Jetting for 720 big bore kit on Z650

[RALPHARAMA]

CB has insisted that I get he baby zed going

I fitted an 720 big bore kit on it. Does anyone have any recommendations for jetting using standard carbs, air box and Harris with road baffle?

Cheers

[z650freak]

Nothing wrong with a z650 (or z810 )

Beyond me but I'm sure I've seen on ebay.com an outfit that you tell them what modifications you are running and they put together a set specific to your bike.....

[Taffus]

contact crofty

[RALPHARAMA]

After a quick FB PM it looks as though it was probably a 720 cc kit. Guy Zed fitted 900 carbs to his, but I'm loath to do that as it will mean changing the stubs and junking the air box.

[z650freak]

After a quick FB PM it looks as though it was probably a 720 cc kit. Guy Zed fitted 900 carbs to his, but I'm loath to do that as it will mean changing the stubs and junking the air box.

Standard z/gpz 750 then? Think they are a straight fit? Been going for around £50 ish a set recently on ebay....

[Crofty]

Never done a 720 and my 810 runs bigger carbs.
Sure I read somewhere that the jetting can stay the same if everything else is the same as before. All that is happening is more air is pulled in, so the corresponding amount of fuel is too. If other things change such as exhaust of air filtration then jetting is required.

I will put a post on the KZ650 info site to see what people have done on there.
Crofty

http://forums.kz650.info/index.php?topic=13625.new#new

[z650freak]

Was the 720 conversion a US rc engineering kit? Did it come with the hi lift cams and different valves and springs?

Advertised back in the day as a kit (poor mans ) to allow the z650 to keep up with bigger bikes...performance exhaust was part of the kit in addition to the above....

[RALPHARAMA]

I'm now getting confused as to what I do have. It's so long ago that I bought the Pistons I can't remember what they were. I thought they were 810, but when I Facebook messaged GuyZed he said his was 720 and suggested I would have had to have used different barrels if it were 810.

I'm guessing that if bigger carbs are used then the original air box is a non starter and a change of intake stubs will be necessary. Though I have a feeling that one or more of the Z650s ran CV carbs?

I'd better try the uphill task of trying to find the paperwork for the pistons


Thanks for the help ladz

[z650freak]

Later model z650s had cv carbs. Lots of interchangeable bits with gpz750 and early z750s that also run cv carbs....will check carb sizes when get a chance...think it's a straight swap...if so standard 750 set up should be ok for your 720 conversion.... Update not quite see below

[z650freak]

All z750(e and l models) should be keihin cv34 or gpz750 is mikuni bs34

Z650cvs were 32's so you would need to change manifold rubbers and air box...should not need rejetting if use 34's

Have all the jet sizes for these if that helps?

[Crofty]

Ralph, you just need to measure piston diameter, if its a700 kit they will be approx 64mm, they did do an earlier 720 kit but slimmed it down due to liners being too thin after boring. They would be just bigger than 64mm.

If the piston is 69mm then its an 810.

There is a set of genuine 1st oversize pistons and rings on ebay at the moment for approx £200 if you wanted to stay standard, that is a good price.

If the bike was running ok before and your just reboring due to oil usage, the consensus is you should be ok with the carbs as they were before, unless it was badly set up. I would do the rebore and then do a plug chop to see if you are close.

[RALPHARAMA]

I built the engine up ages ago, but it ran like a bag o shite, so I assumed carbs were grubby as it hadn't been used for ages. I've just noticed that the vacuum takeoffs on one of the inlet stubs is loose And will have been sucking air. I renewed all of them with pattern stubs, but three are hard and only one is nice! It is clearly a different make. Wemoto do a set of pattern stubs. Can't decide whether to buy another set. Genuine ones are eye wateringly expensive and will have to be ordered..

[RALPHARAMA]

Decided to 'repair' the dodgy stub tonight. Fitted the carbs and Attached a remote tank. Immediately pissed fuel everywhere from the 'tee' piece that feed the carbs with fuel. I turns done tap off and pressed the button - it immediately ran beautifully . Have to take the bloody carbs off again and suss out the leak, but it's a hu ge relief to hear it run soooo sweetly

[Crofty]

Good stuff Ralph, Do a plug chop fairly soon once the carbs are sorted to make sure not too lean or rich.
PTFE tape works great on the t pieces and joiner stubs.
Crofty