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I would like to disagree with many on this site who chant the mantra "do carbs and valves, do carbs and valves" when it comes to fixing up our bikes. Not to say these things aren't important, they're very near the top of the list. But I think the first thing on the list should be to seal up the entire air intake system. Our bikes are built like tanks and can take a lot of abuse, but the carbs are like fussy two-year olds. Carbs want to suck air in just their right way or they have a complete temper tantrum. If there are airleaks in the intake system, the carbs can be perfectly clean and the valves perfectly adjusted, but the engine will still not run well. Symptoms include running on less than four cylinders, bogging/misfiring when throttling up, and the engine dieing at idle (ask me how I know).
For engines with standard airboxes (if you have pods, this isn't for you) there are five steps to make sure your intake system is airtight:
1) Replace sidecover seals - most airboxes have sidecovers that are sealed with foam where they join with the box. Find some adhesive backed, rubber-based dense foam weatherstripping at the hardware store. On my bike, 3/8" thick X 3/4" wide foam worked well. Avoid lightweight plastic-based foam, because gas and oil can turn it to goo.
2) Replace air filter seal - using the same rubber-based foam, probably 1/4" thick, replace the seal that goes on top of the air filter where it jams up against airbox intake. The filter wedges up against the intake with some pressure, so smear some black synthetic brake caliper grease on the top side - then it slides easily and doesn't pull at the foam's adhesive backing.
3) Replace airbox joint seal - most airboxes are in fact built like a clamshell, and where two halves join together there is a (guess what!) foam seal. 1/8" thick as I recall.
4) Clean air filter - whether it's a foam filter or pleated K&N, dirty air filters have a big effect on how the carbs suck air. When you oil the filter after it's clean, be very careful not to spray too much oil. Think about how chicks in the movies spray perfume up in the air, and then walk through the mist - spray that much oil on the filter. If you over-oil, you'll have the same symptoms as mentioned earlier.
5) Replace carb intake o-rings - these become hard over time and leak air. Get some high quality ones from Robert Barr at cycleorings.com or OEM's from the dealer. Yes it's kind of a pain to remove the carbs and carb tubes, but it has to be done. While you're at it, replace the crummy carb tube attachment screws with stainless hex bolts - Robert Barr has those too at a very good price.
All of these steps are inexpensive, none of them are very time consuming, and you get a huge bang for your buck. The go on to adjust the valves and clean the carbs.
For engines with standard airboxes (if you have pods, this isn't for you) there are five steps to make sure your intake system is airtight:
1) Replace sidecover seals - most airboxes have sidecovers that are sealed with foam where they join with the box. Find some adhesive backed, rubber-based dense foam weatherstripping at the hardware store. On my bike, 3/8" thick X 3/4" wide foam worked well. Avoid lightweight plastic-based foam, because gas and oil can turn it to goo.
2) Replace air filter seal - using the same rubber-based foam, probably 1/4" thick, replace the seal that goes on top of the air filter where it jams up against airbox intake. The filter wedges up against the intake with some pressure, so smear some black synthetic brake caliper grease on the top side - then it slides easily and doesn't pull at the foam's adhesive backing.
3) Replace airbox joint seal - most airboxes are in fact built like a clamshell, and where two halves join together there is a (guess what!) foam seal. 1/8" thick as I recall.
4) Clean air filter - whether it's a foam filter or pleated K&N, dirty air filters have a big effect on how the carbs suck air. When you oil the filter after it's clean, be very careful not to spray too much oil. Think about how chicks in the movies spray perfume up in the air, and then walk through the mist - spray that much oil on the filter. If you over-oil, you'll have the same symptoms as mentioned earlier.
5) Replace carb intake o-rings - these become hard over time and leak air. Get some high quality ones from Robert Barr at cycleorings.com or OEM's from the dealer. Yes it's kind of a pain to remove the carbs and carb tubes, but it has to be done. While you're at it, replace the crummy carb tube attachment screws with stainless hex bolts - Robert Barr has those too at a very good price.
All of these steps are inexpensive, none of them are very time consuming, and you get a huge bang for your buck. The go on to adjust the valves and clean the carbs.
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