Topic: Backfiring / Timing / Carb issue CB750 - Help!

[jodangler]

if you are sync'ng your carb with gauges you might want to calibrate your gauges to make sure they are all measuring the same. another thing that comes to mind that you could check would be the float plungers with the little filter/screens, maybe the little screens are blocked or the plunger are stuck or wrong size and check to c if  u have a clean fuel tank it could be dirty/rusted/kremed-lined.  its all a guess.

if your rubber boots are new maybe you dont have them clamped down if not you should really inspect them for fine hair cracks and if they are old maybe you need to re-soften to get a better seal...

[g8ts]

Update? 6 pages of replies, I need an update of how this progressed?
Thanks

[jodangler]

I was tuning my carbs yesterday to give my bike a tuneup and noticed that my gas wasn't flowing properly down to my carbs and thought this could be something for you to look at so what I have read in other post is that if your carb vent tubes are clogged you can get a vapor lock symptom which would give you the problems you r experiencing. I don't remember if it was covered already but you could also do  a clear tube check to c where your gas sits inside your carbs to make sure you have enough gas to run your bike. I attached some pics for ref... You might also want to check this website for more info it helped me out and it might help you to... http://www.hondachopper.com/garage/carb_info/carb_info.html

[PeWe]

I had a long lasting problem due to one bad ignition wire. Sometimes it acted as too rich, sometimes as too lean. I tested a lot of carb jetting until the intermittent wire problem became less intermittent and I could not miss it.
The ign wire was new and I could not dream about a faulty wire. 
Thats why I earlier recommended to swap the entire ignition set, only as a fault tracing routine.

[flybox1]

I don't remember if it was covered already but you could also do  a clear tube check to c where your gas sits inside your carbs to make sure you have enough gas to run your bike. I attached some pics for ref..http://www.hondachopper.com/garage/carb_info/carb_info.html

Waaaay to low in your bowl there jodangler 

[flybox1]

When i vacuum synced my carbs again this weekend i was also working with the air screws.  It seems that when closed them (rich) they didnt stutter or really respond at all.  When i started to turn them out past 2 turns the idle actually sped up.  Pilot jet #40 Keihein - clean.  Does this help indicate a lean circuit?

These air screws need to be set and then left alone.
They are set based on Air/fuel ratio....or plug color, if you dont have access to an O2 sensor.
get them dialed in, and then leave them alone.  the only thing to adjust in a vacuum sync are the slide adjusters and their lock nuts.

Please state again what the main symptom or issue you continue to have....
Thanks....

[gypsywind]

make sure the advanse weights are not sticking or wore out its happened to me before

[BestBoy]

So... after 6 pages... no solution after 3 years?