Backfire caused by?.....

[rocko]

So last night on my way home my bike started backfiring. It has always popped on occasion which I heard is okay but these were definite backfires complete with flames. I cranked up the settings on the JD jetting unit but that didn't seem to help.

I read some other backfiring threads that said to change the fuel filter and to make sure the air box/intake didn't come loose.

I realized I may have brain farted last time I refueled and put 87 octane in it. Could this cause backfiring? Should I add octane booster or siphon out the tank?

 

[MotAd]

i notice my 610 backfires more when using lower octane fuel so always stick to 97 now. mine also does it if the air filter needs cleaning or even if it's got damp. are you on a 610? those holes in the airbox let a lot of water in when you wash it if you don't cover them! also if you've been riding in lots of rain but san diego location suggests you don't have that problem!

start with the air filter. check if it's damp, over oiled or covered in engine oil. if it's ok then maybe octane booster or drain the tank. never used octane booster so i'd just drain the tank to a quarter full then fill with highest RON you can find.

 

[Motosportz]

Also check for exhaust leeks.

 

[rocko]

Thanks for the help, guys. I am on a 630. I'll check the filter. Unfortunately, 91 is the highest octane I can get And you're right about San Diego. I haven't ridden everyday, but my bike has never seen a drop of rain.

Does your bike pop on decel when using high octane fuel?

How would I check for exhaust leaks?

 

[MotAd]

maybe occasionally but not so much. i have a power commander on mine and a custom map though. it did it really bad once, to the point it was even cutting out but it was because i'd over oiled the air filter. a clean and less oil sorted it out. it still pops every now and again though. another way of checking if it's the air filter is by taking it out, replacing the cover and seeing if it runs ok. a few miles won't hurt as long as it's not dusty etc.

91 octane will be ok, i suppose that's what everyone else is using. i don't think the 630 has the holes in the airbox like the 610 so def sounds like it's not damp. worth checking it though.

exhaust leaks - start bike up and hold your hand close but not touching (you'll burn it otherwise!) along the length of the pipes. check the joins and at the headers too. you feel the breeze if it's leaking. also a cold morning will show it with steam escaping from any leaks.

if this has only just happened with you putting the lower octane fuel in there it's probably that. if you have the facility, a video of the bike popping would be useful but to be completely honest, i wouldn't have thought it's much to worry about. check filter, swap the fuel out then see what it's doing.

 

[1lunger]

+1 on exhaust leaks. I bet you will find one by the can or header.

 

[rocko]

If I find a leak, how do I fix it? If it's at the header I imagine I would take it off or retighten...or is there some kind of sealant?

Thanks again, guys.

 

[BiG DoM]

Agreed - zorst leak and dirty airfilter often main culprits for popping. If you find a leak loosten and unslip the joint, cleanany residue soot off and apply thin layer of heat resistant silicone gasket cement and rejoin ... tighten clamp to a moderate stage ... leave overnight ... next day tighten fully. If only a spring slip joint as before just use silicone a bit more generously (wipe off excess before it dries).

 

[maxyb]

To find the leak a bit easier, push/hold a rag at the end of the exhaust (only do it when the bike's cold, otherwise you will burn your hand!)

at work, to seal any exhaust leaks we use mani seal - it's like a builders bog that sets really hard, especially made for the job. failing that you find that, a high temp silicone/exhaust sealer would be the way to go.

 

[BiG DoM]

Exhaust cements will seal well but personally I do not like the fact that it sets so rock hard = difficult when you want to get the zorst off and difficult to get off the joint when refitting.

 

[rocko]

Good info, guys.

So this weekend added some octane boost to the fuel tank and I cleaned the air filter. It only seemed dirty near the intake holes so I don't know how clogged it was but cleaned it anyways. I have only had street bikes in the past and this was my first time cleaning and oiling a foam filter so hopefully I put the right amount of oil****************************************

Starting the bike was a little difficult. It would just crank. Then I tried pulling that starting lever near the clutch lever. Sounded closer but still didn't start. It made some ugly clunky sounds but when I twisted the throttle a bit it finally started. I warmed it up and put the JD settings back to where I had them before. The bike idled smoothly and did not backfire when I blipped the throttle like it did last time I rode it.

Will road test tomorrow when the streets are dry...Thanks guys!