Sputtering engine - need help

[gentlemanjim]

The Roadster build is 99% finished, but still have isssues. The engine fires right warms quickly and has excellent throttle respone in neutral. Out on the road its a different story. Spits and farts struggles to reach 5000 rpm on the interstate. Idles fine and fairly smooth up to 3500 rpm.

The mods: 2-1 free flow exhaust, K&N air cleaners. Rebuilt and rejetted carbs - 137.5 main jets and 47.5 pilot jets, I did not adjust the needle, mixture screw out 2.4 turns. High output coil.

I pulled the plugs BPR7EXI and they looked good, put in the original old dirty BPRE7ES ran a few miles no improvemetn, but when pulled they were bright white. Tried BPR8ES no improvement.

I'm thinking lean condition, but why? The oversize jets should have prevented lean out.

So I appeal to you my brothers and keepers of the XS secrets for help.

 

[gggGary]

Give it a little choke on the road if it runs better there's a clue. could be not enough fuel for reasons other than jets too. Timing/advance checked?

 

[gentlemanjim]

Added choke a little no change, added full choke a brief power surge, then no improvement. No check on timing/advance all stock I believe. So how is that check done. Fuel starvation, Hmm maybe dual petcocks 3/4 full tank, looped fuel lines through mini filters. What next?

 

[gggGary]

Unless you have a tank full O grunge, I'd try removing the loops and filters see if it makes a difference. Not an XS tuning guy though so don't know what to tell you as far as your jetting goes. Intake spigot vacuum ports sealed off? Or are you running diaphragm petcocks? Check for air leaks.

 

[gggGary]

Timing light for timing and advance what ignition are you using?

 

[gentlemanjim]

Tank is spotless, with dual feeds and filters, one vacuum petcok, one manual new vacuum hose and cap. Stock TCI ignitioin no mods there. By the look of the plugs it sure appers to be a lean condidition as the old plugs I put in were a bit sooty and came out brilliant white in just a couple miles of riding. IF it is a vacuum leak its strange that it is on both cylinders.

 

[Sundie]

what year/model carbs?

 

[gentlemanjim]

1983 Heritage Special, stock carbs for the year and model.

 

[gggGary]

GJ you might want to read through this thread, it is possible the taper jet is not assembled correctly for your year.
http://www.xs650.com/forum/showthread.php?t=1017&highlight=jetting+guide&page=2

 

[Tech7]

+1 on the taper jet. Those carbs are notoriously lean from the factory.

 

[gentlemanjim]

I may have assembled them incorrectly after cleaning. I pull the carbs and inspect. I have BS34's anything unique abour these? THe above thread seemed to be primarily about the BS38's

 

[Sundie]

did you swap the needle jet/needle out for an adjustable set? Either the cdn set, or XSjohn's needle with the us needle jet is pretty much a requirement.

You've got the floats set to 22mm?

A friend has cdn needles/jets, third position, stock jetting, idle screws set to 1.5, with open pipes and pods, running fine.

 

[gentlemanjim]

Needles are stock. Main jet 137.5, pilot 47.5, float 22 mm. As I said it runs and starts great in neutral revs freely no backfire, crisp throttle response. Out on the road its a nightmare. With the severity of the situation I have to think it is something more drastic than just a needle change. XSJohn seems to have faded into the woodwork. Where are you John?

 

[bloodthirstysystem]

same thing happened to me last week. it was spark problems. mine is older and has points but it sounds exactly the same..
idle was fine, around my yard was fine - on the road was hesitating, backfiring, etc.

 

[Sundie]

the stock us needles/jets are terribly jean for stock intake/exhaust, let alone open.

 

[Joesxs650bobjob]

I’m having the same issues starts an runs fine but sputters in the mid range played with the carbs lots starting to think it’s ignition any tips on where to head??

 

[gggGary]

first try bs34 needle shim washer (search that)

 

[Joesxs650bobjob]

Seems to be super common the mid range sputter I’m having it to wish there was some answers... thinking it’s ignition

 

[gggGary]

BS34's, do you have TCI ignition? Checked timing with a timing light, strong blue spark? The canadian carbs came with adjustable needles the US carbs did not. plugged pilot jets are common. what air filters, exhaust, correct clean sparkplugs?