Bonneville America Forums Forums Technical Forums General Tech Single 'pop' on start-up

Guys,
The last couple of days I've had a single back-fire...hardly even that...just a 'pop' but loud enough, when I start her up. Anything to be concerned about ? I never re-jetted after removing the snorkel figuring all was OK since it was jetted when the pipes were fitted. It runs great apart from that. Thanks for your help.

If you give throttle when you start you can get the carbs to backfire (which can, and will, crack the airbox).
There is no need to use throttle when starting, if this is the case. Just use the choke.

Thanks man but I don't touch the throttle on start-up (I've read the threads on that !)

Hmmm
Is the pop while cranking or just after the start?
Exhaust or carbs?

Exhaust and it is immediately on start-up...a split second after cranking.

Did you ever try backing out your mixture screws about a 1/4 turn (possibly a 1/2)?
When you remove the snorkel, you should have to back the screw out a bit, but shouldn't have to re-jet.
This would give you a tad more air in the idle circuit. You may just be a hair rich and unburnt fuel is slipping into the header and buring there. The tad of air may help it combust in the cylinder.

I think you're right. I haven't backed out the mixture at all since removing the snorkel. I was thinking that was the likely answer. I'm going to order a set of Brent's screws but until they arrive I guess it'll be OK ??? So....which way is out ? Towards the front is richer or leaner ?

Looking up at the bottom of the carbs. Counterclockwise is out . You shouldn't have to turn much, try just 1/4 turn at a time.
You don't need new screws, just a D tool to turn the screws.

Got it. Thanks again man.

Also, it's always good to synch the carbs after you do any adjustments. F.Y.I. The carbs come from the dealer out of synch. Ask me how I know this.

Also not a bad idea to check the couplers from head to carb. They seem to work themselves loose a bit and can cause a backfire on ignition if not tight.

Yep and the stock clamps can be completly tightend and still not be tight enough.

...and they can be sinked with just the carb screws (and a carb tuner of course) ???

Thanks 77t140v.

couplers = Rubber between carbs and engine. If your clamps are all the way "closed" tightened, you may want to pick up some Stainless Steel Hose Clamps.

Cool - thanks again guys. Appreciate your help.

Nice catch Bill!