The International CBX Owners Association

Hi everyone - finally got my dream bike after many years...79 X. Running great but crazy hard to start after sitting. I've read all the posts and yes the chokes are fully closing. I'm wondering if the bowls are evaporating dry and the needles stick in their seats blocking off the flow of fuel.?? Any cures or suggestions. It's tuned up- timing,valves etc. and the carbs are clean and woking fine ( a little lean on the top end), but really fine running otherwise. Again.... glad to be here !!

There seems to be a lot of recent western Canada owners.
Welcome to the site, Hondell.
A lot of good info in this thread about hard starting. viewtopic.php?f=6&t=3804&p=23763&hilit= ... ing#p23763

Welcome to the site Hondell, since you own a 79 you don't have the vacuum fuel shutoff to contend with so my suggestion to you is to turn the fuel tap to the on position, wait 30 seconds for the bowls to fill and twist your throttle five or six times, this will allow the fuel pump to prime your cylinders and hopefully ease your hard starting.

If your cylinders aren't getting fuel by doing this it's a good bet your fuel pump diaphragm is torn, has a pin hole in it or the nozzles that feed each cylinder are plugged and you'll need to pull your carbs and do some cleaning. After you clean the carbs you can bench test the fuel pump before reinstalling.

There are many good threads here on the forum detailing the cleaning process.

Good luck,
jb

Jeff Bennetts wrote:Welcome to the site Hondell, since you own a 79 you don't have the vacuum fuel shutoff to contend with Good luck,
jb

Jeff: That is not necessarily a given. Quite a few 79s were retrofitted with the vac valve. Maybe he should check.

EMS wrote:

Jeff Bennetts wrote:Welcome to the site Hondell, since you own a 79 you don't have the vacuum fuel shutoff to contend with Good luck,
jb

Jeff: That is not necessarily a given. Quite a few 79s were retrofitted with the vac valve. Maybe he should check.

Mike makes a good point, if your's has been retrofitted there are threads here that explain how to defeat the vacuum diaphragm without removing the system and also threads on how to boost the diaphragm manually before cranking the motor or remove it altogether, either way don't throw it away if you remove it.

Thanks for the responses !

No, the petcock is stock and the acc. pump diaphram is ok. I'm pulling off the carbs soon to fatten up the mains so I'll check the diaphram again. Suggestions for a liquid other than gas to bench check the acc. pump action ??

By the way, really nice folks on this forum. I own other bikes and this forum is easily the most friendly !!!!!

If you are running the stock airbox, the mains are way rich enough. It's the low speed and mid-range you need to richen. On the '79 carbs you can go up to a #68 or #70 on the primary main (smaller one) and shim the needle .020 inch. That will be all you need. You can use brake cleaner to check the accelerator pump, but gas is way cheaper.

Dave

Hondell, Mike and I are referring to to vacuum shutoff mechanism that sets atop the carb rack, if you don't have it which no 79's did unless they were retrofitted with one.

The only way to check if the fuel pump is working is to make sure fuel exits all six of the brass posts in the throat of the carbs that have a very tiny orifice.

Here is a little tip, when starting the bike cold and using the choke, hold pressure on the choke lever while starting the bike, if you just pull the lever back and take your hand off it the choke will open a bit and not be 100 percent closed.

My GPZ has a vacuum shutoff integral with the petcock and I assumed the later CBX had the same type, but no, there isn't one on this. It has K&N pods on it and I have the screws out 2 1/2 turns and the needles shimmed .040 . I'm trying to decide on 120's or 125's on the mains. I'll check the acc. pump for sure and thanks for the choke holding tip. I wasn't doing that.

Hondell750 wrote:My GPZ has a vacuum shutoff integral with the petcock and I assumed the later CBX had the same type, but no, there isn't one on this. It has K&N pods on it and I have the screws out 2 1/2 turns and the needles shimmed .040 . I'm trying to decide on 120's or 125's on the mains. I'll check the acc. pump for sure and thanks for the choke holding tip. I wasn't doing that.

The vacuum valve on the CBX is different to the systems other Japanese OEMs used. The CBX unit is a separate valve that sits on top of the carbs. It does not affect the petcock at all. Fuel flow is cut off right there and not at the petcock on the tank.

I've had my 79 for a little over a year now. When I first got it, it was very hard to start when it was cold but otherwise it ran OK. Being a newbie, I had no reference to judge how well it ran but it seemed OK. It ran on all 6 cylinders, didn't skip and had good power. After removing the carbs I discovered that the accelerator pump was completely non functional. The diaphram was so hard and inflexable that it just wouldn't pump fuel. I bought Mike Nixon's "how to" book and purchased the Randak carb kit and went to work over the winter. After a thorough carb cleaning and rebuild (and getting all 6 accelerator pump nozzles squirting fuel) the cold start problem was gone and I couldn't believe the throttle response and how much better the engine runs!

My money is on your accelerator pump as the root of your starting problem.

Well after another carb removal , the starting problem is SOLVED!!!! I took the carb bank off and discovered zero accelerator pump. The diaphram was flexible but not great - plus the spring seemed really weak and flabby. I shimmed the spring and installed a new diaphram. This morning after letting the carbs fill and twisting the throttle about 4 times THE ENGINE STARTED AFTER ABOUT 2 REVOLUTIONS. Thanks 6 pipes- my engine had the same conditions as yours- ran fine-- I thought. Throttle response is now off he chart. I have 6 bikes - this is now my favorite. Thanks to all who posted suggestions you made my year.

Wow, what fun. Thanks for closing the loop Hondell! Now go ride!

N.

Glad to hear it all worked out!