Backfiring into air filter?

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Coach · #1 Unread post by **Coach** » Fri Apr 01, 2005 3:57 pm

My bike is running a little rough at low RPMs and sometimes will backfire/pop into the air filter. It generally only happens at low RPMs when taking off from a stop but it does not happen all the time. It will occassionally pop a little at higher speeds if I have to roll off the throttle quick. I also feel a slight stutter at low RPMs (in any gear). I think the chain needs a slight bit of adjusting so that may be the cause of the stutter, but any ideas on the backfiring? My knee rest on the side of the air filter cover and I can feel when it happens.

TechTMW · #2 Unread post by **TechTMW** » Fri Apr 01, 2005 7:01 pm

Your bike is most likely running a little lean on the idle/slow-speed circuit. The jets might need a cleaning, or you've got a slight air leak somewhere.

Other possibilities ...
- Idle mix screw out of adjustment (Probably not as it's sealed and 'supposed to be' tamper free)
- Carbs slightly out of synch

poppygene · #3 Unread post by **poppygene** » Sat Apr 02, 2005 2:39 am

Hey, Coach, Your bike has the baffles removed, right? Vulcan 800s with the baffles removed from the original exhausts always do this. You have a couple options: Find a set of unmolested, factory exhaust pipes; replace the exhaust system with a high quality aftermarket system (a little tuning may still be needed); if this hasn't been done already, remove the "tamper-proof" plug covering the idle mix screw and richen the mix a little (if you want to try this, let me know - I'll try to walk you through it)

Coach · #4 Unread post by **Coach** » Mon Apr 04, 2005 2:32 am

That is correct. Mine does have the baffles removed. I am looking for a stock exhaust, but lost 2 auctions on Ebay so I don't have them yet. I did remove the plug and richen the mixture some - 2 turns out on the screw. It was set only about 1/4 turn out. It seemed to help some but not entirely maybe I just need to go another turn. Thanks.

poppygene · #5 Unread post by **poppygene** » Mon Apr 04, 2005 4:17 am

2 turns seems like a lot, Coach, but it's hard to say...

How about the airbox? Is it stock and unmodified with the regular filter? Some guys drill holes or cut off part of the airbox thinking they'll get better performance, but what usually happens is just the reverse. Same with the modified exhaust - they get a nice rumble but lose both HP and smooth running in the bargain.

If you're able to find a set of stock pipes (be patient, they're out there) you probably should pull the float bowl and check the size of the main jet just in case it has been changed.

The 800 is my favorite of the middleweight cruisers. Enough power to embarass a lot of cruisers with twice the displacement and, unlike a lot of Kaws, it has a superb transmission. They look great and handle well, too.

Hope you get the bugs worked out soon - summer's almost here!