Starting

[tazz]

Hi all 81 cbx do you guys have a hard time starting your bike after it sitting for 3,4 day to a week if so did you do something to fix this or is the nature of the BEAST.

[EMS]

From 1980 on, the CBXes have a vacuum valve between the petcock and the carbs. this prevents accidental overfill and overflow of gasoline into the cylinders due to a stuck open float valve.
This causes hard starting after the bike sits for a while and gasoline has evaporated out of the float bowls. They will only refill when the valve is opened by cranking the motor and creating a vacuum to the valve. You can accelerate the bowl filling process by applying pressure to the vent line of the vacuum valve. This line usually ends at the bottom of the bike. Look for the valve on top of the carbs and follow the black tube into the frame to the bottom.
When you blow into this open end, gasoline will flow through the open (!) petcock into the float bowls.

[daves79x]

Try searching 'hard starting'. You'll find about 3 day's worth of reading.

Dave

[robsgreen]

I all,
I also seems to have this problem on my 79 z. Just rebuilt the engine, cleaned the carbs out and set the fast idle as per the manual and mixture screws 2 1/4 out. I've done about 60 miles on it so far and all seems very good with a nice quiet motor and smoke free motor. When I come to start it after a week or so, I put on the choke full, throttle closed, fuel on, and spin the motor over for a few seconds. Its starts but coughs and splutters like its not running on all cylinders, so i knock the choke off a little, open the throttle slightly and it starts catching and then suddenly bursts into life on all cylinders. Once warm, idles and revs smoothly. I though that when you start from cold, it should run on a high idle. As I've got the mixture screws further out than standard, is this affecting the starting from cold? I will check out the pages as per Dave's recommendation.

[Silver]

I have a routine which starts my 79Z first crank every time. Full choke, open and close the throttle quickly about 12 times (so that the accelerator pump loads the intake ports with gas), then hold the throttle a fraction open and hit the starter. It seems that these bikes especially mine need a very rich mixture to start from cold.

[herdygerdy]

My '78 used to be a bear to start (even with no fuel vacuum shut off valve), but after I fitted an ignition coil relay and Procom igniters, it starts almost first press of the key, even when left for weeks at a time. And seems MUCH happier everywhere.

Let me know if you need some help on how to do that.

My two cents worth and YMMV...

Cheers..Tony