wheels/tires, air pods, Kirker and misc parts off. the pods are probably 52mm because the almost go on, but not all the way. too bad i cant find a way to adapt them. i bought the 78E from a race car mechanic, so he had a jet kit, air pods and the Kirker on it. when i bought the 81S it had a Windjammer on it and was all stock.
i get more interest on my Yammy than i do with my Honda CBR. i think mostly the current trend is in the retro nude bike look. i wouldnt expect the power of my Honda (its fast), but i feel theres more in the Yammy. if i was able to adapt the pods, put in 120-122.5 mains and 45 pilots, i think thats where the sweet spot would be. does anyone have experience adapting the 52mm to 54mm?

Just giving it more fuel does not mean it will run better. All you are going to end up doing is making it run way to rich and possibly flood out.

[mjpxs11sh]

air pods

from the re-jetting specs
MAINS
+3 for Kirker 4/1
+2 for air pods
= +5

110+5= 122.5

PILOTS
+1 for every 3 main
42.5+1= 45

twistin a handful with the pods on the 78 sounded like a deep growl. thats what i want to hear on the 81

[BA80]

If your going to go to the trouble of rejetting you may as well go with the Dynojet Kit.

http://www.motorcycle-superstore.com.../PITEM/Dynojet