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84 yam xj650 alternative carburetors?

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Stalk
Brolly Dolly



Joined: 26 Dec 2005
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PostPosted: 15:47 - 20 May 2017    Post subject: 84 yam xj650 alternative carburetors? Reply with quote

Hi All!
We have this Yamaha xj650 with Hitachi 32 mm carbs that we can't get right. They have been cleaned, rebuilt with new jets and float needles, balanced with the YICS blanked off, and they just seem to work when they feel like it. Remade gaskets to the cyl head, set the floats, done it all, suspect the throttle spindle seals may be leaking. The reason that I say carbs rather than electrical is that when easy start is sprayed into the carb of the cylinder that is missing, it picks up, so I am getting to the bin the carbs and get some others stage. Problem is that they are now all so old that I may just be buying the same problem.

I need a set of carbs, side-draft, from a similar size 4 cylinder bike. We can make brackets if the carb spacing is not exactly correct, and if the jetting is slightly out, we can play with that later. We just want it to run consistently on all 4 cylinders.

Has anyone got any suggestions as to what bike I should be looking at for carbs?

Cheers All!

Should also have said, diagrams and inlet rubbers ok
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stevo as b4
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Joined: 17 Jul 2003
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PostPosted: 19:46 - 20 May 2017    Post subject: Reply with quote

Don't Yamaha Fazer 600's use 33mm carbs? Those should be close enough size wise if they are physically small enough to fit the space available and you can get all the fiddly details right like carb spacing, inlet rubbers to fit properly, and get the cable routing and fuel lines in the right places etc etc.
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Robby
Dirty Old Man



Joined: 16 May 2002
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PostPosted: 19:56 - 20 May 2017    Post subject: Reply with quote

I had one of those, and had exactly the same problem, until it got nicked.

I did a fair bit of research into it, and was bidding on a set of carbs when it was stolen. I'm trying to remember what they were now.

Certainly not anything vaguely modern. I think they were from an 80s CB750. Didn't look a perfect fit, but good enough to make them work - possibly with a cut and shut job on the inlet rubbers.

Hazy memories, but I think the problem with a lot of modern carb blocks was the size and the spacing - the XJ650 runs a wide centre cam chain, so there is a bit of space in the middle of the carb block.

So have a look for some 80s CB750 carbs and see if they are likely to fit. I was also suspecting throttle shaft seals. The idle was going up as the bike got hotter.
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stevo as b4
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PostPosted: 09:59 - 21 May 2017    Post subject: Reply with quote

I can understand that other air cooled 80's bikes with probably physically smaller and simpler banks of carbs are more likely to be a near straight fit or close enough to make work.

My thinking was that most 80's bikes you could pull a set of carbs off could be totally worn and not worth bothering with, especially if the OP was going to have to do alot of work to make them fit, and that's before the re-jetting and hours of testing and adjustment required.

My thinking was you want as newish and low mileage set of carbs as possible, and ones from a bike where you can get all the little spares and individual parts for quite easily by walking up the the dealers parts counter.

I think the Fazer has a central cam chain, but I guess it depends on if the carbs are physically small enough and spaced close enough together. If they are too close together then spacing them out is possible, but if they are too widely spaced you can't make them narrower especially if the carb bodies are almost touching each other due to their size.

Don't some of the 400cc Grey bikes use sidedraught 32mm carbs though? Maybe an XJR/ZRX 400 if you could find a set of cheap carbs?
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temeluchus
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Joined: 01 Oct 2008
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PostPosted: 18:56 - 23 May 2017    Post subject: Reply with quote

measure the spacing between the stubs so we can see what might fit.

If the fit is close, late Bandit 600/650 carbs would do the trick.
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redeem ouzzer
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Joined: 06 Oct 2015
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PostPosted: 19:27 - 23 May 2017    Post subject: Reply with quote

Flat slides. Job jobbed. Usually at least a 20% power increase as well. CV carbs are very restrictive as well as prone to wear.
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temeluchus
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Joined: 01 Oct 2008
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PostPosted: 19:45 - 23 May 2017    Post subject: Reply with quote

Allens performance list a kit, CRS-31-212, for the XJ650. Brand new Keihin CR specials.
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 11:13 - 24 May 2017    Post subject: Reply with quote

Hiya

As above, a set of custom flat slides (ie, spacing and everything taken account of) won't be cheap but might be the easiest solution.

All the best

Katy
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