1984 GPz750 Running Issue

650 air box will probably work, we used a 83 GPz750 air box on my nephew's 650.

Well, the struggle continues, cleaned the carbs again and installed. Idles on choke and now allows me to drop into the second choke position for a while before dying, it even idles for about five seconds before dying with the choke pushed all the way in.

I am at a loss and want to ride as the weeks pass this is growing extremely frustrating. Do I have to have an air-filter to idle, it seems that the idle circuits would run fine enough with out a box? If anyone can offer any more insights, as it is driving me insane, it would thoroughly be appreciated.

im sure you will need a filter of some sort to get it to run good, and jetted for which type of filter and exhaust your running

rogerdotcom wrote: Well, the struggle continues, cleaned the carbs again and installed. Idles on choke and now allows me to drop into the second choke position for a while before dying, it even idles for about five seconds before dying with the choke pushed all the way in.
I am at a loss and want to ride as the weeks pass this is growing extremely frustrating. Do I have to have an air-filter to idle, it seems that the idle circuits would run fine enough with out a box? If anyone can offer any more insights, as it is driving me insane, it would thoroughly be appreciated.

Thinking pilot circuit issue.








Would check fitment of the plugs and o'rings at bottoms of pilot jets.


Good Fortune!

Ive run stock pilots & mains with an RC 4-1 pipe, screws out 3 turns since my 82 GPZ750 was new. Thanks for these carb cut aways you post Patton, big help !

So as I was cleaning the carburetors, this spring and ball bearing fell out of one of them. I have looked at the schematic and tried to figure out where they go, does anyone know?

Possibly from fuel pump mechanism, if so fitted. :S

Or maybe a pilot screw spring and a passage plug. :blink:

Good Fortune!

Well the saga continues. I completely cleaned and rebuilt the carbs. They look nice. I got the rebuild parts from Z1 and to say say it was cheap, well let's just say it it wasn't. I got them back together and started her up...... Pulled the choke...... She was super smooth better than before and then I pushed the choke in and it died. Just like before. I was flabbergasted at this point. Your help, two shops help, my old auto shop teachers help and my work with no response from the bike.

Since I was going to LA this weekend I thought I would bring them by Garage Company. If you haven't been, they are located in Inglewood and to say it is like a museum to classic and vintage motorcycles. They have always been really nice. Tommy and owner Yoshi took a look at them for an hour and a half and couldn't find anything wrong with them. Yoshi said that at this point he would just get new carbs and test them on the bike. What do you guys think?

www.garagecompany.com/
I attached the bike Kiyo built for Born Free and if you haven't seen their 71' CB custom you should.

Am thinking mal-functioning carb pilot circuits as shown in the posted diagrams.

The small passage between main and pilot might be clogged and thereby preventing sufficient fuel mixture to the pilot outlets.

The pilot plugs are also required.
www.kzrider.com/forum/3-carburetor/510980-pilot-jet-plug

EDIT: Diagram notes that later style BS34 eliminated the small passage between main and pilot.

Good Fortune!

If not already done, would assure float bowl fuel levels are correct by measuring with the clear tube method.

Too low fuel levels could cause the reported problem.

Good Fortune!

Hello and Happy belated Easter! The majority of guys are suggesting the pilot circuit on your carbs, and I completely agree.

Ensure that the AIR side of the pilot circuit is clean, etc etc.......BUT......lets say you are running POD filters as I did before my top-up rebuild.

Are they K&N's?

If not, you have the non-K&N pods as I had, and they not only restrict AIRFLOW, but they altogether alter the function of the airbleeds/ports on the front of the carbs, thus the inability to idle unless you are dumping raw fuel into the cylinders, which will show on your spark plugs.

Can you post a pic of your plugs? Also, what are your mixture screws set on? Stock setting WILL NOT work on non-K&N pod filters unless you play with jetting/needle settings.

Pods are awesome for smoothbores or equivalent, but for all-around functionality you really should use factory jetting with factory airbox on BS34's (CV Carbs).

Good luck, will be looking for your reply!

Well, I know everyone is pointing to the pilots, and I even thought that so that is why I had Garage Company check. They are clean, to my and their best assumptions. At this point I think it must be missing something. I have included photos of them. I think they are the late model BS34's as they don't have the passage between the pilot and the main. Anything missing from your looks?

I checked the floats twice but I am willing to do it again, and I may, because I feel a little crazy at this point. Honestly, this has been one of the most frustrating mechanical issues I have dealt with. Yoshi and Tommy made me feel a little better when they couldn't figure it out.

As expected the plugs are filthy from the rich choke setting.

I could not get the stock box so I have tried idling it sans pods and with brand new Uni pods.

I have an old Vance and Hines 4 into 1.

The air bleed has been set closed to 2.5 turns with no luck.

The jetting and needles have been set to Z1's specifications of +1 on the pilots and +3 sizes on the mains, with the needle set on the lowest clip.

Thanks again, I appreciate it.