Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES
The idle on that engine is unusual, as the carb butterflys are completely closed. The engine only draws fuel through the special idle passages in the upper carb body. When you go into forward, likely the carb butterflies will usually open slightly (with the throttle advance) and the carbs will start to draw fuel through the mids. That is probably why the lean sneezing stops-it is getting enough fuel. You can have pristine carbs and still have dried fuel in the idle passages in the upper carb body....causing a lean sneeze at idle only. The only want to verify is to compare the spray volumes of an aerosol carb cleaner with a passage on one carb, with the same passage on the other, etc.
No one could have known but what a pain in the butt as everything I do has to be ordered. Nothing is open opn the weekends either. The old jets were 1/4x20 thread pitch and the new ones needed for the aluminum assemblies were 8/32. What a thorn in my side. Well I finally got the carbs back together with the new parts and have not had a chance to test as of yet. I did notice the idle jets in the upper carb body are not adjustable. I removed all of them and it looked like one may have been partially blocked with some contaminants of some kind. I blew them out with air on a clean white absorbant towel and the one looked like a couple of pieces of fine matter may have been lodged. I am going to try it out and I hope this may finally solve my issue. 
