Help XS 250 air filters

Well good luck with using K&N on CV type carbs. Most who have tried have spent untold hours and dollars (pounds) on trying to get the carbs to run right before giving up and selling their bikes. The best help I can give is to make some long intake trumpets with the filters on the ends. This will help (a little) to smooth the airflow into the carb mouth. A possibly cheaper option (as Alan Millyard did on his six cylinder FZR engine) is to buy a couple of cheap Chinese made slide carbs and filters and replace the CV carbs.
What is the intended use of the finished bike. If it is only to ride to a cafe and back then the jetting may be ok. As always with carbs, try it and see.

 

Your issue with pod filters is they have a certain (high) level of restriction that works against you and tuning the engine. As Murdo said, if you insert an inlet tube between the carb and pod filter, then you give the carb a bit of additional space to suck in air. It's almost impossible to jet a CV carb for Pod filters as the engine will work fine at idle or low revs (idle jet circuit), but run rich once the revs rise and the amount of air being sucked in is restricted (main jet circuit). The only real way to jet the carbs for pods is to reduce the size of the main jets to properly meter fuel and air at higher revs. To do this, you will have to go down in jet size and that will give you poor acceleration and reduced power. In short, pods look good, but they're awful from a practicality sense. Bell mouth inlets or velocity stacks are way better and easier to tune, but the lack of a filter means bad things can get sucked into the engine. In closing, pod filters look good from afar, but they're far from good!

 

Look's like it's all still available new
https://www.cmsnl.com/yamaha-sr250-1980-exciter1-usa_model8747/partslist/B-10.html#.XrajSHUzZ9M

Part's and postage are pretty cheap through here
https://www.boats.net/search?q=3Y6+14401+00&ui=typeahead

 

It's an XS twin, not the SR single.

 

Sorry my mistake

There's a few genuine new airbox / filter parts on ebay

The airbox/case was also used on the XS400 Part number 3X8-14401-00


https://www.ebay.com.au/itm/Yamaha-...636604?hash=item523487d9bc:g:looAAOSwjoFZrVLP

Filter in UK
https://www.ebay.com.au/itm/NOS-Gen...292162&hash=item340cfeb43e:g:Qg0AAOSwZexdCOrs

https://www.ebay.com.au/sch/i.html?...efLoc=2&_osacat=0&_odkw=3X8-14451-00-00&rt=nc

Nos side cover
https://www.ebay.com.au/itm/Yamaha-...923291?hash=item5da824819b:g:fysAAOSww9Bcpdji


You could try places like boats.net, megazip.net, en.impex-jp.com etc and search using the original part number's

 

I would fit Mikuni VM carbs (real ones not fake Chinese copies). They are cheap, have been around forever and parts are easy to find. Then you can use the pod filters with no problem.

Speak of the devil https://www.mikunioz.com/shop/yamah...-complete-carb-conversion-kit/?v=5b79c40fa7c2

 

Neither to start with. Just run the bike as is and test ride it to gauge performance during acceleration, cruising, high revs etc. Once you have that information, you/we can go from there. Your bike should idle fine even with pod filters. Without an airbox, your carbs will suck in hot air when you're stationary and colder air when moving, which may also have an affect on how the bike runs. The bell mouth or velocity stack (by its design) will condense the air being sucked into the carb, so that may have a slight affect on acceleration/performance. Blair's suggestion to go VM carbs is also an option, but be aware that a restricted air flow is always going to be a restricted air flow. Even if you went to EFI, you're still limiting the amount of air by using a (small) pod filter. The kit Blair has linked looks pretty good as it has a larger pod filter. Even without knowing the exact flow rate of the filter material in those pods, you'd expect them to be a better option than cheap Chinesium rubbish.

 

Try it first and see.

 

Sound's like there's a big vacuum leak/s somewhere ?
Check the intake manifold's for tiny hairline crack's, leaky vacuum hose for petcock etc ?
Otherwise the pilot circuit's in the carby's may be blocked up, float level's too low etc

Here's one side

https://www.ebay.com.au/sch/i.html?...efLoc=2&_osacat=0&_odkw=1M0-13586-00-00&rt=nc

 

Idles OK but the slightest slidetest twist of the throttle and the rev's go though the roof and stay there.

If you put the bike in gear and use the clutch (load) to drag the revs down, do the revs rise again if you pull the clutch in or do they stay low? It could be a balance issue. What main jets were in the carbs?

 

Usually not settling to idle is caused by the idle mixture being too lean. What happens if you engage the choke a little?