need help tuning carbs with velocity stacks on 1980 650

sinister_customs

for starters i have a 1980 xs650, motor is stock, carbs are set up with xsjohns needles, built a new exhaust and have to run velocity stacks to fit around the battery box/oil tank set up. has anyone here figured the correct jetting for velocity stacks? my exhaust has baffles, not much of baffles about 4 inches long but there are baffles in the mufflers, i will add a picture of the bike so you can see my set up and make recomendations on jetting if you have any. hope to get some good info back
thanks
J-

jayel

Quote::

has anyone here figured the correct jetting for velocity stacks? my exhaust has baffles, not much of baffles about 4 inches long but there are baffles in the mufflers

no easy answer to your question, this is about the best anyone will be able to do
www.4secondsflat.com/p...chart.html
compare your plug to this chart and work from there, you've totally changed the intake and exhaust systems so you need to start with a base line reading of what the bike is doing now, how does it start, how does it idle, how does it run at low speed, how does it run at high speed

sinister_customs

well at first i was getting flames out of the left cylinders exhaust just coming off idle, loud poppy flames. So i played with the pilot screw a bit and it seemed to go away. i ride the bike for 20 miles or so and it runs good. not great but good enough to ride. a couple friends and i head out for a run later on and the bike is running like absolut s***, from idle to 1/4ish throttle i could get it to cruise ok soon as i got on the gas some more it cut out, almost sounded like ignition failure. so i limped it home. i swapped to a 1981 coil to see if it was that and now i get flames from the right cylinder exhaust loud - snappy- bang flames soon as it starts, i have not even been able to get it running long enough to come off choke. to answer your question about the plugs, the left cylinder is dry black and sooty. the right plug is clearly lean, its white and crusty looking. valves are in spec and compression is 150psi across the board. i was hoping to find someone that has done a similair set up with the snowmobile velocity stacks and had a jetting spec just so i can get closer in range to fine tuning it. I am also topping out at a top speed of about 55 with stock gearing, that puzzles me, i wanna get this pig to pop wheelies! and still cruise at 70

xsjohn

Although I have never run velocity stacks I have run mine many times with the air box completely off and I couldn't tell a major difference.....and since you have some baffel for back pressure MJ should be 135 or 137.5.....can't remember if I sent you the wire for the 46 or are you using a 45 for the pilot at somewhere around 2 1/4 left 2 1/2 right to start with on the mix screws..........and larger pilots can get rich rapidly if turned just a bit too far.........

I have to assume that the carbs are clean and the black plugs are over the pilots and the pilot circuit is clean and the needle jet is YO and and was removed and cleaned.........all that being said......

If I had set mine up as above ( as have hundreds) and was experiencing the major running problems I would make sure that all wire connections were clean and applied dielectric grease to the connections...........kill switch ignition switch and the two wores at the coil..........allthat being said..........

If running problems still persisted I would swap the TCI box..or maybe even try that first.........

All the needles I send are scrutinized and measured may times before I send them.....and I treat them as if they were going in my bike.......so I am somewhat baffeled here.........let me know if you have trouble shooted the TCI and are sure the harness is clean.......

When I first got mine I had spark problems until the entire harness was cleaned....and it ran pretty crappy untilI did that......it never reappeared.....

xsjohn

sinister_customs

i have no doubt in your needles i ran them all last year and the bike ran at its best. i do have a complete 1981 that is on a longterm chop project so i can swap igniters with that and try that out, i also will check over my wiring again. I am sure the carbs are clean unless i got debri out of the fuel tank. will check all areas over and get back with you.

xsjohn

Are these the same carbs..........and are the plastic floats set at 22MM......I don't own the plastic floats to the first ledge is where I measure from when I clean and set up carbs for other people.......no one has come back to me on that one........and are the Needle Jets YO and not the Canadian ones 336-Y0 which can cause problems....

Hoping you find it's ignition somewhere.....dang if the carbs ran last year......

xsjohn

sinister_customs

carbs are clean, jets are 135 mains, 46 pilot, i will have to double check the needle valves. i got the rebuild kits from mikesxs last year so what ever parts he ships with but i will check. as for the ignition, i have moved all my wiring to fit in the oil tank. to do this i cut the tabs off of the ignition box with an air power buzz saw. perhaps the vibration has knocked something loose, correct me if i am wrong here but doesnt that box control the ignition advance as well? i am going to play around with it some more this afternoon and see what i come up with. i think i am goin to try the 137.5 or 140 mains, i will also set the 22mm float height, may already be there actually but i will double check. thanks

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