Cutting out at high speed/rpm

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garykohl2

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Hey guys! I'm new on here and hoping someone can steer me in the right direction. I just bought a 1980 XS650. It runs great and smooth except I took it on the hwy for the 1st time and it has a problem with anything over 70. Once I hit 70 and up it starts missing pretty bad. I can get it to 75 but it is spitting like crazy...lol. I know these are small bikes but I thought for sure cruising 75-80 would be ok.
Here is what I know about the bike. It was just done less than 200 miles ago but the engine was not gone into because the po said it was a good running engine (and I have no reason to doubt that) It has been converted to electronic ignition of some sort, pod filters and rejetted (don't know the jet sizes). It is running a 17/34 sprocket combo.
I don't have a tach so I'm not sure what rpms its turning at that point but it is buzzing pretty good.
Does this sound normal or is there something I need to look at.
Thanks guys
 
Not even remotely normal. Take a picture of the aftermarket electronic ignition and the entire bike. A 1980 would have come from the factory with electronic ignition but if the p.o. says it's been converted than it could be a 1979.
 
Sorry I didn't realize that. The PO did not tell me that I just assumed because I didn't see points.
It does seem like it is starving for fuel. Is there an easy way to set the floats without pulling the carbs?
 
Another thing to think about once you get the ignition/carbs sorted is a 32 tooth rear sprocket. 650`s kinda feel wound out at 70.
 
There isn't an easy way that I know of to get to the floats without removing them. Find the carb guide and study it if you want to get into carb maintenance. Once you've done it three or four times you can get the carbs out in about ten minutes.
 
Thanks for the help guys. I'm going to check the float levels tomorrow because that's really how it feels....like it just needs more fuel.
I plan on switching the rear sprocket to a 30 probably.
Ill post up some pictures as soon as I can.
Thanks again!
 
Here is a list of things that can cause problems at high speed:

Bike goes slow (< 70MPH)

1. Low battery / charging system. A low battery will produce a low ignition voltage at the plugs which is most evident at higher RPM's.
2. Timing. Did you use a timing light to set the timing?
3. N/A
4. N/A
5. Fouled plugs. Did you install new plugs? Check them after you got it running?
6. Plug wire not making contact in the coil. Measure the resistance from plug cap to plug cap to ensure that both plug wires are making contact in the coil.
7. Brakes dragging.
8. Speedo out of calibration. You are actually going faster than 70 MPH! Use your GPS to check the speedo.
9. Tire pressure. Pump up to 32 PSI for high speed.
10. Drive chain too tight. That will rob you of power to the rear wheel.
11. Enricher plunger stuck partially on.
12. Enricher (choke) left on or partially on.
13. N/A
14. Timing chain needs adjustment.
15. Cheap or bad gas.
16. Low octane gas.
17. Water in the gas.
18. Partially blocked pet cock or fuel filter.
19. Paper filter that has low flow when the tank is not full.
20. Try a run with a full tank of high octane, fresh, expensive gas.
21. Blocked fuel cap vent.
22. Incorrect sprockets. What RPM are you getting at 70 MPH?
23. Rear tire rubbing on brake rod or swing arm.
24. High wind resistance. Are you a large person?
25. Throttle cable not fully opening the throttles.
26. Blockage in the muffler(s)
27. Dirty or blocked air filters
28. High altitude
29. Very hot air, like 95+F
30. Very cold air, like 32F
31. Low oil
32. Really dirty oil
33. Gas in the oil
34. Weak TCI magnet in rotor. Unplug Reg/Rect to test
35. Cracked carb boots
36. Hole in carb diaphragm(s)
37. Cheap pods covering air hole in carb inlet.
 
Last edited:
garykohl2 said:
Thanks for the help guys. I'm going to check the float levels tomorrow because that's really how it feels....like it just needs more fuel.
I plan on switching the rear sprocket to a 30 probably.
Ill post up some pictures as soon as I can.
Thanks again!
Click to expand...

Before you pull the carbs, crack open the gas cap and run it hard. if it runs better it could mean your vent is plugged.
 
Here is a picture of her. It's just one I snapped with my phone today before putting her back up. I know the color combo is not for everybody but thats how I bought it
03959_2833404367803_1640005090_2443394_411276539_n.jpg
 
Personally, I think it looks like a badass mamma jamma. Rear drum and seat make me think it's pre '79 but the carbs look like 80+ 34's.

Those look like stock manifolds. Check them for cracks.

Pete- I think cracked carb boots should be pretty high on your list.
 
Ok I think I know the problem. I have been going through checking things and it has all been checking out. Well I pulled the carb bowl and checked the mains.....they are stock 132.5
Thats the problem...when I am wide open it just isn't getting enough fuel. I just assumed that since it runs so well the rest of the time that it was jetted right. Guess I was wrong.
 
try runing it without the pods on also. mine was doing the same thing and when i pulled the pods off it ran great. the problem i found is that there is a breather on the rear of the carb and the crappy ebay pods i got were covering 1/2 the hole. with no pods it ran like a rapped ape.
 
mikeweyandt18 said:
try runing it without the pods on also. mine was doing the same thing and when i pulled the pods off it ran great. the problem i found is that there is a breather on the rear of the carb and the crappy ebay pods i got were covering 1/2 the hole. with no pods it ran like a rapped ape.
Click to expand...

I added this one to the list.
 
mikeweyandt18 said:
try runing it without the pods on also. mine was doing the same thing and when i pulled the pods off it ran great. the problem i found is that there is a breather on the rear of the carb and the crappy ebay pods i got were covering 1/2 the hole. with no pods it ran like a rapped ape.
Click to expand...

Thanks!
I pulled the filters and now it runs great. I hit 100 no problem :)
Now I just need to order some new pods
 
damn those cheap pods have caused some drama over the years. All you victims of emgoasphyxia should band together for a class action and sue there asses for stress and loss of riding! Some have cut the offending piece of rubber off, might help you keep riding while you wait for new pods. I use K&Ns, others are happy with Mikes, make sure you post your preferance before you buy, as there will be an opinion on them for sure! Cheers:thumbsup:

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