Yamaha Bobber
XS650 New Member
Hello Guys,
I have a freshly rebuilt 1975 XS650, with Mike's XS PAMCO high output electronic ignition/PMA package. It was easy enough to install and get running good. Also upgraded to a flat slide carb set up (again from MIke's XS). Bike ran fine for about 2 weeks, but now I am having issues with the motor popping and sputtering when I get into higher speeds, like 45 MPH and up (in 3rd - 5th gears). Bike idels fine and runs strong through 1st and 2nd gear giving full throttel, but once I hit 3500 RPM in 3rd, 4th, and 5th gear, the sputtering and popping starts. So bad that the bike will only go about 55-60 MPH on the freeway in 5th gear.
Here is what I have done so far with no results:
I have been checking and testing for the last 2 weeks. Please give me some suggestions on what to check next... at this point I am just going in circles.
My primary suspicions are the auto advance is not working at the higher speeds or the engine is not getting enough fuel. Let's hope the auto advance is fine (cuz it is just a month old), so then I am stuck thinking it is somethins with the carbs/fuel. Help
I have a freshly rebuilt 1975 XS650, with Mike's XS PAMCO high output electronic ignition/PMA package. It was easy enough to install and get running good. Also upgraded to a flat slide carb set up (again from MIke's XS). Bike ran fine for about 2 weeks, but now I am having issues with the motor popping and sputtering when I get into higher speeds, like 45 MPH and up (in 3rd - 5th gears). Bike idels fine and runs strong through 1st and 2nd gear giving full throttel, but once I hit 3500 RPM in 3rd, 4th, and 5th gear, the sputtering and popping starts. So bad that the bike will only go about 55-60 MPH on the freeway in 5th gear.
Here is what I have done so far with no results:
- Checked the timing with a timing light, timing seems fine and advance looks good (38 degrees at 3K rpm)
- carbs are getting gas (checked the float bowls)
- bumped up the main jet size up one size (carbs came with 3 sizes and i am now running the largest size)
- put in a new battery cus the guy at auto zone did a battery check and said it was bad. Put in the new battery and had the exact same issue. returned that battery and put the old one back in.
- checked the spark plug wires, spark plugs, gap in the spark plugs, and put in new spark plugs. still nothing
- checked the gas cap vent... it is working fine. Even rode the bike with the gas cap off (very carefully), and no change.
- Opened up my wiring box and checked for shorts, blown fuses, disconected wires, and looked at the auto advance unit to see if it had burnt out. nothing looked broken or disturbed
- checked and adjusted the cam chain tensioner and valves... in that order
I have been checking and testing for the last 2 weeks. Please give me some suggestions on what to check next... at this point I am just going in circles.
My primary suspicions are the auto advance is not working at the higher speeds or the engine is not getting enough fuel. Let's hope the auto advance is fine (cuz it is just a month old), so then I am stuck thinking it is somethins with the carbs/fuel. Help