Low top speed

[pat_in_the_hat]

Alright, just trying to brain storm why my bike isnt running the best and maybe someone has an idea of something I could change/try.

Bike seems run just fine until im in 5th gear trying to get up to higher speeds. It just doesnt want to get above 55 mph. It revs out and doesnt want to go any faster. Ive read that these bikes are capable of much more then 55 and I would like to see that so I wont get ran over if i ever need to take it on the highway.

So I have a '75, pamco ignition, ya mama exhaust, 19/18 wheels with firestone champion tires, stock 17/34 gearing, vm34 with pod filters, I forgot what I have for jetting but it seems to be good since with doesnt show any lean/rich conditions. and bike has compression of 135 in both cylinders even tho there is a small oil leak on the right side just below the spark plug.

Ive set the cam to where the rod is flush with the end of the tube, valves are set to .02 intake and .04 exhaust, timing is set to where full advanced is right on the advanced line. However at idle there is 2 lines that show up, i set the more advanced one inbetween the marks. The chain is tight but shows about 1/2" deflection in one way when pushed down

What am i missing to help my bike get up to a more normal speed?
Maybe move the clip on the needle jet? Im not sure what to do!
i dont have a tach, so i dont know where the engine speed is at, but it sounds pretty high at 55mph

 

[weekendrider]

Are you familiar with the "feeling" of a slipping clutch?
If you had a tach it would be easy to confirm. The speedo stays the same or close but the tach will show a sudden increase in rpms. This visual helps until you have a feel for it (a slipping clutch).
This isn't an uncommon problem with the XS. Usually new stronger springs are the fix.

 

[pat_in_the_hat]

hmm... didnt think about that... at least according the engine noise, it doesnt jump in rpm. Is there any adjustment I could do to help it or see if thats the case?
Also, im guna get some new spark plugs to see if that will help at all. might try the iridium plugs if I can find them locally.

 

[weekendrider]

Other than the feel/sound when the plates lose their grip I'm not aware of any way to tell if the clutch is slipping. The only fix I know of is spring replacement.
But if it is bogging down or simply running out of steam it isn't a clutch slip problem.
It could be a blockage of the vacuum signal to the slides common with some pods gasket or dirty/clogged main jet circuit, or . . . . .

 

[pamcopete]

Here is a list of things that can slow you down:

Bike goes slow (< 60MPH)

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. Stuck or no advance. When checking the timing with the timing light, did you check for maximum advance at 3,000 RPM.
4. Binding advance rod.
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 60 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. Weak or loose advance springs. Weak or loose advance springs cause the advance to use up some of the available movement because you have to essentially retard the advance to get it on the idle advance mark, so there is less movement available at higher RPM's.
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 60 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
1. Which PAMCO do you have?
2. If PMA, then battery or capacitor?
3. Was the bike originally a US TCI engine or points?
4. What octane gas are you using?
5. Which carbs do you have installed?
6. Any mods to the exhaust or air filters?
7. What gear and road speed does the problem occur?
8. What was the most recent work done to the engine besides the PAMCO?
9. Have you tried going up one size for the main jets in the carbs?
10. What is the battery / capacitor voltage at 5,000 RPM?
11. Have the ignition switch and kill switch contacts been cleaned? Ever?
12. What is the altitude where you are?
13. New spark plugs?
14. When you say it won't rev past 5,000 RPM, what does it do? Misses? Backfires?

If you installed the PMA at the same time as the PAMCO, then several issues could come into focus:

1. How did you establish the timing marks?
2. Does the rotor of the PMA have a key to the crankshaft?
3. Are you using a battery or a capacitor?
4. What is the battery / capacitor Voltage at 5,000 RPM?
5. If a capacitor, then what is the capacity and brand of capacitor?
There can be issues with the PMA that manifest themselves as ignition problems. One way to split the difference is to temporarily disconnect the PMA regulator and run the ignition from a fully charged battery.

 

[pat_in_the_hat]

dang.. thanks for the write up! looks like I have alot to go thru

 

[XSLeo]

.02 and .04 don't seem right for the valves. A lot of us use .003 intake, .006 exhaust.
Do you still have the tach drive in the engine? If so mount a tach temporary for a bit of testing.
There is a Sudco tuning manual for the Mikuni VM series carbs, might try reading it.
Leo

 

[FLEA]

Here is a list of things that can slow you down:

Bike goes slow (< 60MPH)

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. Stuck or no advance. When checking the timing with the timing light, did you check for maximum advance at 3,000 RPM.
4. Binding advance rod.
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 60 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. Weak or loose advance springs. Weak or loose advance springs cause the advance to use up some of the available movement because you have to essentially retard the advance to get it on the idle advance mark, so there is less movement available at higher RPM's.
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 60 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
1. Which PAMCO do you have?
2. If PMA, then battery or capacitor?
3. Was the bike originally a US TCI engine or points?
4. What octane gas are you using?
5. Which carbs do you have installed?
6. Any mods to the exhaust or air filters?
7. What gear and road speed does the problem occur?
8. What was the most recent work done to the engine besides the PAMCO?
9. Have you tried going up one size for the main jets in the carbs?
10. What is the battery / capacitor voltage at 5,000 RPM?
11. Have the ignition switch and kill switch contacts been cleaned? Ever?
12. What is the altitude where you are?
13. New spark plugs?
14. When you say it won't rev past 5,000 RPM, what does it do? Misses? Backfires?

If you installed the PMA at the same time as the PAMCO, then several issues could come into focus:

1. How did you establish the timing marks?
2. Does the rotor of the PMA have a key to the crankshaft?
3. Are you using a battery or a capacitor?
4. What is the battery / capacitor Voltage at 5,000 RPM?
5. If a capacitor, then what is the capacity and brand of capacitor?
There can be issues with the PMA that manifest themselves as ignition problems. One way to split the difference is to temporarily disconnect the PMA regulator and run the ignition from a fully charged battery.

thanks pete ,will print this out and put in the manual for future reference ,good checklist

 

[rainycity]

When I first got the one I have now it did pretty much the same thing, not quite as bad but still, anyways, turned out to be the one of the rubber carburetor diaphragms.
Fixed that and it was like a whole different bike.

 

[warrenlevihursh]

You can read through my post on speed if it helps.

http://www.xs650.com/forum/showthread.php?t=44261

Mine is better with foam Uni filters vs the pleated, a muffler and stock gearing. I rode to work this morning on the highway cruising at 85 the whole way. It is much better!