peejay

Bad day in the office.
The short of it is, I got my fresh 12A running today... sort of. It is badly fuel starving, only runs off of the accelerator pump. I am 99% certain that there are no vacuum leaks. The fun is, I had the carb apart and made sure it was spotlessly clean inside, carefully removed all jets and cleaned out, cleaned out all passages, etc.

The PROBLEM is that it's a "stripped" carb. I want to un-do that, but there is only so much one can do in 2021 without spending $bank. I bought another carb for parts but a lot of it was junk and most of the rest was for a different model, but at least I did get a dashpot and A/C idle up motor and a TPS/TPS bracket out of it. (Say, did you know there was a running change between 8mm and 6mm throttle shaft ends? I have 8mm, the parts carb had 6mm...)

The vapor solenoid on the primary side of the carb has been plated off and the parts carb had a completely different species, so it's still plated. I have a '79 manifold so no need for shutter valve paraphernalia. All choke plate control hardware is gone but the choke cable/mechanism is still present, the choke plate just hangs open. I'd like to do something with that but I don't see driving this on cold enough days where choke enrichment is necessary, so I'll let that slide.

BUT. The engine will not stay running unless you keep tapping the throttle for accelerator pump shot, even when warmed up. You can even hold the revs up around 2500 and it will lean out and die. Either I missed a passage that is plugged, or I missed something vital that needs to be done. I know nothing about non-stock Nikkis other than you can get weird problems like this

t_g_farrell

iTrader: (1)

You didn't mix up the base plate or throttle body from one year with a carb from a different year did you? That can mess you up like this. There are 3 pieces to the carb setup, plastic base plate, throttle body and the carb with the floats, jets etc.They should all 3 be from the same model year.

Benjamin4456

The throttle bodies can be swapped around so long as you don't go between SA and FB versions. It's the same situation with the phenolic spacer (base plate). Within those ranges it's a free for all, although some do lack extra functions (like vac advance). Nothing mission critical changes from what I've seen.

Un-stripping a Nikki is probably more of a headache than it's worth, although that would depend on if you still have the computer for the smog system and all the wiring. If you do have it, yeah, it may make sense, although I (probably) still wouldn't.

I'd first check that you have all the jets in the right places. Foxed.ca has carb manuals with labeled locations/sizes for all jets. Once that's all well and good, double-triple check for uncapped vacuum nipples. Also make sure that the secondary's aren't stuck open a hair - depending on the year they do have a set screw and end-stop.

After that, set the idle speed screw. Oh wait, what year carb is this? SA carbs have three idle adjustments whereas FB's have two. Assuming it's an FB carb, set the idle speed screw such that it holds the primaries open just a hair. Set the mixture screw at 3.5 full turns from seated. That should give an adequate baseline. My stripped Nikki will not idle on it's own until it's warm, although it will continue to run if kept above 1.5-2k rpm.

I'd also suggest trying some smaller primary no.2 air bleeds. 120 is a good starting place if the choke is no longer operational. That should make cold starts a little easier, although you may need to play with the idle mixture some more as doing the 120's will richen it slightly. The easiest source of 120's is to grab an extra set of secondary no.2 air bleeds (nickel plated 60's), then drill to 120 (1.20mm) and install them into the primary position.

peejay

The physical, actual carb is original to the car. One of the previous owners removed a bunch of stuff from it. The only added stuff are the aforementioned TPS, dashpot, and A/C idle-up unit. Which annoy me because the carb and what was left of everything on it still has nice bright plating, but the parts I bought for it are rusty/de-plated. Will keep an eye out for better units.

I know someone's been in the carb before, but yes all of the jets and such are in the right place.

I bought the car as a non runner, so I don't know if it stopped running and THEN they messed with the carb, or they messed with the carb and then it stopped running.

peejay

New plugs of the correct species made no difference. Oh well, I needed them anyway.

Unplugged the fuel pump fuse, ran the engine as long as I could on the fuel in the carb, popped the top off and then popped the main body of the carb off. No compressed air in the Batcave, so I used brake cleaner to verify that various passages were not plugged. Nothing was plugged, no gaskets torn. Spraying into the idle air bleeds would shoot brake cleaner out of the main jets, proof that the idle circuit is able to pass fuel from the main circuit. Put it back together, and yes, still no run unless you feed it fuel with the accelerator pump.



I'm starting to think I merely have a vacuum leak. I SHOULDN'T, but I'm running out of things to try. Next step is to remove the air control valve and replace it with a blockoff plate. I thought I'd plugged all passages to the ACV with JB Weld, but anything's possible, and it's foolish to assume.