Bike bogs down under two known conditions?

Question

1990 yamaha virago xv750 starts bogging down and sometimes backfiring when:

1: i am in 5th gear and disengage the clutch and coast to a lower speed (like from 65mph to 55mph) and re-engage the clutch

and

2: i am in fifth gear and start going up a slightly inclined hill.

symptoms are almost identical with above conditions.

the bike will sometimes do this (running off one cylinder) every once in a while at other speeds and conditions. also, when i crank the bike while choked, while warming up the bike, i get pops (some kinda loud, some soft). if i hold my gloved hand next to the front cylinder's tail pipe, i can feel the popping pressure. i am guessing the front cylinder is also where the bogging is coming from when i am having the first 2 symptoms as well. does this sound like a spark or a carburetor problem? could the fact that i set the idle a little higher cause this?

Answer 1

carb(s) need adjustment.... i belive i'ts running too rich

and yes, improperly adjusted carb idle s***w can cause this.... it's actually how i set my dirt bike idle s***w... if it bogs down when i give it gas, or won't idle on it's own (four stroke) i know it's too lean, if i start getting backfires i know it's too rich, speaking of that, it seems mine is far more sensitive then other peoples if it's not at an exact, precise point, it will bog down or back fire...

if that don't work, use the carb needle to make adjustments, if even that doesn't help, it may be time to start looking into some new jetting.

"Backfiring on deceleration is caused by a lean fuel mixture.

Check for intake manifold air leaks.

Richen the idle mixture screws 1/4 turn at a time (no more than 1 turn - jetting is required after that)."

thanks for telling me... i never knew it mattered whether it backfired on accel or decell...

Answer 2

check your intake boots they are made of rubber and may have cracks and be leaking. also might be a bad diaghram on the slide inside the carb. those are c.v. carbs and require vacume to operate. If the diaghram is cracked the carb slide will not operate well or at all.

Answer 3

Backfiring on deceleration is caused by a lean fuel mixture.

Check for intake manifold air leaks.

Richen the idle mixture screws 1/4 turn at a time (no more than 1 turn - jetting is required after that).

http://www.yamaha-motor.com/sport/parts/...

Go to - your bike - Carburetor

The carbs have to be removed from the bike, to remove plugs #28, to adjust the mixture screws # 9