need help with bs 90 trail again

[bhult]

I just put a new carb on the bike.  It seems to run good at an idle but sputters at higher rpm.  When it dies it is really hard to get started back up.  Also when I turn the key to the position to run the lights if bogs out and dies and again is hard to get started again.  Points, coil, or condenser?

[old smokey]

No experience on the 90, but it sounds like 2 issues to me. The "new" carb isn't clean for the off-idle speed fuel control.
Something in the charging circuitry isn't right for the key- headlight issue.

[disc_valve]

Hi,

If you haven't already done so, try a new, correctly gapped plug as a first shot. Otherwise, the engine dying when you turn the lights on sounds like classic symtoms for bad points and/or ignition timing. Put in a new set of points and set the timing carefully to the marks (although the 90 isn't that critical on timing).

The engine sputtering at high revs might also be a fuel supply issue. Pull off the fuel line and check that fuel flows well from the fuel cock. If not, you could have a blocked fuel tap or filter, or a blocked breather hole in the fuel tank cap.

A final thought, have you got the correct sized jets in the carb? If it's a 90 Sport, you may have been sold a carb for a 175 or 100, which are the same body with different jets and slides. Similarly, the other 90s used the same carb as the 50 Sport, but again with a different main jet.  From memory, the 90 Sport needs a #110 main jet (the 175 and 100 used #95) and the 90 Deluxe/Trail/Mountain needs a #130 main jet (the 50 Sport used a #110). Double check these jet sizes against the parts books which you can from the "Manuals/Articles" tab at the top of the page.

Hope that helps,

Graham 

[OldSwartout]

Check all the things Graham has suggested - new or cleaned up points in particular. It's also possible that you have a problem with the ignition switch or wiring connections.  The ignition and the battery/headlight circuit are two completely separate systems. It does not need the battery or the charging system to run, as the ignition is powered by a coil under the flywheel that is separate from the battery/lighting circuit coil.  You could bypass the switch by jumping the black wire from the magneto to the black wire to the external ignition coil.

[Mountaineer]

If you are Not running a battery, you may have burnt the points and spark plug.  Over revving without a battery not good on the electrics.   You have damaged the charging system that way also, which will not provide enough electric for ignition and lights all at the same time.  Also check for bad tail light wires under the rear fender, etc.   Coop

[OldSwartout]

The ignition and the charging (battery and lights) are two separate systems. You can burn up the charging system and still have a good ignition as the ignition is powered by a separate coil not affected by the battery or lights. However, Mountaineer is correct, in that if you run without a good battery, you will probably burn out the bulbs since the battery acts as a voltage regulator in the charging system.