Throttle lagging under 3000

Oprahands

XS650 Enthusiast
Messages
45
Reaction score
11
Points
8
Location
Missouri
I have a 78 650 special with mikes commando exhaust, uni foam filters, and VM 34s. When riding it will take a good bit of throttle to get up to about 3000 rpm and then after that it takes off. Would one of those torque inserts be what i need? It also has trouble getting past 5000 rpm any ideas?
 
Exhaust inserts won't fix that, Hands. Strobe the ignition at 1200 rpm idle, roll the throttle, observe advance until ignition is advanced fully, and tell us what you see. Also, what ignition system are you using?
 
Exhaust inserts won't fix that, Hands. Strobe the ignition at 1200 rpm idle, roll the throttle, observe advance until ignition is advanced fully, and tell us what you see. Also, what ignition system are you using?
I forget what brand it is. It was one of the cheaper kits off of mikes xs. Ill check the advance when i get home. Thanks
 
Sounds like a jetting issue. I pretty much have the same set up as you. Where did you get the VM34's? are they pre-configured for the XS or did you put them together yourself? There's a thread on here on the various jetting scenarios that seem to work best. I did my research and I ended up with a 175 Main, middle clip position and 20 Pilot (one turn out). I think I'm pretty close to being dialed in. I would check your jetting to see where you're at.
 
Sounds like a jetting issue. I pretty much have the same set up as you. Where did you get the VM34's? are they pre-configured for the XS or did you put them together yourself? There's a thread on here on the various jetting scenarios that seem to work best. I did my research and I ended up with a 175 Main, middle clip position and 20 Pilot (one turn out). I think I'm pretty close to being dialed in. I would check your jetting to see where you're at.
i got them from tc bros. I have a 20 pilot 1 turn out. Middle clip position and a 165 main. Bike worked fine before a cam chain guide fell apart and the new exhaust
 
Try going up on your main...could be running lean now that you have a new exhaust and more airflow. Also assuming the cam chain/timing was set correctly when it was reassembled.
 
I'm not saying that ignition is the only problem or even a problem at all, but it's one possible source of trouble, and unlike A/F ratio, it can be inspected directly and easily. In the first shop I worked in, the boss would yell "IGNITION FIRST, YOU IDIOT!" every time I started to mess with a carburetor at the beginning of a job. He yelled loudly enough that I finally got the point and remembered it, especially after he offered to pound it into my skull with a big cheater bar.The low rpm lag can be a tell for a defective advance governor. First rule for carb tuning: Everything else first.
 
the boss would yell "IGNITION FIRST, YOU IDIOT!" every time I started to mess with a carburetor at the beginning of a job.
Sounds like we might have had the same boss. One of mine used to say "never underestimate the ignitions ability to fool you into blaming the carbs."
 
For sure! If the cam/cam chain was messed with...that has to be reconfirmed, as timing, advancer and all that needs to be correct and working.
 
Back
Top