zep Posted July 9, 2012 Share Posted July 9, 2012 Righto, so I've got a 1256 that I'm rebuilding/doing a bit of head work/cam/not a whole lot. I am interested in putting bike carbs on this thing, however, they have siamesed inlet ports, i.e. 1 port for 2 cylinders, like an upside down Y: ⅄⅄ These engines often use twin SUs, which if I'm right are similar to some bike carbs. So, I should be able to use two bike carbs similar to the size of the SUs (1.5"). I have seen one Mini (1275) with dual bike carbs and it appeared to work well. Question is how do I size these? I think the Mini guy used carbs from some Yamaha 850 V-Twin, and made up a linkage. IS i9t best to use V-Twin carbs, or get a bank of 4 and try cut them down? Thanks guys. Quote Link to comment Share on other sites More sharing options...
KIRK Posted July 9, 2012 Share Posted July 9, 2012 maybe some old bmw carbs edit: like these but bigger ones http://www.trademe.co.nz/motors/motorbi ... 095150.htm Quote Link to comment Share on other sites More sharing options...
Testament Posted July 9, 2012 Share Posted July 9, 2012 four of these? http://www.trademe.co.nz/motors/motorbikes/parts-for-sale/other/auction-492283698.htm Quote Link to comment Share on other sites More sharing options...
zep Posted July 9, 2012 Author Share Posted July 9, 2012 Reckon that would work? 2 carbs per inlet port? Quote Link to comment Share on other sites More sharing options...
KKtrips Posted July 9, 2012 Share Posted July 9, 2012 1256 would be cool with an IDA - just saying IIRC 1256 heads are a downport head? Quote Link to comment Share on other sites More sharing options...
Toucan Posted July 9, 2012 Share Posted July 9, 2012 http://www.classicfordmag.co.uk/2011/07 ... ike-carbs/ Assume you have read that one, ford specific but was pretty good iirc I am just guessing here, but I would imagine either 2 big ones or 4 small ones would work, provided they are sized correctly for the engine? Quote Link to comment Share on other sites More sharing options...
zep Posted July 9, 2012 Author Share Posted July 9, 2012 1256 would be cool with an IDA - just sayingIIRC 1256 heads are a downport head? You are correct. Unfortunately I read that and IDA will hit the bonnet. D - I was thinking two big ones would be the best plan. Will look into the IDA,too, KK. Quote Link to comment Share on other sites More sharing options...
Truenotch Posted July 9, 2012 Share Posted July 9, 2012 Single 40mm sidey in this config? Quote Link to comment Share on other sites More sharing options...
zep Posted July 10, 2012 Author Share Posted July 10, 2012 Also another option. There are actual manifolds for this but very hard to find. However, sideys are relatively expensive (compared to those mini bike carbs for $35 each). Quote Link to comment Share on other sites More sharing options...
zep Posted July 10, 2012 Author Share Posted July 10, 2012 These carbs? BMW R80 - http://www.trademe.co.nz/motors/motorbi ... 271786.htm Quote Link to comment Share on other sites More sharing options...
mikuni Posted July 10, 2012 Share Posted July 10, 2012 I think R80's are flat twins, so probably won't be the best. Getting the size right is one thing, a 1256 won't need too much and the standard carb has a throat about the size of your thumb, so really anything would run it. Ease of rejetting is the question I'd be asking. Just make sure the carbs you chose are easy to change the jets on, either drilling or buying some to the right size - you should be able to get it nearly right by searching the interweb to see what people are using on similar setups, mini's etc. Problem with v or flat twin bike engines is that the carbs are independant so you'll need to muck around making linkages to have them opperate in unison. Ideally you want a single dual throat carb or multiples that run an inline engine. Even if you get 4 of them you could seperate them of cut them down to run a pair. I'd say little 32's off a 600 Honda or something would be plenty for a 1256. Honestly people will tell you that you need a pair of 45's or some crap but I really don't think that's the case. Quote Link to comment Share on other sites More sharing options...
Snoozin Posted July 10, 2012 Share Posted July 10, 2012 What about a single IDF or DRLA? Downdraft 36mm off an Alfa 1500 boxer, or 40mm off a 1700 boxer. The Yamaha carbs you mentioned in the first post cooouuuld be from a TDM or TRX 850, as these were parallel twins. Quote Link to comment Share on other sites More sharing options...
zep Posted July 10, 2012 Author Share Posted July 10, 2012 2x 32mm carbs, I imagine, would be similar to 2x 1.25" SUs. Here is a mini with 2x Fireblade carbs (between 900 and 1000cc engines). http://www.miniaddicts.co.uk/forum/show ... php?t=3216 Richie, not sure a big down draft will fit under the bonnet. Quote Link to comment Share on other sites More sharing options...
mjrstar Posted July 10, 2012 Share Posted July 10, 2012 Buy a set of 4 and I will take the other 2 off your hands / then attempt to fit them to my Mini... Something around 38 - 40mm would suit me I reckon. Quote Link to comment Share on other sites More sharing options...
zep Posted July 10, 2012 Author Share Posted July 10, 2012 I am looking at a few sets but they are smaller, around the 32/34mm mark. 32mm http://www.trademe.co.nz/Browse/Listing ... =492339698 http://www.trademe.co.nz/Browse/Listing ... =491902449 34mm http://www.trademe.co.nz/Browse/Listing ... =492006733 36mm http://www.trademe.co.nz/Browse/Listing ... =492336133 Quote Link to comment Share on other sites More sharing options...
mjrstar Posted July 10, 2012 Share Posted July 10, 2012 Fair enough, my car is running a big cam, high compression and oversized valves, carbs would need to be good for a touch over 100HP... As you were. Quote Link to comment Share on other sites More sharing options...
zep Posted July 10, 2012 Author Share Posted July 10, 2012 Sweet as. I'm just going to clean up the ports/chambers, add in a mild cam and perhaps up the comp a bit. 60hp would be cool Quote Link to comment Share on other sites More sharing options...
hmmmnz Posted July 11, 2012 Share Posted July 11, 2012 a set of gs500 carbs, would work pretty well, mikuni cv carbs, easy to get jets for, may be trx/tdm carbs, im thi8nking they possibly may be a bit large though, ebay uk is the place to get em, and postage shouldn't be too bad, i got a set of cams(2) and carbs(4) out of the uk for 30 quid postage, sound expensive but they were only 40 quid to buy, so saved myself about $400 if i got them out of nz second hand Quote Link to comment Share on other sites More sharing options...
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