replacing 274 carbs

[donaldasinduck]

Hi,

I am restoring a MK 5 and am looking to replace the 274 carbs with Amal 600 series 22mm concentrics and wondered if there was anyone out there with experience of doing this who could give me advice on jetting etc.  Or is there an alternative to Amal that you have found works well.

I've given up the unequal struggle to get the originals to work correctly

Thank you

Regards

Don

[Hampshirebiker]

Bear in mind that the 274s have vertical flanges & I don't think that 600s are available spigoted. I could be wrong on this, so have a word with Surrey Cycles 01342 716120. They're very helpful & stock flanged spigots. Another member was considering Japanese (etc.) carbs as an alternative, but I don't know how he got on. Consider also that if you do get involved with adaptors that the new carbs could sit further back.
I was having similar problems with mine (mainly affecting starting) and thinking of something similar. I have now had the magneto refurbished, but to my shame have still not got round to fitting it.
Dave.

[zorro]

Hi, with regards to the use of modern carbs I have used chinese quad bike carbs off ebay at £17 each.Adapters were made and fitted and didnt lose too much clearance.The carbs didnt need any adjustment and the bike ticked over and ran perfect straight out of the box.I would still be using them but for finding a NOS pair of amals.(they are wrapped up ready to use if ever needed).My friend who made me the adapters stated that if he had known about these carbs he would have fitted them years ago.No petrol soaked boots.He's had his bike from new  1948 I believe.

[tck]

were they like ebay item 321695315612? or can you give more details 22mm quad bike throws up a lot...

[Dougiethenoo]

On the topic of Amal carbs on post-war bikes - has anyone tried using air filters such as these:

http://amalcarb.co.uk/274-275-gauze-intake-assembly.html

My bike appears to be jetted to run quite rich and I am concerned at the mount of dirt that gets sucked into the carbs - which must contribute to the high wear rates in the engine.

[zorro]

Carbs used honda quad trx200 ebay item number 321959479194

[cardan]

Hi Don,

You're restoring the bike - do consider restoring the 274 carbs at the same time. I'm sure there are plenty of bikes out there running nicely on carefully assembled pre-concentric AMALs. Yes I know I'm a bit old fashioned, but I enjoy running my bikes on their original carbies if possible, or at least a contemporary carby if the original is not available.

Cheers

Leon

[eddie]

I couldn't agree more, Leon! There is not a lot wrong with a pair of 274's when set up correctly. Having said that, they do need a bit of adjustment to cater for the dreaded unleaded fuel. One size smaller cutaway, along with an increase of 5 or 10 on the main jet, then drop the needle to the bottom setting seems to work well - with no flat spot just above tickover!

  Regards,
                Eddie.

[Hampshirebiker]

I've ordered a couple. At 33 quid, I couldn't resist it. I'll fit them if I need to. I fully appreciate the originality bit, but as I get older, reliable starting is paramount.

[dragonmk5]

In case anyone is interested, I recently bought a pair of Mikuni carbs from a club member who had successfully used them on his MkV.  I made a pair of inlet stubs to suit, funnelling the bore from 24mm dia to 19mm matching the inlet at the cylinder head. The Mikuni's dont have a mixture screw, the jet size being "fixed".  Neither do they have a "tickler".  Prior to fitting, I checked the carb internals and the float height.  When the bike started, it sounded very strong, and I thought I'd cracked it.  Over the next week, starting proved to be difficult, and I got wary of continually booting the kick start, so taking the easy way out, I removed them and replaced them with the original Amal's. Although they are worn, the bike starts usually on first or second kick, so I'm inclined to leave it at that for the moment.   

[tck]

Perhaps the Mk5 was a successful installation because he did'nt 'funnel down' the inlet. I know on my Vincent Comet where the inlet port was smaller than the Mikuni I got better results leaving a step at the inlet tract junction with the carb, I suppose there was more turbulence
incidently those cheap mikunis mentioned above are 27mm

[dragonmk5]

Yes, I agree, and it would be a few moment work to bore out the taper,  but to be honest, I've had enough faffing about with it for the time being, but it's an option to consider in future.
I've spent a lot of time and money on this beast, engine and gearbox rebuilt from our excellent parts dept, but sadly, the shine has gone off it at the moment. Not sure if it's the bike for me, after all that!

[Churchwarden]

When visiting the Club stand at the recent VMCC Founders Day I came across a newly restored Mark V which had been fitted with Dellorto carburettors.  The owner told me that they fitted the bill perfectly.   The details are:-

R2507 PHBG18AS 4 stroke carburettor.
MCM04 Manifold 23mm fitting.

the cost for a pair including delivery packing and insurance was £224.23.   They are available from Eurocarb Ltd., Unit 2 Horseshoe Park, Pangbourne, Reading RG8 7JW.   Telephone 0118 9842811.  e-mail sales@dellorto.co.uk  website www.dellorto.co.uk

I understand that there is likely to be an article on this in the next Conrod magazine.

Hope this helps?

[hoejmark]

Hi Don
Some years ago I renovated the original AMAL 274 carbs on my MK3Sport, they were badly worn. I made a fixing device for my lathe and  turned out sligthly the hole for the throttle valve in mixing chamber until it was round and smooth, and only down to where the throttle valve stops. I another fixing devise I then turned down the throttle valve for wear until it was round, made a sleeve from bronze or brass, and soldered it to the throttlevalve, and once again turned down the throttle valve until a nice fit into the mixing chamber. Lastly I made the cut-outs on the throttle valve again. The main jet is size 80.
I feel the carbs now must be better than new. The bike runs very well with a nice tick over ond it starts immediately, hot or cold.
Half a year ago, I also renovated my T6 carb in the same way (same fixing devices) od it now starts well, cold or hot, and also runs a nice tick over. I attach some photos of turning the T6 parts.
Regards
Hoejmark