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Help - What Carb Should I Get?


shercoben12
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hi, we have a 1975 ossa 250 MAR . its nice and clean but we cant get it running. this is because the original amal carb is shot. needs a whole new carb. the current one is all scored and the float bowel does not join properly and you can see light between the gap. would like to get an after market one on it. just something that will make her run nicely. the ossa we have is where the carb bolts onto the cylinder and not into a rubber boot which some do.( apparantly this is rare?) it also has no choke and just a primer which pi****s fuel everywhere. please can someone point me in the right direction for a new one and where i can get it?

many thanks!

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the cota 200 was sorted ages ago and sold of for good money to a collector , its now in safe hands haha ;) . the ossa is locked away in storage at the moment. almost certain the carb is a 627 therefore must be this? http://amalcarb.co.uk/carburettor-for-a-ossa-trials-8139.html

??

:)

Edited by shercoben12
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Original carb was a 627 Amal, yes 6 for 600 series and 27 for 27mm. They run just fine with these if the carb is in good order, plus you have the benefit of knowing the correct jetting etc as it was an original spec carb.

Yes you can fit Mikuni or Delorto or whatever but if you don't know what jetting etc to use you're in a sea of **** trying to figure it out, plus you'll need an adaptor to take the push on type carb if you can't get a correct fit bolt on Mikuni, the adaptor is £30 - £40. You don't want to be cutting existin inlet manifolds off, there's no need when the adaptor is available. Mikunis are a real pain to jet properly as the combination and sheer number of needle jet / needle combinations is bewildering.

Didn't know that Burlen now do the 627 carb but I think their jetting spec may be out as I'm sure the main is about 150, but been a long time since I ran an Amal, so memory not so good. Pilot was normally 25, not 30.

Good luck buying anything from Burlen as from my experience they rarely have a carb built up and you have to wait weeks for them to do it. Surrey Cycles are usually a better bet for Amal stuff.

Amal also do the premier carb now with an improved pilot circuit with externally fitted pilot jet although they wouldn't have that as a 27mm, only 26mm but it would work fine.

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The Mk1 250 barrels had a flange to bolt the carb to the barrel.

Mk2 and Mk3's had the stub and a rubber coupler.

That is unless it's been converted, but anything could have been fitted over the years.

It's true carb tuning can be a pain and it's typical that what works on one bike won't work on another!

I've had a couple of differnet Mikunis (with different needles, slides and jets) running on mine pretty well, also I messed with two Dellorto VHST flat sides (24 and 26mm) and got it running well on both.

As a quick guide a Beta Rev3 Mikuni from a 250 isn't a million miles off, and if you search for the setting for the 26mm Dellorto upgrade to the Rev3's Mikuni, that'll pretty much work too.

I'm informed a KT250 carb is pretty much a straight swap too.

I've yet to be tempted to try messing (I like messing) with an OKO which are copies of Keihins, but I read they are very simple to tune and boxes of jets are very cheap.

Oddly I read there are copies of OKO's out there (so copies of copies) and they don't use the standard jets, so be careful of where you buy from.

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