89 johnson backfiring flames but wont start

[89johnson]

got a johnson gt 150 that is severly out of timing after a timer base install. I would start it and use a timing light except i cannot get it to start. it is firing to spec on all cylinders and has good compression. according to the manual the backfiring and no start may be a worn fuel pump diaphram. however i cannot find a diaphram replacement so if anyone has insight on either of these issues a response would be greatly appreciated.
-after doing some research i believe it is firing at bottom dead center or bottom top dead center causing the backfire
model number tj150slcem

 

[racerone]

What I would look for.-----Pull flywheel.-----The key is sheared.----Did you tork the nut ?-----And the timing is way out but a timing light fools the novice .----Timing will show right on the money with a sheared key.