An odd one this....

[ajacko]

Got a Suzuki GS500 '02 K2.

Replaced the air filter with a Suzuki one (I assume it's a Suzuki filter, I got it from my local Suzuki dealer), old one was past it's best really, looking tatty and was in when I bought the bike a year ago.

Ok, so, now with the new filter in the bike revs to about 8k then stutters and struggles and won't go any higher, it used to.

I tried a few things, cleaning and re-gapping plugs, checking for fuel starvation etc. and nothing cured it, out of desperation I put the old air filter back in and it shot straight round to the red line just like it did when I got it.

Conclusion? New 'Genuine' air filter is restricting flow. Or is it? I wonder if the carbs were set up to run best with the old filter in and now with a new one there's too much air getting through weakening the mixture and causing the revs to top out at 8k with the noticeable drop in power and lumpy running when it gets there. Is this possible?

I'm now running the old filter and thinking about taking the new one back to Suzuki to see what they say. The new filter doesn't say Suzuki on it but neither does the old one.
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Current bike:- Suzuki GS500 '02 plate. Next bike CBR600F or GSX650F. I'll leave the race reps to the kids.
www.xembly.com

[P.addy]

hey mate,
my gs500 was just being a bastard with this..
although i didnt replace air filter, there is a tube from airbox to fuel tank..
mine was clogged with shite.. clean out and it seems to run great, also i gave it the kick of its life up a steep hill near here..and since then..well yesterday morning, its been running as it should do!
i found it went to about 8k, pushed a bit further, changed gear and the "restriction" seemed to come in at 7k revs

[ajacko]

Thanks for the reply, tube from airbox to petrol tank you say? Can't find a tube linking the two, just the two fuel pipes (to the tap) and the water drain pipe that takes any water from around the filler hole and drains it through a pipe running down past the carbs under the fuel tank.

The only tube I can find leading into the airbox is the engine breather (from the top of the cam cover) and that is free flowing.

I'll investigate further next time i've got the tank off, nice to meet another GS owner, there doesn't seem to be many about, dunno why, cracking bike and cheap as you like to buy and run, bulletproof engine and mine will sit at 90 all day.
____________________
Current bike:- Suzuki GS500 '02 plate. Next bike CBR600F or GSX650F. I'll leave the race reps to the kids.
www.xembly.com

[P.addy]

ill get a pic of mine, i was also confused as to why it was there, but first GS so thought i would leave it.
Im cleaning it up tomorrow, so pics will be sorted.. but tbh if it works..i dont touch it

[Marci]

`nother vote for over-oiled new filter... not getting enough air in to run above that point in the rev range. If the two filters look visually identical, try this:

Weigh them both on kitchen scales. If new is heavier than old, that weight difference will likely be the excess oil on there.

Tube from airbox to fuel tank I presume is just a misidentification of the vacuum tube.
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FAB-Racing MiniMotoSidecars - Back with a vengeance - F1 Class 2011...
CBR170 engine, custom chassis - www.minimotoscene.co.uk

[ajacko]

Thanks for replies.

After replacing the old filter and giving it a quick blast (as described in first post) the full rev range is available and it runs smooth all the way up to the red line, so problem is with new filter, old one is fine.

I cleaned the plugs and have been out on 2 runs (approx 300 miles total) (old filter fitted), checked the plugs, nice even dull coffee colour indicating good running, no black carbon indicating rich mix or air starvation. Conclusion - new filter is a bag of poo.

Someone on one of the runs mentioned that it might be a contaminated filter too, next time I have some time i'll run it up to temp and remove the air filter altogether and give it a quick blast with an empty box, if it runs round to the red line like that then it has to be the new filter starving it of air.

If so I think i'll just take the new one back and get a replacement, if that one does it too i'm stuck with cleaning the old one forever as new ones hold it back.
____________________
Current bike:- Suzuki GS500 '02 plate. Next bike CBR600F or GSX650F. I'll leave the race reps to the kids.
www.xembly.com

[Ichy]

Nothing but a thought really but maybe the previous owner had been playing with the mixture or jets with an old filter fitted causing it to run rich with a new one. TBH I would just take the new one back and tell them its causing problems.