Nikki Masters Please Help: Drilling out the AP Nozzles?
 

This is kind of a specialized question, but I haven't been able to get ahold of Carl or Sterling since the forum has been down. I am very close to finishing the rebuild on the Nikki, but this question is holding me up. For those of you that are familiar with the mechanical secondaries mod from Sterling, this relates to modifying the nozzles on the accelerator pump outlet. (Parts #68, #69 on the diagram).

Sterling told me to hog out the accelerator pump outlet banjo bolt to a larger size. Apparently this used to be what controlled the flow of fuel coming out of the AP. However, when you increase the pump shot then you need to enlarge the orifices to accomodate it. Then he said to drill the holes in the casting (#69) to 0.050". Sterling told me that these two holes would serve the purpose of metering the fuel. So here are my questions:

1) Which holes do I drill out on the banjo bolt. There are two holes on the sides, and then one at the end running axially through the bolt. Do I hog out all three to permit better flow through the fitting? Does anyone have a size recommendation?

2) When drilling out the nozzles on the casting (#69) I don't have a 0.050" drill bit. All I have is a 1/16" bit which is going to be 0.0625". Is this going to give me TOO MUCH of a pump shot? I don't want to go overkill here, but there is no point in all of my previous modifications to the AP if the pump shot is going to be bottlenecked right at the end. Advice would be appreciated here...

Rosie thanks you in advance!
Jamie

I had a '79-'80 and '81-'85 lying around so I could see the difference. One had a small jet pressed into the bottom. Otherwise both were the same. All you should do is find a small drill bit (can't recall the size) and drill out the jet. Don't touch the tiny holes in the side.

It's actually easy to drill the tiny jet out. I found a drill bit of perfect size just digging through my various bits, so you probably have the right size too. You just drill until it's gone. That's what I did anyway. I kept stopping to check my progress and the jet eventually disappeared. I blasted it with compressed air to be safe and installed it. It worked exactly like any '79-'80 banjo bolt. I was proud of myself.

I can't tell you how to drill the tiny holes in the side of the banjo bolt or the AP squirter nozzle thing.

Maybe I'm not supposed to?? Hopefully Sterling will answer me soon so I know for sure. He's a pretty busy guy though.

So did the 79-80 have the jet in the banjo bolt, or was it the 81-85 that had the jet? My carb is for an 83 GS. I haven't studied the bolt carefully enough to remember if there is even a jet in the bottom of the banjo bolt...

Oh, ok. Only the '79-'80 didn't have the jet. All later carbs did as a fuel saving method. Remember the '81 and later had a cat and Nikki took made their carbs leaner for the new catalytic equipt cars. All the thermal reactor carbs were jetted rich, had richer idle circuits, and the accel pump shot was larger (including Hitachi carbs for 13Bs).

Jeff, I drilled out the jet in the bottom of the banjo bolt like you recommended. It was actually pretty easy. I think that I drilled it to 5/64 and it came right outta there. This only leaves me with two uncertainties before I reassemble the carb...

1) Are you supposed to modify the top two holes in the AP banjo bolt? There is one one each side near the head of the bolt, and they are about the size of a pin. Do they get opened up at all to allow more flow?

2) Sterling mentioned to me that the AP casting needs to be drilled to 0.050". I see two small holes on the AP casting that look like they dump into the venturis. Does anyone know about doing anything to this casting? I'm contemplating drilling it to 0.0625, but didn't know if that would be too much fuel...

Sterling/Rx-7 Carl, please advise if you see this... :D

Thanks,
Jamie

1) I don't think so.

2) I never drilled any of that other stuff.

Right on. I guess that I'll go with what I've got for now then. If Sterling or Carl shows up and tells me otherwise then I can dive back into the carb really quick and make the needed changes. Shouldn't take much longer than 10-15 minutes to fix those parts if I need to...

Did you ever modify the top two holes in the AP banjo bolt?
Also what size bit did you use to enlarging the AP casting?

The AP banjo bolt gets all holes drilled out to 5/64". The top two holes, and also the axial hole. All 5/64". The nozzles in the AP casting that shoot into the venturis do get enlarged. I would recommend 0.050". If you can find a #55 drill bit that is just about perfect. You will probably need to buy one of those "micro" drill bit sets. They come in packs of 5, usually with a micro drill bit holder. I have used all of these sizes before on a carb that I rebuilt and it ran great. It was a tad on the thirsty side, but I probably could have adusted the jetting a little bit for better economy. It will run great with these mods though. It definitely adds some life into the Nikki carb.

Awesome! I actually have all that stuff already.
Sounds easy enough.

what jet where jeff and glazed talking about drilling out until it was gone up at the top?