Topic: CB650 MASSIVE backfire

[4cylfun]

Its been a while since i've posted.

I honed the cylinders, put new rings in, set the timing per manual, adjusted cam chain and adjusted tappets to correct specs.....

Its an '82 CB650SC

Here's what happened today. I got it to start by filling up the carbs with the choke on.  I don't have the air box on as its a PITA like we all know i'm sure and i'm fitting uni pods to it.

Well it ran after some attempting to starts and then finally ran.  If you take the choke off it won't even start.  With the choke full on, it will run.  So sounds like carbs right.

OK well they have new jets and all that stuff but after the bike gave off a backfire loud enough to sting my ears i gave up.  I noticed fuel running out of the number 1 carb.  I check the exhaust and its cold.  Pull the plug and its black and oily.  I put ATF in the cylinders before i started it.

Well anyway i clean the plug, put it back in the engine and pull number 3 and 4 since they were hot.  Plug was a brownish color.  Maybe a little rich but then the bike was only running for 2 minutes before it couldn't handle the stress anymore. 

I start it again and while i'm starting it, it has yet another massive backfire.  So what do you guys make of this.  I know bikes with CV carbs won't run correct with the airbox or some sort of velocity stack but it should still idle without it.  And yes i've checked for spark.  Before i pulled the bike apart it would start up and run but smoked and didn't have a lot of power.  At that time i didn't have the air box on either and it would idle with no probs.

[Markcb750]

I would double check the timing, but could be just too much gas going through into the pipes, needs time to dry out and then restart.

[cb650]

Timing with the "CDI" shouldnt be a problem unless you took the plate off and put it back not in the middle of the adjustment.
Check the firing order. 

[dansvs]

Timing should be set at 1-4 f for fire not t for tdc.
Check for clogged pilot jets, this can cause backfiring. You can get them out without removing the carbs. I did even with fat hands. Once you get the bowl screws off, use whatever slotted bit you  have to fit up in the pilot jet to get it out.  Make sure you don't strip the screws. Patience is a virtue.
If they are clogged, you should think about replacing parts in your carbs. I got my kits on flea bay for  $55.00 for all four kits. Runs great.
Mine did the same backfiring on start up before I pulled, cleaned and changed parts in the carbs. New pilot jets, main jets, needle jets, jet needles, sinced the carbs while running, side gapped the plugs, set the timing with a light,and gapped the pulse generators. Don't know which made the most difference but  I don't care. I am happy as a clam.
Dan

[BLUE71TURBO]

 Definitely the carbs, most definitely.   

[dansvs]

These are the kits I got. Don't know where the .78mm came from but the rest is correct.

http://cgi.ebay.com/ebaymotors/4-Honda-CB650-1981-1982-carb-repair-rebuild-kit-Kits_W0QQitemZ330376562038QQcmdZViewItemQQptZMotorcycles_Parts_Accessories?hash=item4cebfa4576