Starting and fettling!
Ihad been looking forward to fitting the rechromed header pipes to my red Z1 Super Six so I was really excited when the postman called with a large package from ACF Howell.
I opened the package to reveal the four header pipes and they looked just perfect, but as I was due to be with Henry Cole filming a new series of the ITV4 Motorbike Show I would have to wait a few more days before I could fit them. The weather was looking good for the weekend so hopefully I could get out for a test ride after fitting the pipes.
I rushed home that evening and couldn’t wait to get started, so went outside to see how the pipes looked on the bike. I had a number stamped on each pipe so I could return them to their original position on the engine because they are all slightly different and on the standard system they are welded on to the silencers at the factory.
The four pipes fitted perfectly and matched the finish of the two new central pipes. I was eager to see if the engine would run but thought it would be best to wait until the weekend. I pushed the bike into the garden, turned on the ignition and kicked over the engine on the kick-starter, and it fired up on the third kick. I was really pleased it started, sounded great and revved freely. The idle was a bit high though so I slowed it down slightly by turning the idle adjusting screw. The idle settled down but was a bit off-beat and I could feel it wasn’t quite right. Also, when I ran my fingers lightly over the header pipes, one was slightly cooler than the other five. I stopped the engine and got ready for a test ride, thinking maybe it would clear when warmed up.
Out on the road the engine pulled well but was slightly slow on the return to idle and the off-beat sound was still there. I had built this bike in slow time during lockdown and I began to wonder if I had set the carbs up right. I continued to ride for around 10 miles then returned home to check over the engine for possible faults.
The engine seemed to be fine with good compression and no apparent oil leaks. I checked the spark plugs and found that two were sooty, three were straw brown and one was white, so I had a problem. I had a similar problem on my first six so decided to remove the carbs and give them a thorough check over and reset all the settings.
The bank of six carbs are easy to remove. First I removed the tank and disconnected the throttle cables, loosened the six clamps on the inlet stubs and six air-filter clamps. The carbs could then be pulled back off the stubs and then pulled out to the right of the bike. When I made the bank of carbs I used parts from several bikes and wondered if I had inadvertently made up a missmatched set. I did some research online and discovered that there were several revisions carried out on the Z1 carbs from 1972 to 1976.
On close inspection two of the carb bodies were slightly different internally, with two having provision for the pilot jet either side of the main jet. I doubted this would affect the operation of the carb, but I changed them with a pair of matching carb bodies just in case. Two needles were slightly corroded and had surface pitting, and one of the air-bleed holes at the rear of the carb was obstructed.
I had a rummage in my box of carb parts and found several 5J9 needles that were in nice condition so I replaced the pitted ones. While the carbs were off the bike I decided I would strip them entirely and check everything. I double-checked all airways were clear and all parts were correct for a Z1B, and matched across the six carbs. With everything cleaned and
checked I started to reassemble the parts in sequence one carb at a time.
I rechecked the float heights and adjusted where needed until all were set to 24mm from the base of the carb body gasket surface to the bottom of the float. At this stage I always check the operation of the petrol shut-off valves by attaching a piece of petrol pipe, blowing into the pipe and listening for a hiss of air. I then invert the carburettors and the hiss should stop and it shouldn’t be possible to blow through the pipe.
With the carbs reassembled I set the throttle stop screw so that the distance between the throttle stop lever and carb bracket was 10mm, then I synchronised the throttle slides using a small drill as a gap gauge. I placed the shank of the drill under the throttle slide on the inlet side of the carb and adjusted the slides individually until the drill just slid in on all six carbs. I still have my special carb adjusting tool that I made in 1985 to adjust the throttle bodies on my GPZ1100B2 and it works on a lot of 1980s fours that have 8mm locknuts, including the Z1. The tool allows the central adjusting screw to be turned, lifting or lowering the throttle slide. Then the central screw can be held still while the locknut is tightened.
With the slides set I decided to check their operation under a vacuum to check the linkage was working oay. When the engine is running the throttle slide is sucked against the front of the carb which can increase friction and the effort required to lift the slide. This is easy to check using my old Dyson vacuum
cleaner with a hose. The hose fitted nicely over the inlet stub on the carburettor, creating a vacuum within the carburettor. I checked one by one, opening and closing the throttles by rotating the central cable pulley. All seemed okay until carb four where I noticed that the slide didn’t move initially, and when it moved it didn’t return instantly when I released the central wheel. It turned out that there was a weak spring in one of the linkage plungers for that carburettor.
I replaced the spring, reset the slide and checked again under vacuum and it was then working properly. Refitting the carbs can be difficult so I smeared some silicon grease on the inlet stubs and intake rubbers to help the carbs slide across and snap into place. I then connected up the throttle cables and filled the carburettors with petrol.
The engine started straight away and returned to a smooth idle after minor adjustments to the idle screw and sounded much better. I replaced the tanks and took it out for a test ride. It was so much smoother to ride and the engine pulled strongly without hesitation.
I will be riding the bike longer distances over the coming weeks to further test the engine: result!