Sounds like it's overfueling to me. After you shut it off, the extra fuel puddling in the intake manifold ignites from the heat.

Do you have any mods, particularly on the intake side (i.e. removed air snorkel)?

 

no, she is totally stock, the previous owner had tried to "clean carbs" made a total hash of it, so i'm chasing my tail to find a good setting for her, I was focusing on the rear cylnder because the plug was black so yes it sounds right she is running too rich, but i have tried a few different float levels & this problem persists. so after 3 months or attempts i'm starting to run out of ideas, wanting a fresh view.

 

If the diaphragm in the fuel pump is holed...the carbs can suck in raw gas through the vacuum hoses to it. You can rebuild the carbs a million times, but if the fuel is coming in through a vacuum hose it'll never fix it. Please take the fuel pump apart and verify that all rubber is sound within!

If you just pull off the vacuum hose/s that run the pump...and you find ANY wetness inside...you've found your problem.

 

well i ran out after your idea. she was in bits, so 3 days later in a storm I got her rebuilt. no fuel in the vacuum line, but now all the pops are gone except the one after i switch off & she is idling at just under 3k rpm, im thinking it is coming from the front carb, which is a living ***** to remove due to the idler setup.

 

My previous bike was a Suzuki Savage...and they were notorious for doing the same thing (was called the Savage Pop)...just to be clear...it sounds like you are talking about an 'after fire' and not a 'back fire'....I would lean towards what Snailman said...you could be running too rich somewhere and stuff is firing after the bike is shut off...or when its not being engaged when you are riding...does it do it when you engine brake...what about when you ride? When riding, does it do it when you let go of the throttle quick...or any other scenarios?

 

I think i cracked it! it was doing both back fire between 4-6k rpm , running on choke & an after pop about 2 secs after ignition was switched off. I reduced the float height a little & found(yet again fifth time now) Idle jet blocked. since I now have 2 fuel filters & all new fuel lines I turned my attention to the airbox, as the filter was almost new, low & behold there was sand in the bottom of the air box, the dip**** who had this thing before me had left off the blanking plug off the air box just to the side on the rear carb. so its been sucking all this crud straight into the venturi also the loss in prussure totally making it run leaner, cleaned it &blocked the hole off, no more popping! there is a little gas smell still so she is running a little rich, but i can live with it, prolly the front carb, but i really am not gonna mess much more, 5 months I've put like 300 miles on her. but while i have you, will a delkavic race can mess with any more & if so will it go leaner or richer? is it worth doing?

 

Slip-on exhaust should require no rejetting. Only worth doing if you want the sound of the exhaust to change or want the rear can to look different.

 

partial on the grunt & the engine just seems so bloody muted & dull with all that restriction in the can. not to mention the weight loss. I have always had race pipes, just thought id check as this SV seems to be a right temperamental pain in the arse. lol

 

The SV's aren't any more tempermental than any emission controlled vehicle that was still working with carburetors back then. It's just that for them to work right...everything must be right! They went to FI for some very good reasons as the carbs were getting to be difficult to get and keep in compliance where the FI is much more accurate and easier to calibrate. Once you get the carbs fixed and working...they'll stay that way.

Agree that the aftermarket can isn't/shouldn't muck around with the A/F much if at all though you'll very likely notice a loss of bottom end grunt with the additional noise generated by the can. That is just the cam timing being optimized for the backpressure conditions within the stock system and will be thrown off a little when you 'pop the cork' so to speak. But it should run just fine for you. Just remember that if you mess around with ANYTHING to do with the airbox that the carbs might stop working as well and need adjusting to the new conditions.

 

Got it & thanks. It's just that I've never had such a hard time with a carbed bike before (all 7 of them) got it about the can, would you recommend a cam timing advance? & thank you to everyone who helped me with this issue. I was ready to cut my losses & scrap her!

Hopefully i can return the favour & help some of you out sometime.:rock:

 

Most people don't find the changes worth messing with, though if you're after every last horse that's hiding inside then you'd want to spend some dyno time tinkering around with the cam timing/s. Right off the bat you'll notice it being slightly less urgent right off of idle with the loud can installed, but it'll be plenty rideable and you then get to enjoy the beautiful music the 90 L-Twin can make.