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Can't rev above 5k rpm and go faster than 65
- Thread starter Glowyeast
- Start date
5twins attributes the problem to pleats, I think the problem is that the still air volume in the filters is too small, but we're in complete agreement that those tapered oval filters don't get the job done.
There's a right way and many wrong ways to deal with a freshly acquired old bike. The right way is to inspect everything and fix what's been neglected. One of the most frustrating and potentially dangerous wrong ways is to wait for trouble to show itself and play whack-a-mole with symptoms. The Tech button at the top of the page and this site's search function are fine resources. There are a couple of sites that will give you a free download of the factory service manual. Here's one: https://www.biker.net. (Once again, thank you, Jean Akers!)
There's a right way and many wrong ways to deal with a freshly acquired old bike. The right way is to inspect everything and fix what's been neglected. One of the most frustrating and potentially dangerous wrong ways is to wait for trouble to show itself and play whack-a-mole with symptoms. The Tech button at the top of the page and this site's search function are fine resources. There are a couple of sites that will give you a free download of the factory service manual. Here's one: https://www.biker.net. (Once again, thank you, Jean Akers!)
While I still believe the pods might be the problem, what about the clutch? You say it won't go past 65 but when you attempt to go past 65 does the tach show an increase in RPM? Can you hear the engine racing up? If yes to either the clutch is slipping.
Pull the pods and do the slide test for leaky diaphragms. If that appears OK take it for a ride and see if the problem persists. At that point, and this is speculation, could there be a problem with the electronic ignition that kicks in at the higher revs?
Since you're running pretty much straight through exhaust, there's a possibility you've got some exhaust reversion goin' on there. Was a member here from Norway or Denmark (I think) had the same problem... with the same symptoms..... wouldn't rev much above 65.
Maybe someone here recalls who that was?
Maybe someone here recalls who that was?
Glowyeast
XS650 Member
How would I go about doing a slide test?
Click the TECH button at the top of the page. Scroll down to "Carburetors." First article has the Carb Guide. It's the bible for Bs34's and 38's.
Glowyeast
XS650 Member
Did a slide test and the diaphragms are all good, I’ll take my bike for a spin without the filters tomorrow and we’ll see what happens
Glowyeast
XS650 Member
Update: took the filters off and went for a ride, only gained 1k rpms and 5 mph
I wonder if the BS carbs really like some kind of velocity stack ( or the OEM air filter connectors ....
What vacuum diaphragm carbs really like is a still air box.
Well it did make a difference so maybe you’re going in the right direction. I have a problem with a set of carbs that I haven’t resolved yet((changed carbs problem went away) and it frustrated the hell out of me. At least I had the luxury of an extra set to try however now I have to really resolve it as I have a bike sitting with no carbs lol.
Oh so many of us have learned this the hard way yet no one ever listens.
As they say in these parts, "Them as won't hear it gonna feel it." Style on, gents.
Glowyeast
XS650 Member
So basically what I’m getting from this thread is that I need to put the stock filters back on?
The vacuum carbs seem to work fine with the foam sock filters.
Yes, if you want pods, get the straight foam UNIs. For your BS4s, that would be the UP4229 or UP4229ST (dual layer). I have the dual layer ones on my '83 but only because I got them cheap from a local guy who bought them for his bobber but they wouldn't fit. The standard single layer ones are fine and what I normally use .....
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