nofrills

Hi guys, I've recently bought and installed a 13b into my series 1 rx7, and I've come across an issue with the carb

first of all, the carb is different to the one that came out of the car (12a, nikki), but it doesn't look like its the original carb either, so I'm not too sure what to make of that.

Secondly, when I turn the fuel pump on, the float bowls happily overfill, and when I look down the barrels I can see fuel pouring into the throat.

One of the main differences I see is with the fuel hoses. The original rx7 setup has a feed and a return, this carb looks like it might have two feeds? I have it set up with the old piping, but I'm wondering if perhaps it's supposed to have a regulator instead, and no return. so the float chambers are overfilling because there's nowhere for the fuel to return back to?

anyway here's some pics of the carb, it's obviously been messed with but I know nothing about it really because I'm a newbie. help!

clykins

iTrader: (1)

It sounds like the floats are sticking. I would rap carefully on the airhorn with a rubber mallet. If that does nothing then I would consider rebuilding it.

It looks to me like you have the same two hose set up - one supply, one return. I believe the return line has a check valve in it. I would check that as well. Good luck.

diabolical1

iTrader: (3)

well, it looks like a Nikki to me. was the car actually running with this setup at some point? as for your problem, what fuel pump are you running? could simply be a need for regulation.

nofrills

Hi guys, thanks for the replies

I've pulled the carb down and everything seems OK... the previous owner said it had been rebuilt recently, and it looks to be the case, the needles look brand spanking new.

The engine itself hadn't run with this carb, so I don't know the history of it. My car was completely standard, and also had a nikki carb. I assume I also have a standard pump.

I haven't had a chance to play with the car again, I wonder if perhaps the check valve isn't sealing, and I have the fuel lines around the wrong way, and the fuel is just pumping in via the outlet?

nofrills

ok update time.

firstly, i've verified that I had the fuel hoses around the right way

secondly, i removed the needles, held them against the seats, and switched the fuel pump on. the needles didnt leak, and returned the excess through the return pipe.

thirdly i dunked the floats in fuel, they floated just fine, no bubbles, gave them a bit of a squeeze, still nothing.

next step is to check the installation and adjustment of the float/needle. i'll need expert eyes here - this is my first time playing with carbs, i really dont know what looks right and what doesnt

first two pics are of how the needles are attached to the floats. third is the float level which i read somewhere as 16mm, mine is pretty much bang on

last two pics are showing how loosely the needle clips seem to sit when the floats are in place, is this normal?

any insights please spill, even if you have to call me a moron in the process!

nofrills

ok attached is my understanding of the fuel flow within the carb. the fuel flow in via the red lines, reaches the needles (yellow) and then depending on the position, continues into the chambers (red) or is diverted to the return galleries (blue).

i've noticed that with the pump on, the reservoir (green) fills up with fuel and pours down into the throat?! this is during normal operation, does that suggest that the return line is somehow blocked? or is this reservoir not related to the return at all? i actually have no idea what it's purpose is, but is sure as heck shouldnt be overflowing like that

i assume that in the case of the float bowl overflowing, the excess comes out the main jet, rather than having a dedicated return path, as that seems to be what is happening here

thoughts, corrections?

nofrills

another update.... think i've found the issue?

after reading a lot about "make sure your vent solenoid is getting power, or the carb will flood", i decided to look into it

....it's not there. instead i have a newish looking frost plug

what does this mean? has it been removed due to a different setup? is it an optional extra that not all carbs have?

i may move this thread into a more specific forum...

nofrills

disregard all that... its definitely the needles. lapped both of them to their respective seats. one stopped overflowing, the other one didnt. tapping the top of the carb made them both start overflowing again, argh

might look at stretching the spring in the needle body a little bit, and someone else has suggested a little bit of vaseline under the needle face while it beds in

clykins

iTrader: (1)

Thanks for keeping this updated. While you are at it I would just double check the return line. I don't think this is necessarily your issue, but it might be contributing. Perhaps try disconnecting the return line and have it empty into a container to see if you have a clog somewhere down line.

Try running some see Sea Foam through your fuel system once you get it running. You might have some gunk in the carb.

I wouldn't adjust your floats unless you absolutely need to, or they have been adjusted before. Sterling, I believe, wrote a great article on "don't adjust your floats" (paraphrased). They don't just go out of adjustment.

Good luck.

nofrills

hi, thanks for the reply... funnily enough, i was eventually able to solve the problem by....

adjusting my floats!

the floats were new, but came already installed in the carb, so it's possible that the previous owner installed them incorrectly or adjusted them prior to installation. everything seems to be sweet now, so it's onto the next problem (which i will post about when i get more information)