The ongoing sage of working on my old Zed !
More Carburettor Work
After fixing the electrics, I started the bike up again. The first thing that happened was that petrol flooded out of the float bowl overflow on cylinder #1. It turned out to be a simple fix, just a case of taking the float bowl off, and cleaning up some crud that had got onto the float hinge pin.
But even after doing that, the bike didn't want to run smoothly; I just couldn't get it to tick over. It was time to take the carburettors of again... I wasn't looking forward to a fourth rebuild !
I've labelled a few of the key bits on these photos, just in case it helps anyone !
For anyone who is interested in the technical details, the carbs are Mikuni VM24SS carburettors, the version with the air screw near the air intake, not the version with the pilot crew under the front of the float bowl. They are the UK version - you can tell, because the US version has different shaped float bowls with an accelerator pump fitted to the bottom of #2 (which I think is far less aesthetically appealing !)
Finding the Real Culprit - Inlet Manifold Rubbers
Luckily, before I did any real work on the carbs, I looked at the bike again, and realised that the inlet rubbers were in absolutely horrible condition. At least one had split quite badly.
I was able to get some new ones quite quickly. They are pattern rather than OEM, but I prefer that with a lot of rubber parts, because it can be hard to tell if original parts have been sitting on a shelf since 1980. While I was at it, I bought some new clamps to replace the jubilee clips I had fitted some time back in the 1990's.
You can see the difference in this photo - the old rubber is on the left, and if you look carefully you can see a split that was letting air in where it shouldn't.
Fitting the new rubbers up was easy, and I added a light coat of Hylomar sealant to help ensure there was no possibility of air leaking between the rubbers and the engine.
This photo shows the new rubbers fitted. The clamps have been slipped onto the rubbers and the screws done up just enough to stop them falling off. If you look carefully, you can see the two inner clamps are not straight - that's deliberate, so that I have the right angle to get a screwdriver in to do them up once the carbs are on.
I also took the opportunity to try to clean the rear fins on the engine block to get rid of years of oxidation on the alloy. So far, a really wet toothbrush and kitchen towel to catch the run-off (to stop it just settling somewhere else) seems to be the best way. At this stage, I don't want to dismantle the engine for vapour blasting or anything, so I am limited to purely manual solutions. If anyone knows a way that is less hard work and gives longer-lasting results, please do tell me !
Putting the carbs back on is always hard work, and even more so with nice sticky new rubber bits ! I find a very small amount of washing up liquid wiped lightly onto the inside of each inlet rubber really helps. Even with this, it needs the strength of Hercules to wrestle them into place at the same time as having extra hands to simultaneously try to fit the throttle cables back into their guides.
Here are the carbs back on the bike, together with the air filter pods fitted.
You can see a minor modification I made years ago which has been incredibly useful, where I replaced the oil filler cap with an oil temperature gauge. The instrumentation on these old bikes is incredibly basic compared to modern machines !
Coming Next...
In the next instalment, it's time to start working on the front end of the bike.
In order to set the carburettors up, I need to get the bike up to normal operating temperature. But these Z650's are cold-blooded machines and need a 10-15 minute run to get them up to temperature. Before I can do that, I need to sort out a badly leaking fork oil seal, and I'll be re-greasing the front wheel bearings while I'm at it.