The Zephyr Zone

Hi guys, first of probably many technical posts.


So I've got this old ZR550 I was given with a fuel problem, it came to me with the carbs off. I was told it was leaking fuel, so I figured needle and seat issue, pulled the float bowl off, checked float heights were all the same, and cleaned the needles and seats, and some residue and junk in the bottom of the floats from previously. I wrestled the carbs back on, added fuel and it sort of ran, I found if I sprayed carb cleaner or similar around the carbs it would run better, replaced clamps and it was better but would not rev, if I sprayed carb cleaner into the left side carb it would pick up and rev up, obviously starving for fuel, so pulled the carbs off again removed and cleaned the jets, put it back together, then found the fuel tap leaking, but ran a little better.

Anyway I've just got a fuel tap repair kit arrive, so I will put that in hopefully in the next couple of days and try again.

Any tips for best results, I think I now have the carbs pretty clean, is it important to have the ducts to the airbox and the filter in to run correctly? Is it worthwhile holding the bike upright rather than just on the stand? Any other tips for maximum chance of getting it started and running reasonably well at least?

install new float valve needles. It won't run 'correctly' if air box is not on. I'd also check valve clearance.

How is the valve clearance set on these things?

And does anyone have an exploded and detailed diagram of where all the drillings and passages are through these CV carbs? I've got them off again to go over and make sure everything is clean since it is obvious the original problem was actually the leaking fuel tap, but the carbs just have some deposits from fuel being left in.

I don't know anything about the 550 carbs but I do know a bit about carbs in general, you have got to clean them properly or you'll be chasing your tail, get them really clean before you put them back on or you'll be taking them off again and again. Have you got access to a decent ultrasonic cleaner and some aluminium safe cleaning fluid? I would personally strip the carbs right down keeping each of the carb parts together. Compressed air and carb cleaner is always good when you are cleaning carbs but keep carb cleaner away from rubber.
The valve clearances on the 750 (so I presume it will be on the 550) is the bucket and shim type. You remove the cylinder head cover then measure the clearance with a feeler gauge, if they are within tolerances then all is good, if they ain't then you use the chart in the manual to work out what size replacement shim you need, order them from a Kawasaki dealer or wherever, then you will have to remove the camshafts, remove the bucket and shims from the top of your valves, replace any shims that are outside tolerance then put the buckets and camshafts back on then replace your cylinder head cover. If you read that really fast it sounds simple, it is really so long as you take your time and don't mix up any shims.

Ryan550 wrote:How is the valve clearance set on these things?

And does anyone have an exploded and detailed diagram of where all the drillings and passages are through these CV carbs? I've got them off again to go over and make sure everything is clean since it is obvious the original problem was actually the leaking fuel tap, but the carbs just have some deposits from fuel being left in.

Unless the carb bodies show signs of heavy corrosion from water sitting in them for extended periods, the most likely place for a blockage is the smallest passage in the carby, the jets. The pilot jet is so small it is near impossible to see through it. Same deal with the main jets. Big enough to see through the main jet, but impossible to tell if the hole size is reduced in diameter due to calcified buildup.

As these bikes were jetted lean to begin with due to emissions controls just starting to come into existence, even the smallest reduction in jet size opening is highly problematic. If there is a dried hard buildup on the jet opening walls compressed air will generally not move it. Same deal for carburetor cleaner and unltasonic cleaners. The only way to ensure the inside of the jets is truly clean is either (a) replace them with genuine original jets (under no circumstances use jets from an aftermarket kit, you'll have no idea what size you're fitting) or (b) mechanically clean the jets. A very light gauge nylon fishing line can be used for the main jets. Put one end of the line in a vice, thread on the jet, pull the line tight and them spin the jet around on the line scraping the internal jet opening. The nylon fishing line will not damage the brass jet.

For the tiny pilot jets you'll probably struggle to find a fishing line gauge thin enough. A single metal 'hair' from a plumbers wire brush should fit trough. Being steel exercise caution not to damage the inside or enlarge the inside of the brass pilot jet.

P.S. Any shims you need for setting the valves can be purchased from this crew. Just tell them the size and type and they'll just post them out. http://www.precisionshims.com.au/

Thanks guys, I've had a bit of experience with car carbs, but not the CV style as used on these bikes. I have cleaned, carefully, the main and pilot jets, which were both blocked on the most problematic carb, I didn't even know there was a pilot jet peened in place the first time around, but I believe the jets are clear, and with compressed air I can get air through what I think is all the galleries, the only one thing I can;t figure out is where the drilling is to get fuel into the pilot jet circuit, I can get from the pilot air bleed to the idle screw and progression holes, but can't seem to find where the fuel comes from, which was actually the one passage that blocked up in my RX-4 when I did that recently.

When I get some pre bent fuel hose I ordered I will put them back on again and see if it works this time.

As for the bucket on shim valve adjustment, I adjust diesel Landcrusier valve clearances all the time at work, so apart from the pulling cams off for access, I know about that.

The parts fiche has a diagram.

https://www.fowlersparts.co.uk/parts/3205198/zr750-c4-1994-luminous-vintage-red-gb/carburetor-parts-1-2

I find Fowlers good for online ordering, if you can't get to your local dealer.

Just realised youve got a 550, but the Parts diagram is on the Website for all 3 Models.

[quote="Ryan550"]Thanks guys, I've had a bit of experience with car carbs, but not the CV style as used on these bikes./quote]

The BIG difference to understand with a CV style carburetor is that it is designed around a tuned airbox. They will not work 100% correctly without one, no matter what anyone will try to tell you. Just one of the functions of the airbox is to control the variable height of fuel in the emulsion tube (the brass tube full of small holes that the main jet screws on the bottom). Even drilling holes in an airbox stuffs up the finely tuned pressure differential internal/external needed to perform this critical task.

That's why the intake system needs to be 100% stock and in good condition. The carburetor is designed to work and matched to a specific airbox. People can change fuel jets till the cows come home and not get a CV to run 100% correctly without the original complete airbox. They've altered 3 things, each critical to the correct functioning of the carburetor, and none of them can be corrected by changing fuel jet sizes.

Just another update, after cleaning out everything I could get to, and fitting some pre shaped fuel lines so they wouldn't kink, and adding a right angle to the vacuum line to the fuel tap, it now runs, of a sort, definitely running on all four because the pipes are all hot, if I tickle it just right I can get it to rev up, but it won;t idle without choke, and it still runs like a dog, uneven, random misfires.

Is this likely to be because of the airbox not being connected? or is there likely to still be a deeper issue? I understand the airbox not being complete will make it not run the best, but not sure how much difference exactly it will make, and my big gorilla hands don't like fitting in between the carbs and the airbox to put the pipes on.

The airbox makes a big difference on these bikes, try to get it put back together correctly.