steve Posted January 15, 2014 Report Share Posted January 15, 2014 Hello all, I recently bought a 250 Armstrong and I'm looking at replacing the carburettor. I know I could buy a new Amal MK2 for a standard replacement but was thinking of upgrading to something newer. I tried the Dellorto from my Gas Gas for size but the choke mechanism fouls the frame plus mounting is different diameter. I also tried a Dellorto from a Beta Zero and whilst the fitting is ok the carb is set up for RH so no good. I am therefore thinking of an OKO, (can't afford a Keihn) I saw a picture of an OKO on Woody's Armstrong plus another member was thinking of trying one on his 250cc (Bossitt??) What size would suit the 250 best? 28mm or 26mm. Any feedback on how well they work compared to the Amal and how good the fit is, any mods necessary? Also can anyone recommend a reliable Ebay supplier for these? Are there any others that might be better suited. John at Armstrong-Trials (very helpful) is satisfied with the Amal when new or in good condition but I just can't help but wonder if 30+ years of carburettor development can provide something better!! Many thanks. Quote Link to comment Share on other sites More sharing options...
andy m Posted January 15, 2014 Report Share Posted January 15, 2014 Amals can be a lottery, even the good ones don't last long. I used an OKO on a Fantic, it was excellent probably the best bet, if Woodys using one he knows his onions, I am sure he will help with info you need. Quote Link to comment Share on other sites More sharing options...
woody Posted January 16, 2014 Report Share Posted January 16, 2014 (edited) I've just bought an OKO off ebay for a Bultaco from a seller called extremeimport who is in Peterborough. Should have it by Tuesday next week, postage was free, cost was £59. The OKO I fitted on my 320 performed pretty well out of the box, as they seem to on all bikes I've tried them on. In general, only slight changes to pilot or main jet have been needed and maybe moving the needle. I've never fitted a different needle or needle jet. I've got one on my 310 Ossa and 340 Sherpa and both run very well (26mm and 28mm respectively) I no longer have the jet sizes I used on the Armstrong unfortunately, I can only guess at 118 main (normally they come with 112 as standard) and something like a 40 pilot. The jets are quite cheap for a box of 12, so worth buying a range of pilot and mains. I'm not convinced that there is any worthwhile performance difference between the various carbs. I think when people fit an OKO and feel a difference, it's more likely that they feel the difference between a new carb and an old worn out original and the same difference would be apparent with a correctly jetted, new Dellorto, Mikuni or Amal. My other 340 Sherpa has a Dellorto fitted and it runs every bit as well as the OKO bike. When I had Armstrongs new, they ran absolutely fine on the Amals which were obviously new as well. I can honestly say that there was no noticeable difference between how the 320 I recently rebuilt with the OKO ran and how I remember my old 320 with the Amal. I thought about buying another Amal as there would be no problem jetting it. The only thing that stopped me putting a new Amal on the rebuild was the price of £140 plus which is a lot more than an OKO and a fair bit more than a Dellorto - and the fact that I had an OKO already. Taking the above into account, if you're prepared to play with the jetting, the cost of the OKO makes it the more favourable option for a new carb. Edit: - forgot to mention that Bostit has an OKO on his 320 with a standard airbox. I can't help with knowledge of the fit of the OKO with standard airbox as I had the alloy one made to use a different filter and hose. Edited January 16, 2014 by woody 1 Quote Link to comment Share on other sites More sharing options...
steve Posted January 16, 2014 Author Report Share Posted January 16, 2014 Thanks for the quick replies guys. Woody, I found that seller on Ebay - extremeimports2 - They are listing a 26mm OKO but it has something called a powerjet which i'm not familiar with. In the listing they mention blocking the pipe for jetting purposes so I presume you could leave it blocked permanently if you didn't want or need it?. Are the carbs identical in other respects? Did you buy a powerjet variant? I don't have a filter or connection for my airbox yet anyway so am waiting to get a carb before sorting that out. 1 Quote Link to comment Share on other sites More sharing options...
woody Posted January 16, 2014 Report Share Posted January 16, 2014 Yes, forgot to mention it's a powerjet but I've no idea what it's supposed to mean or how it works. I just ordered it and I'll play it by ear when I fit it. Not sure if the jetting will be different. The spare jet they mention they'll supply seems bigger than the usual 112 that other OKOs I've had come with. The OKO carbs I have, some have an inlet banjo (ie: fitting to take a pipe the same size diameter as the overflow pipes or the powerjet pipe) in the top of the inlet stub of the carb. No idea what this is supposed to do or be connected to, I blank it off. If you don't it will just suck air in. Others I've had don't have this. They all seem to work the same..? The Armstrong airfilter and hose is one assembly but you can't get them anymore. Because I fitted a non-standard airbox I didn't bother to find out what they use instead now - or more likely I've forgotten.... Bostit will know but not sure how often he's on here. I'll send him a text and ask him to reply. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.