Motoscrubs.com

I am new to this site and was told about it by Franzin- I have had a 1970 Jupiter 450 for a couple of years which is unmolested since it's creation. It runs great and only needs a left tank badge to be how I'ld like it to be. Someone did swipe the guages as well as remove all the yellow paint off the tank- so it does shine. Once she is running and stalls (usually operator error) starting again is rare- so I walk away and upon return....off she goes. Not sure how to outsmart this this might ring a bell with anyone. Any ideas would be welcome. Thanks, Alex

It could be a lot of things. More info might get us in the ball park. but based on your description I would ask; how does your plug look? does it show evidence of rich conditon? or does the insulator have a nice clean tan look? starting easy when cold but not when hot could be it is too rich. next time it happens , check to see if you have spark. if you do, pull the plug and see if it's wet. if it is you might have poorly seating needle valve, a sticking or sunk float, a really badly adjusted carb or wrong jetting. Put in a fresh plug and see if it kicks over with the throttle wide open. my guess so far.

" Once she is running and stalls (usually operator error) starting again is rare-"

____ Many have had confusion concerning which way the choke-lever has to be set for starting/running with THEIR carb...
A (stock) 450 should have the lever relaxed for running with warm-engine, or pulled-tight for cold-starting. _ So perhaps you've been leaving the choke-lever kept-held in it's over-rich position? _ Or maybe the carb's related plunger-block has been lost (from within it's chamber).
__ Or perhaps your battery just gets it's voltage run-down during your motor-runs (with lights on?)...
Have you ever checked your battery-voltage before & after such a motor-run?
Does a push-start attempt provide any better starting results?


Hopeful-Cheers,
-Bob

Oh yeah, I forgot about the choke circuit, I foget that the amal with it's tickler is not stock on the 450. but if it has an amal with tickler, make sure it is returning to the fully upward position when released.

My 450 Jupiter with the 29VHB carb behaved the exact same way when I got it. It would start easily but once I began messing with the idle or whatever and it died, it would not start again until I left it for awhile. Very frustrating to try to work on.

I never did get the carb dialed in before I tore the bike apart. I will be curious on your final solution for the hot starting issue.

Thanks for all the ideas, I am away from home and won't be able to try any of the mentioned remedies until at least the weekend. The artic conditions are slowing down my impulse to wrench as well. As soon as I dig in, I win post the magic fix. Thanks again, Alex