I bought a  1975 DT250 B in boxes last month and have now assembled it and it runs fine although i am waiting on a few electrical bits as it came with new a rexs speed shop 12 volt conversion and electronic ignition kit which i need to finish the electrics.  The bike also came with a new Circle F exhaust system which i have never heard off, a bigger carburettor and a set of  boyson reeds. 

i have built the bike bog standard apart from the ignition kit as easy to set up but has anyone ever fitted one of these exhausts to their bike and what would the carb starting point be. The pipe basically looks like an expansion chamber for a race bike with a dinky wee silencer so looks like it may be a tad antisocial can anyone advise what improvements is this likely to make to performance, if any, on a standard motor. Regards Larry 

 

Greetings from Tennessee  

I have aftermarket expansion chambers on several my enduros. Various manufacturers. Hooker, Bassani, J-R, Torque Engineering, Whispering Smith. They all make a noticeable improvement in performance, based on my seat of the pants dyno. And they all make a considerable amount of noise. It's the noise that I like. The crackle and pop pop brings a smile to my face. It's a sound I've loved since I was a kid. So if you don't like your Circle F pipe, please know that I will buy it off you for a fair price. I've paid as low as $150 and as high as $600. And I don't have a Circle F pipe yet. But I do have a nice 250B. 

Hi Larry , 
 my DT360 has a Circle F pipe on it, basically stock engine .
  It was a rescue bike stock pipe was missing…
  Circle F is not very loud to my ears but have changed the silencer to fit inside the rear shock mount so may have changed the note. Also got a bunch of steel hemispheres & weld them on end with an angled hole like enduros have
 It isn’t a high revving motor but never expected it to be….
  Ordered it new $225 about four years ago then paid almost that much to have it powdercoated locally the quality of welds and fitment is top notch 
 

Hi and thanks for the replies i had another look at the pipe yesterday and took some pictures but getting a failed message so will post them when the issue is sorted. 

the guy i bought the bike from purchased it in 2015 as a running bike then completely stripped it bought lots of nice new bits then never got any further. He told me he imported the pipe from the USA  so im presuming this pipe was bought around 2015. It does look very nicely made and is very light, bigger bore etc so think i will finish the electrics then ride around on it for 100 miles or so to sort out any niggles then fit the pipe and carb etc just to see what it goes and sounds like. it helps that i also have a completely stock 250 A that i use on a daily basis so i can mess about with the B just for fun. 

 

If you use Imgur or such like, you can post a link here to the images there.

Circle F is made.in Houston Texas, I have a pipe of his for the Pursang, never seen Yamaha Enduro version, he had stopped making up pipes , not sure Larry is still.with us, I bought one of his last pipes he made , definitely would be worth it to add to the collection, his pipes are tourqy with fat mid to top end 

Hi and thanks for the info on Circle F pipe which does sound like it would be interesting to fit it to see what it’s like. Right now the bike is completely standard.  

I also have a bigger carburettor with a K&N style filter which I am assuming was bought to go with the pipe does anyone have any thoughts on carb set up. 

could I just tune the std carb and use the original airbox or does it really require the bigger carb set up. 

What I remember was when we'd install a Torque Engineering, Bassani, Hooker, etc pipe we never changed the carb...  rejetting may be required though. 

Aftermarket pipes usually gave a great performance boost to an otherwise stock machine. 

If I got the story right Larry was 1/2 partner with jemco, he bought the rights to all the patterns ,.he cut and rolled each cone then brazed them together with no rod, torch only for close to 50.years, he had more.orders than he could handle in the VMX peak days ,.I'm fortunate to own one of his works of art