Bonneville America Forums Forums Technical Forums General Tech Air box destroyed.

Really pissed off. Last night I left work, started bike up (2007 Speedmaster) and it backfired blowing the top of the airbox to pieces!! It did this about six months ago with the same results. After last time I replaced the airbox (because I ride all year in EVERYTHING) and had the carbs professionally cleaned and rebuilt with the jets slightly altered. Done about 5,000 miles since then at least, with no problems at all. I now turn off the fuel tap after every ride and try to start bike with no movement in the throttle, but tonight I twisted it open causing these results! As this could happen again, unless someone can see something I'm missing??? I'm thinking KN filters, and keep covers handy for the bad weather, I didn't want to go this route due to riding in rain storms when I have to, but don't see any other way. Any advice would be greatly received. Cheers, Ben.

Can you tell us why you twisted the throttle ? Just a mental error ?

Hi Mike, The bike starts up fine with no choke in this weather, maybe just a little lethargic for like the first second but then gets into a gentle plodding tickover, but on the odd occasion it struggles to start, taking a couple of presses of the button. I try to stop myself twisting the throttle (even a little) but yes a mental error lol, my old America used to thrive on a gentle twist as you fired her up. I find it hard not to on this bike!

Hi BB I hadthe same problem with my 2007 speedmaster...heavy backfiring evey now and then the dealer said it was a 'characteristic' of a carb model and same as all my complaints from purchase fobbed me off. Backfired one morning and blew the air box to bits.The cure was a pair of DNA pods and a Firestarter from Mike at TTP and no more probs plus more get up and go and fun riding so screw the air box and go for the other option. Regards Horse.

Proper tuning is the key.I still have the CDI,plugs, wires and all my bike came with from the factory. I tuned my carbs correctly and it starts every time no backfires. I have it jetted correctly and the mixture screws adjusted correctly. I run pods and I ride in all weather and long distances when I can.

Cheers guys, air box will be going in the bin!

Hi, just thought I would log on and give a looooong overdue update:

Speedmaster was all sorted, after the backfire took out the airbox, I replaced it with a new airbox, drilled the top section and added a breather pipe to allow an escape route for air if it happens again. BUT, I didn't stop here, took off carbs as suspected they were badly tuned and unfortunately they were, sorted them and now over a year of happy riding later still no problems!

As a side note, airbox on a carb model CAN be replaced with a FI model, just needs a blanking cap moving which is simple.

Good for you Tell us more about this blanking cap.